Epidemiologia comparativa da mancha parda e queima das folhas da mandioca

Abstract

Leaf spots are one of the main problems affecting the cassava production, especially brown leaf spot (BLS) and blight leaf spot (BliLS) caused by Passalora henningsii and Passalora vicosae, respectively. The occurrence of these leaf spots in commercial areas in the northeastern region of Brazil, mainly in the state of Pernambuco, and the absence of information demonstrate the need for further studies on these diseases. In this study, the effect of temperature and luminosity on conidial growing/germination was evaluated in vitro. The range of temperature that was favorable to the growth of P. vicosae was broader than P. henningsii. This is an intrinsic characteristic of the pathogen that allows the disease to develop in different seasons and growing regions. The percentage of germination of conidia was reduced in the presence of light for P. vicosae, whereas for P. henningsii the germination was similar both in the presence or absence of light. To better understand the behavior of the diseases, a comparative epidemiology of BLS and BliLS was performed in growing areas in the regions of the Agreste and Zona da Mata of Pernambuco. The results demonstrated that BLS occurs more frequently in the Agreste, whose temperatures are lower and the humidity is high. In the Zona da Mata, with higher temperatures during the evaluation period, there was predominance of BliLS. Levels of severity were highest in the lower leaves, and were correlated with the increase of the age of the plants. Defoliation occurred earlier in the Agreste than in Zona da Mata, reaching similar levels in both regions (25% in all growing areas). Both BLS and BliLS severity were reduced by application of the fungicide flutriafol, showing that the chemical control may be a strategy to control these leaf spots. In general, the results obtained in this study allow a better understanding of the epidemiology of BLS and BliLS, which are little studied diseases. The information may be useful in the development of management strategies aiming to reduce the damage caused by these diseases in the cassava crop.