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Cytology and Histology

Comparative Histopathology of Botrytis squamosa and B. cinerea on Onion Leaves. C. A. Clark, Graduate Assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853; J. W. Lorbeer, Professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14853. Phytopathology 66:1279-1289. Accepted for publication 3 March 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1279.

Botrytis squamosa and B. cinerea had different prepenetration activities on onion leaves with and without exogenous nutrients. In water B. squamosa conidia germinated on the side closest to the nearest anticlinal wall juncture or stomate and penetrated immediately, whereas B. cinerea germinated randomly, did not produce appressoria, and did not penetrate the leaf. Addition of exogenous nutrients to inoculum resulted in greater superficial growth by B. squamosa prior to penetration and was requisite for formation of appressoria and penetration by B. cinerea. Development by both fungi with and without exogenous nutrients was similar on leaf surface replicas and onion leaves. Postpenetration activities were the same for both lacuna. Both pathogens produced a cavity within each lesion as a result of collapse and separation of mesophyll and epidermal cells. Swelling of the outer periclinal epidermal wall was pronounced at all stages of lesion development. Pectinase C caused swelling of the outer periclinal epidermal wall, collapse of epidermal cells, and in some cases collapse of palisade parenchyma which mimicked histological changes associated with disease.