Objective  Three yeast strains with herbicidal activity were isolated for the determinations of their efficacy on weeds and application safety on crops.

  Method   In pot culture, the herbicidal efficacies of Strains 6-3, 12-6, and 16-8 on Galium spurium, Elsholtzia densa, and Chenopodium album, the weeds of major concern in Qinghai Province, were examined. A test on the application safety on crops was conducted in a greenhouse. In addition to morphological characteristics, ITS and 26S rDNA gene sequencing were performed to biologically identify the 3 strains.

  Results   Seven days after treatment with the yeast fermentation broths of 16-8, 12-6, and 6-3, the G. spurium plants sustained the injury rates of 90.17%, 87.50%, and 0%, respectively, with the fresh weight losses of 88.63%, 75.80%, and 9.41%, respectively; E. densa showed the rates of 66.67%, 75.00%, and 36.67%, respectively, with the weight losses of 56.90%, 62.72%, and 46.29%, respectively; and C. album displayed the injury rates of 95.00%, 37.50%, and 25.00%, respectively, with the weight losses of 78.77%, 43.25%, and 43.46%, respectively. The treatments on oat, broad beans, barley, wheat, rapeseeds, peas, and potatoes were shown to be safe for food consumption and crop cultivation. Strain 16-8 was confirmed to be Pichia kudriavzevii, 12-6 to be Kluyveromyces marxianus, and 6-3 to be Meyerozyma guilliermondii.

  Conclusion  Of the 3 yeast strains, 16-8 and 12-6 were strong in inhibiting the growth of the weeds of major concern in the province and could be developed as natural herbicides. The results might also lead to a broadened study on microbe-origin herbicides and related research.