The biology of sphaerotheca mors-uvae (SCHW) Berk. with particular reference to its mode of perennation on black currant and gooseberry

• Main Author: Merriman, Peter Robert
• Published: Imperial College London 1968
• Subjects: 571.2
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.623093

This investigation was concerned with the perennation of Sphaerotheea mors-uvae (Schw.) Berk., and in particular the ability of the fungus to overwinter as cleistocarps and as mycelium in the buds of its two hosts, gooseberry and black currant. The development and state of cleistocarps on black currant leaves was followed during 1965-66 and 1966-67, by examining samples at intervals. Cleistocarps were first observed on 5 August 1965, and on 11 July in 1966, and by October in both years approximately 70% contained ascespores. From 21 March 1966 and 15 February 1967, but not otherwise, discharge of ascospores from the overwintered cleistocarps was readily obtained in laboratory tests, and these ascospores were shown to infect black currant leaf discs in the laboratory, and also leaf discs and plants in the field. Sporulating colonies of S. mors-uvae developed-within eight days. Cleistocarps on black currant and gooseberry. shoots were similarly examined and tested during 1966-67 and 1967-68; although their pattern of development was Similar to that on black currant leaves, no discharge of viable and infective ascospores could be demonstrated in laboratory tests. Evidence that S. mors-uvae perennates in buds of gooseberry was obtained by dissecting buds and by inducing buds on surface-sterilized shoots to burst under conditions which precluded chance infection. Field observations also suggested that bud infection occurred on gooseberry. Similar experiments failed to demonstrate the fungus in buds of black currant, and there was no indication of bud infection of this host in the field. In 1966 and 1967 there were further studies related to the perennation of the fungus. Searches were made for the first infections, and the development of the disease was then followed in relation to the growth of both hosts. The ability of overwintered fungus from one host to serve as inoculum for infection of the other was examined in cross-inoculation experiments with ascospores and conidia. The results of these experiments suggested that there are two strains of S. mors-uvae, one capable of infecting both black currant and gooseberry, the other infecting gooseberry only.