selection of genotypes susceptible to Verticillium wilt cotton using morphological and physiological characteristics in greenhouse conditions

Verticillium wilt disease is one of the most important damaging and limiting factors for cotton production worldwide. This pathogen causes leaf chlorosis, necrosis or wilt, leaf or pollen drop, and even plant death. It also reduces the quantity and quality of the product. Because of the economic importance of the cotton disease Verticillium wilt, the best way to control this disease is to use tolerant varieties. Therefore, breeding resistant varieties in a wide range is considered one of the most effective control methods. This experiment was conducted to determine the effect of the disease on the morphological and physiological characteristics of cotton cultivars in order to identify tolerant genotypes

The experiment was carried out during two years 2020-2021 and in a factorial form in a completely randomized design with three replications in the greenhouse of Khorasan Razavi Agricultural Education and Natural Resources Research Center (Plant Protection Department). In the first year, ten Iranian cotton cultivars belonging to Gossypium hirsutum were cultivated. In the first year experiment, cotton agronomic traits such as plant height, number of leaves, number of branches, crown diameter, leaf area size, disease severity, chlorophyll index, relative leaf water content and electrical conductivity were measured. In the second year, two tolerant cultivars (Bakhtegan) and sinsitive (Varamin) resulting from the first-year experiment were cultivated in the greenhouse along with the resistant cultivar of Thermous 14. At this stage, the amount of proline, soluble carbohydrates and total phenol was evaluated at different times after inoculation with the pathogenic fungus. All traits measured over two years using SAS statistical software were analysis of variance and the means were compared using Duncan's test.

In the first year, it was found that among the ten genotypes grown, all agronomic traits (except plant height) were higher in the Bakhtegan cultivar and lower in the Varamin cultivar than in the other cultivars. Under infection conditions, disease severity was highest in Varamin and Cocker100 cultivars. The lowest severity of the disease was in the variety Bakhtegan. Physiological traits such as chlorophyll index and relative water content were higher in Bakhtegan and lower in Varamin. The opposite was true for membrane electrolyte losses. In the second year, it was found that in the three cultivated genotypes Thermous14 (resistant), Bakhtegan (tolerant), and Varamin (sensitive), the amount of biochemical traits proline, carbohydrate, and total phenol was significantly increased in the infected plants compared to the control plants (no inoculation with pathogenic fungi).

Therefore, plants with more leaves, higher chlorophyll index and relative water content, lower electrolyte leakage, more proline, carbohydrates and phenols are more resistant to infection.