Bacilli consortia positively regulates agronomic and growth traits in rice

Abstract

In our study, soil samples from the rhizosphere of various uncultivated weeds were collected from fifteen different locations of Gujarat. Heat treatment was given at 65°C for 20 minutes prior to initial screening for spore-forming Bacilli spp. Among them, 20 nitrogen-fixing (NFB), 27 phosphate solubilizing (PSB) and 15 potassium mobilizing (KMB) isolates were screened primarily. After molecular identification only Bacilli isolates were further selected and characterized. Three superior Bacillus isolates were selected from each category by secondary screening. All three isolates for nitrogen fixation were found nif positive, while Bacillus megaterium (NAUN2) showed maximum 2.04 µmol/ml ammonia production followed by Bacillus sp. (NAUN1) and Lysinibacillus macroides (NAUN3) with 0.64 and 0.99 µmol/ml, respectively. Bacillus sp. (NAUP1) gave maximum 401.94 µg/ml phosphate solubilization on Pikovaskya broth media after third day while Bacillus sp. (NAUP2) and Brevibacillus sp. (NAUP3) showed 376.74 and 308.16 µg/ml phosphate solubilization, correspondingly. Lysinibacillus macroides (NAUK2) showed maximum 228.14 µg/ml potassium mobilization on Aleksandrov after the twentieth day while Lysinibacillus macroides (NAUK1), Bacillus megaterium (NAUK3) and Bacillus sp. (NAUP1) had effective 196.91, 158.18, 59.33 µg/ml potassium mobilization, respectively. Interestingly, no selected Bacilli isolates from the consortia were found to have inhibitory effect on other isolates in compatibility test. Out of the nine Bacillus isolates NAUK1, NAUK2, NAUK3 were found to be effective against rice pathogen Magnaportha oryzae on PDA plates. All the nine isolates were checked for IAA and siderophore production. Isolate NAUN1, NAUP3, NAUK1, NAUK2 and NAUK3 showed 37.2%, 17.9%, 33.6%, 38.9%, 48.2% siderophore production on CAS medium after 72 hrs, respectively. Isolate NAUP3 showed maximum 146.68 µg/ml IAA production while NAUN1, NAUN3, NAUP1, NAUK2 and NAUP2 showed 99.37, 99.37, 114.57, 101.46, 93.48 µg/ml IAA production, respectively after the seventh day. Rice seeds were inoculated with individual isolate and different Bacilli consortia, which significantly improved growth parameters as compared to control in pot study after 60 days of sowing. 100% RDF + NPK consortia gave significantly increased root length (11.65%), shoot length (10.28%), no. of leaves (17.39%), leaf area (11.68%) and chlorophyll content in leaf (4.76%). Similar trends were observed when the data was compared with absolute control. The spore forming Bacilli consortia was able to survive a wide range of temperature and pH fluctuations and found effective N-fixers, P-solubilizers, K-mobilizers, siderophore producers, IAA producers with antagonistic activity against rice pathogen Magnaportha oryzae.