Mitigação dos efeitos do sombreamento na produtividade e qualidade de fibra do algodoeiro pela aplicação de triptofano

Abstract

Brazilian cotton production is mostly carried out in a dryland environment, and plants are subject to shading caused by reduced radiation on cloudy days, which reduces endogenous auxin levels, increases the abortion of reproductive structures and reduces the crop's productive potential. The objective of this study was to evaluate the effect of exogenous application of a product composed of tryptophan, an auxin precursor, on mitigating abortion caused by shade in cotton plants. The experimental design was a 3x4 factorial with four replicates. The factors were the shading levels (0, 30 and 50%) and the tryptophan rates (0, 15, 30 and 60 g ha-1 of the commercial product, with 1.21% tryptophan in its composition). The production and quality components evaluated were: height, number of nodes, boll number (NC), average boll weight, fiber yield, fiber percentage, micronaire, maturity, fiber length, fiber uniformity, short fiber index, fiber strength and fiber elongation. The data obtained were subjected to analysis of variance and the means compared by Tukey's test at the 5% probability level (p<0.05). NC was higher in the absence of shade and without tryptophan, but the average boll weight (PMC) was higher under 50% shade. Fiber productivity and the other components and indexes did not show significant differences. In the absence of shade, the rate of 15, 30 and 60 g ha⁻¹ concentrated more bolls in the lower reaches, while the rate of 0 g ha⁻¹ maintained a more uniform distribution. With 50% shading, rates of 0, 30 and 60 g ha⁻¹ also promoted greater boll retention in the third of the plant. These results indicate that both shading and product dosage affect the way reproductive structures are distributed and accumulate mass in the plant canopy. Production concentration in the absence of shade was higher in the lower third at rates of 15, 30 and 60 g ha⁻¹. With 50% shading, rates of 0 and 30 g ha⁻¹ favored a greater yeld in the lower third and in the middle third, while the rate of 60 g ha⁻¹ showed greater production only in the lower third. The application of tryptophan, an auxin precursor, did not mitigate the effects of shading on cotton productivity.