Infection of Cullen australasicum (syn. Psoralea australasica) with Alfalfa mosaic virus

Abstract

Severe yellow mosaic and leaf distortion symptoms have been observed on Cullen australasicum (cullen) plants growing in experimental plots at Urrbrae, South Australia. The incidence of the affected plants in a 2-year-old stand was ~80%. Symptom distribution on plants was uneven and symptom intensity appeared to vary between seasons. Alfalfa mosaic virus (AMV) was identified in 6/10 symptomatic and 1/10 asymptomatic field plants by reverse transcription-polymerase chain reaction (RT–PCR). Transmission of mosaic symptoms from cullen to cullen by mechanical inoculation was unsuccessful, but a cullen AMV isolate passaged through herbaceous indicators induced systemic mosaic in 1/4 of inoculated cullen seedlings. No seed transmission of AMV was observed in 50 seedlings raised from symptomatic parents. These results show that cullen is a host of AMV, but further studies are needed to determine whether AMV is the sole cause of the mosaic disease.