Studies on crossability barriers between cultivated species and wild allies of crop Brassicas

摘要

Wild species are known to possess reservoirs of genes for resistance to biotic and abiotic stresses. One of the factors responsible for low productivity of oilseed brassicas in India is susceptibility of varieties to a number of diseases and pests. But,there is very little information available on crossability behavior of wild relatives and cultivated species of Brassica. Such information could be useful to the plant breeders in selecting suitable wild species to incorporate disease and pest resistant genes in improving oilseed brassicas through wide hybridization. To understand the extent of reproductive isolation between cultivated species of Brassica and some of its wild relatives, pollen-pistil interaction studies were carried out using decolorized aniline blue fluorescence technique. For this study, pistils of all the six important cultivated species of Brassica were taken as female parents and pollen from 12 to 20 wild relatives of Brassica were used as male parents, depending upon the availability of flowers. Out of the hundred interspecific/intergeneric crosses studied, 73 crosses showed presence of pre-fertilization barriers and 27 crosses showed the presence of post-fertilization barriers. In 49 crosses, pre-fertilization barriers were in the form of inhibition of pollen germination or pollen tube entry into the stigma and 24 crosses due to inhibition of pollen tube entry in the style and ovary. Most of the cultivated species of Brassica permitted pollen germination of Brassica fruticulosa, B. maurorum, Diplotaxis tenuisiliqua and Erucastrum gallicum. Based on the pollen germination, pollen tube entry into the style and ovary, species have been categorized into those showing pre- and post-fenilization barriers. For those crosses in which pollen tubes entered the ovary,application of embryo rescue technique would be very effective. Thus, studies showed that attempts can be made to develop wide hybrids in B. nigra with eight wild species, in B. rapa with three wild species, in B. oleracea with four wild species, in B. carinata with seven wild species, in B. juncea with three wild species, and in B. napus with two wild species, using embryo rescue techniques. On the basis of results, it can be generalized that amongst wild species, B. fruticulosa, B. maurorum, Diolotaxis catholoica, Erucastrum gallicum and E. cardiminoides are likely to be more efficient as male parents for developing wide crosses with cultivated Brassica species. Thus, the present investigation would be useful to breeders for developing distant hybrids among wild relatives and cultivated brassicas.