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Int.J.Curr.Microbiol.App.Sci (2020) 9(12): 1025-1034
International Journal of Current Microbiology and Applied Sciences
ISSN: 2319-7706 Volume 9 Number 12 (2020)
Journal homepage: http://www.ijcmas.com
Review Article https://doi.org/10.20546/ijcmas.2020.912.124
Wide Hybridization in Vegetable Crops
Pooja P. Gowda1*, M. Rafeekher1 and K.R. Nithinkumar2
1
College of Agriculture, Vellayani, Kerala, India
2College of Horticulture, Bengaluru, Karnataka, India
*Corresponding author
ABSTRACT
Green revolution has transformed India into a food grain surplus country
from a deficit one. No other activity has such an immense impact on the
agricultural development as the green revolution has done. It also, has
Keywords reflected its impact on breeding and production of vegetable crops. Side
effects of green revolution were witnessed largely in the form of reduced
Wide hybridization,
Vegetable crops, varietal diversity in major cultivated crop species and increased uniformity
Green revolution in appearance and harvestable products. This predisposed improved
Article Info agriculture to natural calamities. Emergence of new pathogen races lead to
outbreak of diseases and pest attack caused yield losses up to 50 percent.
Accepted: Changing climatic condition has caused abiotic stresses like drought, flood,
10 November 2020
Available Online: salinity and high temperature, which in turn results in reduction of yield
10 December 2020 and quality. To feed the ever-increasing population and to fight with
malnutrition, wild species offers the scope for quality improvement in
vegetable cultivars.
Introduction cultivated crop species and increased
uniformity in appearance and harvestable
Green revolution has transformed India into a products. This predisposed improved
food grain surplus country from a deficit one. agriculture to natural calamities. Emergence
No other activity has such an immense impact of new pathogen races lead to outbreak of
on the agricultural development as the green diseases and pest attack caused yield losses up
revolution has done. It also, has reflected its to 50 percent. Changing climatic condition
impact on breeding and production of has caused abiotic stresses like drought, flood,
vegetable crops. Side effects of green salinity and high temperature, which in turn
revolution were witnessed largely in the form results in reduction of yield and quality. To
of reduced varietal diversity in major feed the ever-increasing population and to
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Int.J.Curr.Microbiol.App.Sci (2020) 9(12): 1025-1034
fight with malnutrition, wild species offers the Insect resistance
scope for quality improvement in vegetable Abiotic stress resistance
cultivars. Quality improvement
Yield enhancement
In order to restore the characteristic of Development of new crop species
ecological sustainability and to combat the Transfer of sterile cytoplasm for hybrids
biotic and abiotic stress in cultivated production
vegetable crops, wide hybridization has been Rootstock breeding
advocated a strong tool in the hand of plant
breeders as wild species are the rich pool of Barriers associated with wide
noble characters, better quality and processing hybridization
traits as well as imparting resistance against
biotic and abiotic stress. Crop wild relatives Spatial isolation
have been used from decades for breeding, in
particular to transfer genes of resistance or It is associated with geographical distance,
tolerance to pests, diseases or abiotic stress to physical separations of time and environment.
the cultivated species. Wide hybridization Sensitivity to photoperiod, introduction to
comprises the efficient conventional breeding different latitudes and separation by
and modern molecular techniques as its geographical and political barriers can isolate
effective tool in crop improvement (Table 1– two species reproductively. Development of
8). different maturity groups in knol khol, radish
and cauliflower are consequences of spatial
Wide hybridization isolation.
Wide hybridization as a norm is an attempt of Pre-fertilization barriers
intermating two species of a genus or two
genera of a taxon with an intention of These barriers are operative between the
introgression of genes of economic value into parental species. They prevent crossability by
the cultivated species. Wide hybridization hindering the fertilization process. Such
invariably comprises crosses between wild, disturbance of fertilization in interspecific
primitively cultivated species and genera. crosses is also termed as interspecific
Interspecific hybridization means incompatability or incongruity. Lack of
hybridization between individuals from pollen-stigma recognition is mainly
different species belonging to same genus. responsible for incongruity. The reaction is
Intergeneric hybridization means sporophytic in nature and reported to be
hybridization between individuals from associated with pollen wall substances.
different genus belonging to same family (Liu
et al., 2014). Failure of pollen germination
Interspecific and Intergeneric Interspecific hybrid in Cucumis species
hybridization through conventional breeding procedures
was unsuccessful because of the existence of
Role of wide hybridization a pre-fertilization barrier. The barrier was
characterized by non-germination of pollen
Disease resistance against various even up to 72 hours after pollination
pathogens (Chatterjee and More, 1991). Kaneko and
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Int.J.Curr.Microbiol.App.Sci (2020) 9(12): 1025-1034
Bang (2014) reported the same problem in Hybrid inviability
case of Brassica campestris and Raphanus
sativus. It results from various factors and manifests
from zygote development to seed formation.
