Qinfei Li

Identification of resistant sources against Sclerotinia sclerotiorum in Brassica species with emphasis on B. oleracea

Stem rot caused by Sclerotinia sclerotiorum is one of the most devastating diseases of rapeseed (Brassica napus L.) which causes huge loss in rapeseed production. Genetic sources with high level of resistance has not been found in rapeseed. In this study, 68 accessions in six Brassica species, including 47 accessions of B. oleracea, were evaluated for leaf and stem resistance to S. sclerotiorum. Large variation of resistance was found in Brassica, with maximum differences of 5- and 57-folds in leaf and stem resistance respectively. B. oleracea, especially its wild types such as B. rupestris, B. incana, B. insularis, and B. villosa showed high level of resistance. Our data suggest that wild types of B. oleracea possess tremendous potential for improving S. sclerotiorum resistance of rapeseed.

Genomic relationships between wild and cultivated Brassica oleracea L. with emphasis on the origination of cultivated crops

Wild taxa in Brassica oleracea L. play an important role to improve cultivated crops, but the genomic relationships between wild and cultivated forms have not been well clarified. An overall survey of genomic relationships among 39 accessions covering 10 wild and 7 cultivared types in B. oleracea was performed using amplified fragment length polymorphism and simple sequence repeat. The cultivated types were clustered together with B. oleracea ssp. oleracea,B. incana, B. bourgeaui, B. montana, B. cretica and B. hilarionis, while 4 wild taxa from Sicily, B. rupestris, B. insularis, B. macrocarpa and B. villosa formed the other group. It implies the low possibility that current B. oleracea crops originated in Sicily.

DNA Methylation Alterations at 5'-CCGG Sites in the Interspecific and Intraspecific Hybridizations Derived from Brassica rapa and B. napus.

DNA methylation is an important regulatory mechanism for gene expression that involved in the biological processes of development and differentiation in plants. To investigate the association of DNA methylation with heterosis in Brassica, a set of intraspecific hybrids in Brassica rapa and B. napus and interspecific hybrids between B. rapa and B. napus, together with parental lines, were used to monitor alterations in cytosine methylation at 5′-CCGG sites in seedlings and buds by methylation-sensitive amplification polymorphism analysis. The methylation status of approximately a quarter of the methylation sites changed between seedlings and buds. These alterations were related closely to the genomic structure and heterozygous status among accessions. The methylation status in the majority of DNA methylation sites detected in hybrids was the same as that in at least one of the parental lines in both seedlings and buds. However, the association between patterns of cytosine methylation and heterosis varied among different traits and between tissues in hybrids of Brassica, although a few methylation loci were associated with heterosis. Our data suggest that changes in DNA methylation at 5′-CCGG sites are not associated simply with heterosis in the interspecific and intraspecific hybridizations derived from B. rapa and B. napus.

Microspore culture reveals high fitness of B. napus-like gametes in an interspecific hybrid between Brassica napus and B. oleracea

The strategies of crossing B. napus with parental species play important role in broadening and improving the genetic basis of B. napus by the introgression of genetic resources from parental species. With these strategies, it is easy to select new types of B. napus, but difficult to select new types of B. rapa or B. oleracea by self-pollination. This characteristic may be a consequence of high competition with B. napus gametes. To verify the role of gamete viability in producing new B. napus individuals, the meiotic chromosome behavior of the interspecific hybrid between B. napus (Zhongshuang 9) and B. oleracea (6m08) was studied, and microspore-derived (MD) individuals were analyzed. The highest fitness of the 9:19 (1.10%) pattern was observed with a 5.49-fold higher than theoretical expectation among the six chromosome segregation patterns in the hybrid. A total of 43 MD lines with more than 14 chromosomes were developed from the hybrid, and 8 (18.6%) of them were B. napus-like (n = 19) type gametes, having the potential to broaden the genetic basis of natural B. napus (GD = 0.43 ± 0.04). It is easy to produce B. napus-like gametes with 19 chromosomes, and these gametes showed high fitness and competition in the microspore-derived lines, suggesting it might be easy to select new types of B. napus from the interspecific hybrid between B. napus and B. oleracea.

Identification of quantitative trait loci for Clubroot Resistance in Brassica oleracea with the use of Brassica SNP microarray

Increasing clubroot resistance (CR) of Brassica oleracea by ascertaining the molecular mechanisms has been the key focus in modern B. oleracea breeding. In order to identify the quantitative trait loci (QTLs) associated with CR in B. oleracea, 94 F2 vegetative lines which were developed by tissue culture of selfed seeds from the F1 generation between a clubroot-resistant B. oleracea inbred line and a susceptible line, were identified for disease incidence and six CR-associated traits under a lab inoculation by Plasmodiophora brassicae and were genotyped with the 60K Brassica SNP array. Significant correlations were detected for numbers of fibrous roots and P. brassicae content in roots with disease incidence. Nine linkage groups were constructed from 565 bins which covered around 3,000 SNPs, spanning 1,028 cM of the B. oleracea genome with an average distance of 1.82 cM between adjacent bins. A total of 23 QTLs were identified for disease incidence and the other two correlated traits, individually explaining 6.1–17.8% of the phenotypic variation. Several overlaps were detected among traits, including one three-traits-overlapped locus on linkage group C08 and two important overlapped regions between the two CR-associated traits on C06. The QTLs were compared with known CR loci/genes and the novelty of our QTLs was discussed.