Fungos sapróbios do semi-árido nordestino no controle de Alternaria solani em tomateiro

Abstract

Tomato plant is susceptible to many diseases, being black spot one of the most important ones, caused by Alternaria solani. The occurrence of many diseases during the tomato cultivation cause economic losses, being necessary effective management control. Chemical is the most available method to producers, providing negative effects to the human being and environment. The need of alternative strategies to reduction and rational use of pesticides is urgent. Therefore, this study aimed to evaluate the use of saprobe fungi from the northeast semi-arid, for controlling Alternaria solani from the tomato plant through its possible direct action over antibiosis or production of volatile compounds by inducing resistance mechanisms (activation of proteins related to pathogenesis) and the physiological mechanism (chlorophyll), as well as evaluate the effect of treatments in the fruits postharvest quality. The antibiosis was evaluated by the direct confront of the saprobe fungi Stachylidium bicolor, Periconia hispidula, Brachysporiella pulchra, Myrothecium leucotrichum, Dictyosporium tetraseriale, as well as the basidiomycetes Pycnoporus sanguineus with A. solani in two different medium culture the potato-dextrose-agar (PDA) and corn-carrot-agar (MCA). To evaluate the mycelia growth of A. solani, mycelia discs were transferred to Petri dishes containing PDA medium with the filtered saprobes fungi at concentrations of 0,5, 10, 15 e 20%. The production of volatile compounds was verified using polystyrene plates halved containing PDA medium. On one side mycelia plates from antagonists were placed. Three days later, on the opposite site, a disc of mycelia phytopathogen was peaked. In the direct confront it was observed that the isolated B. pulchra, M. leucotrichum, D.tetraseriale and P. sanguineus, in both cultures, inhibited the mycelia phytopathogen growth. The fungus M. leucotrichum, was the only one to form halo inhibition, followed by further growth of saprobe fungi over the pathogen, indicating hyperparasites. In vitro, the treatment with the filtrate of M. leucotrichum at concentrations of 10, 15 and 20%, inhibited the growth in 28,9; 27,4 and 32,6%, respectively. The production of volatile compounds able to reduce the vegetative growth of the pathogen was not verified. The experiment in the greenhouse was composed by the filtrated of the saprobe (20%), in addition to water controls, BION® (0,5 mg i.a.mLvii 1) and filtrated of P. sanguineus (20%) where tomato plants were treated three days before the inoculation to evaluate the severity, enzyme activity, chlorophyll contents and biometric of plants. Severity was reduced in the 4th leaf treated by S. bicolor, M. leucotrichum and BION®in 96%, 35,8% and 92,3%, respectively. The activity of peroxidase β-1,3 glucanase and lipoxygenase were higher at 120 hours post-inoculation in plants treatment with the filtrate of S. bicolor, M. leucotrichum and BION® in 96%, 35,8% and 92,3%, respectively. The filtrates of S. bicolor and M. leucotrichum have increased the contents of chlorophyll a, b and total as well as the plants height. However, pre-harvest treatments performed in the field did not affect the post-harvest quality in tomato fruits. This study indicates the efficiency of the saprobe S. bicolor and M. leucotrichum in the alternative control of the black spot in the tomato plant.