Swollen pollen tube growth It operates in F1 seedlings causing high
mortality, hybrid plants are characterized by
This has been widely reported in case of poor growth, chlorotic leaves and die before
failure of wide crosses. Incompatibility in maturity. The reason may be disharmony
Cucumis spp. is characterized by delayed between nucleus of one species and
growth of pollen, or arrested pollen tube cytoplasm of other or between nucleus of both
growth in the stigma, or inability of pollen the species or due to action of specific genes
tubes to reach the ovules (Chen and Adelberg, known to cause lethality, chlorosis and
2000). Based on pollen tube growth weakness in F hybrids. e.g. Cross between
1
behaviour, crosses between African groups of Cucumis sativus × C. melo and Abelmoschus
Cucumis were classified into three groups, esculentus × A. tetraphyllus.
namely bilateral congruity, bilateral
incongruity and unilateral incongruity. Hybrid sterility
Lack of fertilization F hybrids are characterized by lack of seed
1
set. Hybrid sterility is due to manifestation of
In such cases, pollen tube effectively lethal genes, genetic imbalance due to
delivered the two sperm nuclei to embryo sac. chromosomal non-homology, chromosomal
In one case, zygote was formed but no elimination and endosperm abortion. Several
endosperm development while in second case interspecific hybrids of Abelmoschus
10 percent crosses developed endosperm but esculentus × A. ficulneus and Abelmoschus
no embryo. esculentus × A. tuberculatus show very poor
seed set.
Post fertilization barriers
Failure of flowering in the progenies
These barriers are operative in the distant
hybrids and their progenies. These are also Either hybrid is devoid of reproductive
known as post syngamic barriers and include structure or highly deformed non-functional
embryonic breakdown, failure of zygote structures are formed. It is due to failure of
development, abnormal fertilization, physiological differentiation while non-
inhibition of endosperm and embryo functional reproductive systems are attributed
development. to failure of meiosis in either one or both the
sexes.
Hybrid embryo abortion
Hybrid breakdown
Arrest of embryo development or its abortion
has been noticed in several interspecific It is manifested in the form of inviable and
hybrids. The major barriers to interspecific weak F generation or later generation. In
2
hybridization in Phaseolus sp. i.e. Phaseolus some wide crosses seed setting is normal,
vulgaris × P. acutifolius is embryo abortion. even F plant progenies show normal
1
In case of Phaseolus coccineus× P. vulgaris, development and good fertility but in the F2
abnormal embryo development is observed generation performance of hybrids fall below
(Andradf‐ Aguilar and Jackson, 1988). satisfaction and sometimes may be complete
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Int.J.Curr.Microbiol.App.Sci (2020) 9(12): 1025-1034
sterility. Afful et al., (2018) observed failure Shortening of the style
in fruit set, when the wild accessions were
used as female parents in the crossability In some species, the incompatible reaction
study of cultivated brinjal with Solanum can be overcome by reducing the length of
torvum, S. anguvi and S. aethiopicum. style. Incompatible reaction in radish can also
be overcome by reduction of stylar tissues.
Techniques to overcome pre-fertilization
barriers Mentor pollination
Taxonomic position of parental species Pollen grains of distant species do not
germinate on the stigma of cultivated species.
An ease in hybridization is expected when the However, when these pollen grains are mixed
species more resemble phenotypically. with killed maternal pollen grains,
Taxonomic classification is based on germination of the incompatible pollen grains
morphological features but by and large is the take place as in case of Cucumis (Beharav
outcome of genetic factors in association with and Cohen, 1994). It happens because cell
environment. wall proteins of pollen play pivotal role in
pollen-pistil interaction. Pollen killed in
Doubling of chromosome number ethanol and mixed with incompatible pollens,
release the proteinaceous recognition factors,
When the failure of hybridization is due to thereby masking rejection reaction of the
different ploidy level then this technique is recipient stigma. The killed maternal pollen is
followed. In many polyploid cultivated known as mentor pollen.
species, their wild progenitors are diploid and
crossing attempts are difficult. One may Use of growth regulators and
increase ploidy level of wild type by immunosuppressants
colchicine treatment. This enhances the
success rate in crops like potato, Cucumis and Growth Regultors (GRs) enhance the zygotic
Brassica spp. formation in distant hybrids of many
cucurbits, okra and tomato. Commonly used
GRs are IAA, IBA, GA . GA 75ppm
Bridging species technique 3 3
application to maternal plant 1 or 2 days
In many crops, two species which are before and after pollination improved zygote
otherwise incompatible, may be hybridized formation, faster pollen tube growth, more
with the help of third species. The third embryo survival and more seed set in wide
species acts as bridge in recombining the two crosses. Application of auxin in Solanum
incompatible species so known as bridging prevented flower abscission and enhanced
species. This technique has been used in fruit set.
making wide crosses in potato, lettuce and
In vitro fertilization
sugar beet.
It is effective when stigma and style inhibit
Hayes et al., (2005) were successful in using pollen tube growth and embryo abortion
S. verrucosum as a female bridging parent to occurs at early stages of development. The
access 2x (1EBN) S. pinnatisectum. Solanum whole gynoecium is excised and placed on
simplicifolium was used as bridging species in MS medium followed by dusting of pollens
crossing S. acuale and S. tuberosum on the stigma and fertilized ovule is reared to
maturity (Ondrej et al., 2002).
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