Effects of Soybean Cultivar, Foliar Application of Azoxystrobin, and Year on Seed Vigor and Microflora Under Delayed Harvest Conditions

The effects of cultivar and foliar fungicide applications on soybean seed germination, vigor, microflora, and yield after delayed harvest were determined at the University of Arkansas Vegetable Research Station in Kibler, AR, from 2008 to 2010. Seven cultivars with varying levels of resistance to spp. or spp. were treated or not treated with a foliar application of azoxystrobin at the R5 growth stage. Plots were harvested 3 weeks after the plants had reached harvest maturity. Yields were recorded, samples of seed were collected, and standard germination (SG) and accelerated aging (AA) were assessed. Seeds were also assayed for infection by fungi on modified potato dextrose agar and by bacteria on nutrient agar. Seed vigor was significantly reduced by infection with spp, spp., and , but not with spp. Cultivar had a significant impact on yield, seed vigor, and seed infection levels. The cultivar Osage had consistently high seed vigor and low overall seed infection incidence throughout the study. MO/PSD-0259, AG 4403, and UA 4805 also had relatively high seed vigor and low seed infection rates. PI 80837 had a low incidence of seed infection by spp. and spp. in 2008 and 2010, but high levels in 2009, when environmental conditions were especially favorable for these pathogens. AP 350 and Suweon97 had relatively high seed infection incidences, particularly of spp. and spp., and relatively low seed vigor. Application of the foliar fungicide azoxystrobin at the R5 growth stage significantly increased AA across years and cultivars and increased seed infection by spp. in 2009 across cultivars. There were significant negative correlations between yield and seed infection by spp. and during 1 year and with spp. during all 3 years. Overall, resistance to seed infection can persist even when harvest is delayed. In addition to spp., other seedborne pathogens may reduce seed vigor and yield.