LAUSR

Phalaris minor is a problematic weed of wheat (Triticum aestivum L.). Repeated application of herbicides to control this weed causes environmental pollution and some of the weeds even develop herbicide resistance. Recently, phytohormones and allelochemicals produced by rhizosphere microorganisms have been found to suppress the growth of different weeds. Therefore, 32 bacterial isolates obtained from the rhizosphere of wheat were screened for the production of phytohormones indole-3-acetic acid (IAA) and 5-aminolevulinic acid (ALA). Rhizobacterial isolates, having variation in IAA and ALA production ability, were tested for their effect on seedling growth of P. minor on 0.8% water agar plates and four rhizobacterial isolates i. e. HWM 7, HWM 11, HWM 17 and CP 43 caused significant retardation of P. minor seedling growth on 5th and 10th day of seed germination. Under pot house conditions, seed inoculation with Bacillus subtilis strain SYB 101 caused 70.8 and 80.7% decrease in root and shoot dry weight of P. minor and its inoculation showed 136.8 and 316.6% increase in root and shoot dry weight of wheat at 75 days of wheat growth. P. minor growth was also suppressed in the pot house by inoculation of Providentia rettgeri strain CPS 67 and Pseudomonas isolate HWM 11. Maximum growth stimulation of wheat was observed by inoculation with rhizobacterial isolates SYB 101 and HWM 11. Maximum growth retardation of weed was observed by inoculation of B. subtilis strain SYB 101 having moderate level of IAA and ALA production, followed by high IAA and ALA producing P. rettgeri strain CPS 67, suggesting that besides phytohormones, some other metabolite was also involved in growth retardation of P. minor. These rhizobacterial isolates could be further tested for suppression of weed growth under field conditions for their subsequent application as bioherbicide.