RESUMEN
The physiological and molecular responses of five strains of Streptomyces sp. (CAI-17, CAI-68, CAI-78, KAI-26 and KAI-27), with their proven potential for charcoal rot disease control in sorghum and plant growth-promotion (PGP) in sorghum and rice, were studied to understand the mechanisms causing the beneficial effects. In this investigation, those five strains were evaluated for their PGP capabilities in chickpea in the 2012-13 and 2013-14 post-rainy seasons. All of the Streptomyces sp. strains exhibited enhanced nodule number, nodule weight, root weight and shoot weight at 30 days after sowing (DAS) and pod number, pod weight, leaf area, leaf weight and stem weight at 60 DAS in both seasons over the un-inoculated control. At crop maturity, the Streptomyces strains had enhanced stover yield, grain yield, total dry matter and seed number plant(-1) in both seasons over the un-inoculated control. In the rhizosphere, the Streptomyces sp. also significantly enhanced microbial biomass carbon, dehydrogenase activity, total nitrogen, available phosphorous and organic carbon in both seasons over the un-inoculated control. Of the five strains of Streptomyces sp., CAI-17, CAI-68 and CAI-78 were superior to KAI-26 and KAI-27 in terms of their effects on root and shoot development, nodule formation and crop productivity. Scanning electron microscopy (SEM) micrographs had revealed the success in colonization of the chickpea roots by all five strains. Quantitative real-time PCR (qRT-PCR) analysis of selected PGP genes of actinomycetes revealed the selective up-regulation of indole-3-acetic acid (IAA)-related and siderophore-related genes by CAI-68 and of ß-1,3-glucanase genes by KAI-26.
RESUMEN
Seven isolates of bacteria (SRI-156, SRI-158, SRI-178, SRI-211, SRI-229, SRI-305 and SRI-360) were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum and plant growth promotion (PGP) of the plant. In the present study, the seven isolates were characterized for their physiological traits (tolerance to salinity, pH, temperature and resistance to antibiotics and fungicides) and further evaluated in the field for their PGP of rice. All the seven isolates were able to grow at pH values between 5 and 13, in NaCl concentrations of up to 8% (except SRI-156 and SRI-360), temperatures between 20 and 40°C and were resistant to ampicillin (>100 ppm; except SRI-158 and SRI-178) but sensitive (<10 ppm) to chloramphenicol, kanamycin, nalidixic acid, streptomycin (except SRI-156 and SRI-211) and tetracycline. They were tolerant to fungicides benlate and captan, except SRI-158 and SRI-178, bavistin and sensitive to thiram (except SRI-156 and SRI-211) at field application level. In the field, four of the seven isolates (SRI-158, SRI-211, SRI-229 and SRI-360) significantly enhanced the tiller numbers, stover and grain yields, total dry matter, root length, volume and dry weight over the un-inoculated control. In the rhizosphere soil at harvest, all the isolates significantly enhanced microbial biomass carbon (except SRI-156), microbial biomass nitrogen and dehydrogenase activity (up to 33%, 36% and 39%, respectively) and total N, available P and% organic carbon (up to 10%, 38% and 10%, respectively) compared to the control. This investigation further confirms that the SRI isolates have PGP properties.