Susceptibility, inhibition of infection in stolons, and induced resistance to rugose leaf curl virus infection in white clovers

Abstract

Rugose leaf curl virus (RLCV) disease is more widespread in legumes of agricultural importance than was previously recorded. The presence of the virus was confirmed in stoloniferous white clovers (Trifolium repens L.), red clover (T. pratense L.), lucerne (Medicago sativa L.), and peanut (Arachis hypogea L.) from Queensland, and T. repens and T. pratense from New South Wales.

In greenhouse experiments, differences in susceptibility to infection were demonstrated between nine varieties and strains of T. repens and T. pratense. The varieties Lodi and Ladino were significantly more resistant than others tested. A number of stolons that developed from severely infected plants in the greenhouse were apparently free of virus. Attempts to transmit virus from clones established from these plants, by means of the insect vector and by grafting, failed. Clonal plants derived from symptomless stolons of infected plants were observed to be more resistant to infection with RLCV than were clones taken from previously uninoculated seedlings.

In further experiments, infection of plants derived from apparently virus-free stolons arising out of severely infected plants was significantly lower than that of similar plants taken from previously uninoculated clonal plants of the same seedling material. The degree of resistance to infection varied between varieties and between seedling lines within varieties. The results suggest acquired or induced resistance to infection and provide an explanation for the apparent recovery from, and low incidence of, RLCV in susceptible white clovers in the field. The nature of the resistance is not known, but the evidence suggests a mechanism associated with necrosis of stolons. The effect of virus infection on pasture yield and the implications of the development of virus-free plants resistant to RLCV are briefly discussed.