Trigenomic hybrids from interspecific crosses between Brassica napus and B. nigra

Abstract

Interspecific hybridisation was carried out between five cultivars of Brassica napus and five accessions of B. nigra in all possible cross combinations including reciprocals. Crossing success was higher when B. napus genotypes were used as female parents. Pollination of 799 B. napus flowers with B. nigra pollen resulted in 433 pods set and 2063 putative hybrid seeds. In the reciprocal direction, pollination of 877 B. nigra flowers with B. napus pollen resulted in 281 pods set and 113 putative hybrid seeds. Pod and seed set varied with genotype and only 19 out of 25 combinations of B. napus × B. nigra and 14 out of 25 combinations of B. nigra × B. napus yielded seeds. Hybridity of 2176 putative hybrid seeds (2063 from B. napus × B. nigra and 113 from B. nigra × B. napus) was tested. Microsatellite markers with known locations for the A, B and C genomes indicated that six plants were true hybrids and one more plant remained unconfirmed for hybrid status. All other plants from putative hybrid seeds had the same DNA banding patterns and similar morphological characters as the female parent. However, the true hybrids had DNA bands from both parents and an intermediate morphology for colour and hairiness of leaf, stem and petiole. Anthers were shrunken and thin with a very limited number of sterile pollen grains. Cytological examination confirmed the triploid status of the hybrid with 27 chromosomes. The unconfirmed hybrid had 9% pollen viability and chromosome count was 27 as with the true hybrid; however, there was no clear B-genome marker from B. nigra.