Date of Award

1989

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Lowell L. Black

Abstract

Colletotrichum gloeosporioides, C. capsici, C. acutatum, and C. coccodes incite pepper anthracnose. Species were differentiated based on their conidial and colony morphology as well as colony growth rates. In a survey of southern Louisiana pepper fields in September, 1987, anthracnose incidence ranged from 5 to 75 percent. Colletotrichum capsici, C. gloeosporioides, and C. acutatum were the incitants of anthracnose in the fields surveyed. Reactions of bell pepper and tomato fruit to isolates of C. gloeosporioides, C. capsici, C. acutatum, and C. coccodes from pepper and tomato were determined by injecting mature fruit with conidial suspensions. All isolates caused characteristic anthracnose symptoms on both hosts. Pathogenicity of 10 Colletotrichum spp. to pepper, tomato, apple, strawberry, snap bean, and blueberry fruit was determined by inoculations with conidial suspensions. Isolates of C. gloeosporioides, C. fragariae, and C. acutatum, regardless of host origin, were pathogenic on all fruit inoculated except snap bean and could not be separated based on the reactions of fruit inoculated. Isolates of C. coccodes, C. capsici, and C. truncatum were pathogenic to pepper, tomato, and apple but not to strawberry, blueberry, or snap bean. Isolates of C. orbiculare, C. higginsianum, C. lindemuthianum and C. falcatum were not pathogenic to most fruit tested. Crop debris and seed were investigated as sources of inoculum for pepper anthracnose. Incidence of anthracnose incited by C. capsici and C. gloeosporioides ranged from 36 to 93% throughout the season on pepper pods grown in fields with infested debris and on pods from plants grown from infected seed. Low levels, 3 to 6%, of pod infection by C. gloeosporioides occurred during early and midseason in fields with no known source of inoculum, suggesting the presence of a native plant host(s). Fungicide timing studies were conducted to determine the efficacy of maneb and chlorothalonil sprayed at 1 to 4 wk intervals for the control of anthracnose on cayenne and bell peppers. Applications at 1 and 2 wk intervals significantly reduced disease losses. Mean disease loss int he unsprayed plots was 76%, while losses in the weekly sprayed chlorothalonil and maneb plots were 25 and 37%, respectively.

Pages

86

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