Studies On Pathogenicity Differentiation Of Verticillium Dahliae Of Cotton In Naturally Infested Soil

Verticillium dahliae kleb. is the worldwide soil-borne fungus which causes severe vascular wilt in more 660 hosts, including cotton, strawberries, red pepper, water melon and many other crops. The pathogenic differentiation of strains isolated of V.dahliae kleb. from different ecological regions is obvious, it could be divided into three patho-types, strong, mild and weak. However, that of it from one field ecological system can also be observed and that could be divided into three patho-types, too. Typeâ… (a severe defoliating virulence), Typeâ…¡(an intermediate one), Typeâ…¢(a mild one). In order to reveal the genetic relationship among the strains, definite the pathogenic differentiation, author first studied the symptom types in one field ecological system, and spatial pattern of verticillium wilt on cotton, then the determination of control of pathogenicity of verticillium wilt under artificial incoculation in laboratory were carried out and the result were as follows:1. The variance of pathogenic types was obvious. It could cause following symptom types in the shan 2365 cottonfield: defoliating type, spotted wilt and leaf scorch type and yellow spot type. When disease incidence was 62% defoliating and non-defoliating symptom was 25.7% and 36.7%. The characteristic of defoliating type symptom was that annual epidemic on-set phase was early, fast and defoliating. Spotted wilt and leaf scorch type could cause blight. Yellow spot type only caused mild mosaie in few plants.2. Determing verticillium wilt was easier from leaves, Stem, fruit branch, root and so on. But determination microsclerotia of verticillium dahliae kleb. from cotton field was harder to use PDA or PDS. Selective mediums should be used. Among 5 selective mediums which were used determed verticillium wilt from soil, MSEA is one of the simplest, so it was used for determing verticillium wilt in this experiment.3. The variance of disease incidence of different organs in cotton plant was obvious. Among leave, fruit branch and up stem, the disease incidence in leaves was the most, up to 82%; The disease incidence in fruit branch was the second most, average up to 49.5%. What's more, the distribution of V. wilt in different positions of fruit branch was also different. From the tip of branch to intermediate to end, that was 70%, 51.7% and 26.79%, respectively. The...