Intergeneric hybridization between Erucastrum cardaminoides and two diploid crop Brassica species

Two intergeneric hybrids involving wild species Erucastrum cardaminoides (2 n=18, E(cd) E(cd)) and two crop brassica species, Brassica rapa (2 n=20, AA) and B. nigra (2 n=16, BB), were synthesized through in vitro sequential ovary culture. Morphological, molecular and cytological studies were conducted to establish their hybridity. Both hybrids, though morphologically distinct, were intermediate phenotypically between their respective parents. Cytological analysis of the E. cardaminoides x B. rapa hybrid (2 n=19), revealed the occurrence of 17 I+1 II at diakinesis/metaphase in the majority (28%) of the pollen mother cells (PMCs), whereas in E. cardaminoides x B. nigra hybrid (2 n=17), 13 I+2 II was the predominant (32%) meiotic configuration. A maximum of 5 II was recorded in both hybrids, indicating homoeologous pairing in the respective combined genomes. Chromosome doubling by colchicine application gave rise to two new amphiploids (AA E(cd)E(cd) and BB E(cd)E(cd)) having normal chromosome pairing and pollen fertility. The occasional occurrence of one quadrivalent in the amphiploids confirmed partial homoeology between the E(c) and A/B genomes. The E. cardaminoides x B. nigra hybrid and amphiploid appeared to be tolerant to alternaria blight under field conditions.