Study On Key Technology Of Cotton Verticillium Wilt Resistance Evaluation And Molecular Identification Method

Verticillium wilt, which is the soil-borne vascular disease, severely restricts the cotton production.This disease can exist long period and is difficult to be controlled by chemical and biological method.Cultivating the resistant varieties is considered as the most effective strategy. Accurate resistance evaluation of cotton varieties is the key technology for screening or validation of cotton resistant varieties. The effects of Verticillium wilt on cotton are comprehensive and multifactorial, which need fully assessment. In this study, 14 mainly Department of Agriculture suggested cotton varieties were tested for the different disease resistance evaluation technical procedures, including pathogen inoculation concentration of the standard disease nursery, grading standard related to cotton yield. The28 cotton varieties with different resistance were studied to explore the rapid resistant testing method based on qPCR. Our main results are as following:1. The plot trail was conducted in the manual disease nursery. The optimal inoculation amount of different inoculation methods was determined by the disease index of susceptible variety Jimian11 in concentration gradient. The disease occurrence of Jimian11 in different inoculation concentration exhibited consistency with parabolic dynamic relationship in both inoculation methods. Finally, the ideal concentration of plot inoculation and column inoculation was set as 60g/㎡ and 10g/m based on disease uniformity and credibility.2. Zhongzhimian 2, Lumianyan 28, Zhongmiansuo 50, Zhongmiansuo 49 and Zhongmiansuo63 were tested varieties. 10 plant was set as a unit. The divergence rate from the comparison between different units and big group with 100 plants respectively was used for minimum investigated plants number. Results showed that 50 was the minimum investigated plants number with the divergence rate less than 5%.3. The new grading standard was updated based on the analysis between the yield and disease levels of tolerant varieties Lumianyan28 and Zhongmiansuo 63. It was ranked as five levels by diseased rate, as following: 0 level(0%)、1st level(1%-33%)、2nd level(34%-66%)、3rdlevel(67%-99%)and 4st level(100%). Compared with healthy plants(0 level), the cotton yield of 1st level, 2nd level, 3rd level and 4st level was significantly reduced 20.9%、34.4%、50.1% and 71.6%, respectively.4. Fourteen mainly recommended cotton varieties in 2014 and two control Zhongzhimian 2,Jimian11 were used to assess the resistance evaluation methods with the comparison between disease index and relative AUDPC in 2014 and 2015. Compare with disease index with 75% consistency rate,relative AUDPC will be more scientific and reliable to evaluate cotton variety resistance, which showed100% consistency.5. The effects of Verticilium wilt severity on fiber quality of two cotton varieties Lumianyan 21 and Zhongmiansuo 63 were investigated and analyzed at the different growth period of cotton. Results showed that the fiber length and micronaire obviously reduced following with the increase of disease level. Meanwhile, Verticillium wilt could affect the Fiber strength, Fiber elongation and Fiber uniformity, and the effects were different in different years and varieties.6. With the aid of qPCR technology and disease occurrence in severe disease field, 28 cotton varieties with different resistance were used for analysis of the relationship between pathogen colonization in the root and resistance. 1 day post inoculation was the best point to collect samples,since the colonization amount showed significant difference among varieties with different resistant levels. There is some kind of correlation between pathogen DNA colonization amount and disease index.The varieties were categorized as resistance, tolerance and susceptible with the fungal DNA amount as0~1 pg ng-1, 1~2 pg ng-1 and more than 2 pg ng-1, respectively.In summary, it is the key technology to clarify the pathogen inoculation concentration, reliable disease grading standard and scientific investigated plant number to make sure the resistance evaluation.This study provided the scientific evidence for improving cotton variety resistance technological regulation, resistance evaluation, stimulating new resistance variety breeding, authorized and promotion.