Identification of heat tolerance and screening of heat tolerance indexes in different Chinese cabbage seedlings

Under the trends of global warming, the high and stable yield of Chinese cabbage has been affected by high temperature and heat damage. Establishing a simple, convenient, effective, and replicable heat tolerance evaluation model for Chinese cabbage is the key to screening and innovating of heat tolerance germplasm resources and to developing new Chinese cabbage varieties. In this experiment, 31 Chinese cabbage varieties were used as experimental materials. By experimentation with normal and artificially high (40 degrees C) temperatures, 12 seedling physiological indexes were determined. Based on the heat resistance coefficient (y) of every index, the heat resistance of different fast-growing Chinese cabbage varieties was comprehensively evaluated with multivariate analysis. The results showed that high-temperature stress had different effects on each index, and that the correlation between candidate indexes exhibited information overlap and a cross phenomenon. Principal component analysis transformed 12 single indexes of Chinese cabbage seedlings under high-temperature stress into 2 independent comprehensive indexes and generated the comprehensive evaluation value (D value) of heat tolerance for different varieties. On this basis, the evaluation equation for heat resistance in Chinese cabbage was established with the stepwise regression method. Cluster analysis enabled the classification of 31 Chinese cabbage varieties into four categories: extremely heat-resistant, moderately heat resistant, non-heat resistant heat intolerant. Extremely heat-resistant varieties and extremely heat intolerant varieties can serve as materials for the breeding of heat-resistant varieties and for the study of the heat-resistance and regulatory mechanisms of Chinese cabbage. chlorophyll a, malondialdehyde, and stomatal conductance can be used as evaluation indexes of the heat tolerance in Chinese cabbage at the seedling stage. Finally, six commercial Chinese cabbage varieties were used to verify the model. The verification results show that the model is accurate and reliable and can be used in production practice.