Indutores de resistência em pepineiro (Cucumis sativus L.) contra a mancha de Corinéspora [Corynespora cassiicola (Berk. e Curt.) Wei]

Abstract

The search for alternative methods for plant disease control has been the target of several researches aiming to reduce the use of pesticides. Accordingly, this research evaluated the effect of chemical resistance inductors in the control of the corinespora s leaf spot [Corynespora cassiicola (Berk. end Curt.) Wei] in cucumber plants in a green house. Initially, an experiment was established to evaluate the effect in vitro of the inductors in the development of C. cassiicola. The products studied were the following Bion® in dose of 0.050 and 0.025g/500, Ecolife® in dose of 1.0 and 2.5 mL/500 and Fertisil® in dose of 0.025 and 0.05g/500 incorporated the BDA culture medium. The experiment was was randomly delineated with ten repetitions. The evaluations were achieved by measuring the colony diameters and evaluating the spore s production by the counting method in drop. The following commercial genotypes of cucumber plants were evaluated regarding the resistance and susceptibility to the aforementioned disease: Aodai, General Lee F1, Hokushim, Hybrid Japanese F1 (Soudai), Joia, Marketmore 76 (long green), Natsubayashi, Natsu suzumi, Sprint 440 II and Tsuyataro. The plants were inoculated at an age of 30 days with an inoculum s suspension in the concentration of 104 conidia/mL of the pathogen..The evaluation of the disease severity was made in agreement with the scale of gradings described by Oliveira et al. (2006). The genotypes Tsuyataro and Aodai were selected as susceptible and disease resistance, respectively, and used in the experiments with the resistance inductors. The inductors were tested in a green house, using plants of the Tsuyataro and Aodai genotypes, in random delineation with five repetitions. Doses in the range of 0.025, 0.050, 0.075 and 0.15g of Bion®/500mL; 1.0, 2.5, 3.0 and 7.5 mL of Ecolife®/500mL; 4.0, 7.5, 12.0 and 22.5g of Fertisil®/500mL were tested in cucumber plants. These products were applied 48 hours before inoculation with the pathogen. The severity, number and lesion size and the fungal incubation period were evaluated for each treatment. The data was statistically analyzed and the average compared by the Tukey s test (5%) using the SAEG statistic program. In the in vitro assays, the fungus was highly sensible to Fertisil® for the dosage used, causing a fungitoxic effect. The treatments with Bion® and Ecolife® had no effect upon mycelial growth and the fungal spore production. The application of inductors in a green house was not efficient to control the disease in the tested dose.