Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2014
Publication Date: 7/18/2014
Publication URL: http://handle.nal.usda.gov/10113/59383
Citation: Lygin, A., Hill, C., Pawlowski, M., Zernova, O., Widholm, J., Hartman, G.L., Lozovaya, V. 2014. Inhibitory effects of stilbenes on the growth of three soybean pathogens in culture. Phytopathology. 104(8):843-850. Interpretive Summary: Plant diseases pose a major threat to crop production worldwide. The economic importance of plant diseases varies among crops, between geographic areas, and from season to season, due to a multitude of factors. To withstand and survive stresses produced by different biotic constraints, different resistance mechanisms have evolved in plants. In this study, the effects of resveratrol and pterostilbene, two stilbenic antimicrobial compounds, were tested to determine if these compounds could inhibit the growth of three soybean pathogens (Macrophomina phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum) based on laboratory tests. All three fungi were very sensitive to pterostilbene and relatively less sensitive to resveratrol. With this discovery, the next proposed step would to engineer plants with enhanced production of pterostilbene and test these plants for their resistance to these and other pathogens. This information is useful to researchers interested in antimicrobial compounds and to those interested in developing disease resistance soybean plants through genetic engineering.
Technical Abstract: The effects of resveratrol and pterostilbene on in vitro growth of three soybean pathogens were tested to determine if these stilbenic compounds could potentially be targets to increase innate resistance in transgenic soybean plants. Growth of Macrophomina phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum was measured on solid and in liquid media amended with resveratrol and pterostilbene (concentration in the media of 100 µg/ml resveratrol and 25 µg/ml pterostilbene). All three fungi were very sensitive to pterostilbene in potato dextrose agar (PDA), which reduced colony area of each of the three pathogens to much less than half of the control 3 days after inoculation. The three fungal pathogens were relatively less sensitive to resveratrol compared to pterostilbene; however, colony area was significantly (P<0.05) less than the control 2 and 3 days after inoculation for S. sclerotiorum and at 3 days for R. solani on PDA amended with 100 µg/ml resveratrol. Colony area for M. phaseolina on PDA amended with 100 µg/ml resveratrol was consistently lower than the control but the differences each day were non-significant (P>0.05). In potato dextrose broth (PDB) shake cultures, growth of R. solani was significantly (P<0.05) suppressed in resveratrol and pterostilbene by day 4 after inoculation, compared to the control, with nearly 100% growth suppression in resveratrol and 80% less growth in pterostilbene. In contrast, mass of mycelia of S. sclerotiorum in PDB amended with the phytoalexins was suppressed at day 2 after inoculation, compared to the control, but by day 4, the mycelial mass in resveratrol or pterostilbene was not significantly different (P>0.05) from the control. Mass of mycelia of M. phaseolina in PDB amended with resveratrol or pterostilbene was consistently lower than the control over 4 days of growth, but the differences in mass were not significant (P>0.05). Results of biochemical analyses of the PDB over time indicated that the three fungi degraded resveratrol, with nearly 75% reduction in concentration in M. phaseolina, 80% in S. sclerotiorum, and 60% in R. solani PDB cultures by day 4 of fungal growth. M. phaseolina and S. sclerotiorum were able to resume growth after early inhibition by resveratrol after its concentration was reduced in the cultures through degradation, while R. solani was less efficient in resveratrol degradation and was not able to overcome its inhibitory effects on growth. The capacity to degrade pterostilbene was lowest in M. phaseolina compared to S. sclerotiorum and R. solani and the recovery of M. phaseolina cultures after initial growth inhibition by pterostilbene was minimal. The potential products of resveratrol and pterostilbene degradation by fungi were identified to be dimers and various oxidation products.