Introduction
This review of the research undertaken on the most important fruit species
is the result of the contributions of some French fruit breeders working
at INRA (Institut National de la Recherche Agronomique) and CIRAD (Centre
de coopération Internationale en Recherche Agronomique pour le Développement)
This review aims at proposing some trends for the future as well as emphasizing
questions to be answered by the scientific community in the short term.
The review deals mainly with banana, citrus, pineapple, mango for tropical
species, apple, peach and apricot for temperate species. Other species are
also considered and the information obtained is synthetically summarized
: this is the case of strawberry, sweet cherry, almond, kiwi, chestnut and
walnut. For each species, objectives and breeding methods are considered
first, then leading teams in the world, and lastly, the main results of
the last years and perspectives for international cooperation.
Part 1 : TROPICAL SPECIES
The exploration, collection, conservation, research and utilization of fruit
germplasm resources started in the fifties. According to the incomplete
statistics of fruit germplasm collected and conserved by 15 institutes,
6812 accessions had been collected from China and foreign countries and
totally 889.2 mu germplasm nurseries had been set up. In addition, some
cultivars have been collected and conserved by the provincial ( autonomous
regions, municipalities). The institutes which established the nurseries
were doing the research on the germplasm utilization while they are exploring
and collecting more genetic resources.
Through long tenn exploration, some nelected superior cultivars have been
found, such as Kuerhlei Xiangli (P. Sinkiangenses Yu) , Yellow flesh flat
peach at Kashi, Walnut fruiting biannually at Aksu, Xinjiang and Fufeng,
Shaanxi, continuously fruiting walnut at Ziyang County, Shaanxi, late maturity
peach in Qinling Mountain and Henan, extremely late peach at Changyi County,
Shandong, Xuetiao (red flesh peach) peach in Shandong and Hebei, Jiefangzhong
Loquat, continuously fruiting lichee at Huidong County, Guangdong, red flesh
lichee at Guangzhou, seedless clausena lansium.
BANANA
 Main research
objectives: Since the beginning (1920's), the objectives of banana breeding
were to create new varieties resistant to diseases: research on new clones
of export bananas in the 1940's for replacing the "Gros Michel" variety,
highly susceptible to Panama disease. Today, after a wide replanting programme
with the Panama resistant Cavendish clones, the main objective is the research
of hybrids resistant to Black Leaf Streak disease (BLS). BLS is a worldwide
fungus producing large necrotic areas of the banana leaves and, consequently,
important yield losses.
The recent development
of biotechnologies with bananas (genetic transformation, molecular biology)
opens the way to new objectives such as resistances to viruses, nematodes,
banana borer and modification of the fruit ripening patterns. Finally, some
authors are planning to use transgenic bananas for human vaccinations in
developping countries.
Breeding methods:
Two different strategies were developed in breeding. The first aims at producing
tetraploid hybrids by pollinating triploid varieties with wild or improved
fertile male parents. Originating from female gametic restitution, the few
selected tetraploid hybrids aim at combining the agronomic and commercial
features of the variety with disease resistances contributed by the male
parent. The second strategy developed by CIRAD, aims at producing triploid
hybrids but starting from natural or improved diploid germplasm. After selection,
diploid clones are doubled with a colchicine treatment. Thereafter, the
auto- or allotetraploids are backcrossed with another diploid clone in order
to create large segregating progenies of triploids. This last strategy offers
the opportunity to benefit a larger natural variability than the first option.
The development of biotechnologies
with bananas by the beginning of the 80's led to significant results in
the in vitro multiplication of banana plantlets (about 20.106
vitroplants /year are used today worldwide as planting material), in tissue,
cell and protoplast culture and regeneration through somatic embryogenesis
(France, Belgium, Australia, USA), genetic transformation (Belgium, France,
Australia, USA) and molecular biology (marker assisted selection, research
of genes of agronomical interest).
Leader teams: Historically,
banana breeding started in the new world, first in the Bristish West Indies
(Trinidad and Tobago; Jamaïca), and later in the 1960's in Central
America (Honduras), which is high producing region for export bananas. Other
countries later (in the 1980's) developed their own sweet banana breeding
research: national programmes in Brasil and in the French West Indies (Guadeloupe),
regional and international programmes on cooking bananas in Africa (Cameroon;
Nigeria). It should be noticed that, today, there is no identified breeding
research work located in the primary centre of diversity of the species.
Noticeable results:
Despite so much work during this century, we must state that no new banana
hybrid is available to replace the current Cavendish varieties for export
markets. For the more diversified local markets which require less constraints
of commercialisation, some oustanding dessert and cooking tetraploids hybrids
(FHIA01, FHIA21) were obtained but none of them reaching the fruit quality
of the current natural varieties. Some good hybrids were also obtained by
the triploid strategy (IRFA909, IRFA910, IRFA914) but they still need to
be extensively evaluated before release.
Conclusion and international
cooperation: Since 1994, all these initiatives in banana improvement are
coordinated by the "International Network of Banana Breeders", organized
and supported by INIBAP (International Network for the Improvement of Banana
and Plantains.
This organisation, which
is a programme of IPGRI (International Plant Genetic Resources Institute),
has a mission (among others) of organizing and coordinating a global research
effort on banana and plantain, aimed at the development, evaluation and
dissemination of improved cultivars and at the conservation and use of Musa
diversity, as to coordinate, facilitate and support the production, collection
and exchange of information and documentation related to banana and plantain
Owing the high sterility
of the cultivated bananas, it is commonly accepted today that it will be
fairly unpossible to obtain a "super disease resistant Cavendish" through
crosses. In the other hand, facing the high pathogen variability and given
our current knowledge about resistant genes, there is little chance of conferring
durable resistance to BLS by genetic transformation only. In the near future,
success in banana improvement will come to pass through a close interaction
and cooperation between all the partners of different disciplines. The current
undergoing collaboration between the biotech-laboratories and field experimental
stations e.g. for linking crosses and new biotechnologies, illustrates the
necessity for an integrated approach as a key for success in banana breeding.
