Factors that Affect Development of Collar Rot on Tobacco Seedlings Grown in Greenhouses

Abstract

Collar rot, caused by Sclerotinia sclerotiorum, is an important disease of tobacco transplants produced under greenhouse conditions. Factors that affect the development of the disease were studied, including age of seedlings, presence of an external source of nutrients (leaf extract), clipping (leaf removal) practices, exposure to low temperature, and leaf injury caused by heat and a chemical. Flue-cured tobacco seedlings, cultivar K-326, were grown in polystyrene cell trays floating on a nutrient solution. Trays were maintained in a phytotron growth chamber with a 28/18°C day/night temperature regime. Seedlings were inoculated with ascospores of S. sclerotiorum at the desired stage of growth by placing mature apothecia in the growth chamber and inducing ascospore release and deposition. Disease incidence was determined by examining seedlings for the presence of stem lesions over the next 15 to 21days. Seedlings between 35 and 53 days old were more susceptible to collar rot than younger or older seedlings. Inoculum efficiency was highest and disease was most severe when an external source of nutrients was present on leaf surfaces. Clipping of leaf tips did not increase disease, but if the leaf pieces created by clipping were left on seedlings, collar rot development was enhanced compared with treatments where debris was removed. Heat and chemical injuries that resulted in necrotic tissue provided highly susceptible infection courts for ascospores of S. sclerotiorum, but exposure to low temperature, which caused no visible injury, did not enhance infection. Adoption of cultural practices that minimize accumulation of leaf debris and eliminate factors that cause necrotic injury on leaves should greatly reduce the severity of collar rot of tobacco seedlings.

New Phytotron for Studying the Effect of Climate Change on Plant Pathogens

“…At present, at least in Europe, several kinds of phytotrons are already in use for studying the effect of environmental conditions and stresses on plant diseases, but in most cases experiments were carried out in small chambers, on seedlings or small plants, without monitoring and controlling carbon dioxide concentration and not specifically designed for studying plant-pathogens interactions, in particular on foliar diseases [Tani 1996;Thiel 1996;Uprety 1998;Schmadel-Hagebolling 1998;Gutierrez 2000;Grote 2001;Yazaki 2004;Cherukuri 2005;Luedemann 2005;Pritsch 2005]. Consequently, available phytotrons are not really suited to study the effect of climate change on plant disease or there is no scientific evidence of the possibility to use commercially available chambers for such purposes.…”