Plant growth regulation: a method for fine-tuning mepiquat chloride rates in cotton1

Abstract

Plant growth regulator management has been a challenge for cotton growers, due to the increased weather instability and the adoption of early cultivars, in off-season crops. This study aimed at proposing a new method, called Crop Growth Rate, to define mepiquat chloride rates in cotton crops, as well as to compare it with traditional management practices. Except for micronaire, there was no difference in cotton growth parameters, neither in yield nor fiber quality, between the new method and the traditional one. The mepiquat chloride rates were, on average, 24 % higher and 43 % lower in late and early maturity cultivars, respectively, for the new method. The number of bolls in plants treated with mepiquat chloride was lower than in non-treated plants, for the IMA5672B2RF and IMA5675B2RF cultivars, but a higher average weight of bolls was observed for these genotypes. The new method is efficient in defining the plant growth regulator rate to avoid an excessive growth and results in less mepiquat chloride applied to early cycle cultivars, preserving lint yield and fiber quality.

Cotton root growth response to mepiquat chloride application in early reproductive stages are cultivar dependent

“…In most of our examples, this effect persisted up to 15 DAA (Figure 2b). Previous studies indicate that cultivars have different sensitivity levels to MC, and plants in early or mid‐cycle stages are the most sensitive (Bogiani & Rosolem, 2009; Echer & Rosolem, 2017; Zhao et al., 2017). Our study indicates that late group cultivars may have different sensitivity to MC application at the initial phase of development depending on temporal environmental factors.…”

“…Most Brazilian cotton crops are sown in wide row spacings (0.75–0.90 m) with populations ranging from 50,000 to 130,000 plants ha −1 . Under these conditions, management of growth regulators is mostly performed via foliar spraying (Echer & Rosolem, 2017; Leal et al., 2020). However, there is no consensus regarding appropriate application rates, especially for early sprays (Pinhead square stage).…”

“…Low MC rates can lead to uncontrolled growth, especially for cultivars in the late reproductive stage in highly fertile soil (Echer & Rosolem, 2017; Leal et al., 2020). High rates can result in temporary growth disruptions.…”

Reguladores de crescimento na cultura do algodão (Gossypium hirsutum L.)

“…O intervalo entre as aplicações foi dado de acordo com a distância média entre os cinco últimos entrenós da haste principal. As plantas com distância média de entrenós igual ou superior a 3,5 cm indicavam necessidade de nova aplicação dos reguladores (Echer & Rosolem, 2017).…”

“…Apesar dos benefícios oriundos da aplicação dos reguladores de crescimento, o manejo destes produtos ainda é um desafio para os cotonicultores, devido a temperaturas elevadas e déficit hídrico (Echer & Rosolem, 2017). Aliado a isso, deve-se considerar a sensibilidade da planta aos reguladores, observada a diversidade de cultivares em uso oriundas do melhoramento genético, que, por sua vez, apresentam características variadas de porte (alto, médio e/ou baixo) e de ciclo (precoce, médio e/ou tardio), tais diferenças podem interferir diretamente na resposta da planta ao regulador (Bogiani, 2008).…”