CITRUS
Main research objectives:
the Citrus industry is currently facing many increasing biotic (diseases)
and abiotic (drying, high salinity soils) constraints justifying the research
of new rootstocks as support for a sustainable citriculture in developing
countries. The increasing demand of citrus markets throughout the world
encourages diversification strategies with new varieties, especially for
small fruits. Owing the diversity of the climatic and ecological conditions
in citriculture, a variety selected for its proper qualities should have
an international appeal whereas a rootstock would be more adapted to specific
soil conditions and soil pathogens present in a given region. Moreover,
it must be considered that rootstocks should modify the variety features
for many characters.
Selection priorities
for the varieties are disease resistance (tristeza, greening, Phaemularia
angolensis, variagated chlorosis) which generate high yield losses in orchards.
Others criteria of selection should be retained according to the final products.
Juice processing relies on varieties having good productivity and high sugar
content. For fresh fruit markets, variety selection is oriented towards
a longer harvest period, of small fruits displaying higher pomologic and
organoleptic qualities (easy-peel seedless mandarins for example). Cold
tolerance is also subject of many breeding objectives in citrus.
Breeding methods: Most
present-day cultivars of oranges, mandarines, lemons grown in the main commercial
producing areas arise from sports selected by the productors themselves
and propagated by grafting (Spain, Morocco, ....). In the same way, pomelo
varieties were derived from a common natural ancestor pummelo/orange hybrid
originated in the Carribean and the common ancestral clementine (natural
mandarin/orange hybrid) was found in a backyard by the Franciscan Clément
Rodiez in 1902 in Algeria.
Germplasm characterization
showed some sources of rootstocks to be tolerant and/or resistant to various
strains of tristeza (virus), to Phytophtora and nematodes, resistant to
drought and high salinity soils.
Disease and pest resistance
of the scion cultivars (particulary to greening in Asia and blight in USA)
are desirable but is difficult to accomplish because gene resources either
are not available or are so distantly related to the scion cultivar that
recovery of acceptable cultivars is unlikely.
Classical breeding programmes
rely on intercrossing varieties which usually do not display hygh levels
of sterility. Rarely, backcrossing was carried out. Identification of zygotic
seedlings in progenies containing high percentages of nucellar seedlings
is a problem. Analysis of leaf or bark isozyme showed to be the most usefull
technique for distinction because of the advantage of specific codominant
alleles of known inheritance. In another way, somatic hybridization and
regeneration of protoplasts involving a wide range of citrus varieties is
now applied for the synthesis of tetraploid rootstocks and varieties and
also triploid scions by fusion of haploid and diploid material.
Leader teams: Historically,
first crosses on citrus started at the USDA in Florida by the end of the
last century (1893). This programme extended later in California in 1948.
The University of Florida (1923) and California (since 1914) developped
also their own breeding programmes. Today, USA, Israël and Japan are
the most active countries in citrus improvement. Spain, Itali and Morocco
which have a long tradition of sport selection, are now initiating breeding
projects as in Australia, Brazil (EMBRAPA), China, Georgia, Italia and France
(CIRAD and INRA).
Noticeable results:
Programmes developed in the USA resulted in the creation of some good new
rootstocks: citrumelo hybrids (Poncirus x pomelo, USDA) and Troyer and Carrizo
citranges (Poncirus x orange, University of Florida). Nevertheless, more
rootstock varieties are still needed with tolerance to tristeza.
For market purposes,
out of sport selection, some new varieties were released from crosses between
pomelos and mandarins (tangelo Nova, Orlando, and Minneola). Some mandarin
hybrids were also selected for small fruit diversification (Fairchild, Frémont,
Fortune, Wilking and Honey). All these new varieties, obtained than more
25 years ago, are not yet well developed on the international markets with
one exception: the Sunburst cultivar (Florida, 1961) which is the main small
fruit variety cultivated in USA today.
Conclusion and
international cooperation: An oustanding new rootstock is still needed with
the tolerance to tristeza, Phythophthora, and nematodes displaying also
a good adaptibility to high salinity and calcaerous soils, and drought.The
research of new small fruits clones needs to be maintained looking for easy
peel seedless mandarins harvested on a wider period of time.
Finally, it has to be
recognised that no work was reported on breeding of orange which still represents
about 70 % of the world citrus production. Moreover, most of the researchs
and results reported here were developed in a competitive context with an
apparent lack of global organisation at the international scale. Within
a worldwide network covering all the types of production, it must be considered
that citrus improvement has to evolve towards new breeding strategies including
the current available technologies (sport selection, crosses, somatic hybridization)
with new tools such as molecular markers (and linked methodologies), haplomethods
and genetic transformation.
PINEAPPLE
Main research objectives:
'Smooth Cayenne' fruits are fragile and poor in ascorbic acid content. The
clone is sensitive to many known pests and diseases (fusariosis, nematodes,
Thecla fruit borer) and is a poor producer of planting stock. A first objective
of pineapple improvement is the creation of hybrids close to 'Smooth Cayenne'
with resistance to the main diseases and high quality fruit, preserving
the good agronomic features of the variety (high productivity; leaf margins
with very few spines). A second objective is the creation/selection of completely
new varieties for market diversification in developed countries in order
to increase the choice for consumers. A third objective, as result of wide
crossing, should be the selection of some exotic forms as ornamental plants.
Favourable traits have been identified in pineapple germplasm: pulp firmness,
completely smooth ("piping") leaves, high ascorbic acid content, resistance
to fusariosis in the Colombian cultivars Perolera and Manzana, as well as
in in the Brazilian 'Primavera', and resistance to fruit borer in the Peruvian
'Samba'.
Breeding methods: As
a vegetatively propagated crop, pineapple has been mainly maintained through
clonal selection. However some new characters, as resistance to wilt were
identified in 'Smooth Cayenne' in Hawaï and in Mexico. Breeding methods
rely on a simple strategy. Pineapple is an allogamous species. Owing the
absence of self-pollination (autoincompatibility), it is not necessary to
emasculate the seed parent of a cross. The female parent inflorescence is
protected before flowering by placing a mosquito net cover of a weather-resistant
paper bag on the inflorescence.
