Abstract
Key message A major novel QTL was identified in a recombinant inbred line population derived from a cross of ‘Wyandot’ × PI 567301B for Fusarium graminearum, a seed and seedling pathogen of soybean. Fusarium graminearum is now recognized as a primary pathogen of soybean, causing root, seed rot and seedling damping-off in North America. In a preliminary screen, ‘Wyandot’ and PI 567301B were identified with medium and high levels of partial resistance to F. graminearum, respectively. The objective of this study was to characterise resistance towards F. graminearum using 184 recombinant inbred lines (RILs) derived from a cross of ‘Wyandot’ × PI 567301B. The parents and the RILs of the mapping population were evaluated for resistance towards F. graminearum using the rolled towel assay in a randomized incomplete block design. A genetic map was constructed from 2545 SNP markers and 2 SSR markers by composite interval mapping. One major and one minor QTL were identified on chromosomes 8 and 6, respectively, which explained 38.5 and 8.1 % of the phenotypic variance. The major QTL on chromosome 8 was mapped to a 300 kb size genomic region of the Williams 82 sequence. Annotation of this region indicates that there are 39 genes including the Rhg4 locus for soybean cyst nematode (SCN) resistance. Based on previous screens, PI 567301B is susceptible to SCN. Fine mapping of this locus will assist in cloning these candidate genes as well as identifying DNA markers flanking the QTL that can be used in marker-assisted breeding to develop cultivars with high levels of resistance to F. graminearum.
Highlights
The incidence of seedling diseases in soybean [Glycine max (L.) Merr] caused by both oomycete and true fungi has increased substantially as the number of acres and the number of fields in continuous soybean has increased (Broders et al 2007; Ellis et al 2011)
The mean disease severity index (DSI) was significantly different among the two parents and the checks indicating that plant introduction (PI) 567301B had a high level of resistance and Wyandot had a moderate level of resistance towards F. graminearum (Table 1)
We characterized the resistance towards F. graminearum in PI 567301B and identified a major quantitative trait loci (QTL) using a population with over 2,500 molecular markers
Summary
The incidence of seedling diseases in soybean [Glycine max (L.) Merr] caused by both oomycete and true fungi has increased substantially as the number of acres and the number of fields in continuous soybean has increased (Broders et al 2007; Ellis et al 2011). Phytophthora sojae and Pythium spp. have long been known in Ohio for association with seed and seedling diseases causing pre- and post-emergence damping-off in soybean and are responsible for severe production losses in the state (Schmitthenner 1985). Another residue-borne pathogen, Fusarium graminearum [telemorph: Gibberella zeae (Schwein) Petch] has been identified as a primary pathogen of soybean causing seed rot and seedling damping-off in North America (Broders et al 2007; Díaz Arias et al 2013a; Xue et al 2007). Symptoms of seed rot and seedling damping-off caused by F. graminearum appear first as water soaked lesions followed by light brown or pink discoloration around the inoculation point. In South America, infections can occur at pod filling and symptoms include spreading of discoloration vertically on the stem, interveinal chlorosis of leaves leading to plant wilting, pod blight and death (Martinelli et al 2004; Pioli et al 2004)
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