QTL Map Associated with Wax Content and Disease Resistance in Wheat.

Leaf rust is the most common and one of the most important cereal diseases of the world. Leaf rust, Puccinia triticina is an obligate parasite that redirects nutrients from the plant and as a consequence lowers grain amount, size, milling and baking quality.  Yield losses due to leaf rust average from 1-20% over a large area and can cause up to 40% yield loss on susceptible wheat varieties.  Severity of infection is dependent on the developmental stage of the host plant where epidemics that occur during or before the flowering stage are the most serious. Wax has long been shown to act as a protective structure against pathogen infection by providing a physical barrier between pathogen and host. The objective of this study is to identify QTLs associated with wax deposition that contribute to disease resistance to leaf rust.  Our hypothesis is that an increased epicuticular wax deposition on leaf surfaces may prevent infection by forming a hydrophobic layer that prevents attachment and penetration of spores to the leaf.  We studied a set of 120 recombinant inbred line (RIL) population derived from a cross of Halbred and Karl 92 that has a genetic map available. Halberd cultivar has significantly higher wax content than Karl 92. The RIL population was evaluated for two years. The leaf wax content was quantified using a colorimetric technique.  We have scored the RIL population for leaf rust severity and measured leaf length. We will perform composite interval mapping to identify significant QTLs.