Two Convenient Methods to Evaluate Soybean for Resistance to Sclerotinia sclerotiorum

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Abstract
Several greenhouse inoculation methods are available to evaluate soybean (Glycine max (L.) Merr.) for resistance to Sclerotinia sclerotiorum (Lib.) de Bary. Most of these methods are labor intensive and often produce inconsistent results among the tests. The objective of this research was to develop a low-cost and high-efficiency greenhouse inoculation method that can generate a consistent result. We developed a spray-mycelium method in which mycelia were cultured in liquid potato dextrose broth and homogenized before spraying on the soybean leaves. We also developed an inoculation method (the “drop-mycelium” method) in which a drop of homogenized mycelium suspension was dropped on the tips of main stems. Inoculated plants were incubated in a greenhouse chamber with 60 to 80% relative humidity. Plant mortality and area under the wilt progress curve (AUWPC) were used to measure disease severity daily from 3 to 14 days after inoculation (DAI). Eighteen soybean genotypes, including partially resista... Sclerotinia stem rot is a major soybean disease in north-central regions of the United States and in southern Canada. It can cause substantial yield losses of 170 to 330 kg/ha for every 10% increase in Sclerotinia stem rot incidence. Using resistant soybean cultivars is the most economical and efficient method to control the disease. Evaluation of soybean for resistance to the disease with currently available methods is labor intensive and the results can be inconsistent among repeated tests. The objective of this research was to develop a low-cost and high-efficiency greenhouse inoculation method that can generate a consistent result. We developed a spray-mycelium method in which mycelia were cultured in liquid potato dextrose broth and homogenized before spraying onto the soybean leaves. We also developed a drop-mycelium method in which a drop of homogenized mycelium suspension was dropped on the tips of main stems. The results obtained with the spray-mycelium and drop-mycelium inoculation methods were ...