Impact of the ahas Gene and of Imazapyr Herbicide on Soil Microbial Communities

Scientist Rosinei Aparecida Souza of Embrapa in Brazil, together with other researchers, conducted a study to evaluate the effects of herbicide tolerant soybean to soil microbial community. The biotech soybean (Cultivance) used in the study expresses ahas gene that confers resistance to herbicides of the imidazolinone group.

The research team carried out 20 field experiments during three growing seasons from 2006 to 2008, in nine different municipalities in Brazil. They used a completely randomized block design with four replicates and three treatments: (1) conventional soybean (Conquista) with conventional herbicides; (2) near-isogenic transgenic soybean (containing the ahas gene, with conventional herbicides; (3) transgenic soybean with specific imazapyr herbicide. They took soil microbial samples at 0-10cm layer before planting and at R2 growth stage.

A comparison of biotech soybean with conventional and imidazolinone-group herbicides applications showed no significant differences that could be attributed to the specific use of imazapyr, even after three consecutive croppings at the same site. No differences were also detected between conventional (Conquista and conventional herbicides) and transgenic soybean managements (Cultivance and imazapyr). Differences were observed in microbial biomass carbon and microbial biomass nitrogen between the different sites and times of year.

Based on the findings, microbial community evaluations were found to be sensitive and viable for monitoring different technologies and agricultural management methods, but no differences could be attributed to the ahas gene expression.

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This article is part of the Crop Biotech Update, a weekly summary of world developments in agri-biotech for developing countries, produced by the Global Knowledge Center on Crop Biotechnology, International Service for the Aquisition of Agri-Biotech Applications SEAsiaCenter (ISAAA)

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