Ação inibitória de extratos vegetais, óleo de nim, produtos abióticos e bacillus sobre corynespora cassiicola, agente da mancha-alvo do mamoeiro

Abstract

The Spot target of papaya caused by the fungus C. cassiicola, is a disease that has attracted increasing attention in recent years due to early utbreaks and intense, resulting in damage to the production of papaya. Therefore, the objective was to characterize the disease in the field, proving the pathogenicity of the fungus causing the disease, pathogen characterization, test the effect aqueuos extracts of neem, citronella and eucalyptus, neem oil, to evaluate the effect of isolates Bacillus, apart from in abiotics products Ecolife ® and Stubble-Aid ® on the fungus C. cassiicola. The experiments were conducted at the Laboratory of Plant Pathology and at the experimental Farm of the School of São Luís/UEMA, this was conducted in a randomized block design, with four replications and eleven treatments (varieties and selections), with six plants each. To take the data from the characterization of the disease, the pathogen and the confirmation of the causative agent was considered two useful plants (central) in the plot. The parameters evaluated in the field under conditions of natural infection were: a) number of leaves/plant, b) number of leaves with lesions, and c) number of lesions/leaf. For the inhibition of in vitro mycelial growth of C. cassiicola added to the neem oil at 0; 1,25; 2,5; 3,75 and 5%, to the aqueous extracts of neem, citronella and eucalyptus to 10, 15 and 20% and abiotics products Ecolife ® and StubbleAid® to 0; 0,25; 0,5; 0,75 and 1% on PDA. In assessing the fungistatic effect of Bacillus were nine isolates, assessed by the percentage of inhibition. All varieties and selections provided to patients ranged from 89,69 to 100 % of lesions per leaf, causing a reduction of plant xii 13 development. The selection Golden presented lesions/leaf of order 17,87 showing some promise in breeding programs aimed at obtaining cultivars less susceptible to this disease. Selections Canaã Golden and Canaã Sunrise Solo showed lesions/leaf, 98,75 and 77,12, respectively. Symptoms started by white dots, with yellow halo, evolving into brown circular spots. Spores of the fungus C. cassiicola on PDA showed formats straight and slightly curved, forming 3-8 septa, measuring 76,76 – 165,26 µm length and 13,50 – 2190 µm wide (average of 16,54 x 98,15 µm) hilum presenting at the junction of the conidiophore with conidia. The neem oil and extracts of neem, citronella and eucalyptus showed inhibitory effect on mycelial growth of C. cassiicola. Emphasizing that neem oil hit percentage of inhibition ranging from 61,66 to 69,88 % in the four periods, shown to be effective at low concentrations. The Bacillus isolates showed antagonistic potential in vitro mycelial growth of C. cassiicola. However the isolates 31 were more promising as a biological control agent, showing percentage inhibition of 63,36 %. The products Ecolife ® and Stubble-Aid ®, in all concentrations inhibited the growth of C. cassiicola, ranging from 31,56 to 100 %. These results indicate that the use of alternative control has potential in the management of Target Spot of papaya.