QTL Mapping For Resistance To Tip-burn In Chinese Cabbage

Tip-burn of Chinese cabbage is a physiological disease.In recent years,the disease has become more and more serious,which mainly damages the northern region of China,and greatly affects the quality and economic benefits of Chinese cabbage.The genetic factors of tip-burn disease in Chinese cabbage are complex and belong to typical quantitative traits.In order to explore the occurrence regularity and genetic characteristics of the disease,the susceptible inbred line’TBS-3’and the high resistance inbred line’TBR-2’were selected to preliminarily construct the water culture system of tip-burn in Chinese cabbage,to explore the optimal time for laboratory identification of tip-burn,to summarize the characteristics of disease and the disease progression.At the same time,a F₂ population with 179 individuals was constructed by using’TBS-3’and’TBR-2’,and a F₃family was constructed from F₂self-crossing.In this study,SSR and Indel molecular markers were used to construct a genetic map of ten linkage groups in Chinese cabbage,and QTL mapping for resistance to tip-burn in Chinese cabbage was carried out,and the following results were obtained:1.Water culture of Chinese cabbage seedling stage was carried out with calcium deficient afdonin nutrient solution（using 10%Ca Cl₂）.Through observation,the best observation period of tip-burn disease was 40-45 days.2.By observing the hydroponic seedlings of Chinese cabbage,we found that the disease became more and more serious with the passage of time in the initial stage.The color of cotyledon edge deepened or even turned yellow and withered,and the symptoms were serious.According to the number of cotyledon diseases,it was divided into five grades:0-4.3.After 40-45 days of hydroponic cultivation with afdoning nutrient solution,the F₂population with high susceptible material’TBS-3’and high resistant material’TBR-2’was used.After 40-45 days of hydroponic cultivation,it was found that each population had different degrees of inductive resistance separation,and the disease index was calculated.The curve trend was normal distribution by Origin software analysis,and further proved that the trait belonged to the characteristics of quantitative traits.4.Based on 179 F₂ populations and 96 pairs of polymorphic SSR and Indel Markers,and with the help of joinmap4.0 software,a genetic linkage map with a total length of 893.9c M,including 10 linkage groups and 64 loci,with an average map distance of 14.4c M,was constructed.5.Based on the genetic linkage map constructed from F₂ population of susceptible and resistant cultivars’TBS-3’and’TBR-2’,three QTL loci were detected for resistance to tip-burn in Chinese cabbage,which were located on A01,A03,and A06 linkage groups respectively,Their contribution rates were 12.1%,15.7%and 9.4%,respectively.