| In recent years,the proportion of defoliating type in the two strains of Verticillium dahliae in Xinjiang cotton has increased and become the dominant strain in the field.In view of this phenomenon,the conidia of the defoliating strain V592 and the non-defoliating strain I6 were used to infect a number of different cotton varieties in equal amounts to explore whether the difference in infection ability and colonization ability of the two strains was related to that defoliating strains becoming the dominant strains.At present,no effective control agents have been found for this disease.In this study,8 chemical agents and 1biocontrol agent were used to determine the biological characteristics and pathogenicity of two strains of Verticillium dahliae to screen effective agent for the control of cotton verticillium wilt.The main findings are as follows:1.The defoliating strain V592 and the non-defoliating strain I6 were mixed in equal amounts to inoculate the 39 cotton varieties,respectively.The PCR detection results showed that the infection rate of the defoliating strain V592 was 72.44%,and that of the non-defoliating strain was 7.33%,and the mixed infection rate of the two strains was 6.24%,indicating that the infection ability of the defoliating strain was stronger than that of the non-defoliating strain,and the non-defoliating strain was mainly mixed with the defoliating strain to infect cotton.Among the three cotton series varieties,Xinluzao series varieties had the worst resistance to Verticillium wilt,and Gossypiam barbadense cotton series varieties had the best resistance.The biomass of the two pathogenic strains in the infected cotton plants was determined,and the results showed that among the 13 cotton varieties infected by the two strains alone,the biomass of the defoliating strain V592 in the 10 varieties significantly higher than the non-defoliating strain I6;among the10 varieties infected mixedly by the two strains,the biomass of the defoliating strain V592 in cotton plants was significantly higher than that of the non-defoliating strain I6,indicating that the colonization ability of defoliating strain is stronger than that of the non-defoliating strain.To sum up,the defoliating strain in Xinjiang cotton fields became dominant strains due to their stronger infection ability and colonization ability than those of non-defoliating strain.2.The inhibitory effects of the 8 chemical agents on the two strains of V.dahliae showed that each chemical agent could inhibit the colony growth rate,conidial and microsclerotial production of the two strains and their penetration ability when each inhibitor reached a certain concentration.Among them,the98% tricyclazole has the best inhibitory effect on the two strains,followed by 98% imazethapyr;and 98%flumetsulam has the worst inhibitory effect.Although acetolactate synthase(ALS)inhibitors have no effect on the pathogenicity of the two strains,they can effectively inhibit the microsclerotia production of the two strains,which are the resting structures produced by V.dahliae and play an important role in the disease cycle,therfore,in practical production,ALS inhibitors maybe be used to reduce the source of primary infection in the next year.3.The control effects of 5 chemical agents and 1 biocontrol agent against two strains of V.dahliae were measured by three ways including: inoculating fungi first and then applying agent,inoculating fungi and applying agent at the same time,applying agent first and then inoculating fungi.The results showed that the control effect of 40% tricyclazole SC 1000 times diluent on the defoliating strain V592 was 54.22-71.20%,and the control effect on the non-defoliating strain I6 was 40.74-55.09%;The control effect of the biocontrol inhibition Paenibacillus polymyxa KN-03 SC against defoliating strain V592 was 38.36-74.75%,and that of the non-defoliating strain I6 was 28.47-70.79%.40% tricyclazole SC and Paenibacillus polymyxa KN-03 SC was applied with the two strains of V.dahliae at the same time,respectively,the control effect was the best and both were higher than 55%.The above shows that 1000 times diluent of 40%tricyclazole SC and biocontrol inhibitor Paenibacillus polymyxa KN-03 SC have control effects on both strains of V.dahliae. |
