Genomic in situ hybridization analysis of Brassica napus x Orychophragmus violaceus hybrids and production of B-napus aneuploids

To further utilize the valuable germplasm Orychophragmus violaceus for Brassica genetics and breeding, a B. napus x O. violaceus cross was repeated with embryo rescue. All F-1 plants except one B. napus haploid were mixoploids (2n = 17-39 in ovaries) with 2n = 31, 37, 38 and 39 as the maximal chromosome numbers in individuals, but the higher numbers mostly appeared in pollen mother cells (PMCs) with a preponderance of 2n = 30, 37 and 38. Only one chromosome and one chromosome segment of O. violaceus were detected at a low frequency in some ovary cells and PMCs with 2n = 37, 38 and 39 as determined by genomic in situ hybridization analysis. The fatty acid profiles of seeds from the majority of the F-1 and F-2 plants were similar to those of female B. napus cv. 'Oro', but some were obviously different in the percentages of oleic, linoleic and erucic acids, and some F-2 plants (2n = 38) with good seed set had high percentages of oleic (> 70.0%) or linoleic (to 38.3%) acids and low erucic acid (< 1%). Subsequently, many kinds of B. napus aneuploids (2n = 28, 30, 34, 36, 37, 39 and 42), without O. violaceus chromosomes, were derived from F-2 progeny and microspores of partial F-1 plants. Finally, the cytological mechanisms behind the variations in chromosome numbers were discussed together with the implications of these aneuploids for Brassica genome research and of the plants with altered fatty acid profiles for improving the oil quality of B. napus.