Does function follow form? Principal QTLs for Fusarium head blight (FHB) resistance are coincident with QTLs for inflorescence traits and plant height in a doubled-haploid population of barley

Fusarium head blight (FHB), an important disease of barley in many areas of the world, causes losses in grain yield and quality. Deoxynivalenol (DON) mycotoxin residues, produced by the primary pathogen Fusarium graminearum, pose potential health risks. Barley producers may not be able to profitably market FHB-infected barley, even though it has a low DON level. Three type s of FHB resistance have been described in wheat: Type I (penetration), Typ e II (spread), and Type III (mycotoxin degradation). We describe putative m easures of these three types of resistance in barley. In wheat, the three r esistance mechanisms show quantitative inheritance. Accordingly, to study F HB resistance in barley: we used quantitative trait locus (QTL) mapping to determine the number, genome location, and effects of QTLs associated with Type-I and -II resistance and the concentration of DON in the grain. We als o mapped QTLs for plant height, heading date, and morphological attributes of the inflorescence (seeds per inflorescence, inflorescence density, and l ateral floret size). QTL analyses were based on a mapping population of F-1 -derived doubled-haploid (DH) lines from the cross of the two-rowed genotyp es Gobernadora and CMB643, a linkage map constructed with RFLP marker loci, and field evaluations of the three types of FHB resistance performed in Ch ina, Mexico, and two environments in North Dakota, USA. Resistance QTLs wer e detected in six of the seven linkage groups. Alternate favorable alleles were found at the same loci when different inoculation techniques were used to measure Type-I resistance. The largest-effect resistance QTL (for Type- II resistance) was mapped in the centromeric region of chromosome 2. All bu t two of the resistance QTLs coincided with QTLs determining morphological attributes of the inflorescence and/or plant height, Additional experiments are needed to determine if these coincident QTLs are due to linkage or ple iotropy and to more clearly define the biological basis of the FHB resistan ce QTLs. Plant architecture should be considered in FHB resistance breeding efforts, particularly those directed at resistance QTL introgression and/o r pyramiding.