The Influence of Nutrition on Conidial Production by Rhynchosporium alismatis and on Their Subsequent Infectivity to Alisma lanceolatum

Abstract

Nutrient composition of liquid-shake cultures significantly influenced conidial production by five isolates of Rhynchosporium alismatis after 6 days at 25 C. Lima bean broth at pH 7.5 produced the most conidia (4.99 x 10 7 /ml). The zwitterionic buffers PIPES and HEPES did not significantly affect broth pH, but did significantly affect yield of conidia. pH per se did not appear to affect yield directly. The medium in which an isolate was grown had a significant effect on the virulence of the resulting conidia as measured by disease severity scores in leaf discs of Alisma lanceolatum after 3 and 13 days. There was a significant difference between isolates, produced in the same medium, in the subsequent rate of disease development. The correlation between image analysis of diseased leaf discs with visual assessment was low, and it was considered that automatic assessment of disease severity was not cost-effective with the equipment used. Isolate DAR 73158 and lima bean broth are considered to be the combination of choice for further studies to explore the fitness of conidia produced in small-scale biofermentors.