Isolation, Characterization, and Herbicidal Activity of Streptomyces spp. from Diseased Potato Scab Tubers

Abstract

Background A highly effective and environmentally friendly method of controlling weeds is biological herbicides, which typically constitute of naturally secondary metabolites, such as bioherbicidal metabolites produced by Streptomyces sp. However, the isolation of phytotoxic compounds from pathogenic Streptomyces has not been fully studied. Results Here, a total of 50 strains of Streptomyces genera were isolated from the potato tubers with typical common scab (CS) symptoms using the culture-dependent method. The radish seedling test indicated that 32 fermentation broths of potato common scab-associated Streptomyces could produce phytotoxic metabolites that affect the normal growth of radish seedlings’ radicles. Of note, two potential new pathogens (NKY-4 and L7-2) of potato scab were discovered by combining the methods of radish seedlings, potato tuber slices, and PCR detection of pathogenic genes txtAB. Moreover, the phytotoxic test demonstrated that the fermentation broths of 31 strains exhibited phytotoxic activities against at least one of the tested weeds (Echinochloa crusgalli, Digitaria sanguinalis, and Abutilon theophrastis). Furthermore, one novel metabolite and three known compounds, including new N-(2,5-dihydroxyphenyl)-3-acetamide-4-hydroxybenzamide (1), thaxtomin A (2), nicotinic acid (3) and pyrrole-2-carboxylic acid (4) were isolated from S. bottropensis (AMCC400023). Among them, compound 2 exhibited strong phytotoxic activity against E. crusgalli, D. sanguinalis, and A. theophrast with IC50 values of 0.99, 0.78, and 1.95 µg/mL, respectively, which was comparable to those of the positive control 2,4-D. Conclusions Based on the results of these findings, phytotoxic metabolites from the potato scab pathogen may be one of the effective ways to develop new biological herbicides.