Genomic Analysis of Tan Spot and Stagonospora Nodorum Blotch Resistance in Wheat
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Abstract
Host-selective toxins, or necrotrophic effectors, are important determinants of
disease in both wheat-Stagonospora nodorum and wheat- Pyrenophora tritici-repentis
pathosystems. This study describes the identification, validation, and genomic analysis of
compatible host gene-effector interactions in these systems. In the wheat-S. nodorum
system, the Snn4-SnTox4 interaction was identified and validated using the hexaploid
wheat ( Tri ti cum aestivum L.) recombinant inbred populations 'Arina' x 'Forno' ( AF) and
Salamouni x 'Katepwa' (SK), respectively. The single dominant gene, Snn4, which
mapped to the short arm of chromosome 1 A in both populations, governs sensitivity to the
proteinaceous effector, SnTox4, which is estimated to be 10-30 kDa in size. The
compatible Snn4-SnTox4 interaction played a significant role in disease development in
both the AF and SK populations accounting for 41 % and 23.5% of the phenotypic
variation, respectively. Effects of the additional minor QTL were largely additive in both
genetic backgrounds. Molecular mapping in the SK population using microsatellites and
markers developed using bin-mapped expressed sequence tags (ESTs), and from ESTs
identified based on colinear studies with rice (Oryza sativa L.) and Brachypodium,
delineated Tsc2 to a 3.3 cM interval and confirmed its location on 2BS of hexaploid wheat.
The compatible T.~c2-Ptr ToxB interaction accounted for 54% of the disease variation in
the SK population. The marker XBE44454 l, which co-segregated with Tsc2 is diagnostic
of the gene and will be useful in marker-assisted selection (MAS).