Occurrence of Race-Specific Elicitors in the Host Pathogen Interaction Tomato-Cladosporium Fulvum

Abstract

Cladosporium fulvum Cooke (syn. Fulvia fulva), the causal agent of tomato leaf mould, is an economically important disease in glasshouse tomato crops and also in field grown tomatoes, where humid and high temperature conditions prevail. The disease was first described in 1883 in England, but presumably originates from South America (Butler and Jones 1949). C. fulvum is a biotroph entering the host through natural openings like stomata. After penetration the fungus colonizes the intercellular space around the leaf mesophyll cells. Under natural conditions the infection cycle takes 2 to 3 weeks. Ten to twelve days after inoculation conidiophores emerge through stomata and produce conidia. Until 1930 no genes for resistance were available in commercially grown tomatoes. Since a number of resistance genes have been introduced in a number of tomato cultivars. Resistance factors were obtained from several Lycopersicon species such as Lycopersicon pimpinellifollium, L. hirsutum, L. peruvianum var. glabatrum and L. glandulosum. In Canada Bailey and later Kerr have done much of the breeding for resistance to C. fulvum in tomato (Bailey and Langford 1947; Kerr and Bailey 1964). However, soon after introduction of new resistant varieties, resistance was overcome due to appearance of new races of the fungus. At present many races exist and many genes for resistance are known.