Masters Theses

Date of Award

6-1985

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Ernest C. Bernard

Committee Members

Charles H. Hadden, James W. Hilty, Effin T. Graham

Abstract

Cultivated species of Spiraea are sometimes damaged and defoliated by leaf spot fungi in the genus Cylindrosporium. The disease they cause is especially damaging to S x vanhouttei. An epidemic of spirea leaf spot encountered at a west Tennessee nursery prompted this study, The presumed causal organism was tentatively identified as C. filipendulae. A comparison with descriptions of others placed in C. filipenduale confirmed the original identification. C. filipendulae was isolated from S. x vanhouttei and pathogenicity to that host was proven by Koch's postulates. C. filipendulae is transferred to the genus Phleosporella and renamed Phleosporella filipendulae on the basis of acervulus formation and conidial morphology. Numerous apothecia observed on overwintered S. x vanhouttei leaves were determined to be the perfect state of P. filipendulae by cultural methods. Conidia collected from ascospore isolates infected spirea leaves and induced symptoms identical to those caused by P. filipendulae. Histological methods were used to further elucidate the life cycle of the fungus. Microconidia formed in distinct fruiting bodies prior to leaf fall. These spores were also found in pure cultures of the fungus. Nascent ascocarps containing trichogynous hyphae developed below the microconidial structures. Development of the perfect state may be stimulated through fertilization by the microconidia. Morphology and development of the perfect state were compared with that of Blumeriella jaapii (Rehm) v. Arx (=Coccomyces hiemalis Hig.) and found to be quite similar. Therefore, it is proposed to place the new teleomorph into Blumeriella and to name it Blumeriella haddeni.

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