Studies on the Physiology and Pathogenicity of Sclerotium Rolfcii Sacc. Causing Fruit - Rot of Tomato (Lycopersicum Esculentum Mill.)

Abstract

Salerotium rolfsii Sacc. grew best at 27 to 32 C, and maximum infection of tomato fruits occurred at 32°C„ S^_ rolfsii showed a double maximum of growth in relation to pH: a major peak at pH 1+.8 and a minor one at pH 9.31 with a minimum of pH 8.2 in between. Light had no effect on growth. Growth occurred only at 100$ R. H. whereas infection of tomato fruit occurred at a relative humidity of 957° and above. A moisture level of 55% W. H. C. of soil caused the greatest infection, and degree of infection diminished with a deviation in % W. H. C. in either direction from this level. Even though externally supplied thipmine v/as not essential for initiation of growth, subsequent development depended on it„ Thiamine at 25 Mg and 50 Aig supported the greatest growth. rolfsii was capable of using simple as well as complex carbohydrates as sources of carbon. Starch supported the best growth, followed by Maltose, Fructose and Glucose, whilst galactose and cellulose gave the poorest vegetative growth. Of the nitrogen sourcjig^Peptone and Asparagine were best used by the' fungus,"’and the least suitable was Alanine. S. rolfsii can enter the host through the intact fruit skirf. Rate of infection increased almost directly proportional to increase in size of inoculum. Prior to infection, rolfsii formed infection cushions on the fruit wall. Penetration was achieved by hyphae, emerging from the infection cushions, mechanically piercing through the cuticle and epidermis. Growth within the fniiit was both intercellular and intracellular. Pericarp cells were ultimately dissolved by substances produced by the fungus leaving the dead epidermis and cuticle intact. The disease was not seed borne. Tomato fruits of all ages were infected, and Molokai was the only Ghanaian tomato variety whose fruits were completely resistant to 3. rolfsii.