Synthesis of intergeneric hybrids and establishment of genomic affinity between Diplotaxis catholica and crop, Brassica species

Intergeneric hybrids of the wild crucifer Diplotaxis catholica (2n = 18, (DDC)-D-C) as female with two crop Brassica species, namely Brassica rapa (2n = 20; AA) and Brassica juncea (2n = 36; AABB) as male, were developed, using ovary and sequential culture. Reciprocal crosses were not successful, suggesting unilateral cross incompatibility. Morphologically, the hybrid plants resembled the crop brassica parents, but were nearly male- as well as female-sterile. Induction of amphiploidy helped to improve pollen fertility for the D. catholica x B. rapa cross (73%), but less so for the D. catholica x B. juncea cross (35-40%). Female fertility was also higher in both the amphiploids. Cytological analysis of the F-1 hybrids revealed aberrant meiosis with predominant occurrence of the univalents. Partial genomic homoeology between the A genome of B. rapa and the D-C genome of D. catholica was indicated by the presence of up to five bivalents in 14.7% of the PMCs in the D. catholica x B. rapa hybrid, and 1-2 trivalents or a quadrivalent in nearly 44% of the PMCs in the derived amphiploid. In the second cross, D. catholica x B. juncea, up to six bivalents and one trivalent were observed indicating homoeology between the A/B genomes of B. juncea and the D-C genome of D. catholica. The possibility of introgression of desirable genes from D. catholica into crop Brassica species exists in view of significant affinity between the D-C and A/B genomes.