Flower induction using
etephon must be programmed for synchronying flowering of the parent plants.
Germination rates of the seeds vary between 80 and 100 % among species and
cultivars according to different methods reported by several authors. In
the world, the breeding strategies undertaken by almost all the programmes
are based on intercrossing two clones followed by three to four cycles of
field observation on the progenies to evaluate the potential of the best
clones. These clones are then multiplied and submitted to extensive field
trials including acceptance or canning tests. With few exceptions, no strategy
of recurrent selection nor production of inbred lines has been reported.
Leader teams: Pioneer
hybridization work started in Florida in the beginning of the 20th century
succeeded by other initiatives (Philippines, in 1921; Formosa, in 1926).
But in fact, it might be considered that systematic improvement really started
in Hawaii where the main breeding programme was implemented from 1942 to
1975 by the Pineapple Research Institute (PRI).In Asia, the Malaysian Pineapple
Industry Board (MPIB) developed in the 1970s its own improvement programm
relying initially on clonal selection but rapidly shifted towards hybridization
of Smooth Cayenne and Singapore Spanish. The programme was continued by
the Malaysian Agricultural Research and Development Institute (MARDI) which
completed the selection of the newly created hybrids.In West Africa, the
Institut de Recherche sur les Fruits et Agrumes (IRFA) established in 1978,
in Ivory Coast, a breeding programme aimed at creating new hybrids well
adapted to fresh export markets as well as processing. In the late 1980s
the programme involving 'Smooth Cayenne' and 'Perolera' clones was progressively
split between the fruit departement of the Ivorian "Institut des Forêts"
(IDEFOR) and the Centre de Coopération Internationale en Recherche
Agronomique pour le Développement (CIRAD) in its experimental station
of Martinique (F.W.I.) where selection was completed. Since 1978, the Empresa
Brasileira de Pesquisa Agropecuaria (EMBRAPA) in the Bahia State has been
involved in a breeding programme for the creation of resistant hybrids.
Other research institutes active in pineapple improvement are in Philippines,
Cuba, South Africa and Australia.
Noticeable results:
In Hawaii several hybrids were released to PRI member companies for potential
commercial use. Finally, a cross between two of these hybrids led to the
Golden Ripe variety commercialized by Del Monte in 1995. In Malaysia a first
hybrid, 'Nanas Johore' was released by MARDI but failed to compete because
of its susceptibility to marble disease. A second hybrid, 'Josapine', was
officially released last year. In France a clone with good potential has
been released but it needs to be further evaluated at the field scale. In
America, the Brazilian production relies on the cultivars Pérola
and Smooth Cayenne, both highly susceptible to the fusariosis present throughout
the country. Some existing clones were distributed (Perolera, Primavera)
but not yet hybrids.
Conclusion and international
cooperation: This review of the main breeding programmes shows that most
hybridization work is based on the same crossing strategies using clones
from the few world leading cultivars, neglecting the large genetic pool
available. Noteworthy is the extreme paucity of the results. As already
stated, despite millions of seedlings produced since 1905, breeding work
has been done over all the continents resulting in a significant contribution
of knowledge in cytology and genetics but not to the list of new cultivars.
This statement underlines the necessity for redefining the objectives of
pineapple improvement (e.g. more focus on a "Super Cayenne" ?) and the needs
to rethink the improvement methodologies: is hybridization the most efficient
strategy ? If the answer is positive, what crossing scheme and parent choice
have to be done ? Moreover, more communication is needed between the different
actors worldwide in order to avoid duplication of works and to favour cooperation.
Finally, a relevant feature of pineapple breeding is the lack of significant
progress in advanced biotechnologies (tissue culture, cell regeneration
systems, haplomethods, genetic transformation). More focus has to be placed
on such methodologies to increase the chance of obtaining satisfactory new
varieties in the future.
MANGO
Main research objectives:
Breeding objectives vary from region to region, depending on specific traits.
However, they can be broadly listed as following: For varieties: 1. Regular
bearing - 2. Dwarf tree habit with precocity - 3. Attractive colour, good
sized and shaped fruits and flesh quality - 3. Resistance to major diseases
and pests - 4. Freedom from physiological disorder - 5. Good shipping qualities
(for export) and shelf life - 6. Enhancement of the production period. For
rootstocks, the main desirable traits are : 1. Polyembryony- 2. Dwarfing
- 3. Tolerance to biotic stresses and to physical and chemical adverse soil
conditions - 4. Good scion compatibility.
Breeding methods: Mango
breeding is undertaken by a few countries around the world. There are two
main types of mango. The Indian types have monoembryonic seeds and tend
to be susceptible to anthracnose. The Indo-chinese types have polyembryonic
seeds and might be more tolerant to anthracnose. As other tree crops, many
constraints have to be faced in breeding: high clonal heterozygocity ; early
post zygotic autoincompatibility; recalcitrant seeds; shortening of the
juvenility phase for earlier field evaluation by grafting the new seedlings.
Moreover, hand pollinations are problematic and do not lead to consistent
fruit setting. Therefore, parent neighbour trees have to be cagged with
bees for undertaking controlled cross pollinations. At present, most of
the hybrids arise from selection among two varieties or primary hybrids
and no strategy of recurrent selection is reported. In another way, with
regard to natural mutations, important agronomical traits (such as precocity,
yield, regular bearing and resistance to diseases) might be improved by
sport selection.
In a parallel direction
with breeding, tissue culture was developed to assist mango improvement
through somatic cell biotechnologies. During the past 15 years of research
in this areas, significative results have been obtained in the regeneration
of somatic embryos recovered from nucellar tissue derived callus and cell
suspensions of the same origin. Nevertheless, entire plant recovery has
been problematic and no report has been published on the agronomic behaviour
of the vitroplants, especially in relation to the occurrence of somaclonal
variations in the field. In another area, co-infections of A. tumefaciens
with embryogenic tissus led to the development of stable transformed plantlets.
