Identification and Characterization of Disease Resistance Genes in Alfalfa and Medicago truncatula for Breeding Improved Cultivars

Alfalfa plants are susceptible to numerous diseases caused by fungi, oomycetes, bacteria, and nematode pests that significantly reduce forage yield, quality, and productive stand life. Disease resistance is the most common and effective means of reducing damage from pathogens. Using phenotypic recurrent selection, plant breeders have successfully developed alfalfa cultivars with high levels of resistance to major yield-limiting diseases. This chapter summarizes the cases in which the mechanisms of disease resistance and inheritance of resistance have been investigated. DNA markers associated with resistance have been identified for several diseases. However, alfalfa lags behind other major crops in the identification of disease resistance genes and the use of molecular markers in cultivar improvement. A better understanding of disease resistance and the use of marker-assisted selection of superior germplasm should accelerate the breeding and development of more productive cultivars.