Identification And QTLs Mapping Of Resistance To Black Spot (Alternaria Brassicicola) In Brassica Rapa

Brassica rapa comprises many different vegetable crops which account the highest cultivation area and yield in China. In the process of planting, B. rapa always suffered from the harm of various diseases. The black spot is one of the main diseases of B. rapa, which is widely distributed throughout the country. In addition to causing significant decrease yield, low quality and bitter taste, the black spot can also affect seed yield and seed infection. However, ecological control and chemical control of B. rapa black spot is not ideal. Therefore, breeding disease-resistant varieties of B. rapa is the most security, economic and effective way to prevent the black spot disease.In this study, the resistance evaluation method for black spot was firstly optimized. Using the optimized method,70B. rapa accessions were evaluated for the resistance to black spot disease. Furthermore, we carried out QTL mapping for the black spot resistance in B. rapa using a RILs population. Conclusions were derived from the result of above study.1.Leaves collected from infected B. rapa plants in Yunnan open field were used for the pathogen separation. Combining of observation of single pathogen colony morphology, conidia characteristics and molecular analysis by specific primer PCR, we confirmed that the pathogen was Alternaria brassicicola.2.Infection of A. brassicicola on detached leaves or intact plants was compared which revealed that no obvious difference between two methods. Meanwhile, the result showed that resistance levels were clearly distinguished when the detached3rd/4th true leaves from30days old plants being kept in dark and wetness circumstance for5days after being inoculated with inoculum of5X104conidia mL"1. 3.A collection of70B. rapa accessions was screened for resistance to A. brassicicola, including Chinese cabbage, non-head Chinese cabbage, Caixin, yellow sarson and turnip. Amongest these accessions,14were identified to be resistant to black spot disease materials and three were highly sensitive. This result indicates that A. brassicicola can infect virtually all types of B. rapa crops.4.A B. rapa RIL population was used for QTL mapping of resistance to black spot disease. The parental lines R-O-18and L58were different on resistance to black spot disease. Two QTLs related to black spot disease resistance were identified from twice phenotyping in January2013and March2013respectively by MQM embedded in MapQTL4.0. One of them named ABS-1, is located on chromosome A06. ABS-2and, ABS-3were co-localized on chromosome A05and were deemed as same locus.