ACCESSING AND EXPLOITING GENES OF BREEDING VALUE OF DISTANT RELATIVESOF CROP BRASSICAS

The Brassicas are an important group of crops in India yielding edible oils and many vegetables. For improving cultivated Brassicas, the wil d relatives are of considerable value. The Brassica group of seed oil and vegetables comprises six cultivated species, out of which three ar e diploids and three are digenomic tetraploids. Brassica juncea is the major seed oil crop in India which can be improved for several traits by incorporating genes from its distant relatives. The early work in India relating to genome manipulation consisted of synthesis of B. jun cea by crossing B. campestris with B. nigra, experimental resynthesis of Brassica species and non-homologous pairing and genetic exchange at the interspecific level. The alloploid species B. napus and B. carina ta have not been successful in India due to agrometereological limitat ions. However, synthetic forms of B. napus have been produced which ha ve a desirable maturity period with good yield potential. Also, throug h non-homologous pairing, pod shatter resistant B. napus has been obta ined, B. napus ordinarily suffers from pod shattering. Similarly, synt hetic forms of B. carinata have been derived from reciprocal crosses b etween morphotypes of B. oleracea and B. nigra and also through protop last fusion of B. nigra with B. oleracea. Molecular analysis has revea led that one of the somatic hybrids had a novel cytoplasmic combinatio n which carried B. nigra mitochondrial and B. oleracea chloroplast gen omes. A range of wild and weedy species related to crop Brassicas poss ess extensive genetic variability. Work for utilizing this variability included hybridization between wild and crop species, analysis of chr omosome pairing and induction of alloploidy. Among Brassicas of intere st to India, protoplast culture and regeneration has been successful i n the case of B. oleracea, B. juncea, B. nigra and B. carinata (cultiv ated species) and Eruca sativa and Diplotaxis muralis (related wild sp ecies). Polyethylene glycol mediated protoplast fusion has been the mo st commonly used method in India for producing somatic hybrids involvi ng Brassicas. The eight somatic hybrids produced and studied showed th at in the majority of cases the fusions led to symmetric hybrids combi ning the complete genomes of the donor species. For developing suitabl e male sterile lines, B. juncea, B. campestris and B. napus nuclei hav e been combined with the cytoplasm of six wild species and stable male steriles have been developed. Protoplast fusion methodology has been used extensively for improving these CMS by manipulating cytoplasmic o rganelles, including production of new combinations of cp and mt.