ABSTRACT
The aim of this study was to evaluate the reaction of eleven cotton genotypes to the fungus Rhizoctonia solani AG-4, at seedling stage, with potential for use in future genetic breeding programs, as well as the benefits of cotton seed treatment with fungicides for each tested cultivar. This experiment was carried out during two years at Embrapa Western Agriculture, in Dourados, Mato Grosso do Sul State, Brazil, under greenhouse conditions. Seeds of each cultivar, treated and untreated with the fungicide mixture tolylfluanid + pencycuron + triadimenol (30+50+50g a.i./100kg of seeds), were sown in sand contained in plastic trays, by placing in equidistant 3-cm-deep wells. Inoculation with R. solani was done by the homogeneous distribution of the fungus inoculum onto the substrate surface (2.5g of the fungus inoculum/plastic tray of 56x35x10cm). The fungus was grown for 35 days on autoclaved black oat seeds and then ground to powder by using a mill (1mm). The evaluations were done based on symptom development and seedling survival, using initial and final data on emergence, post-emergence damping-off and seedlings lesioned by the pathogen. Significant effect of the interaction cultivars x fungicide treatment was observed (P<0.05). The importance of cotton seed treatment with fungicides was clearly demonstrated, and the best results in relation to emergence and disease level (damping-off and lesioned seedlings), regardless of the tested cultivar, were obtained when the seeds were treated. In the absence of seed treatment with fungicides, different behaviors among cultivars in relation to the attack of R. solani were observed, being distinct in BRS Aroeira, followed by BRS Cedro, BRS Ipê and FMT 701, which showed higher tolerance to R. solani. It is emphasized that resistance alone is not sufficient for proper control of this pathogen. However, it may be useful if integrated with other complementary control strategies, including seed treatment with fungicides, strengthening the concept of integrated disease management.
Keywords
Gossypium hirsutum; damping-off; emergence; lesioned seedlings