No abstract

. 1990. Effect of row spacing and seeding rates on summer rape in Southern Manitoba. Can. J. To determine the effects of varying plant densities on summer rape (Brassica napus L.), the cultivar Westar was seeded in 15-and 30-cm row spacings at seeding rates of 1.5, 3.0, 6.0, and 12.0 kg ha-r. Plants seeded in 15-cm rows yielded more per area, produced more pods per plant and lodged less than those in 30-cm rows. Higher yields were associated with a more even plant distribution and a lower degree of intrarow competition. There were no significant protein, oil and chlorophyll conce!tration differences between the row spacing treatments. The highest yields (kg ha ') were achieved with the 1.5 and 3.0 kg ha 'seeding rates. Summer rape compensated for lower plant densities with the production of more branch racemes. As seeding rate increased, competitive mortality increased, resulting in greater etiolation at bolting, and greater lodging at harvest. Seed

A glabrous, yellow-seeded doubled haploid (DH) line and a hairy, black-seeded DH line in Chinese cabbage (B. rapa) were used as parents to develop a DH line population that segregated for both hairiness and seed coat color traits. The data showed that both traits completely co-segregated each other, suggesting that one Mendelian locus controlled both hairiness and seed coat color in this population. A fine genetic map was constructed and a SNP marker that was located inside a Brassica ortholog of TRANSPARENT TESTA GLABRA 1 (TTG1) in Arabidopsis showed complete linkage to both the hairiness and seed coat color gene, suggesting that the Brassica TTG1 ortholog shared the same gene function as its Arabidopsis counterpart. Further sequence analysis of the alleles from hairless, yellow-seeded and hairy, black-seeded DH lines in B. rapa showed that a 94-base deletion was found in the hairless, yellow-seeded DH lines. A nonfunctional truncated protein in the hairless, yellow-seeded DH lines in B. rapa was suggested by the coding sequence of the TTG1 ortholog. Both of the TTG1 homologs from the black and yellow seeded B. rapa lines were used to transform an Arabidopsis ttg1 mutant and the results showed that the TTG1 homolog from the black seeded B. rapa recovered the Arabidopsis ttg1 mutant, while the yellow seeded homolog did not, suggesting that the deletion in the Brassica TTG1 homolog had led to the yellow seeded natural mutant. This was the first identified gene in Brassica species that simultaneously controlled both hairiness and seed coat color traits.

Sequence related amplified polymorphism (SRAP) was used to construct an ultradense genetic recombination map for a doubled haploid (DH) population in B. napus. A total of 1,634 primer combinations including 12 fluorescently labeled primers and 442 unlabeled ones produced 13,551 mapped SRAP markers. All these SRAPs were assembled in 1,055 bins that were placed onto 19 linkage groups. Ten of the nineteen linkage groups were assigned to the A genome and the remaining nine to the C genome on the basis of the differential SRAP PCR amplification in two DH lines of B. rapa and B. oleracea. Furthermore, all 19 linkage groups were assigned to their corresponding N1-N19 groups of B. napus by comparison with 55 SSR markers used to construct previous maps in this species. In total, 1,663 crossovers were detected, resulting in a map length span of 1604.8 cM. The marker density is 8.45 SRAPs per cM, and there could be more than one marker in 100 kb physical distance. There are four linkage groups in the A genome with more than 800 SRAP markers each, and three linkage groups in the C genome with more 1,000 SRAP markers each. Our studies suggest that a single SRAP map might be applicable to the three Brassica species, B. napus, B. oleracea and B. rapa. The use of this ultra high-density genetic recombination map in marker development and map-based gene cloning is discussed.

Significant heterosis for seed yield in oilseed rape (Brassica napus L.) has created interest in the development of hybrid cultivars. The objective of this study was to determine the value of restriction fragment length polymorphism (RFLP) markers in predicting hybrid performance. The hybrids and parents of two sets of diallel crosses were evaluated at three environments for seed yield and other agronomic traits. The parents of the first diallel were seven oilseed rape cultivars and the parents of the second diallel were seven unselected $6 lines derived from the cultivars. Genetic distances (GD) between the parents crossed in the diallels were estimated by RFLP data from 43 DNA clones. Both general combining ability (GCA) and GD estimates were significantly (P < 0.05) correlated with hybrid seed yield in both diallels, although GCA was more greatly correlated than GD. Genetic distance was significantly correlated with heterosis for seed yield only in the inbred diallei whereas GCA was significantly correlated with heterosis only in the cultivar diallel. Midparent yield was significantly correlated only with heterosis for the cultivar diallel. A multiple linear regression model that included both the GD and GCA of the parents was more greatly correlated with hybrid seed yield than any variable alone. The GCA values were significantly correlated with hybrid plant height, and seed oil and protein concentration in both diallels whereas GD was significantly correlated only with hybrid plant height. These results suggest that GD estimates alone do not identify high yielding hybrid combinations with the consistency to be useful in breeding programs.