Seletividade de herbicidas influenciada pelo estado nutricional da cana-de-açúcar

In order to validate the hypothesis that sugarcane crop adequately fertilized is less damaged by herbicides, phytotechnical characteristics and isoenzyme profiles of α-esterase and peroxides in IACSP96-2042 and IACSP95-5094 sugarcane genotypes were evaluated, submitted to different planting fertilizers and treated or no with herbicides. In field conditions, two experiments were conducted, one for each cultivar, in vases (43 L), by using the randomized completely design with treatments arranged in factorial scheme 3 x 3 + 1, with four replications. The first factor consisted of herbicides: clomazone (1000 g ha -1 ), diuron (1440 g ha -1 ) + hexazinone (396 g ha -1 ) and sulfentrazone (800 g ha -1 ) and the second factor was characterized by fertilization: NPK doses (absence, 20-120-100 and 40-240-200 kg ha -1 )  and a control without fertilizers and herbicides. In herbicides application the plants showed 20 cm height and 3 to 4 leaves. In the field, were evaluated the visual symptoms of intoxication, total chlorophyll content, plant height, leaf length, number of tillers and fresh and dry mass of plants. In laboratory conditions, it was characterized the profile of α-esterase and peroxidase isozyme before herbicide application and 58 days after, by electrophoresis on acrylamide gel. IACSP96-2042 genotype was less sensible to herbicides, without damaging fresh and dry mass, total chlorophyll content, plant height, leaf length and number of tillers. Peroxides’ isoforms were different in number and intensity; α-esterase’ isoforms were changed in bands intensity. IACSP95-5094 genotype was sensitive to phytotoxicity effects of herbicides for damaging in height, fresh and dry mass, particularly in the treatment with diuron + hexazinone.