Comparação de escalas de avaliação de queima de turcieum e mancha branca, e incidência de fungos causadores de grãos ardidos em genótipos de milho

Abstract

In recent years, the incidence and severity of diseases affecting maize has increased considerably in Brazil. Among the main foliar diseases that occur, the burning of turcicum and the white spot require some attention, especially in second crop planting. To assist in the control of these diseases, some authors have developed methods of evaluation based on diagrammatic scales. Another common concern in corn crops in Brazil are the fungi that cause burned grains, such as those of the genus Fusarium and Penicillium, which may develop in the plant in the field or after harvesting. In addition to devaluing the final product, such fungi can produce toxic substances, called mycotoxins. The objective of this work was to compare two foliar disease evaluation scales and to observe the incidence of fungi causing burnt grains in 75 maize genotypes. Two experiments were conducted at the Federal University of Uberlândia. The first was in Campus Glória Farm, with a randomized complete block design, in a factorial design of 75 genotypes x 2 evaluation methods, with three replications. Two diseases, turcicum burning and white spot, were evaluated. The evaluation was visual, considering the leaf area affected by the diseases, assigning values established in the diagrammatic scales used. From the field data the Area Under the Disease Progress Curve (AUDPC) was calculated. In the second experiment, carried out in the Laboratory of Mycology and Plant Protection, the grains harvested in the previous experiment were used, which were kept in a refrigeration chamber for the analysis. 100 grains, divided into 4 gerboxes, were used for each genotype evaluated, being 3 replicates. The analyzed variables were weight and the development of fungi, being the identification of them visual, through a magnifying glass and stereoscopic microscope. The data of both experiments were submitted to analysis of variance, applying Scott-Knott's test, and the evaluation scales compared through the Pearson's correlation coefficient. There was a difference between the genotypes for the two diseases. The zero sheet scales presented lower AUDPC values, differing from the whole plant scale. However, the correlation coefficient was positive, indicating a linear relationship between the methods. Only the weight of a thousand grains presented a significant difference between the genotypes. Fusarium and Penicillium fungi were identified in all genotypes and at high incidence, but did not affect the weight of the grains.