These new technologies might be used in the future for the improvement of
specific traits such as fruit ripening, tree size, insect and insect resistance
and so on.
Leader teams: In India,
following last 4-5 decades of intensive breeding, many new hybrids have
been released from several research centres. Mango breeding in Israël
has resulted in the identification of 15 hybrids. In Australia, very promising
progenies were obtained from crosses between the referenced clone 'Kensington'
(with typical good flavour) and 'Sensation' (bringing favourable agronomic
traits). In South Africa, past genetic improvement was achieved by selection
and released in 1990 of four new cultivars.
Noticeable results:
Baring a fex hybrid varieties resulting from planned hybridization programmes,
almost all known cultivars have resulted from the selection chance seedlings
from natural cross pollination mainly in India. However, in Florida, following
intensive introduction by the end of the 19th century, some important export
varieties have resulted from seedling derived from open pollinated (or not)
identified mother plants. Today, most of the new Indian hybrids are regular
bearing, with good quality fruits (free from spongy tissue) and attractive
skin colour. Compared to the cultivars of reference, all the hybrids have
a marginally higher pulp yield and possessed lower peel, stone and fibre
content. Nevertheless, owing problems of commercialisation and promotion
in markets, the adoption of these new varieties is still fairly low. In
Israel, interesting seedlings were selected for peel colour, fruit quality
and favourable harvesting season. With regard to rootstocks resistant, or
tolerant to calcaerous and high salinity soil, several monoembryonic and
polyembryonoic hybrids have been identified but none performed better than
'13-1', the currently preferred rootstock in Israël. In South Africa,
the oustanding new variety "Heidi" was released in 1990 and is already commercialized
at the international level. Thereafter, a comprehensive breeding programme
was initiated on a sound genetic strategy.
With regard to sport
selection, there are two reports of somatic mutants giving rise to new cultivars.
In USA, "Davis Haden" has been identified as being larger and flowering
one month earlier than the donor parent "Haden". Another cultivar is "Rosica"
from Peru which is a bud mutant of the Peruvian cultivar "Rosado de Ica".
Unlike the parent, this mutant is high-yielding and regular bearing and
does not produce seedless fruits.
Conclusion and international
cooperation: As a result of the implementation of controlled pollinations,
good procedures of evaluation and selection in the field, new outstanding
hybrids of mango were released. Nevertheless, as stated by Israeli breeders,
mango breeding is still in their infancy phase; thus , it must be emphasized
that considerable genetic and varietal progress should be expected from
long term integrated programmes including all available strategies. In the
next few years, mango improvement will have to take into account also the
improved knowledge of inheritance of specific characters (recessivity for
polyembryony, dwarfism, regular bearing and precocity for example) and the
recent findings on heritability pointing out that the additive genetic variance
was small and non-significant whereas the non-additive variance was found
to be large and significant in most traits. Moreover, the integration of
protein (isozymes) and molecular markers (RAPD's, AFLP's, VNTR) will bring
more information regarding the global genetic diversity in mango and the
identification of genetic relatedness between clones. The use of this markers
might allow the breeder to predict the parent combination which will led
to superior progenies and in the future, and might assist selection in early
screening in nurseries.
In the future, it might
be expected that better efficiency in mango breeding will rely on planned
hybridization assisted by the new tools offered by biotechnologies. The
recent emergence of molecular markers and the application of somatic embryogenesis
to genetic transformation will enable the integration of specific genes
from cultivated varieties or wild species into popular current cultivars.
Part 2 : TEMPERATE SPECIES
APPLE
Main research objectives
- breeding methods.
From the objectives
that breeders are mainly looking for, two are most often mentionned : fruit
quality and disease resistance. Adaptation to climatic conditions is also
of prime interest for the countries located in extreme areas. Many apple
breeders are also involved in tree habit studies; their objective is to
obtain productive and regular cropping trees. Storage ability, and harvesting
period are also objectives developed in some programmes. Several institutes
are involved in breeding for fruit processing cultivars; two have a specific
activity on breeding for cider apples.
Fruit quality
Selection criteria
Releasing apple cultivars
with high fruit quality is obviously the major aim of each breeder. All
around the world, the same criteria are taken into account to assess fruit
quality:
fruit appearance : ground colour, overcolour and type of colour are the
first criteria. Fruit shape and fruit size are also frequently assessed.
fruit taste is appreciated by various characters. The most important are
quality of the flesh texture, firmness, juiciness, sugar and acid content.
Flavor also is a very important criteria. No objective measurements are
carried out to assess it.
In Finland and Russia,
emphasis is also put on vitamine C content.
Breeding for cultivars
intended to processing market requires very specific criteria. Fruit appearance
is not taken into account but sensory and technological characters are carefully
assessed and measured. Criteria are closely dependent of the type of final
product : juice, cider, dried fruits, compote.
Breeding objectives
Fruit quality perception
is very subjective and its assessment varies between people and countries.
Breeding programmes in China, Japan, Brazil or India focus on sweet fruits
: Fuji, Gala, Red Delicious are the references. People from Northern countries
prefer more acidic fruits as Braeburn, Jonagold or Elstar.
But most of the apple
breeders don't focus on only one type of cultivar . They aim to release
a wide range of selections, including various coloured types, taste, harvesting
periods. However some breeders select very specific types of fruit adapted
to the preference of local consumers or growers. In India, for example,
the breeding aim is to release resistant sweet-flavored cultivars similar
to Red Delicious. Many apple breeders are concerned with storage ability,
but very few advanced studies which are performed on this character.
Parents
All over the world,
the great commercial cultivars are included on a large scale in breeding
programmes to improve fruit quality. Golden Delicious and its derivatives,
as Gala, are the parents the most often used in the crosses. Jonathan, Red
Delicious, Granny Smith, Idared and more recently Fuji and Braeburn are
also frequently used.
