Management strategies and distribution of Aphanomyces root rot of alfalfa (Medicago sativa), a continuing threat to forage production in the United States

Abstract

Alfalfa (Medicago sativa), often called the "Queen of Forages," is grown worldwide as a forage crop for livestock due to its high biomass production and nutritional quality. It is the third most valuable crop in the United States and plays key roles in dairy and beef livestock feeds, protecting water and soil resources, enhancing soil fertility, breaking pest and pathogen cycles and sequestering soil carbon (Fernandez et al., 2019). Alfalfa is used as dry hay, for silage, and in grazing, as well as providing nectar for bees and habitat for wildlife. Early attempts to grow alfalfa in the United States were unsuccessful because of the differing climate from alfalfa's centre of origin in the Fertile Crescent, acidic soil and interactions with plant pathogens. The first successful alfalfa crops in the United States were produced in the warm, western part of the country. Alfalfa was not widely cultivated in the Midwestern United States until the late 1800s. The crop became successful in the Midwest by the development of varieties that displayed better survival in the region's harsh winters. Today, autumn dormancy and freezing tolerance are critical characteristics that effect the productivity and persistence of alfalfa in cold climates (Liu et al., 2019).Early alfalfa breeding efforts focused on improving resistance to root rot and bacterial wilt diseases caused by Phytophthora