A Combined Identification Method for the Verticillium Wilt Resistance in Cotton by Using Pathogen Toxin

【Objective】 The Verticillium dahliae is the most harmful fungus for cotton plants and belongs to quarantine fungus.It is restricted to use Verticillium fungus to identify the Verticillium wilt resistance of cotton in the field. Some identification methods were compared in this research. In order to replace this traditional identification method, a new combined method by using Verticillium toxin instead of using its fungus was found in this paper. And this research provided an accurate, environment-friendly,convenient method to breed the cotton varieties with resistance to Verticillium wilt. 【Method】Method Ⅰ: The cotton was sowed in the greenhouse with conventional management and their roots were soaked in the toxin of Verticillium after 21 days. Then the disease indexes were counted after 72 h. Method Ⅱ: The antepenultimate leaves were collected at full-bloom stage of cotton, and they were cut to about 10-20 small leaf disc(the diameter is 1.5 cm) by hole puncher. Whereafter it was put into the Verticillium toxin, and counted the disease indexes and yellowing degree after 24 h. The final results were combined with two methods to evaluate the Verticillium resistance of candidate cotton lines. 【Result】This paper suggested that it would spend longer time in identifying the Verticillium wilt resistance by using dipping the root with toxin, sprinkling the spore suspension on root in non-bottom plastic film bottle and dipping the root with spore suspension. However, it would spend shorter time in identifying the Verticillium wilt resistance by using soaking the leaf disc with toxin and soaking the root with toxin. The best concentration of toxin in this research was 15μg·m L-1, when soaking the root with toxin was used to identify the Verticillium wilt resistance. Compared with the conventional method, the correlation coefficient was 0.94(P 0.01) in that concentration. When soaking the leaf disc with toxin was used to identify the Verticillium wilt resistance, the best concentration of toxin in this research was 18 μg·m L-1. The antepenultimate leaves should be collected at full-bloom stage of cotton and the correlation coefficient was 0.92(P0.01) compared with the conventional method. The combined method was a quick, accurate and environment-friendly method to identify the Verticillium wilt resistance of cotton. Compared with the conventional method, the correlation coefficient of combined approach was higher through the experimental results in 2013 and 2014. In 2013 and 2014, the correlation coefficient was 0.94(P 0.01) and 0.95(P 0.01),respectively.【Conclusion】 Using the combined method which includes soaking the leaf disc with toxin and soaking the root with toxin can identify the Verticillium wilt resistance accurately, environment-friendly and conveniently. It can replace the conventional method by using this combined method. The combined identification method was more reliable than the single identification method in identification.