Poster Session: Biology of Pathogens - Mycology

38-P

Phytotoxicity of the mycotoxin (±)-botryodiplodin (Bot) produced by Macrophomina phaseolina to soybean and duckweed in vitro.
H. K. ABBAS (1), W. T. Shier (2), T. W. Allen (3), R. E. Baird (4), N. Bellaloui (5), A. M. Butler (6)
(1) USDA ARS BCPRU, Stoneville, MS, U.S.A.; (2) College of Pharmacy, University of Minnesota, Minneapolis, MN, U.S.A.; (3) Delta Research and Extension Center, Stoneville, MS, U.S.A.; (4) Entomology and Plant Pathology, Mississippi State University, Starkville, MS, U.S.A.; (5) USDA-ARS, Crop Genetics Research Unit, Stoneville, MS, U.S.A.; (6) USDA-ARS, Biological Control of Pests Research Unit, Stoneville, MS, U.S.A.

The fungus M. phaseolina causes charcoal rot (CR), a major soybean disease. M. phaseolina also produces a toxin, Bot. Our objective was to determine if phytotoxic responses to Bot are consistent with the toxin’s mechanism of soybean root infection. Bot was tested for phytotoxicity in leaf disc assays using leaves from soybean cultivars with different reactions to CR using one moderately resistant and two susceptible cultivars. Phytotoxicity was defined as brown, necrotic tissue on the edge of leaf discs, when symptoms were absent in controls. Bot phytotoxicity (0 to 320 µg/mL) in leaf disc assays was consistent with the cultivar’s reported CR reaction. The resistant cultivar developed symptoms more slowly than the susceptible, but all showed phytotoxicity at 72 h at greater concentrations. Similar responses to Bot were observed in duckweed, except phytotoxicity occurred at reduced concentrations compared to soybean (> 10 µg/ml Bot). Root toxicity to Bot was measured as soybean seedling lateral and/or tap root growth inhibition in a hydroponic culture medium system containing Bot following four days. Bot caused dose-dependent inhibition of both tap and lateral root growth, but lateral root growth was inhibited at reduced Bot concentrations (4 µg/mL) than tap root growth (23.5 µg/ml). The phytotoxic responses to Bot outlined in this research suggest that Bot plays a role in the mechanism of root infection by M. phaseolina.