Date of Award

1985

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Colletotrichum fragariae Brooks, the causal agent of strawberry anthracnose (referred to herein as anthracnose-crown rot), has been reported to infect all above ground parts of the strawberry plant. Colletotrichum acutatum Simmonds is known to cause ripe rot of several fruits including strawberry. Twenty-four Colletotrichum isolates obtained from strawberry plants from several southeastern states and California were compared. Based on conidial morphology and cultural characteristics, 15 of the isolates were identified as C. fragariae and nine as C. acutatum. Two of the C. acutatum isolates were obtained from field grown plants exhibiting crown rot symptoms. This is the first report of C. acutatum causing a crown rot of strawberry plants. A wide range in pathogenic variation was evident among isolates of both C. fragariae and C. acutatum. In general, C. fragariae isolates caused more severe petiole and crown symptoms than C. acutatum isolates. However, some cultivars were more susceptible to certain C. acutatum isolates than to some C. fragariae isolates. Most of the C. fragariae and some of the C. acutatum isolates caused a crown rot on certain cultivars. Inoculation methods and conditions were compared. A plant spray inoculation method was best for evaluation of petiole response to C. fragariae. However, crown injection was necessary to reliably assess the crown rot response. Incubation in a dew chamber at 32 to 35 C for 48 hr immediately following inoculation was necessary for rapid disease development. Increasing the temperature from 25 to 32 C in the greenhouse in which inoculated plants were held resulted in substantially more severe disease symptoms on some cultivars tested. Two- to 4-wk-old seedlings (age after transplanting at the first-true-leaf stage) were in general more susceptible to C. fragariae than 14- to 18-wk-old seedlings; however, three seedling populations expressed juvenile resistance. More than half the strawberry seedlings derived from crosses involving previously reported anthracnose-crown rot resistant parents were found to be resistant to the crown rot phase in crown injection tests. Plants of most commercial cultivars were very susceptible to crown injection by C. fragariae and died within 50 days of inoculation.

Pages

83

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