Evaluating Soybean Genotypes for SDS Resistance Using Canopy Spectral Reflectance.

Sudden Death Syndrome (SDS) in soybeans, (Glycine max ( L.)  Merr., caused by Fusarium virguliforme, is an increasing problem in commercial soybean production due to the yield loss associated with the disease.  The primary method of control for the disease is growing soybean varieties with resistance to F. virguliforme.  Screening for genetic resistance requires extensive visual evaluations. Canopy spectral reflectance have been used of identify soybean lines with higher grain yield in breeding programs.  The objective of this study was to identify specific regions of the canopy spectral reflectance that could be used in high-throughput screening to select for resistance to SDS in soybean varieties. Spectral reflectance measurements were taken on a soybean population of 160 genotypes and 145 commercial soybean cultivars in Manhattan and Topeka, KS in 2015 and 2016. Spectral reflectance measurements in wavelengths ranging from 350 to 1027 were taken after canopy closure through R7 and plots were rated for SDS foliar symptoms using the SIUC SDS Scoring Method at R6. Genotypes in the mapping populations and the commercial cultivars differed significantly in SDS resistance as measure by foliar symptoms. DX ratings ranged from 0 to 76. Differences in reflectance were detected among genotypes during early seed fill and continued through R7. Correlations between dx tended to be the largest for wavelengths 465 through 695. In the mapping population selecting the 20% most resistant genotypes using reflectance as the selection criteria identified the 6 out of the top 16 genotypes with the lowest dx, whereas selecting the 10% least resistant genotypes as identified but spectral reflectance identified 7 of the 10 genotypes with the highest dx.  Canopy spectral reflectance measurements are able to identify the less resistant lines, which could help eliminate undesirable material from a breeding program faster and allow for more lines to be evaluated.