Preparation and Herbicidal Activity of a Microbial Agent Derived from Alternaria gaisen Strain GD-011

Microbial herbicides, recognized for their target specificity, environmental compatibility, and simple production processes, hold promising potential for sustainable agriculture. This study isolated a strain of Alternaria gaisen (designated GD-011) from infected Medicago sativa L. in Qinghai Province, China, and evaluated its herbicidal potential through systematic development and efficacy assessment. Using single-factor and orthogonal experimental designs, the optimal sporulation substrate was identified as wheat bran, and the fermentation medium was optimized to consist of 14.5 g wheat bran, 19.4 g wheat middlings, 1.5 g rapeseed cake, and 14.6 g corn flour. Based on colony diameter and OD600 measurements, diatomite was selected as the most suitable carrier, while bentonite, humic acid, and polyvinyl alcohol were chosen as the stabilizer, protectant, and dispersant, respectively. Pot trials under controlled conditions demonstrated strong herbicidal activity of GD-011 against three common weed species: Chenopodium album L., Elsholtzia densa Benth., and Galium aparine L. The highest efficacy was observed against C. album, with disease incidence and fresh weight inhibition reaching 80.83% and 79.87%, respectively. Inhibition rates for both E. densa and G. asparine exceeded 60%. A wettable powder formulation developed from GD-011 showed particularly effective control of C. album and E. densa, providing a practical foundation for the application of GD-011 as a novel bioherbicide.