In addition cultivars
more adapted to local preferences, and their derivatives, are used : Mac
Intosh in Canada, Cox Orange Pippin in Great Britain, Lobo and Aroma in
Nordic countries, Elstar, Gloster, Melrose in the North of Europe.
Some institutes include
also landraces or old cultivars to improve fruit quality, especially in
former USSR, Nordic countries, Belgium, and in Spanish and French cider
and juice breeding programmes. Generally, these local cultivars besides
good fruit quality, transmit also a good environmental adaptation.
Disease and pest resistances
In most of the countries,
scab is the major apple disease. It is the first disease targeted in the
breeding programmes. Mildew resistance is also commonly introduced. The
final aim of the breeder is to release cultivars carrying multiple resistance.
Example of scab resistance
Although various sources
of scab resistance have been identified in different wild Malus species,
Vf gene is widely used in all the scab resistant breeding programmes : more
than 80% of the scab resistant cultivars released today and the parents
currently included in the breeding programmes carry the Vf gene. One breeding
strategy has been performed all over the world: a succession of modified
backcrosses between scab resistant hybrids and commercial scab susceptible
cultivars. For 50 years, several crosses have been made from the initial
cross : 7 or 8 successives crosses for the last Vf selections.
Breeding for durable
resistance to scab is for some institutes a main objective. This tendency
has increased since the recent discoveries of new strains of scab which
overcome the Vf gene. This leads apple breeders to change crossing strategies
: the aim is now to combine several types of resistance in one genotype.
Molecular markers will be essential to detect in the progenies, seedlings
which carry more than one gene of resistance.
The other alternative
is to use polygenic resistances. In almost every country, some landraces
or old varieties which show good field resistance have been included in
breeding programmes. But, usual scab screening technics are difficult to
adapt to this material : progenies are very difficult to screen in glasshouse
(very high level of susceptible plants; difficult assessment of resistance
symptoms); the correlation between leaf and fruit resistance is low. Thus,
the use of polygenic resistance in apple breeding programmes needs new scab
screening processes and new selection strategies.
Climatic adaptation
Main programmes are
developped in the Nordic countries and in Canada. Objectives are to release
winterhardy cultivars adapted to short and cool growing season. Most progenitors
are local cultivars.
An important programme
is also underway in Brazil : releasing cultivars with low chilling requirements
adapted to the various major apple areas in South America as its main aim.
Usually, the aim of
these programmes is not to develop worldwide cultivars but to release local
cultivars not only adapted to local climatic conditions but also to the
economic and industrial environment of the production area.
Tree habit
Almost all the apple
breeders highlight their tree habit programmes on compact trees . Spur sports
important commercial cultivars, i.e. spur mutants of Golden Delicious, Red
Delicious, are widely used to transmit this character. Mc Wijcick, a sport
of Mc Intosh with columnar habit is also often used. But this type of tree
is very susceptible to biennial bearing.
The French breeding
aim for tree habit is to create weeping and not vigorous trees, which give
good and regular cropping and are easy to prune and harvest. Parents which
transmit the character "one fruit per cluster" are also included.
Noticeable results
Many apple breeding
programmes have been reviewed . In spite of very different locations and
very different means, programmes show a great "uniformity" : breeding objectives
are quite identical; except in countries situated in extreme climatic conditions,
all the institutes aim to release scab resistant cultivars with high fruit
quality. Progenitors are also very similar between the programmes : the
pool of progenitors on which apple breeders have been working with is very
limited : to improve fruit quality, all the great commercial varieties have
been used; they are already derived from a very narrow genetic base; to
improve scab and mildew resistances, very few progenitors have been used,
despite the large diversity in the genus Malus. Furthermore, the main sources
of resistance are mono or oligogenic, Vf for scab resistance and Pl2 for
mildew resistance. But with the discovery of new strains of scab capable
of overcoming the major genes of resistance, apple breeders begins to develop
new strategies which aim to pyramid various types and sources of resistance
in one individual. At the same time, great emphasis is put on the development
of molecular markers. The mapping of different major genes for resistance
is progressing. To enlarge the variability of the sources of resistance,
Malus species and landraces are screened for various resistances.
Apple breeding programmes
have already been very successful : among the varieties of interest today,
several issued from controlled hybridization, i.e. Jonagold, Fuji, Elstar,
Gala and also Quinguan , in China. They give significant improvement compared
with older cultivars. Furthermore, many new selections are currently being
tested in variety trials throughout the world. The number of promising scab
resistant selections is increasing.
International Cooperation
These successes must
not hide problems for the future. Apple breeding programmes could be more
efficient if more real scientific collaborations could be developped; on
the one hand with scientists from other disciplines (pathologists, zoologists,
specialists in fruit quality , of storage...). Apple breeding institutes
must not only to exchange budwood but also to manage more efficiently the
breeding programmes and the diversity of sources of resistance. But the
increasing privatization of breeding programmes with the related strong
commercial interest should not be a constraint for future collaboration.
PEACH
1. Main research objectives - breeding methods
Main selection criteria
in breeding programmes deal with fruit characteristics such as large size,
firmness, attractive shape and color, good quality and transpor-ability.
Breeding programmes also often aim at extending the ripening season both
toward earlier and later productions. Adaptation to specific environmental
conditions (low chilling requirements for subtropical areas, winter hardiness
for northern areas, resistance to spring frost through for example high
flower bud density) appear to be important concerns for the setting of national
or regional breeding programmes. Treehabit has arisen as a possible breeding
goal in the eighties. Reduced-tree size and growth have been looked for,
using dwarf or compact mutants as progenitors. Surprisingly, apart from
a few exceptions, disease and pest resistance is not directly evaluated.
In most cases, hybrid susceptibility is only assessed in experiments designed
for fruit evaluation.
The genetics of peach
fruit and tree characteristics has been studied for many years. These studies
have mainly lead to the identification of major genes governing fruit characteristics
(yellow/white flesh, melting/non melting flesh, cling/free stone, peach/nectarine
skin) that correspond to distinct commercial fruit types. Major genes governing
tree habit and some flower and leaf characteristics have also been identified.
