Incidence of Colletotrichum trifolii on lucerne in New South Wales, its host range and reaction of lucerne cultivars to inoculation

Abstract

Colletotrichurn trifolii, the cause of stem anthracnose and crown rot of lucerne, was detected in all major lucerne growing areas of New South Wales. The disease was more common and more severe in regions north of latitude 33�S. Most outbreaks occurred from February to June. The highest concentrations of spores for inoculations were produced on lima bean agar. Carnation leaf-piece agar was also satisfactory and was used as a routine medium for spore production. Viability of spores declined rapidly in cultures older than 7 days. Isolates of C. trifolii from New South Wales were most virulent on lucerne. Less severe symptoms were produced on other Medicago spp. and some Trifolium spp. Several grain legumes were inoculated but only chickpea showed slight symptoms. Two methods were used to evaluate the reaction of a range of lucerne cultivars and breeder's lines to C. trifolii. The standard inoculation method used in experiments in other countries and in local experiments produced the most severe symptoms and the ratings obtained agreed generally with known field reactions. A germination-inoculation method resulted in less severe symptoms and the ratings were poor indicators of field performance. Several cultivars showed a significantly higher resistance (P< 0.05) to C. trifolii and should prove useful in areas where the disease is endemic.