Resynthesis of Brassica napus aiming for improved earliness and carried out by different approaches

Abstract

Brassica napus L. was resynthesized through interspecific hybridization between B. campestris L. and B. oleracealalboglabra Bailey with the aim to improve earliness. Four different methods of amphidiploidization via sexual crossing were tried for comparison. It proved, however, impossible to show definite superiority of any one method because of low crossability. Tetraploidization of the parent species improved crossability slightly, and resulted mainly in balanced amphidiploids (2n=38, AACC) and a comparatively low frequency of genomically unbalanced hybrids. The cross ♀ 4x campestris♂ 2x oleracea gave a high fraction of am-phidiploid hybrids as well. The rest of the hybrids were triploids (2n=29, AAC). Triploids (2n=28, ACC) were frequent as hybrids, and no balanced (2n=38, AACC) allotetraploids were produced when the cross was performed at the diploid level. This was true irrespectively if the hybridization was followed or not by colchicine treatment. Failure in germination, matromorphous seed production, and genotypic influences added to difficulties in evaluating the different approaches properly. All hybrids had inferior pollen fertility compared to the natural species. Compared to the balanced AACC constitution, the highly sterile AC, AAC, ACC hybrids showed vegetative luxuriance as demonstrated by increased height, leaf and petal size, and branching habit. The primary aim to improve earliness of natural B. napus and the ability to flower and mature at short-day regime was clearly reached.