A Fisiologia Milho

Physiological response of corn subjected to the action of herbicides

Abstract - In Brazil, corn is grown in different production systems, and in all of them, inadequate weed control is the major factor related to yield reduction. They represent the energy imbalance created with the disturbance in middle and affect the yield and quality of product. This study aimed to evaluate the effect of different herbicides and combinations in physiological and biometric characteristics of corn. Treatments consisted of the application of herbicides and their combinations: DKB 177RR corn and Atrazine without Cropstar, Atrazine, Glyphosate, Glyphosate + Atrazine, Tembotrione + Atrazine, Mesotrione + Atrazine, and Nicosulfuron + Atrazine. Gas exchange and physiological evaluations were carried out as follows: Photosynthetic CO2 assimilation (A), stomatal conductance (gs), carbon internal concentration (Ci), transpiration (E), and vapor pressure deficit between the leaf and the air (VPDleaf-air). The following biometric parameters were also evaluated: plant height (PH), stem diameter (SD), ear height (EH), number of leaves (NL), and leaf area of the plant (LAP). Herbicides interfere differently in corn, and Glyphosate and the combination Atrazine + tembotrione presented the best physiological performance and development, with higher photosynthetic rates, stomatal conductance, Ci, transpiration, and VPDleaf-air, with no detectable phytotoxicity.

Key words: Zea mays, gas exchange, transgenic.

Resposta fisiológica de milho submetido à ação de herbicidas

Resumo - No Brasil, o milho é cultivado em diferentes sistemas de produção, e em todos eles, controle de plantas daninhas inadequada é o principal fator relacionado para produzir redução. Eles representam o desequilíbrio energético criado com a perturbação no meio e afetar a produtividade e qualidade do produto. Este estudo teve como objetivo avaliar o efeito de diferentes herbicidas e combinações nas características fisiológicas e biométricos de milho. Os tratamentos consistiram na aplicação de herbicidas e suas combinações: milho DKB 177RR e atrazina sem Cropstar, atrazina, o glifosato, glifosato + Atrazina, tembotrione + Atrazina, mesotriona + Atrazina, e nicosulfuron + atrazine. A troca gasosa e avaliações fisiológicas foram realizadas como se segue: a assimilação fotossintética de CO2 (A), a condutância estomática (gs), a concentração de carbono interno (Ci), transpiração (E), e vapor de défice de pressão entre a folha e o ar (VPDleaf-ar ). Também foram avaliados os seguintes parâmetros biométricos: altura da planta (AP), diâmetro (SD), altura da espiga (EH), número de folhas (NL), e área foliar da planta (LAP). Herbicidas interferem de forma diferente em milho, o glifosato e a combinação atrazina + tembotrione apresentou o melhor desempenho fisiológico e  desenvolvimento, com maiores taxas fotossintéticas, condutância estomática, Ci, transpiração, e VPDleaf ao ar, sem fitotoxicidade detectável.

Palavras-chave: Zea mays, troca gasosa, transgênica.

1. INTRODUCTION

Corn (Zea mays L.) is a grass species of higher commercial value, which is present in small, medium and large properties in Brazil. In Sergipe, this crop has both commercial and cultural importance, and covers approximately 176,300 ha, with yield of 4,862 kg/ha, which has been kept stable for the last harvests (Conab, 2015). Even being considered very competitive and with efficient nutrients uptake, corn crops may be severely affected by weeds, which consequently reduces grain yield, which may lead to total loss (Balbinot Junior & Fleck, 2004).

The latest technology used in corn crops against weeds is the transgenic, with commercial cultivars resistant to herbicides. However, the trend of large-scale use of transgenics increases the concern for weed management, since one of the factors responsible for the occurrence of weeds resistant to herbicides is associated with the selection pressure imposed by agricultural systems (Monqueiro, 2005), making this technology another ordinary tool and, rather than unique and exclusive.

In addition to transgenic, there are several methods of weed control. Chemical control stands out for its efficiency, fastness and low cost. However, the efficacy of herbicides depends on factors such as the molecule, the environmental conditions, the application period, and the weed species to be controlled (Jakelaitis et al., 2005). One of the most widely used herbicides is glyphosate, mainly due to its broad spectrum of action. The accumulation of shikimic acid is one of the main metabolic changes resulting from glyphosate application to plants (Buehring et al., 2007, Petersen et al., 2007, Matallo et al., 2009, Orcaray et al., 2010, Reddy et al., 2010, Franco et al., 2012).

For corn crops, atrazine is a frequently recommended and used herbicide, whose combination with other active ingredients has become usual, such as the combination with nicosulfuron, aiming at expanding the weed control spectrum and at reducing the dose to be used (Rizzardi et al., 2008; Silva et al., 2005). However, the tolerance of corn hybrids to sulfonylurea post-emergence herbicides may be high or low, depending on the herbicide, and may present sensibility, according to the plant development stage, to the environment, and to the dose (Cavalieri et al., 2008)

Besides the most commonly used herbicides, such as Atrazine, Nicosulfuron and Mesotrione (Zagonel, 2002), Tembotrione, which belongs to the Isoxazolidinonas group, is another option for weed control in corn crops. Either alone or in combination, herbicides should not cause damage to the plant development. A way to verify this possible interference is the use of physiological tools, which indicate the presence or absence of damage in the photosynthetic process (Campostrini et al., 2010). Thus, this work was carried out to evaluate the action of herbicides on the photosynthetic and biometric performance in transgenic corn.

2- MATERIAL AND METHODS

The experiment was carried out in the Rural Campus of the Federal University of Sergipe - UFS, located in São Cristóvão – SE (lat. 11º 01’ S;  long. 37º 12’ W, at  20m asl). DKB 177 RR hybrid corn seeds were cultivated in the field, at local climate conditions, by means of the data obtained by the National Institute of Meteorology, from an automatic weather station, which measured the average maximum and minimum temperature (ºC) and the and rainfall (mm) (Fig. 1).

Soil analysis was carried out in the layer up to 0.20m depth of the experimental area: Organic matter: 16.5g/ dm3; H + Al: 3.08 cmolc/dm3, K: 44.2 mg/dm3; P: 3.00 mg/dm3; sum of exchangeable bases: 2.71 cmolc/dm3; cation exchange capacity (CEC): 5.79 cmolc/dm3; base saturation (V): 46.8%; pH: 5.09; and Al + 3 0.52 cmolc/dm3.