Conversely, very few resistance genes have been identified and the inheritance
of complex characters has been given comparatively little attention.
Released cultivars are
mainly obtained from control crosses, sometimes after a further generation
of selfing, but selection among seedlings from unknown origin or open pollination
is not uncommon. A few cultivars are mutants ; they appeared in production
orchards. As a very general rule, individual selection is performed. Progenitors
are mainly choosen on empirical knowledge about their own characteristics
and, when available, their past performance as progenitors. Biotechnology,
except for the rescue of immature embryos, is hardly used in breeding programmes,
due to difficulties in the regeneration of explants from mature plants.
2. Leader teams
Peach cultivar development
has been and is still mainly performed by USA teams, and noticeably USDA
laboratories and Zaiger and Bradford (private breeders). USA cultivars are
cultivated worldwide and used as progenitors in most breeding programmes,
sometimes for decades. However, significant releases (54 %) are from other
countries. In several countries, a trend toward the separation of basic
research and strict cultivar development is now being observed.
Accordingly, the relative
importance of private breeders' introductions increases. Public programmes
more and more aim at understanding the physiological and genetic basis of
some characteristics (fruit ripening , fruit color, chilling requirement,
tree growth and development, diseases and pests resistance). No clear leadership
is observed in that respect, as several teams, often in interdisciplinary
associations, contribute significantly to knowledge improvement.
3. Noticeable results of last years
In the field of cultivar
development, steady improvement of fruit characteristics is observed. For
the development of genetic studies, the development of saturated maps with
RFLP markers is an important step, that is being achieved for peach.
4. Possibilities for international cooperation
International cooperation
could develop between countries encountering the same specific problems.
The major pests and diseases are not the same in all productions areas,
but some (Sphaerotheca pannosa, plum pox virus in Europe, Myzus persicae
in Europe and Asia, Monilia laxa or fructicola in most countries) are found
in extensive areas. Exchange of germplasm, development of screening tests,
assessment of germplasm in several countries could be helpful to design
breeding programmes for durable resistance. Similarly, germplasm exchange
exist and could intensify between countries with similar climatic environments.
Physiological and genetic
research about fruit quality are developing in several fields (sugar and
acid contents, polyphenols, evolution of firmness, anthocyanins). The application
of the results obtained for the breeding of fruit quality would benefit
from collaboration between breeding teams involved in the study of the various
aspects of fruit quality.
APRICOT
1.Main research objectives ? Breeding methods
The main research objectives
in apricot breeding programmes deal with different types of products :
Fresh market fruits
for Western and Eastern European countries, America,
Dried fruits for Turkey,
South Africa, New Zealand,
Canned fruits for Greece,
Others (jam, brandies)
for Eastern European countries.
The main common selection
criteria are : local fruit tree adaptation expressed in terms of productivity
and regularity of production, and directly related to specific environmental
conditions. Limited adaptability is one of the peculiarities of apricot
species. It requires evaluation of the apricot cultivars within each production
area. Concurrently it needs to take into account frost resistance (Eastern
European countries), and blooming period to avoid frost and self compatibility,
fruit characteristics such as large fruit, firmness, shape, color, attractiveness,
transport and handling ability, post-harvest characteristics, fruit taste,
period of production, expansion in the direction of early and/or late ripening
cultivars, disease resistance, sharka, Apricot Chlorotic Leaf Roll (Mediterranean
countries), Bacterial canker, Xanthomonas pruni (America and South hemisphere),
Monilinia, Gneumonia (Eastern European countries), Tree habit (Italy).
Breeding methods Just
few facts are known about apricot genetics. Most of the studies have been
conducted on the characterization of the genetic resources for the main
agronomic traits so as to optimize selection procedures.
Released cultivars are
mainly obtained from open pollination, selfings, and now from controlled
crosses within a frame of a controlled breeding program. The part dedicated
to mutations (natural or induced) is close to zero. The cultivars issue
from an individual selection procedure.
The choice of the parents
is mainly based : on their phenotypic value and their complementarity, on
their performances as genitors (when the results are available)
2. Leader Teams
Most of the apricot breeding programmes are developed by National Institutes
or Universities.
1 - The largest part of the research effort conducted in the Mediterranean
basin (70 % of the world production) is based on the European Union organized
within an Apricot Working Group (under the Mediterranean Fruit Research
Station INRA management. Within the European Union 4 relevant laboratories
(*) are fully involved in breeding programmes with common objectives and
complementary approaches.
| Laboratories |
Main axis |
SRFM (*) - INRA (France)
Pisa University (*) (Italy)
Bologna University (*) (Italy)
IAF Naoussa (*) (Greece)
IST Roma (Italy)
CEBAS Murcia (Spain)
INIA Alcobaca (Portugal)
|
Resistance to diseases
(sharka, Apricot Chlorotic Leaf Roll, Bacterial canker)
Fruit Qualities / Graft compatibility
Biology and Adaptation
Fruit Quality
Sharka resistance / Canning
Tree habit / Resistance to Xanthomonas pruni
Floral Biology and Sharka resistance
Local adaptation
|
2 - Among the Eastern European Countries 2 laboratories have clearly relevant
activities in apricot breeding
Lednice University (Czech)
Baneasa Fruit Research Station (Romania) |
Resistance to sharka and Gneumonia, Fruit quality
Breeding |
Other laboratories exist in Eastern Europe and in the Mediterranean countries
but their activities remain based on selection and Genetic Resources preservation
much more than breeding.
3 - American groups are involved in Apricot breeding :
in USDA ? ARS (California ? USA) USDA - ARS (main objectives : floral compatibility,
firmness),
in New Jersey University (New Brunswick - USA),
in Harrow Research Station (Canada)
4 - Two groups in Southern Hemisphere :
in South Africa and in New Zealand: breeding for fruit firmness, early ripening
and high sugar content cultivars
3. Noticeable results of last years
1 - Characterization of the Apricot Genetic Resources issued of the Western
European Countries and America for the main agronomic traits and identification
of sources of resistance to sharka and Apricot Chlorotic Leaf Roll.
