Cytomorphological and Molecular Characterization of F₁ Hybrids between <i>Brassica tournefortii</i> and <i>B. rapa</i>

Abstract

Summary Interspecific F 1 hybrids were synthesized between Brassica tournefortii (2n=20, TT) and B. rapa var. yellow sarson (NRCYS-05-02) (2n= 20, AA) by sexual mating. The F 1 s were obtained only when B. tournefortii was used as the female parent. Morphological, cytological and sequence tagged microsatellite sites (STMS) based molecular analyses were carried out to confirm the hybrid nature of F 1 plants. Morphologically, the F 1 plants were intermediate for most of the morphological attributes. Although, the F 1 s showed poor pollen fertility, a few seeds were obtained from open pollination in the surroundings of B. rapa. The F 1 plants showed predominance of univalents (53.66%), a typical feature of wide hybrids. The occurrence of chromosome association ranging from bivalents (0-4), trivalent (0-1) and quadrivalent (0-1) in the F 1 s indicated homeologous pairing between the T and A genomes. STMS analysis of the parents and the F 1 s revealed a high degree of similarity (75%) and rearrangements in the two genomes during or after their fusion. The study suggests that B. tournefortii has partial genome homeology with B. rapa which could be exploited in crop improvement programmes, particularly breeding for tolerance/resistance to white rust and mustard aphid. Brassica rapa L. (2n=20, AA), belonging to the family Brassicaceae (Cruciferae), is one of the most important oilseed crops worldwide (Warwick 2011). Among the Brassica species, B. rapa is of special interest because it flowers and matures earlier than any other species of U s Brassica triangle (Nagaharu 1935). B. rapa is well adapted to dry and arid ecosystems and yields seed oil typically low in total saturated fatty acids (Downey and Rimmer 1993). Moreover, the yellow seeded cultivars of B. rapa tend to have thinner hulls and therefore lower fibre content compared to brown and black seeded cultivars (Stringam et al. 1974). Key wordsThe taxon B. rapa has been subdivided into: (1) Indian forms; sub-species trilocularis (yellow sarson) and sub-species dichotoma (toria and brown sarson), and (2) western European and north American form; B. rapa sub-species oleifera (Kimber and McGregor 1995). In general, B. rapa is an obligate out breeder due to the presence of self-incompatible genes. However, amongst the Indian forms toria is cross pollinated, yellow sarson is self pollinated and brown sarson includes both self (tora type) and cross (lotni type) pollinated forms (Becker et al. 1999, Das et al. 1999. The presence of variable degrees of self-incompatibility and temporal isolation imposed by changes in flowering and maturity have restricted and narrowed down the variation within each of the sub-species which has resulted in slower genetic gain and increased risk of genetic vulnerability. Studies have shown that the available cultivars of B. rapa are highly susceptible to white rust and

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