Avaliação do dano provocado por Bipolaris maydis em Panicum maximum cv. Tanzânia-1

Abstract

The leaf spot caused by Bipolaris maydis represents one of the main diseases of the tanzania grass (Panicum maximum cv. Tanzania-1), however there is no information about the damage produced by this disease. The aim of this work was to evaluate the damage caused by B. maydis in the amount and quality of the tanzania-1 grass production. Initially a diagrammatic scale was elaborated for the disease evaluation and afterwards was made an assay in greenhouse. Tanzania-1 grass plants was cultivated in tubes of PVC (50 cm of height x 15 cm of diameter) containing a mixture of soil and sand (3:1). Four treatments were used (water and 102, 104 and 106 conidia/ml) for obtaining different levels of disease, with seven repetitions. Severity and number of tillers were evaluated weekly. After four weeks was evaluated the weight of the fresh matter of leaves (FM), percentage of dry matter (PDM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF). The diagrammatic scale presented the following severity levels: 0.4; 1; 3; 6; 13 and 26%. The severity of inoculated plants varied from 0 to 20%. The disease reduced significanthy the tillering and FM after the second evaluation (P <0.05). There was not significant correlation among the variables PDM, ADF and the area under disease progress curve (AUDPC). However, there were positive (P<0.01) and negative (P <0.05) correlations among CP and NDF, respectively, with AUDPC, as possible result of the activity of the pathogen. These results showed that B. maydis inhibits the development of the tanzania-1 grass and it promotes alteration in the quality of the forage, but further studies are necessary to understand the involved mechanisms