Study on the control potential of Alternaria alternata against four species of weeds in agricultural fields on the Tibetan Plateau

ABSTRACT The aim of this study was to investigate the potential and pathogenic mechanism of the pathogenic fungus Alternaria alternata strain GD-011-B against four major agricultural weeds on the Tibetan plateau, and to lay a foundation for the commercial production and application of this strain. The mycelial masses had herbicidal activity against the isolated leaves of the weeds Chenopodium album, Elsholtzia densa, Malva verticillata, and Amaranthus retroflexus L., with a descending herbicidal activity order of M. verticillata > E. densa > A. retroflexus > C. album. The fermentation broth also showed herbicidal activity by treating the whole plants of these four weeds in the descending order of C. album > E. densa > M. verticillata > A. retroflexus. Scanning electron microscopy revealed that GD-011-B mycelia invaded the inner part of the leaf of A. retroflexus through the stomata and epidermal tissue gap and extended to the back, damaging the leaf epidermis and tissues and sporulating on the leaf surface, ultimately resulting in leaf disease. The fermentation broth of pathogen GD-011-B was not pathogenic to Vicia faba L., Pisum sativum L., Hordeum vulgare L., or Triticum aestivum L., but it was slightly pathogenic to Brassica napus L. Therefore, Alternaria alternata can be used as a herbicidal microorganism with high potential for biological control of four major agricultural weeds on the Tibetan plateau.