The role of disease resistance in alfalfa persistence

To evaluate the effect of disease resistance on alfalfa persistence, a five-year field study was conducted using sixteen cultivars with release dates from 1940 to 1996. Fusarium wilt and anthracnose were the prevalent lethal diseases observed. Disease was present in all cultivars, with higher incidence in older cultivars and cultivars with lower disease resistance levels. Percent stand was lowest in cultivars with lower disease resistance levels. To assess if individual plant survival in the field was the result of superior disease resistance, greenhouse studies were undertaken to assess the change in frequency of disease-resistant individuals between populations derived from original plant material used in the field study and populations derived from intermating field study survivors. Fusarium wilt, anthracnose and Verticillium wilt resistance was determined for parental and field selected populations. Increased frequency of Fusarium wilt and anthracnose resistant individuals was generally observed in progeny of the field selected populations compared to the progeny of parental populations suggesting that long-term survival in field situations partially results from disease resistance to naturally-occurring pathogens.