Assessing heritability of brown root rot (Phoma sclerotioides) resistance and forage yield in nine alfalfa (Medicago sativa ssp. sativa) populations

Brown root rot (BRR) of alfalfa, caused by Phoma sclerotioides G. Preuss ex Sacc., is associated with widespread winter mortality. Dark lesions form on susceptible plant roots and Rhizobium species nodules. As the disease progresses, lesion circumference enlarges and roots can be girdled, eventually causing substantial tissue rot. Advanced disease symptoms result in reduced plant vigor, or death. Current control strategies for BRR are limited to rotation with annual small grains and proper management of the alfalfa stand.; Primary objectives of this research were to ascertain whether plants naturally exposed to BRR in the field for six years were selected for BRR resistance and to determine if resistance was heritable. A secondary research objective was to breed selected alfalfa plants to produce a BRR resistant experimental line. Wyoming producers need BRR resistant alfalfas that can maintain economically sufficient levels of forage production during disease exposure.; Data from Disease Reaction Studies #1 and #2 determined Cycle 0 plants (those not exposed to the fungus in a field situation) exhibited significantly increased BRR disease severity symptoms on roots compared with Cycle 1 plants (those bred from plants surviving six years of disease pressure in the field). Plant tap roots in both studies were inoculated with P. sclerotioides . Plants were then exposed to two winter seasons in Laramie, Wyoming.; Forage totals from the establishment and first production years of an alfalfa field study grown in the absence of disease (located at the UW College of Agriculture Greenhouse in Laramie, WY) indicated the BRR resistant experimental line (WY-BRRR) produced increased biomass compared with plants used as parent breeding material. Future research will continue on field forage production of the experimental line at locations naturally infested with BRR throughout Wyoming and Montana.