Qualidade fisiológica de sementes de soja colhidas em duas épocas após dessecação com glyphosate

Abstract

RESUMO -A dessecação de plantas de soja em pré-colheita com glyphosate vem se tornando prática rotineira entre os produtores, apesar de não ser recomendada, pois pode comprometer a qualidade fisiológica das sementes. Objetivou-se avaliar os efeitos da dessecação das plantas em pré-colheita com glyphosate na qualidade fisiológica de sementes de soja colhidas em duas épocas após a aplicação. O delineamento experimental foi em blocos ao acaso, com quatro repetições, em esquema de parcelas subdivididas. As parcelas principais consistiram da dessecação ou não das plantas de soja com glyphosate em pré-colheita, no estádio R7, e as subparcelas da colheita das sementes 7 e 14 dias após a aplicação. As sementes foram avaliadas quanto ao teor de água, dano mecânico, viabilidade, massa de 100 sementes e teor de proteína. A qualidade fisiológica foi avaliada por meio dos testes de germinação, envelhecimento acelerado, condutividade elétrica, comprimento de plântulas e massa da matéria seca das plântulas. A dessecação das plantas de soja em pré-colheita com glyphosate ocasiona redução da germinação das sementes e do desenvolvimento inicial das plântulas. O atraso na colheita reduz a germinação das sementes oriundas de plantas de soja dessecadas com glyphosate em pré-colheita, mas minimiza os efeitos fitotóxicos no desenvolvimento das plântulas.Termos para indexação: Glycine max, fitotoxicidade, germinação, maturidade fisiológica.Physiological quality of soybean seeds harvested at two periods after glyphosate desiccation ABSTRACT -Pre-harvest desiccation of soybean plants with glyphosate has been routinely conducted by seed producers, although it is not recommended because it may reduce seed physiological quality. The objective of this study was to evaluate the effects of the pre-harvest desiccation of plants with glyphosate on the physiological quality of soybean seeds harvested at two different periods after application. The experimental design was completely randomized blocks, with four replications and subdivided plots. Main plots consisted of the presence and absence of a pre-harvest desiccation of soybean plants with glyphosate at the R7 stage, and subplots of seeds harvested 7 and 14 days after application. Moisture content, mechanical damage, viability, weight of 100 seeds, protein content and accumulation of glyphosate residues were determined after harvest. Physiological quality was evaluated by tests for germination, accelerated aging, electrical conductivity, seedling length and seedling dry matter. Pre-harvest desiccation of soybean plants with glyphosate reduces seed germination and seedling development. Delayed harvesting reduces the germination of soybean seeds produced by plants desiccated with glyphosate, but minimizes phytotoxicity in seedling development.

Productivity and quality of soybean seeds of determinate and indeterminate growth types desiccated in pre-harvest

“…They found that only seeds produced from plants desiccated with glyphosate at R6.5 showed a reduction in seedling length. A similar result was also observed by Toledo et al (2012) who found glyphosate effect on root length, hypocotyl length and total height of the seedlings. Lamego et al (2013) obtained a higher rate of soybean seedling emergence when seeds were derived from plants desiccated in R6.0.…”

“…During the seed maturation period, when the rapid translocation of reserves is still occurring and the photosynthesis rate is lowest, premature death of the plant prevents the complete degradation of chlorophyll, which results in the production of greenish and low quality seed (Marcos Filho, 2005). Toledo et al (2012) verified that delay in harvesting reduces the germination of seeds produced by soybean plants desiccated with glyphosate in pre-harvest. According to Carvalho and Nakagawa (2012) seeds have maximum strength at the physiological maturity point (stage R7.0) and from that stage onwards the value decreases as a function of the environmental and microbiological conditions to which the seeds are submitted.…”

“…In contrast, the root length of seedlings from 'MSoy 7211' differed depending on the desiccation time. However, the type of paraquat product used did not affect root lenght, unlike glyphosate (Daltro et al, 2010, Toledo et al, 2012. 'MSoy 7211' had higher average seedling dry matter, about 7% greater than 'BRS Valiosa' (Table 4).…”

Yield, specific mass and coloration of azuki seeds after desiccation and storage

“…The lack of significance found in the results may be because desiccant applications were held by the time bean seeds were at physiological maturity, when they reach a maximum dry matter accumulation (TOLEDO et al, 2012). These results are supported by observations made by KAPPES et al (2012), who found no differences for yield components of common bean grown in winter and desiccated with paraquat at physiological maturity.…”

“…Nevertheless, some key factors must be considered including herbicide type and application rate to avoid drops in production and seed quality (TOLEDO et al, 2012).…”