Selection of Genotypes Susceptible to Verticillium wilts Cotton using Morphological and Physiological Characteristics in Greenhouse Conditions

Verticillium wilt disease is one of the most important damaging and limiting factors of cotton cultivation worldwide. This disease reduces the quantity and quality of the product. Due to the economic importance of Verticillium wilt cotton disease, the best way to control this disease is to use tolerant cultivars. This experiment was performed to determine the effect of disease on morphological and physiological characteristics of cotton cultivars in order to identify tolerant genotypes.

The experiment was conducted in 2020 in the greenhouse of Khorasan Razavi Agricultural Education and Natural Resources Research Center (Mashhad Plant Protection Department). Ten commercial Iranian cotton cultivars belonging to Gossypium hirsutum including Varamin, Sahel, Bakhtegan, Khorshid, Armaghan, Mehr, Koker, Khordad, Kashmar and Deltapine were planted in factories in a completely randomized design with three replications in the greenhouse. The first factor was cotton cultivars and the second factor was the contamination of cotton cultivars with fungal isolates.

The results of analysis of variance of the measured traits on the studied genotypes showed that the tested cultivars in terms of leaf number, crown diameter, number of branches, leaf area, chlorophyll index, disease severity, relative leaf water content and electrolyte leakage membranes were significantly different at the 1% probability level. This difference was not observed in terms of plant height. Comparison of the mean of the above traits (except plant height) in the treatment of contamination levels, indicated that the cotton plants  inoculated with the pathogenic fungus Verticillium wilt compared to control plants (no fungal infection) had lower number of leaves, number of branches , leaf area and crown diameter. Mean comparisons of the above traits were performed between genotypes. Some genotypes can be selected for field experiments in terms of superior study traits. The results of comparing the mean interaction of infection × cultivar for all traits (except plant height) were significant at 1% level. Under the conditions of infection, the highest severity of the disease was related to Varamin and Cocker-handard cultivars. While the lowest severity of the disease was related to Bakhtegan cultivar.

The results showed that Verticillium wilt disease reduces the number of leaves, number of branches, leaf area, crown diameter, chlorophyll index and relative water content. While this disease increases the electrolyte leakage of cell membrane. In this regard, a negative and significant phenotypic correlation was observed between disease severity and number of leaves, branch, crown diameter and chlorophyll index. There was a positive and significant phenotypic correlation between disease severity and membrane electrolyte leakage. Therefore, plants with more leaves, higher chlorophyll index and relative water content and lower electrolyte leakage are more resistant to infection.