Biopesticidal potential of noxious weeds against leaf blight of rice caused by Xanthomonas oryzae

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae (Xoo), threatens global rice production. The biopesticidal potential of six weed species, namely Parthenium hysterophorus, Ammi visnaga, Chenopodium album, Cannabis sativa, Amaranthus viridis, and Dysphania ambrosioides, was evaluated against Xoo. Crude extracts and their ethyl acetate and n-hexane fractions were tested using agar well diffusion, minimum inhibitory concentration (MIC) assays, and in vivo pot experiments under a factorial completely randomized design. C. sativa (1.13 g) and A. viridis (1.03 g) yielded the highest crude extracts. Parthenium hysterophorus n-hexane extract (63.7% inhibition at 100 ppm), D. ambrosioides n-hexane (55.2%), and A. visnaga n-hexane (167% at 25 ppm) showed significant antibacterial activity. Ethyl acetate fractions, particularly D. ambrosioides, reduced Xoo infection most effectively in vivo. Parthenium hysterophorus (31 to 70%) and A. viridis (59 to 65%) ethyl acetate extracts promoted seed germination and growth, while A. visnaga and D. ambrosioides n-hexane extracts reduced growth by 24 to 29% and 19 to 25%, respectively. Chenopodium album ethyl acetate extract increased chlorophyll content (61 to 68%). Electrolyte leakage was highest in P. hysterophorus crude extract (75%) and lowest in D. ambrosioides n-hexane (17%). These weed-derived extracts show promise for sustainable BLB management, warranting further compound isolation and field validation.