Epidemiology of Cotton Verticillium wilt in Golestan Province, the North of Iran

Aims: The efficiency of Verticillium dahliae inoculum density (ID) on tolerant cotton Verticillium wilt in cotton growing of northern province of Iran (Golestan) and the influence of temperature (T) and relative humidity (RHA) on this relationship.
Place and Duration of Study: In several fields in Golestan province, northern Iran, between 1992-2009.
Methodology: The microscleotia per gram of soil samples and disease severity of cotton Verticillium wilt were determined in several fields. Physiological time was determined as the cumulative number of degree-days from the time of sowing.
Results: ID for overall fields and years varied between 2 and 47 propagules per gram of air-dried soil with average 18.961 ± 0.730. The pattern of diseased plants varied with fields and years. Linear regression analysis between ID (propagules per gram of air-dried soil) of V. dahliae at planting time and the disease severity for all years closely followed the linear curves. The straight line models described the increase in disease intensify index over the accumulated physiological time from sowing. The effect of temperature, number of days with above 28ºC and the area under RHA from sowing with respect of pathogen ID in soil (MS) on the final disease severity (Y) were significant and fitted a Y= 65.840- 0.0034 RHA + 0.57MS- 1.7T model with R2 = 0.859 and significant F function (p≤ 0.0001).
Conclusion: this study revealed that Verticillium wilt severity of cotton related to V. dahliae ID in soil at planting and negative exponential models described the relationships. This work also demonstrated the influence of temperature (days with above 28°C) and relative humidity on the efficiency of Verticillium ID for disease severity. This simulation may be important to consider when selecting a cotton cultivar for planting or in breeding programs.