Glyphosate tolerance in maize (Zea mays L.). 2. Selection and characterization of a tolerant somaclone

Abstract

The progeny of 104 regenerated maize plants were screened for tolerance to the safe broad-spectrum herbicide glyphosate during seed germination and early growth . Seven somaclones showed varying degrees of resistance to the application of the herbicide at 1 .2 mM (0.1 kg ad . in 400 1 ha ' of water) . Plants capable of a normal growth following treatment with 2 .4 mM (0 .2 kg ha ') glyphosate at the three leaf stage were selfed, and their progeny analyzed . A family able to tolerate the exposure to glyphosate at 2 .4 mM was isolated and shown to maintain a photosynthetic rate comparable with control after the application of the herbicide .The selfed progeny of the tolerant somaclone was characterized as to the properties of two targets of glyphosate, the shikimate pathway enzymes 5-enol-pyruvyl-shikimate-3-phosphate (EPSP) synthase and 3-deoxy-D-arabinoheptulosonate-7-phosphate (DAHP) synthase . In vitro tests ruled out the possibility that the tolerance was due to altered forms of these enzymes . Families showed significant variability with regard to EPSP and DAHP synthase levels, measured at different stages during seedling growth ; however, not even these traits were correlated with in vivo response to glyphosate. The possible role of other physiological processes in determining the increased tolerance to the herbicide is discussed .Abbreviations: DAHP -3-deoxy-D-arabino-heptulosonate-7-phosphate, EPSP -5-enol-pyruvyl-shikimate-3-phosphate, CER -carbon-exchange rate, ID50 -concentration causing 50% inhibition

Herbicidas inibidores da EPSPs: revisão de literatura

“…A produtividade, morfologia e constituição das cultivares de soja com a resistência incorporada permaneceu igual às linhagens susceptíveis correspondentes. Linhagens de soja com esse gene tratadas com glyphosate, nas doses comerciais, não apresentaram sintomas de fitotoxicidade ou redução da produtividade e qualidade do produto, viabilizando seu uso comercial (Padgette et aI., 1995;Racchi et aI., 1995;Scott et aI., 1998). Várias outras culturas tem recebido atenção no sentido de introdução desse gene que confere insensibilidade de EPSPs ao glyphosate, incluindo milho, arroz, fumo e tomate.…”

The Effect of the Application of Different Rates of Herbicides on the Growth and Yield Component of Zea mays L

“…The finding of this study can however be explained by several reasons including the fact that several varieties of maize, including the variety used for this study have been found to be resistant to the toxic effects of glyphosate, the herbicide used to prepare the treated plots. (Racchi et al, 1995;Sergiev et al, 2006). Racchi et al (1995) had found that several species of maize have physiological processes that make them resistant to glyphosate, while Sergiev et al (2006) had noted that the maize plant is able to protect itself against the toxicity of glyphosate through the use of phenylurea cytokinin 4PU-30.…”

“…(Racchi et al, 1995;Sergiev et al, 2006). Racchi et al (1995) had found that several species of maize have physiological processes that make them resistant to glyphosate, while Sergiev et al (2006) had noted that the maize plant is able to protect itself against the toxicity of glyphosate through the use of phenylurea cytokinin 4PU-30. The marked decrease in germination count noted in the experimental plots in which overdose of the herbicides were applied can be explained by the fact that the atrazine and metolachlor, that were used as postemergent herbicides in the plots are known to be particularly toxic in overdose, and therefore have the capacity to adversely affect the germination of the maize (Yazdanpak et al, 2014).…”

Somaclonal Variation and Induced Mutations in Crop Improvement

“…Somaclones that are resistant may have an altered transport ability, modified target enzyme or a detoxification mechanism. This has been the case of glyphosate tolerance in maize, in which a variation in the EPSP and DAHP was detected (Racchi et al, 1995). Herbicides interfering with the photosynthetic electron transport system cannot be used for in-vitra selection unless the callus exhibits photosynthetic activity.…”