TOWARDS COMMERCIAL HYBRIDS IN MUSTARD (Brassica juncea (L.) Coss)

摘要

Mustard is a major edible oilseed crop in India. Necessitated by a largely self-pollinated behavior of the crop, pure line varieties are the mainstay of current Brassica breeding endeavours. However, ever increasing supply demand gap for edible oilseeds, require alternate strategies like heterosis breeding to realize enhanced productivity levels. Yield heterosis up to 100 percent has been reported and it was generally found to be associated with geographic diversity among the parents. Attempts to associate heterosis with genetic distances based on molecular and morphological markers have largely failed. Development of heterotic gene pools has just been initiated. To achieve circumvention of selling in this hermaphrodite crop, several pollination control mechanisms, especially cytoplasmic male sterility (CMS) and chemical hybridizing agents (CHA), have been widely investigated. CHA's (mainly ethereal, DPX 3778, GA_3) proved ineffective because of small window of CHA application, incomplete and inconsistent male sterility induction and carry over effects. A number of CMS systems have been developed by substituting Brassica nucleus in alien cytoplasmic sources. Of these siifolia, moricandia and lyratus have received greater emphasis. As euplasmic lines act only as maintainers for all the alloplasmic systems evaluated, gene(s) for fertility restoration were introgressed from cytoplasm donor species for both lyratus and moricandia CMS sources through homoeologous pairing between native Brassica juncea and alien chromosomes of cytoplasm donor species. Transmission frequency of introgressed alien chromosome segment or gene(s), which was initially low, could be improved by repeated selections using male gametic sieve. The chlorophyll deficiency associated with mori CMS was also rectified through chloroplast substitution or genetic introgression of chlorosis correcting genes from Moricandie arvensis. Preliminary analysis of hybrids based on lyr and mori (genetically corrected) CMS revealed stability of fertility restoration over environments and minimal biological penalty associated with these CMS systems. Hybrid seed production technology has also been perfected. This has now paved the way for producing commercial hybrids in this crop of great economic significance.