Susceptibility of Australian rice cultivars to the stem rot fungus Sclerotium oryzae

Abstract

Eleven rice cultivars and two breeding lines were tested for their susceptibility to Sclerotium oryzae. In one experiment, tillers were inoculated by spreading sclerotia over the pot surface before flooding to simulate a very heavy natural inoculum load in the field. In two further experiments, tillers were inoculated by placing agar discs bearing sclerotia against the stem at water level. This second method is considered to impose a more severe disease pressure on the plant and to be a better test of susceptibility. The reaction of the cultivars was mild by comparison to disease levels reported overseas. The length of stem tissue colonised by the pathogen was not correlated with loss of yield. In some cultivars, infected tillers yielded higher grain weights than uninoculated tillers. Cultivars Amaroo, Kyeema and Millin are considered to be the most susceptible to yield reduction with losses as high as 30%. It is suggested that growers with infested fields avoid these cultivars.