Studies On The Mechanism Of Resistance To Verticillium Dahliae In Cotton

In this paper, Two cotton varieties with different resistance to verticillium dahliae that were cultivated indoors were used as experimental material to studied disease resistance mechanism. The activities of superoxide dismutase (SOD), peroxides (POD), MDA content, relative electrical conductivity and dissoluable protein content in leaves and roots cell of different cotton cultivars were measured after inoculated with V. dahliae and treated with crude extract of V.dahliae. The relationship between physiological-chemical changes and disease resistance were analyzed. Meanwhile, on the base of pathological plant anatomy, The continuous section slices of different position of disease plants were observed by means of optical microscope .The results showed as follow:1. The cotton have symptom coming on in four real leaf time. Originally, disease leaf appeared chlorotic , water stain and slight wilt .Then, symptom spread around whole leaf. Finally, whole leaf deficit water and wilt.2.As for activity of POD, before inoculated with V.dahliae and treated with toxin , both leaves and roots, the activity of POD of the resistant cultivar were higher than the susceptible cultivar. After inoculated and treated, the activity of POD of both the resistant and susceptible cultivar were higher than control, but the change range of both sides were different. As for activity of SOD, After inoculated with V.dahliae and treated with toxin, The difference exists between cultivars and positions. After treated, in leaves ,the activity of SOD of the resistant cultivar increased, but that of the susceptible cultivars decreased. While in roots treated, both the resistant and susceptible cultivar were lower than control.3.After inoculated with V.dahliae and treated with toxin , The change tendency MDA content and relative electrical conductivity were similar between cultivars and positions. After treated, MDA content and relative electrical conductivity increased, and MDA content and relative electrical conductivity of the susceptible cultivar were higher than the resistant cultivar significantly. Meanwhile, the change range of the susceptible cultivar were larger than the resistant cultivar.4. After inoculated with V.dahliae and treated with toxin , The change of dissoluble protein content have difference between treatment and position. But in total level, the content of the resistant cultivar were larger than the susceptible cultivar.5. It was observed that there were more pith rays, more quality of xylem parenchyma cell and more thickness of vessel cell in the resistant cultivars, comparing with the susceptible ones through optical microscope.6. Through optical microscope, Mycelia, tylose, and gum in the infected vessel were found. Also infected vessel walls of disease were thicker than which of the vessels of health plants.7. The infected vessels rate of disease plants became lower with the different position of disease plants from bottom to top. And the inferior the resistance, the more the infected vessels are.8. All results showed that vessel blockage was not the major fact causing plant wilting . while toxin was the major factor.