Genotypic and Phenotypic Selection for Head Scab Resistance in Wheat.

Head Scab or Fusarium Head Blight (FHB) is a highly destructive fungal disease caused by Fusarium graminearum that affects wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.).  It causes considerable reduction in yield and diminution in grain quality due to mycotoxin contamination. Breeding for resistance to FHB is arguably the best way to combat this disease. However, phenotypic screening for FHB resistance is laborious, expensive and environmentally influenced. In recent years, molecular markers have emerged as a promising new tool in plant breeding programs. The objective of this work is to compare phenotypic with genotypic selection for FHB resistance.

 An F_2:3 population derived from a cross between a FHB susceptible parent (KY93C-1238-17-2) and a FHB resistant parent (VA01W-476) was divided into two subpopulations. The first subpopulation was subjected to genotypic selection. Thus, 10 seeds from each of 48 F_2:3 heads were planted in pots in the greenhouse in 2006. Each plant was evaluated for the presence of the major 3BS QTL associated with FHB resistance using three markers (barc147, gwm533 and Fhb1). Seeds coming from plants homozygous resistant and susceptible for the 3BS QTL were planted in headrows in 2007 to form two contrasting genotypically selected populations. The second F_2:3 subpopulation comprised 48 heads planted in headrows in 2006; the objective was to subject this population to phenotypic selection.  Seed from the phenotypically selected subpopulation formed the third population planted in headrows in 2007. In 2008, disease ratings will be recorded in the field ; percentage of Fusarium damaged kernels (FDK) and deoxynivalenol (DON) content will be measured in seed harvested from the headrows. The three populations will be compared for genetic progress in scab resistance.   The results of this experiment will help to determine the optimal balance for genotypic and phenotypic selection in FHB resistance selection programs.