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, DCDC) 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 × B. rapa cross (73%), but less so for the D. catholica × B. juncea cross (35–40%). Female fertility was also higher in both the amphiploids. Cytological analysis of the F1 hybrids revealed aberrant meiosis with predominant occurrence of the univalents. Partial genomic homoeology between the A genome of B. rapa and the DC genome of D. catholica was indicated by the presence of up to five bivalents in 14.7% of the PMCs in the D. catholica × 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 × B. juncea, up to six bivalents and one trivalent were observed indicating homoeology between the A/B genomes of B. juncea and the DC 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 DC and A/B genomes.