Chinese Cabbage Soft Rot Resistance-related Functional Molecular Marker Development And Genetic Mapping

Chinese cabbage (Brassica rapa ssp. pekinenesis) is one of the most important vegetables in China and east Asian countries. Soft rot disease caused by the pathogen Erwinia carotovora. subsp. carotovora (Ecc) has been one of the three most important diseases of Chinese cabbage. There has no report about molecular markers for soft rot resistance in Chinese cabbage up to now, therefore, developing new molecular marker technique is very important for breeding Chinese cabbage resistant to soft erwinia.This study was based on our own ESTs database which included those for disease resistant genes, stress-resistant genes, defense genes, signal transduction genes, and other related genes. We designed 60 pairs of PCR primers based on the ESTs, in which 56 pairs amplified successfully in PCR reaction. The effective primer ratio was 93.3%. In total, 11 EST-PCR markers and 19 EST-CAPS markers which had polymorphism in their parents were obtained, and9 pairs of them did not march exclusively with restriction enzymes. The co- dominant markers were 16 and dominant markers 14, therefore, the polymorphic ratio was 50%. At the same time, the above polymorphic primers were then identified in the F₂ population in 142 Chinese cabbage individuals. The results demonstrated that the new functional molecular markers were effective and dependable, and established an improved method for developing new molecular markers which were correlative with functional genes about soft rot resistance in Chinese cabbage. Furthermore, 21 of 10-base RAPD random primers were used to detect DNA polymorphism between the parents, 7 of them shown distinctive polymorphism and 11 polymorphic segregating loci were identified in polymorphic detection with reproducible and stable electrophoresis patterns. Among 41 markers, 10 markers (24.4 %) showed the genetic distortion (P < 0.05). 8 markers (19.5 %) showed the genetic serious distortion (P < 0.01).The 142 Chinese cabbage population used in this study were derived from the F₂ of the resistant A19-2 and the sensitive A32-2 to soft rot disease. A preliminary molecular linkage map is constructed by Mapmaker/ exp version 3.0 software. 47 of the informative loci were in the linkage map, including 16 EST-CAPS markers, 11 EST-SSR markers, 10 EST-RCR markers and10 RAPD markers, which were made up of 9 linkage groups. Distortion markers were distributed among 5 different chromosomes (90%). The number of markers varied from 3 to 8 at different linkages, and the length of linkage group varied from 46.3cM to 212.8cM. The linkage distanceranged from 1.7cM to 47.6cM, covering 980.3 cM in total. The average interval of the adjacent loci is 20.9cM. This research is significant for the development of ESTs derived molecular markers for constructing genetic linkage map and for the localization of genes conferring resistance to soft rot disease in Chinese cabbage.