Urrea, K., Rupe, J. C, and Rothrock, C. S. 2013. Effect of fungicide seed treatments, cultivars, and soils on soybean stand establishment. Plant Dis. 97:807-812.Seedling diseases are one of the major production problems for soybean. The pdmary control of soybean seedling diseases is by fungicide seed treatments but compadsons of seed treatments are difficult because stand responses are often erratic in the field. The objective of this study was to determine the efficacy of soybean fungicide seed treatments in naturally infested soils under controlled environments at three temperatures. Seed of three soybean cultivars were treated with six fungicide treatments or not treated and planted in two soil types collected from two fields in Apdl, May, and June 2008 and 2009. Tests were conducted in growth chambers at 21°C (Apdl planting), 25°C (May planting), or 28°C (June planting). Stands were determined when at least 25% of the seedlings reached the V4 growth stage. Seed treatments improved stands at all three temperatures, in both soils, and in both years. In general, the broad-spectrum fungicides tdfloxystrobin + metalaxyl and mefenoxam + fludioxonil + azoxystrobin resulted in the highest stands. The selective fungicide treatments metalaxyl and pentachloronitrobenzene + carboxin were effective at all three temperatures, implying that Pythium spp. and Rhizoctonia solani, respectively, were involved in seedling disease and active over a range of temperatures. The efficacy of fungicides was not consistently associated with the cultivars used in this study.

The soybean [Glycine max (L.) Moench.] cultivar ‘Archer’ has a single gene for resistance to hypocotyl infection by Pythium aphanidermatum (Rpa1) but it is not known if this source of resistance limits pre‐emergence damping‐off caused by this pathogen. Resistance in Archer to pre‐emergence damping‐off caused by P. aphanidermatum was characterized in 84 F2:6 soybean lines derived from a cross of ‘Archer’ (the resistant parent) and ‘Hutcheson’ (the susceptible parent). The lines and parents were evaluated for percent germination at 7 days and percent stand at 14 days via a seed plate assay and an infested vermiculite assay, respectively. The lines were assayed with 5403 single‐nucleotide polymorphism (SNP) markers and the results compared with the assay data. Seed germination and plant stands for the Archer × Hutcheson population fit the model for a quantitative trait indicating that Pythium resistance was controlled by multiple genes or quantitative trait loci (QTLs). Two QTLs were identified by each of the two phenotyping methods on chromosomes 4 and 7. The QTL on chromosome 4 explained 8.29 and 13.76 % of the variation and the QTL on chromosome 7 accounted for 4.5 and 13.85 % of the variation in the seed plate and infested vermiculite assays, respectively. Heritability of resistance was 0.8534 and 0.6955 in the seed plate and the infested vermiculite assays, respectively, indicating that Pythium resistance from Archer could successfully be incorporated into soybean breeding programs. These QTLs were not associated with Rpa1, the gene for resistance to hypocotyl symptoms.

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