Differential plant growth promotion and nitrogen fixation in two genotypes of maize by several Herbaspirillum inoculants

Herbaspirillum spp. has been described as bacteria that colonizes not only maize roots but also stems and leaves. This study aimed to access the growth-promoting effect of 21 strains of Herbaspirillum on maize plants. This study is composed by 12 strains of the H. seropedicae, 5 strains of the H. rubrisubalbicans and 4 strains of the H. frisingense. Bacterial selection was performed in two phases, consisting on planting the BRS4157 maize variety and hybrid SHS5050 in the greenhouse, with sterile and non-sterile substrate and in the field. After 40 days, the greenhouse plants were harvested and the dry matter accumulation of the aerial part and roots were measured. The best-performing strain was tested in field trials treated with 40 and 80 kg ha(-1) of N fertilizer, parallel to the same treatments without inoculation. In this trial, the grain yield was evaluated as well as the contribution of biological nitrogen fixation (BNF), using the technique of natural abundance of (15) N. The results showed that H. seropedicae ZAE94 was the best strain under controlled conditions and its application as a field inoculant increased maize yield up to 34 %, depending on the plant genotype. The BNF quantification revealed that 37 % BNF-derived plant nitrogen in the hybrid SHS5050 inoculated with the H. seropedicae strain ZAE94. The difference in response to nitrogen as well as to inoculation depends on the selected plant genotype and the bacterial inoculant. H. seropedicae ZAE94 can promote plant growth and contribute biologically with fixed nitrogen in the maize hybrid SHS5050.