Cytogenetic studies of aneuploids in rapeseed. II. Morphology, fertility, and cytology of self-pollinated progenies of monosomic plants of Brassica napus L

Cytogenic studies were conducted on self-pollinated progenies from two monosomic lines of Brassica napus to ascertain the mode of transmission of the monosomic chromosome. An approximately 1:1 ratio of disomic to monosomic plants was obtained. Only one nullisomic plant was found among a total of 71 plants analyzed. The 1:1 ratio and the anaphase I disjunction (19–18) suggest that the gametes (n) were twice as competitive or functional as their counterpart (n − 1). Since quadrivalents were observed in the disomic plants and only trivalents in the monosomics, the monosomic chromosomes were believed to be the ones that were involved in the formation of multivalents. The percentage of multivalent association in monosomic plants was almost double that in disomic plants. In the disomic plants, an average of 11.96% of pollen mother cells had one to two quadri-valents. The average frequency of trivalents in the monosomics was 23.63%. It was suggested that pairing of these homologs was genetically controlled with a dosage effect. The absence of one chromosome increased the frequency of multivalents.

Key words: monosomic, Brassica, rapeseed, aneuploid.

Male sterility in Brassica napus L. associated with an extra chromosome

Male sterility was investigated in backcross populations from hybrids between Diplotaxis muralis and Brassica napus using the former as the female parent. The F1 was male sterile and low frequencies (less than 20%) of male sterile plants were obtained from subsequent backcross generations. The data did not fit any Mendelian genetic ratios. Cytological examination of pollen mother cells from 52 plants of these backcross populations indicated the presence of an extra chromosome in all 22 male sterile plants and the normal chromosome number (2n = 38) in the remaining 30 fertile plants. Thus an extra chromosome which is derived from Diplotaxis muralis appears to be the sole cause of male sterility in these backcross populations.Key words: male sterility, Brassica napus, Diplotaxis muralis.

Inheritance of resistance to Albugo candida in rape (Brassica napus L.)

Canadian cultivars of Brassica napus are resistant to white rust caused by Albugo candida while many cultivars of this species grown in China are susceptible. Two Chinese lines susceptible to race 7, GCL, and 2282-9, and one Canadian resistant cultivar, 'Regent,' were chosen for a genetic study of resistance to this pathogen. Inheritance of white rust resistance is conditioned by independent dominant genes at three loci; these were designated Ac7-1, Ac7-2, and Ac7-3. The resistance is conferred by dominance at any one of the three loci and plants with recessive alleles at all loci are susceptible. Since different F2 and BC ratios were obtained for populations derived from different individual plants of 'Regent,' this 'Regent' population is not homogeneous for resistance to white rust. All 'Regent' plants appear to be homogeneous for resistance at two loci while, in addition, some may also carry resistance at a third locus.