Yield Evaluation of the Grey Mildew (Ramularia areola) Resistance Trait in Two Cotton Cultivars

The success of the Brazilian cotton production, in terms of yield potential and fiber quality, is recognized worldwide. However, in many production regions, cotton yield improvement is hindered due to the occurrence of many constrain factors. In the Cerrado, one of the main causes of yield losses is the high incidence of Grey Mildew (Ramularia areola) disease, which in some cases, requires up to 10 applications of fungicides for its control. The objective of this research was to evaluate the performance of two cotton cultivars (FMT705 and FMT707) that confer resistance to Grey Mildew. The experiment was conducted in two different regions of Mato Grosso, with each location having a specific cultivation method: conventional (0.90 m) and narrow row spacing (0.45 m).  The treatments of the experiment consisted of two factors: cultivars and fungicide application that were arranged in a randomized complete blocks design with four replications. Three susceptible cultivars (FMT701, DP604 BG, and FM993) were used as a control check and for the narrow row experiment the cultivar FMT523 was also added to the treatments. The fungicide treatment consisted of 2, 3, 4 and 5 applications using a commercial product with a mixture of Azoystrobin & Cyproconazole. The parameters measured included severity of the disease and yield. Results of the experiment indicated that the cultivars FMT705 e FMT707 were immune to Grey Mildew. As expected, fungicide application decreased the severity of the disease in all susceptible cultivars.  However, yield parameters were not affected by the fungicide treatments, the highest yields were observed by the two resistant cultivars, FMT705 and FMT707. In conclusion, the use of Grey Mildew resistant cultivar is an effective tool to protect cotton yield potential in Mato Grosso.