Tolerância de genótipos brasileiros de feijoeiro ao sulfentrazone

Abstract

In the bean crop there are limited options of herbicides to control eudicotyledons weeds in pre-emergence. There is little information on the tolerance of Brazilian dry bean genotypes to the herbicide sulfentrazone and the relationship between genotype characteristics and tolerance. Five studies were carried out investigating the tolerance of Brazilian dry bean genotypes to the sulfentrazone herbicide and possible mechanisms involved with tolerance. Study 3 was carried out in the field and the others in a greenhouse or laboratory conditions. In Study 1, 40 Brazilian dry bean genotypes (Phaseolus vulgarisand Vignaspp.) were characterized for sulfentrazone tolerance (400 g i.a. ha-1). In Study 2, a sulfentrazone dose-response curve (0, 50, 100, 200, 400, 600, 800, 1000 g i.a. ha-1) was used to evaluate the different levels of tolerance among genotypes. In Study 3, it was investigated the tolerance of different brazilian market classes of beans to sulfentrazone (400 g a.i. ha-1). In Study 4, the activity of antioxidant enzymes (superoxide dismutase, catalase and peroxidase) in dry bean genotypes was determined and their relationship with sulfentrazone tolerance. In Study 5, it was assessed the response of bean genotypes to the association of sulfentrazone with metabolism inhibitors (organophosphate insecticides). In Study 1, a large tolerance variation of the genotypes to sulfentrazone was observed. Higher tolerance levels were related to larger seed size, center of Andean origin and predominantly the carioca and special market classes. Vignaspp. genotypes did not follow the same tolerance pattern as common bean genotypes, since cowpea was tolerant, the adzuki was highly sensitive and intermediate mung bean. In Study 2, doses higher than 400 g a.i. ha-1of sulfentrazone caused decreases above 50% in relative tolerance, height, leaf area and shoot dry matter, while doses between 100 and 200 g a.i. ha-1caused reductions of nearly 10%. The obtaining of the tolerance factor presented that the Bico de Ouro and Pérola genotypes are capable of resisting doses of sulfentrazone up to three times higher than the most sensitive genotype (IPR Uirapuru). Considering the large commercial classes of beans, the levels of tolerance observed were: cowpea> carioca> special> mung> black. In Study 3, in the field conditions, it was possible to order the tolerance to sulfentrazone (400 g a.i. ha-1) in decreasing order among bean classes: cowpea> mung> carioca> special> black, so there were variations in relation to Study 2. Even detecting significant injury and reductions in the plant final density of 17% and 10% for the special and black classes, there were no reduction in yield. Cowpea, mung and carioca beans exhibited a potential safety margin for 400 g a.i. ha-1 of sulfentrazone. The results related to the mechanisms of tolerance (Studies 4 and 5) indicate that metabolization is the main mechanism of tolerance of the genotypes to sulfentrazone, while the different levels of tolerance observed were more related to the activity of antioxidant enzymes.