Relationship of Verticillium Wilt Resistance with Plant Anatomical Structure and Biochemical Metabolism in Upland Cotton

Verticillium wilt is an important disease in the world, and it threatens the development of cotton production seriously. Since 1980' s, this disease has become more and more serious in China, especially in 1993 when a disaster broke out all over the main cotton production regions in China, which led to a huge economic loss caused from the decrease in the cotton yield and quality due to the disease, and it has threatened the cotton production in China greatly. It is useful to study the mechanism of cotton resistance to Verticillium wilt for the resistant cotton breeding and the integrated controlling. In this paper, the mechanism of cotton resistance to verticillium wilt was studied via the comparative analysis of the plant anatomical structure, enzyme activity and root exudates in the plants at the different time after inoculation with Verticillium dahlias , an Anyang strain with intermediate virulence, using 8 upland cotton cultivars with different level of the disease resistance as the materials. The results showed that there were more pith rays, xylem parenchyma cells, and vessels with thicker wall and smaller diameter in stems and taproots of the resistant upland cotton cultivars, comparing with that of susceptible ones (Table 1), which may conduce to the plant resistance to the infection and spreading of Verticillium dahliae. The relationship between the POD activity and verticillium wilt resistance in the upland cotton cultivars was not obvious at the different time after inoculation ( Fig. 1) , but the PAL activity was increased in the disease resistant cultivars much more greatly after inoculation than that in the susceptible cultivars. After reached the peak value, the descent rate of PAL activity in resistant cultivars was much less than that in susceptible ones, and the high level of PAL activity was hold longer in resistant cotton cultivars than that in susceptible ones as well (Fig. 2) . The amino acids in the root exudates of resistant cultivars were much less than that of susceptible ones. Compared with susceptible cultivars, there were lack of aspartic acid, threonine, glutamic acid, alanine, isoleucine, leucine, phenylalanine, lysine and proline in the root exudates of resistant cultivars, but arginine that was lack in the susceptive cultivars on the contrary ( Table 2) . The saccharide types in the root exudates were no difference between the two kinds of cultivars, but the contents of glucose,fructose and sucrose in the root exudates of susceptible cultivars were much higher than those in resistant ones (Table 3) . The results indicated that the character of PAL activity expressed after inoculation with Verticillium dahliae, as well as the kinds and contents of araino acids and soluble sugars in the root exudates can be used as the important biochemical criterions in the judgment of cotton cultivar resistance to Verticillium wilt.