Fusarium oxysporum f.sp. medicaginis (fusarium wilt of alfalfa)

Dark or reddish-brown streaks occur in the stele of the taproot, appearing in cross section as small, partial, or complete rings. An olive to brown discoloration extends into the basal portion of the stem. As the disease progresses, the vessels become plugged and the plants wilt. Bleaching of leaves and stems follows, and a reddish tinge often develops in the leaves. Only one side of a plant may be affected at first. After several months, the entire plant dies. The disease usually progresses slowly in alfalfa stands and only scattered plants show symptoms at any one time. Considerable stand loss may occur over several years (Frosheiser and Barnes, 1978). Fusarium wilt is more severe in association with root-knot nematodes (Griffin and Thyr, 1978).