Effect of root infection by Macrophomina phaseolina on stomatal conductance, canopy temperature and yield of soybean

Abstract

Charcoal rot, caused by Macrophomina phaseolina, is a widespread drought-associated, soilborne disease of soybean. Generally, disease severity is assessed indirectly as host colonization at the end of the growing season. Few studies have measured the effects of disease during the season. Two moderately charcoal rot resistant cultivars (‘DT 97-4290‘ and ‘Delta Pineland 4546‘), a drought tolerant cultivar (‘R01-1581F’) and a susceptible cultivar (‘LS 980358‘) were planted in microplots filled with uninoculated steam pasteurized soil or pasteurized soil infested with M. phaseolina. Half of the plots were irrigated and half were drought stressed. Stomatal conductance and infrared canopy temperatures were measured 47, 70, 77 and 98 days after planting (DAP) in 2008 and 52, 63, 72 and 84 DAP in 2009. Yields were taken at the end of the season. There were significant differences in stomatal conductance. In 2008, stomatal conductance was significantly lower 47 DAP in the non-irrigated/inoculated plots than the other treatments. At 98 DAP, stomatal conductance was highest in the irrigated/non-inoculated plots. In 2009, stomatal conductance was significantly higher in the non-infested plots than the infested plots of ‘LS 890358‘ and ‘R01-1581F’ across sample times, but not in plots of the resistant cultivars ‘DT 97-4290‘ or ‘DPL 4546‘. These differences were reflected in significantly greater canopy temperatures and lower yields in the infested compared with the non-infested plots of the susceptible, but not the resistant cultivars. These results show that root infection by M. phaseolina can reduce water movement in soybean and reduce yields in susceptible cultivars.