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Etiology

Chrysanthemum Foliar Necrosis: Symptoms, Histochemistry, and X-ray Analysis of Leaf Lesions. R. H. Lawson, Florist and Nursery Crops Laboratory, Beltsville Agricultural Research Center, USDA, Beltsville, MD 20705; M. M. Dienelt, Florist and Nursery Crops Laboratory, Beltsville Agricultural Research Center, USDA, Beltsville, MD 20705. Phytopathology 81:1071-1078. 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-81-1071.

Foliar necrosis in the Marble cultivars of Dendranthema grandiflora (Tzveler) is characterized by necrotic spotting in the lower leaves with associated chlorosis and premature senescence. The disorder is associated with manganese sensitivity and symptoms are amplified by the addition of supplemental manganese. Symptoms of foliar necrosis were produced in a high percentage of scion grafts of the D. grandiflora ‘Fanfare’ control when rootstocks of the Marble cultivars were treated with supplemental manganese. Marble and control cultivars with manganese-induced necrotic lesions showed degeneration in the palisade and spongy mesophyll cells adjacent to the vascular bundle. Bundle sheath cells were distorted, xylem vessels were occluded, and some sieve elements and companion cells were obliterated. Cell wall appositions were present in bundle sheath and epidermal cells abutting collapsed mesophyll cells. Supplemental manganese enhanced the cytological changes associated with necrosis. Normal, non-necrotic tissue in the Marble and control cultivars showed obliteration of some sieve elements and companion cells that was enhanced in necrotic Marble and control tissue. X-ray analysis revealed manganese accumulations in necrotic lesions in Marble cultivars with and without supplemental manganese, but not in symptomless tissue. We conclude that foliar necrosis in the Marble cultivars is associated with manganese toxicity.