Host plant resistance genes for fusarium head blight: Mapping and manipulation with molecular markers

Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein.)], or scab, causes severe reductions in yield and quality of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Evaluation of FHB resistance is laborious and subject to environmental influence; therefore, molecular markers for FHB resistance genes will greatly enhance selection for FHB resistance. This review seeks to summarize information on molecular markers associated with quantitative trait loci (QTL) for resistance to FHB in wheat and barley and the use of those markers for marker assisted selection. Our goal is to summarize the current state of knowledge on the genetics of FHB resistance, the map locations of QTL for FHB resistance, and the future directions and potential applications of this research. In wheat, five types of resistance have been described, and Type If resistance (expressed in Chinese wheat cultivar Sumai 3) is the easiest type to assess. Several research groups are developing molecular markers associated with genes for FHB resistance from Sumai 3, a widely used source of Type II resistance in wheat breeding programs worldwide. In four different populations, each having Sumai 3 or a derivative as one parent, one to four QTL have been identified that explain up to 63% of the variation in resistance. QTL were identified on chromosomes 3BS and 6BL, in three or more populations. Recently, in barley, restriction fragment length polymorphism (RFLP) markers associated with genes for FHB resistance, deoxynivalenol (DON) accumulation, and kernel discoloration were identified on all seven chromosomes. Three regions, located on chromosomes 2,3, and 5 were identified in several mapping populations. Comparing the QTL locations between wheat and barley shows that the barley chromosome 3 QTL is located in a syntenous region in wheat. The following areas of research on molecular markers associated with FHB resistance should be emphasized: (i) identifying and mapping better resistance sources in wheat and barley; (ii) validating QTL in additional populations; and (iii) developing markers that can be easily used in breeding programs and across populations.