A field study of rugose leaf curl virus infection in stoloniferous Trifolium species

Abstract

A field study was made of rugose leaf curl virus (RLCV) infection in four stoloniferous clovers ; New Zealand White and Irrigation White, cultivars of Trifolium repens, and two species from Africa, T. semipilosum and T. burchellianum. Half of the plants used were inoculated in the greenhouse, and, of these, 20 per cent showed symptoms of RLCV when they were planted in the field. The plants were grown in two field experiments on different sites at the Queensland Agricultural College, Lawes. The disease vector Austroagallia torrida was generally present over site 1 in larger numbers than over site 2. Pre-inoculated plants maintained a higher level of infection throughout the experiment. Over 40 per cent of plants not pre-inoculated developed the disease symptoms in the field, but the level of infection was consistently higher at site 1. T. semipilosum showed higher rates of infection than other species, but this species has greater drought resistance, and drought stress tended to mask symptom expression in the other species. Of 733 plants that showed infection during the experiment, 530 wholly or partially recovered from the disease, and, of these, only 38 became re-infected later in the experiment. The high percentage of recovery of infected plants, and the low percentage of re-infection of these recovered plants in the field supports earlier greenhouse studies, and suggests a possible reason for the low incidence of RLCV in old established stoloniferous clover pastures in southern Queensland.