Effects of Verticillum Wilt on Leaf Microstructure,Photosynthesis of Cotton

Objective] The purpose of this study was to determine the change of microstructure and photosynthetic characteristics in cotton leaves under different disease index levels (b0～b4)．Method] Through investigation and sampling in cotton fields, five treatments were designed based on disease index levels of cotton leaf, and the leaf photosynthesis was tested by WFS-3000 and microstructure was observed with Microscope ECLIPSE Ni-E. Result] With the increase in disease index levels, cotton leaf gradually lost green color, serious necrosis area occurred, with the leaf withered up till dried to death. The stomata of disease leaf incurred abnormally, increasing intercellular space in mesophyll tissue. Total thickness, upper and lower epidermis thickness, palisade tissue thickness and spongy tissue thickness all decreased significantly among all treatments; the trend showed as followed: total thickness was b0>b1>b2>b3>b4, upper epidermis thickness was b0>b1>b2>b3, lower epidermis thickness, palisade and spongy tissue thickness were consistent as b0>b1>b2. As a whole leaf of total thickness, upper, lower epidermis thickness, palisade and spongy tissue thickness were very significantly negatively correlated with leaf disease index levels, The correlation coefficient reached -0.6. The net photosynthesis rate, transpiration rate, stomata conductance gradually decreased and reached significant different with b0, leaf temperature increased, internal CO₂ first went up then down but no significant difference with b0. Conclusion] The results indicated that Verticillum wilt damaged leaf microstructure and impaired photosynthesis of cotton leaf.