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Etiology

Chrysanthemum Foliar Necrosis: Transmission Electron Microscopy of Leaf Lesions. M. M. Dienelt, Florist and Nursery Crops Laboratory, Beltsville Agricultural Research Center, USDA, Beltsville, MD 20705; R. H. Lawson, Florist and Nursery Crops Laboratory, Beltsville Agricultural Research Center, USDA, Beltsville, MD 20705. Phytopathology 81:1079-1087. Accepted for publication 2 April 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/Phyto-81-1079.

Plants of the Marble cultivars of Dendranthema grandiflora (formerly Chrysanthemum × morifolium) often display necrotic spotting of lower leaves and premature leaf senescence. Ultrastructural cytopathology from leaves of cultivars Pink Marble, White Marble, and Florida Marble was compared with that of leaf tissue from unaffected chrysanthemum cultivars Vero, Fanfare, Surf, and Bonnie Jean. P-protein and plastid complexes in sieve elements of the Marble cultivars were often highly electron-dense and sieve and companion cell obliteration sometimes appeared enhanced over controls. Mature sieve elements contained endoplasmic reticulum, plasmalemmae, plastids with starch grains, mitochondria, vesicles, and P-protein. Mycoplasmalike organisms were not observed. Necrosis was distinguished by collapse of mesophyll and epidermal cells, formation of papillae-like appositions on cell walls bordering necrosis, and accumulations of electron-dense spherical or filamentoid substances in central vacuoles. Similar features were present in necrotic foliar lesions from Vero, Fanfare, and Bonnie Jean treated with toxic levels of manganese. Results are consistent with earlier evidence indicating that chrysanthemum foliar necrosis in the Marble cultivars is associated with manganese toxicity and not a biotic agent.