Environmentally responsive QTL controlling surface wax load in switchgrass

Key message Quantitation of leaf surface wax on a population of switchgrass identified three significant QTL present across six environments that contribute to leaf glaucousness and wax composition and that show complex genetic x environmental (G x E) interactions. The C4 perennial grassPanicum virgatum(switchgrass) is a native species of the North American tallgrass prairie. This adaptable plant can be grown on marginal lands and is useful for soil and water conservation, biomass production, and as a forage. Two major switchgrass ecotypes, lowland and upland, differ in a range of desirable traits, and the responsible underlying loci can be localized efficiently in a pseudotestcross design. An outbred four-way cross (4WCR) mapping population of 750F(2)lines was used to examine the genetic basis of differences in leaf surface wax load between two lowland (AP13 and WBC) and two upland (DAC and VS16) tetraploid cultivars. The objective of our experiments was to identify wax compositional variation among the population founders and to map underlying loci responsible for surface wax variation across environments. GCMS analyses of surface wax extracted from 4WCRF(0)founders andF(1)hybrids reveal higher levels of wax in lowland genotypes and show quantitative differences of beta-diketones, primary alcohols, and other wax constituents. The full mapping population was sampled over two seasons from four field sites with latitudes ranging from 30 to 42 degrees N, and leaf surface wax was measured. We identified three high-confidence QTL, of which two displayed significant G x E effects. Over 50 candidate genes underlying the QTL regions showed similarity to genes in eitherArabidopsisor barley known to function in wax synthesis, modification, regulation, and transport.