Associative diazotrophic bacteria inoculated in sugarcane cultivars: implications on morphophysiological attributes and plant nutrition

ABSTRACT

Sugarcane is one of the first activities of economic importance in Brazil. The understanding of the nutritional dynamics at different phenological stages of the sugarcane crop with the use of nitrogen-fixing bacteria has been one of the alternatives to decrease fertilizer consumption and increasing plant production. This study aimed to assess the morphophysiological attributes in the initial growth and nutrition of two sugarcane varieties inoculated with strains of diazotrophic bacteria, individually and in an association, in a greenhouse. The experimental design was a randomized block design in a 2 × 8 factorial arrangement with two cultivars (Co 1341-76 and RB 867515) and eight treatments consisting of bacteria inoculated individually with BR 11140^T (Azospirillum amazonense), BR 11175^T (Herbaspirillum seropedicae), BR 11192^T (Herbaspirillum rubrisubalbicans), BR 11281^T (Gluconacetobacter diazotrophicus), and BR 11366^T (Burkholderia tropica), inoculation associated with the studied bacteria, N fertilization with 120 kg ha^-1 of N, and absolute control without inoculation and nitrogen fertilization. Plants were conducted for 75 days after germination, and biometric variables and nutrient accumulation were measured. The sprouting rate index and root fresh matter were significant for inoculation (p<0.01). Inoculation with the strains BR 11192^T (H. rubrisubalbicans), BR 11281T (G. diazotrophicus), and RB 11366^T (B. tropica) showed the best results for root fresh matter regardless of the cultivar. The strains RB 11366^T (B. tropica), BR 11192^T (H. rubrisubalbicans), and BR 11175^T (H. seropedicae) stood out regarding the sprouting rate index. Inoculation showed a significant effect for stem diameter (p<0.01), especially the strains BR 11140^T (A. amazonense) and RB 11366^T (B. tropica). All inoculations were efficient for the biometric variable related to leaf length. Nitrogen, Fe, and Zn contents showed a significant effect of the interaction between cultivars and inoculation. The inoculation with the strain RB 11366^T (B. tropica), total N fertilization, followed by the other inoculations and the control stood out compared to the cultivar Co 1341-76 within the factor inoculation, indicating that the association of this strain with the cultivar Co 1341-76 is more efficient regarding the recommended commercial N dose for sugarcane. The cultivars Co 1341-76 and RB 867515 responded positively to the individual inoculation of strains of diazotrophic bacteria. The strains promoted improvements in some morphological and/or nutritional attributes of sugarcane plants. The strain B. tropica showed the best interaction with the tested cultivars for the biological N fixation, resulting in gains of biomass productivity and nutrient contents when not inoculated.

biological nitrogen fixation; growth-promoting bacteria; Saccharum spp