Usefulness of 10 Genomic Regions in Soybean Associated With Sudden Death Syndrome Resistance.

Sudden Death Syndrome (SDS) is an important soybean [Glycine max (L) Merrill] disease caused by the soilborne fungus Fusarium virguliforme. Currently, 14 quantitative trait loci (QTL) had been confirmed associated with resistance or tolerance to SDS.  The objective of the study was to evaluate usefulness of 10 of these QTL in controlling disease expression.   Six populations were developed providing a total of 321 F2-derived lines for the study.  Recombinant inbred lines (RIL) used as parents were obtained from populations of ‘Essex’ x ‘Forrest’ (EF), ‘Flyer’ x ‘Hartwig’ (FH), and ‘Pyramid’ x ‘Douglas’ (PD).  Disease resistance was evaluated in the greenhouse at three different planting times, each with four replications, using sorghum infested with F. virguliforme homogeneously mixed in the soil (Luckew et al., 2012).   Four disease assessment criteria - foliar disease incidence (DI), foliar leaf scorch disease severity (DS), area under the disease progress curve (AUDPC), and root rot severity were used.  QTL were identified in more than one of the disease assessment criteria, mainly associated with lines in the most resistant categories. Five QTL (qRfs4, qRfs5, qRfs7, qRfs12, and Rfs16) were associated with at least one of the disease assessments across multiple populations. Of the five qRfs4 was associated with DI, AUDPC, and root rot severity, and Rfs16 with AUDPC and root rot severity. The findings suggest it may be possible for plant breeders to focus on stacking a subset of the previously identified QTL to improve resistance to SDS in soybean.