Among the disease causing leaf spot in cotton, the gray mildew (Ramularia areola Atk.) has become important due to environmental conditions favorable for development of the disease susceptible cultivars, consecutive and intensive and extensive cultivation. This work evaluated the resistance of the cultivars Delta Opal, Acala 90, Makina, Delta Penta and Sure Grow 821 to resistance the R. areola, in field conditions in FCAV-UNESP. The disease occurred under natural infection and, its severity was evoluated weekly, in thirty previously marked plants using the following rating scale: 1 = 0%, 2 = up to 5%, 3 = 5,1 to 25%, 4 = 25,1 to 50% and 5 = over of 50% of foliar area with symptoms. The monomolecular model was better adjusted to the data in comparison with the logistic, exponential and Gompertz models, for elaboration of the curves of progress of the disease. The analysis of the data indicated significant differences between the genotypes.The cultivars Delta Opal, Makina and Sure Grow 821 were more susceptible and Delta Penta and Deltapine Acala 90 more resistant to gray mildew.
Gossypium hirsutum; Cultivars reaction; Curves of progress of diseases