2 - Improvement of the selection procedures by an optimization of the selection
test :
Sharka, Apricot Chlorotic Leaf Roll, Bacterial canker, Sampling procedures,
Identification of the components involved in fruit quality.
3 - Creation of the European Apricot Working Group
exchange of advanced selection
multidisciplinary approach
partitioning of the scientific activities
development of progenies for genetic studies
4.Prospects for International cooperation
1 - Common objectives exist between most of the Western European, American
and Southern Hemisphere breeders. So, exchanges of cultivars exist but they
could be improved with some advanced selections and the constitution of
an apricot framework where the information related to all the registered
cultivars should be concentrated in order to optimize the maintenance and
the protection of the plant material.
2 - Exchange and assessment of germplasm in all the countries.
3 - The Apricot European Working Group should be modified in 98 as a Mediterranean
Apricot Working Group. It will give the opportunity :
- To extend the exchanges between breeders, geneticists, physiologists,
plant pathologists within a multidisciplinary approach,
- To exchange the results and the progenitors able to be used within
peculiar breeding programmes applied to the different areas of production,
- Tto improve a methodological cooperation in order to contribute to
the construction of a durable resistance and to improve fruit quality.
However, if it is possible
to construct a cooperative network based on the exchange of released plant
material or of already published scientific results, more limited is the
cooperation within a framework on some methodological aspects because it
is mainly due to personal scientific relationships.
A discrepancy exist
between basic research based on some peculiar specialized laboratories and
the necessity of applied research where Research/Development transfers have
to be taken in consideration. We need at the European level a clear identification
of the bottle-necks and an identification of the laboratories of excellence
able to attack these important problems; concurrently procedures for technology
transfers have to be highlighted. Those are the aims of the Apricot Working
Group.
SWEET CHERRY
1. Main research objectives ? Breeding methods
The first breeding efforts were developed after world war II ; two methods
were used : intra-specific hybridization and mutegenesis. Some results obtained
after mutagenesis generated mutants with self-fertility and others with
the spur phenotype ; these results were mostly obtained in England, Canada,
Italy.
1. Main breeding objectives for scion varieties :
- for fruit : quality, size, flesh firmness and resistance tot manipulation,
resistance to fruit cracking, extension of the season and market, easy
harvesting, resistance to fungi especially Monilia.
- for tree : precocity and productivity, self-fertility, late blooming
and resistance to spring frost, resistance to Pseudomonas, spur type.
Leader Teams and noticeable
results
Canada, Hungary and
France mainly - then USA, Czech republic, Germany.
Canada : self-fertility,
compact types - Summerland, BC.
Main cultivars : Stella
(1968, first self fertile variety), Summit, Lapins, Sunburst, Newstar, Van,
Sylvia, Sumleta, Sumpaca, Sumtare, Skeena and Sandra Rose - all self-fertile
except Summit, Van and Sylvia.
Resistance to fruit
cracking - Vineland, Ontario.
Main cultivars : Vista,
Venus, Vega, Viva, Viscount.
France : extension of
the season and market, obtention of bigarreau with firm and big fruit. INRA-Bordeaux.
Main cultivars : Ferprime
(1 week before Burlat), Ferbolus (10 days after Hedelfingen), Fercer, Fernier
and Ferrador (big fruits).
Hungary : several cultivars
as : Margit, Linda, Katalin, Kavics, Botond.
These 3 countries develop
a close cooperation, exchanging material for experimentation.
The sour cherry is improved
mainly in Germany, United States, Rumanie, Hungary.
2. Main breeding objectives for rootstocks :
- vigor control, from dwarfing to medium vigor.
- earbly fruiting with a good fruit size.
- good compatibility with the main scion varieties.
- resistance to abiotic and biotic stresses (drought, waterlogging,
Armillaria, Agrobacterium ...)
The methodes used are : intra and inter specific hybridization, inbreeding
effect.
2. Leader Teams
France : Mahaleb SL64 and Ferci® SL405, Tabel®, Edabriz, merisiers
Pontaris®, Pontavium®.
Belgium : Damil®, Camil®, Inmil®.
Italy : Bologna Selections, CAB®
Czeck Republik : PHL - A, B, C - under experimentation.
Germany : Gisela® n5 at Giessen, Pi-Ku at DRESDEN-PILLNITZ.
USA : Maxma (Mahaleb x merisier), mm14 and mm60.
At present, the teams working on rootstock breeding are declining ; the
teams from USA, Belgium, Germany disappeared but new ones are now in South
of Italy and Denmark.
3. Prospects for International cooperation
Because of the reduction of the breeding teams, especially for rootstock
breeding, cooperation is highly relevant. These collaborations have to be
strengthen in Europe between France, Spain, Czeck republik, Germany.
WALNUT
1. Scion varieties
Main research objectives ? Breeding methods
To breed by intra-specific hybridization for new varieties with late blooming,
fruiting on lateral brindles, tolerance to bacterial disease and good quality
of the nut kernel.
Leader Teams
USA : Davis University in California for more than 50 years. 15 varieties
fruiting on lateral brindles were released.
France : INRA - 2 new varieties were released with late blooming and fruiting
on lateral brindles.
China, Hungary, Italy are also involved in breeding work.
2. Rootstocks
Main research objectives ? Breeding methods
To breed by interspecific hybridization for new varieties with vigor control
and tolerance to the cherry leaf roll virus (CLRV). The rootstocks have
to induce vigor in order to maintain a good equilibriurn between growth
and fruiting. This material originated from Juglans hindsii x Juglans regia
(California), Juglans nigra x Juglans regia (INRA).
3. International cooperation
Good cooperation within Europe between France, Spain, Italy, Greece and
Portugal.
A network " nuts " FAO is operating for Europe, middle East and Northern
Africa.
The contacts between Europe, USA, China, India have to be developed.
