Competition amongBradyrhizobium strains for nodulation of green gram (Vigna radiata): Use of dark-nodule strain

Abstract

The competitiveness of dual-strain inoculum of Bradyrhizobium strains S24 and GR4 was demonstrated for nodulation of green gram (Vigna radiata). Strain S24 formed pink nodules, GR4 produced visually distinguishable dark-brown nodules. When a mixture of these Bradyrhizobium strains was applied as inoculum, nodules of both pink and dark-brown types were formed on the same root. The strain GR4, which was less competitive than strain S24, was mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine to obtain pigment-diverse mutants and six selected mutants were screened for symbiotic parameters. One mutant produced pink nodules and appreciably increased plant dry mass. The competitive ability of this mutant lacking brown pigment was compared with that of strain S24 by using antibiotic resistance markers; it showed increased nodulation competitiveness than its parent strain GR4. The dark-brown nodule-phenotype could be useful in evaluating nodulation competitiveness of "cowpea miscellany" bradyrhizobia in soil where dark-brown nodule-forming strains are not indigenous.

Selected indigenous drought tolerant rhizobium strains as promising biostimulants for common bean in Northern Spain

“…Therefore, to evaluate the efficiency of these selected rhizobia (353, A12 and A13), a field trial will be carried out under drought conditions. Although the results obtained in the field often differ from those obtained under controlled conditions, very favourable results have been achieved, even with the inoculation of strains with little history of edaphoclimatic adaptation ( Sindhu & Dadarwal, 2000 ; Omari et al., 2022). Thus, taking into account the long tradition of bean cultivation in the Basque Country ( Eustat, 2019 ), that the selected strains were isolated from stressed soils and that common bean is a highly promiscuous species ( Shamseldin & Velázquez, 2020 ), we expect to obtain promising results under field conditions, for Arrocina de Álava genotype, of great economic interest, such as those obtained by other authors with common bean, in other edaphoclimatic zones ( Aserse et al., 2020 ; Rodiño et al., 2021 ).…”

“…However, commercial or reference inoculum may vary in effectiveness with soil type or legume genotypes. Firstly, rhizobia strains need to survive for long time in the soil in the absence of the legume ( Sindhu & Dadarwal, 2000 ; Ruiz‐Díez et al., 2012 ) meaning that different geographical areas with different edaphoclimatic characteristics may not be favourable for the survival of the commercial inoculum or for the establishment of the symbiosis ( Sindhu et al., 2020 ; Omari et al., 2022). Secondly some commercial inoculum lost effectiveness when translated from greenhouse to field due to the competition with indigenous rhizobia strains that are more effective in the establishment of the symbiosis ( Kumar & Verna, 2018 ; Sindhu et al., 2020 ).…”