Wheat an important staple food crop has attained significant genetic gains with an increase in yield of 0.7 t/ha/decade (BSPA, 2015). The crop fed million of people and increased food security via ushering green revolution in the country. But the glare of the revolution has been faded by population explosion accompanied with emergence of new biotic and abiotic stresses. Thus, augmentations of breeding techniques are desired for quick varietal development. A varietal development process requires eleven to twelve years for its identification and release through conventional breeding programmes which is time consuming. By the time the variety obtains homozygosity and is identified, new variability in the pest and disease population emerges. Therefore, the complementation of the current breeding techniques with the biotechnological interventions is indispensable. Doubled haploidy technique reported by two Indian Scientists (Guha and Maheswari, 1964) was a major breakthrough in haploid breeding of higher plants. A “doubled haploid” is a genotype formed when haploid (n) cells successfully undergo either spontaneous or artificial induced chromosome doubling. This biotechnological tool can be instrumental in bringing quick varietal gains in wheat.
Different techniques of DH induction
There are several techniques for development of haploids and doubled haploids. In vivo haploids can be produced by Parthenogenesis, pseudogamy, or wide crossing. The in-vitro methods include gynogenesis (ovary and flower culture) and androgenesis (anther and microspore culture). The most important methods currently being utilized for DH development in wheat include, anther culture (Patel et al., 2004) and wide hybridization of wheat with barley (Barclay, 1975), maize (Laurie and Bennet, 1987), Imperata cylindrica (Chaudhary et al., 2005) and various other grasses belonging to the Gramineae (Pratap et al., 2005). Of these approaches, anther and chromosome elimination techniques (via maize and Imperata cylindrica) appear to be the most effective for DH production.
Advantage of Imperata cylindrica over other sources uses for DH production in wheat
Though many DH induction techniques have been identified but each has its own limitations. The anther culture technique has a strong genotype specificity and high rate of albinism in regenerants, while the maize mediated system is genotypic non-dependent but lacks efficiency and maize needs to be grown offseason thereby increasing the cost of production.
I. cylindrica (2n=20), a wild grass first identified by Chaudhary and his associates (2005) is an efficient alternative to the existing maize mediated techniques of DH induction in wheat. This wild weedy perennial grass doesn’t require its repeated sowings and is available under natural conditions in almost all parts of the world wherever wheat is cultivated. Its flowering synchronizes with wheat and abundant pollen can be picked up. Also the pollen viability is long and results in high frequency of haploid and doubled haploids in wheat and Triticale. Pratap et al. (2005) had reported its high efficiency among all the Graminae genera tested for haploid plant production and Chaudhary (2008) reported that I. cylindrica performed significantly better than maize for all the haploid induction parameters in wheat, triticale and their derivatives.
Potential areas for exploiting the DH technique in wheat breeding
The traditional method of stabilizing the genes and developing a pure line requires self-pollinating plants for eight or nine generations. Double haploid (DH) breeding not only helps in accelerating conventional plant breeding programmes and make early release of cultivars but also provides 100 per cent homozygous lines. Doubled haploidy breeding also offers unique advantages to breeders which include saving time, space and labour; small selection population size; elimination of deleterious mutations and weak plant types; useful in development of transgenics; additional variation in the form of gametoclonal variation and elimination of dominant alleles controlling undesirable traits. The DH system has been widely used in wheat breeding programs and numerous new wheat cultivars of DH origin has been released in Europe, USA, Canada, Brazil and China (Pauk et al., 2003, De Pauw et al., 2010). In India Him Pratham is the first variety released via I. cylindrica mediated chromosome elimination technique.
1. Chaudhary, H.K., Sethi, G.S., Singh, S., Pratap, A. and Sharma, S. (2005). Efficient haploid induction in wheat by using pollen of Imperata cylindrica. Plant Breeding 124: 96â€"98.
2. Laurie, D.A. and Bennett, M.D. (1987). Wide crosses involving maize (Zea mays). Annual Report of the Plant Breeding Institute, 1986-87, pp.66.
3. Guha, S. and . Maheshwari, S.C. (1964). In vitro production of embryos from anther of Datura. Nature, 204: 497.
About Author / Additional Info:
I am Scientist Senior Scale working in wheat and barley breeding for Northern Hills of the country. I have three varieties to my credit.