S. CHAKRABORTY¹, R. CHARUDATTAN² and J.T. DE VALERIO²

¹Division of Tropical Crops and Pastures, CSIRO, Brisbane, Queensland, Australia
²Department of Plant Pathology, University of Florida, Gainesville, Florida, USA

Abstract

Eleven accessions of Cassia rotundifolia, including the cv. Wynn, and one of C. pilosa were screened against 6 fungal pathogens, of which two are exotic to Australia. Colletotrichum dematium f.sp. crotalariae and Sclerotium rolfsii were pathogenic on several accessions, whereas isolates of Phomopsis sp., Macrophomina phaseolina and Pseudocercospora nigricans were non-pathogenic on Cassia. Alternaria cassiae, a possible mycoherbicide for the control of sicklepod (C. obtusifolia), produced small necrotic lesions on young leaves and stems in 8 of the accessions. Accessions Q9862, 57503, 86178 and cv. Wynn were considered susceptible and the others were grouped as being moderately resistant to resistant. Symptoms were mainly restricted to the youngest leaves, making the 2.5-week old seedlings more prone to severe damage than the 5 or 9-week old seedlings with many mature leaves. This could have serious implications for Wynn-based pastures as regular seedling recruitment is essential for long-term persistence of Wynn. The work demonstrates the potential damage that may be caused to Cassia based pastures if A. cassiae was introduced for the biological control of sicklepod weed in Australia or if the fungus is already present in Australia.