Interference of Herbicides in Association of Diazotrophic Bacterium Nitrospirillum amazonense and Sugarcane Pre-Sprouted Seedlings

Abstract

Microbial inoculant containing cells of Nitrospirillum amazonense is a recent technology that has been used in association with pre-sprouted seedlings to sustainably increase the productivity of sugarcane. This study aimed to assess the sensitivity of the rhizobacterium N. amazonense to the herbicides imazapic and indaziflam and the effect of this inoculation and herbicide treatments on sugarcane pre-sprouted seedlings. The In vitro sensitivity of the N. amazonense to the herbicides was assessed using the minimum inhibitory concentration technique (first assay). In this research, we evaluated imazapic (200 g a.i. ha-1) and indaziflam (100 g a.i. ha-1) at five doses: recommended dose (1×D), twice the recommended dose (2×D), one and a half of the recommended dose (1.5×D), half the recommended dose (0.5×CD), a quarter of the recommended dose (0.25×CD) and control treatment. The sensitivity of N. amazonense to imazapic and indaziflam applied at commercial doses on autoclaved soil was assessed in the second assay. The bacterial population count was performed using the most probable number technique (McCrady Table). The third assay assessed five herbicide treatments (clomazone (720 g a.i. ha−1), imazapic (200 g a.i. ha−1), tebuthiuron (800 g a.i. ha−1), indaziflam (75 g a.i. ha−1), sulfentrazone (800 g a.i. ha−1) and control without herbicide) applied in pre-planting of pre-sprouted seedlings of the variety RB 966928 in the presence and absence of the inoculant N. amazonense. The results showed that the presence of indaziflam did not interfere with the In vitro growth of the bacterium N. amazonense, regardless of the dose. Imazapic caused significant inhibition of bacterial In vitro growth from the recommended dose (200 g a.i. ha-1). The N. amazonense count in the soil of treatments that received indaziflam and imazapic application did not differ compared to the soil without herbicide. The pre-sprouted seedlings of the variety RB966928 showed high sensitivity to the herbicide imazapic, regardless of N. amazonense inoculation. Clomazone, tebuthiuron, and sulfentrazone did not interfere with the growth-promoting effect of N. amazonense. The results showed that the recommended dose of the herbicides tested does not impair the growth promoting effect of N. amazonense, and the inoculation of the pre-sprouted seedlings does not alter their sensitivity to herbicides, although the selectivity of the seedlings is differential among herbicides. Therefore, it may be concluded that the combined use of these technologies is a viable alternative to increase sugarcane productivity in a more sustainable way. © 2022 Friends Science Publishers