Abstract
Seed treatment with chemical pesticides is commonly used as an initial plant protection procedure against pests and diseases. However, the use of such chemicals may impair the survival and performance of beneficial microorganisms introduced via inoculants, such as the plant growth-promoting bacterium Azospirillum brasilense. We assessed the compatibility between the most common pesticide used in Brazil for the treatment of maize seeds, composed of two fungicides, and one insecticide, with the commercial strains Ab-V5 and Ab-V6 of A. brasilense, and evaluated the impacts on initial plant development. The toxicity of the pesticide to A. brasilense was confirmed, with an increase in cell mortality after only 24 hours of exposure in vitro. Seed germination and seedling growth were not affected neither by the A. brasilense nor by the pesticide. However, under greenhouse conditions, the pesticide affected root volume and dry weight and root-hair incidence, but the toxicity was alleviated by the inoculation with A. brasilense for the root volume and root-hair incidence parameters. In maize seeds inoculated with A. brasilense, the pesticide negatively affected the number of branches, root-hair incidence, and root-hair length. Therefore, new inoculant formulations with cell protectors and the development of compatible pesticides should be searched to guarantee the benefits of inoculation with plant growth-promoting bacteria.
Highlights
Global population reached 7.6 billion people in 2017 and, according to the predictions, will increase to 11.2 billion by 2100 [1]
It is necessary to produce more food and to search for production strategies resulting in minimum environmental impact. e inoculation of crops with plant growth-promoting bacteria (PGPB), especially those that can contribute to the reduction of chemical fertilizers usage, attends to these concepts of agricultural sustainability [2]
E strains are deposited at the “Diazotrophic and Plant Growth-Promoting Bacteria Culture Collection of Embrapa Soja” (WFCC Collection #1213, WDCM Collection #1054) in Londrina, State of Parana, Brazil. ese two strains have been broadly used in the production of commercial inoculants for the maize crop in Brazil since 2009 [3]
Summary
Global population reached 7.6 billion people in 2017 and, according to the predictions, will increase to 11.2 billion by 2100 [1]. In this context, it is necessary to produce more food and to search for production strategies resulting in minimum environmental impact. E use of fungicides and insecticides for seed treatment has been broadly employed in Brazil, with maize representing the second crop that receives more pesticides, after soybean (Glycine max (L.) Merr.) [11]. The use of inoculants with A. brasilense for the maize crop is impressively increasing, for example, in Brazil, from zero to 7 million doses per year−1 in less than a decade, and agrochemicals could affect bacterial survival and plant growth. In the Bradyrhizobium-soybean symbiosis, the incompatibility with pesticides may cause lower nodulation and, lower BNF rates [12, 13]
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