First report of yellow stunt and root rot of standing milkvetch caused byEmbellisiasp. from China

Standing milkvetch (Astragalus adsurgensPall.) is important perennial forage in China. A new disease occurred severely in Huan County, Gansu Province (northern China) in 2004–2006. Symptoms were characterized by yellowing and necrosis of leaf blades, brown lesions of petioles (Fig. 1), discoloration of stems from brown to black (Fig. 2), overgrowth and stunt of shoots (Fig. 3, left side), root and crown rot, and plant death. Healthy plants were free from these symptoms (Fig. 3, right side).

A fungus was observed intercellularly and was consistently isolated from symptomatic tissues and seeds. The fungus was identified asEmbellisiasp. (Simmons, 1971, 1983), but it differs from all describedEmbellisiaspecies. Specimens of diseased plants and fungal isolate (MHLZU 0408) were deposited in the Mycological Herbarium of Lanzhou University.

Pathogenicity was confirmed with three methods of spraying, wounded root and seed inoculation, respectively with 75-day-seedlings, 35-day-seedlings and seeds that were pre-germinated for 2 days. Plants grown in pots containing disinfested soil were maintained in a greenhouse where the temperature was 23±2°C. The symptoms exhibited on inoculated seedlings and seeds were similar to those observed in the field, and the fungus was reisolated from inoculated plants. Untreated seedlings remained asymptomatic.

This is the first report of yellow stunt and root rot of standing milkvetch caused byEmbellisiasp. Some similar symptoms were previously observed in fields in Inner Mongolia of China (Hou and Bai, 1986; Hou, 2003). However, only in the present study were Koch’s postulates fulfilled and preliminary identification of the pathogen achieved. The disease causes serious degradation of standing milkvetch pastures.