Crescimento radicular do algodoeiro em função da aplicação de cloreto de mepiquate

Abstract

In the cotton crop, one of the recommended technologies is the use of plant regulators to manipulate plant architecture, with mepiquate chloride (CM) being one of the most used. Its main effects on culture are the reduction in growth, number and size of reproductive branches and an improvement in the proportion between vegetative and reproductive parts. In this work, the response of different doses of mepiquate chloride on the root growth of cotton plants and its relationship with vegetative and reproductive growth was studied. The experiment was carried out in greenhouse, in PVC pipes adapted with a glass front wall (rizotrons). The experiment was divided into two parts, because it worked with two different stages, B3 and F1. The experimental design was a randomized complete block design and the treatments consisted of four doses of mepiquate chloride: 0, 10, 20 and 40 g i.a ha-1 and three replicates. The foliar application in the B3 and F1 stages occurred 30 and 50 days after plant emergence, respectively. Plant height and number of leaves were evaluated at 0, 7, 10, 14, 17 and 21 days after application (DAA). Root growth was evaluated at 0, 7, 14 and 21 DAA, after which the plants were cut at the height of the colon, the roots were washed and analyzed for length, diameter and volume using WinRhizo software. The specific weight of leaf, leaf area, leaf dry mass, reproductive and root structures, and root content and carbohydrate accumulation were evaluated at 21 days after application for each stage. The application of mepiquat chloride in B3 and F1 reduced plant height and number of nodes as dose increased, but the height in B3 and the number of nodes in F1 was only controlled until 17 DAA. The leaf area, in F1, decreases as CM doses increase. In B3 the leaf dry matter mass, reproductive structures, root and total, decreases as the dose of regulator increases. In F1, these masses of dry matter showed increase up to the dose of 20 g i.a. ha-1 and then there was decrease in the values. The content and accumulation of carbohydrates in the root increases in the B3 stage, as there is an increase in CM doses. The total root length decreases with the application of 40 g i.a ha-1 in the B3 stage, but also decreases the length of the main and lateral roots. On the other hand, the application of mepiquate chloride in F1 increases the total root length of the main root and lateral roots. It was concluded that the application of mepiquate chloride in the B3 stage balances the growth between the vegetative and reproductive parts, but higher doses such as 20 and 40 g ai ha-1 can reduce root length, and this requires special attention in areas of sandy soils, water deficit at the end of the cycle, occurrence of nematodes, as root system compromise may limit productivity.