CHESTNUT
1. Main research objectives - breeding methods
Chestnut fruit production
is relatively stable on a world scale (470 000 tons). However it has been
in decline in Europe and particularly in France. China is the first world
producer (100 000 tons) followed by Turkey (90000 tons), Korea and Italy.
Three species are cultivated according to the geographic location, between
the East and the West of the Euro-Asian continent. They include C. crenata
(Japan, Korea), C. mollissima (China) and C. sativa (Europe). Besides these
traditional producers, a few other countries are currently undertaking research
and planting i.e. New Zealand, Australia, USA (California, Oregon and Florida)
and Chile.
The main international
breeding aim seems to be the creation of performing plant material for the
setting up of new profitable orchards with a genetic resistance to the two
main diseases Bark Canker (Cryphonectria parasitica) and Ink disease (Phytophthora
spp.).
Among the programmes
that led to the creation of resistant plant material, the INRA programme
in France produced interspecific (crenata x sativa) hybrids. Several of
these rootstocks and fruit varieties are currently used to set up new orchards.
This material represents a genetic improvement as regards to Ink disease
resistance.
Another relatively old
programme was aimed at Bark Canker resistance (USA, Switzerland) but with
no results. Other programmes developed elsewhere, mainly for clonal selection,
have remained limited so far.
2.Leader teams
In the last few years, various European countries have shown new willing
to approach chestnut breeding in a more rational way. This led to the European
COST project involving Italy, Spain, Austria, Switzerland and France, which
can be considered as the current leading countries in the Western Europe.
3.Noticeable results
In this context, the main recent results and developments concern : analysis
of intraspecific genetic variability through the study of isoenzymes or
RAPD, search for molecular markers, heredity study of some agronomic characters
and the first genetic transformations (Lisbon University, Portugal).
4.International cooperation
Thanks to a European project, a collaborative work on Ink disease was developed
with Portugal (INIA, Alcobaça), the Fruit and Forestry Research Station
in Lourizan (Spain), and France. A wider collaboration is being developed
within the COST project.
Further collaboration may also be stimulated or initiated with countries
outside Europe with the attendance of the Second International Chestnut
Congress (ISHS) in Bordeaux in October 1998
ALMOND
1. Main research objectives - breeding methods
The main traits considered in the almond breeding programmes in the world
are :
- Yield : high kernel yield, no alternate bearing ; early bearing.
- Self-fertility : self-fertile varieties reduce the need for bee pollinizers
; and allow to have single-cultivar orchards.
- Late blooming : to avoid spring frost.
- Resistance to diseases :
- Fungus (Fusicoccum, Monilinia) in Mediterranean countries
- Bacterial disease : Pseudomonas amygdali specially in Turkey
- Insect : Navel orangeworm in USA (improvement of the shell seal)
- Kernel quality : to increase the commercial uses.
The last important results concern :
- Release of self-compatible varieties : Lauranne, Guara.
- Relation between alleles of self-compatibility and ribonucleases.
2. Perspectives for International cooperation
There are two major programmes for almond breeding : the californian programme
of the UC Davis and the European program. These two programmes are not redundant
because the objectives are different and they select soft shell in the USA
instead of hard shell in Europe.
The last ISHS almond programme was in Davis in California and some information
was exchanged. The European programme is led by Spanish and French programmes.
There is a good cooperation with all Mediterranean countries thanks to the
GREMPA. This working group initiated by C. Grassely continues to have some
meetings every two years (next in 1998 in Turkey). Various objectives to
work are discussed in that framework. A good communication and cultivars
exchanges between the different countries are stimulated.
KIWI FRUIT
1.Main research objectives - breeding methods
1.1 Cultivars
1.1.1 Male
Objectives :
- flowering at the same time as the female cultivar,
- producing large numbers of flowers, many of them in multiple inflorescences,
- producing large quantitites of viable pollen,
- moderately vigorous vegetatively.
Breeding strategies : intraspecific crosses.
Countries concerned : New Zealand, Spain.
Plant material already relasead : M Series (NZ), Chieftain (NZ).
1.1.2. Female
Objectives : a novel Actinidia fruit with new characteristics concerning
:
- fruit size and shape,
- skin thickness, hairiness and colour,
- flesh colour
- flavours, sweetness ...
Breeding strategies : interspecific crosses with wild species such as A.
arguta, A. kolomikta, A. melanandra, intraspecific selection within A. chinensis.
Plant material already released : Topstar (Italy, a hairless mutant of 'Hayward'),
MontCap (France, an early maturing cultivar).
1.1.3. Hermaphrodite
Objectives : hermaphrodite and self fertile cultivar, avoiding the planting
of non-producing male plants (normally between 10 and 20 % of the orchard)
and improving pollination.
Breeding strategies : intraspecific hybridisation, crossing with and between
'fruiting' males.
Countries concerned : New Zealand.
1.2. Rootstocks
In New Zealand, kiwifruit is mostly propagated by grafting onto Bruno's
seedlings while in France it is propagated by cutting.
Objectives : a clonal rootstock which could induce.
- more precociuous and consistently heavier cropping,
- a reduction in vegetative vigour and vine size,
- agreater resistance of adverse soil or climatic conditions,
- a resistance to pests and diseases.
Breeding strategies : clonal selection, interspecific hybridisation.
Countries concerned : New Zealand, China, France.
Plant material already released : Kaimaï (NZ, a clonal rootstock).
2. Leader groups in the world (in alphabetic order)
Italy :
Many workers including :
TESTOLIN R. and COSTA G. (Università di Bologna).
BELLINI E. (University, Italy).
PILONE N. (University, Naples).
France :
Cultivars : BLANCHET P. (Lycée Agricole, Montauban).
Cultivars and rootstocks : CHAT J. (INRA-Bordeaux).
New Zealand :
Cultivars : SEAL A., BEATSON R.A., FERGUSON A.R., Mc NEILAGE M.A., PRINGLE
G.J. (HortResearch, Auckland).
Rootstocks : LOWE R.G. (HortResearch, Tee Puke) and PATTERSON K.J. (HortResearch,
Auckland).
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