Improved seedling health, yield, and stand persistence with alfalfa resistant to Aphanomyces root rot

Alfalfa (Medicago sativa L.) breeders have made substantial progress in rec ent Sears to develop cultivars,vith resistance to Aphanomyces root rot (ARR , caused bg Aphanomyces euteiches), yet data showing the agronomic benefits of this resistance under natural field conditions are limited, Two trials were seeded into naturally infested soils with alfalfa cultivars ranging fr om susceptible to highly resistant to ARR, The trials provided a test of th e hypothesis that ARR-resistant cultivars would provide improved performanc e. In one test, the combination of high rainfall during the 4 wk following seeding on a soil,vith a slow percolation rate led to a severe outbreak of ARR, with symptoms typical of a syndrome commonly observed in commercial al falfa Gelds in Kentucky. Under these conditions, the ARR-resistant cultivar s provided dramatically improved seedling health, yield, and persistence. C ultivars hating a resistance (R) or high resistance (HR) rating provided th e most consistent performance. In the other test, a near-normal rainfall am ount on a deep soil with good internal drainage led to moderate disease pre ssure. In that case, the ARR-resistant cultivars exhibited a slight improve ment in seedling health, but yield trends were not as clear as in the forme r trial. Based on these findings and previous research, ne conclude that th e use of cultivars with R or HR ratings to ARR may solve a common stand-est ablishment problem in spring-seeded alfalfa in Kentucky.