4 MASS. EXPERIMENT STATION BULLETIN 427 



Spot, Blight, and Canker 



This disease, caused by the fungus Alternaria dianlhi Stev. & Hall (Fig. 1 , 2), 

 is manifested by spotting of the foliage, flowers, and stems; blighting of the 

 foliage; and cankering and rotting of the branches, followed by wilting, brown- 

 ing, and death of the branches. The discolored diseased areas become covered 

 with a black layer of spores especially under moist atmospheric conditions. 

 The spots at first have a slightly purplish color and are surrounded by a halo; 

 later they become brown and shriveled, and as they coalesce the disease assumes 

 the character of blight. The calyx and corolla lobes are also infected, especially 

 in the field. The branches are infected most frequently at the nodes just above 

 the stem, and this is the most common form of infection among the benched 

 plants in the greenhouse. The brown discolored areas at the nodes partially or 

 completely girdle the branch. At first the fungus is restricted to the bark or 

 outside of the cambium. Ultimately, the canker progresses deeper into the 

 branch. The leaves become dull green and marked with whitish or pale streaks, 

 and then wilt. The infected portion of the branch below acquires a brown or 

 blackish color, and the dark-colored rot extends to the pith. Black crusts of 

 spores form over the region of the branch where the rot is localized, and some of 

 the black deposit remains long after the branch has died. The branches become 

 completely desiccated and assume the color of straw. 



The fungus is associated with a brownish or blackish basal and axillary decay 

 of cuttings in the sand bench (Fig. 3). 



History 



The Alternaria blight of the carnation was recognized as one of the important 

 plant diseases in the United States in 1905 and considerable damage was reported 

 among varieties of the Mrs. Thomas Lawson type (Orton 48, Woods 81). In 

 October 1902 Irving Gingrich of South Bend, Indiana, submitted blighted car- 

 nation plants to Professor B. O. Longyear, Michigan State College, with informa- 

 tion that the disease was especially severe on the variety "White Cloud." The 

 fungus was identified as Macrosporium nohile Vize. The writer learned of the 

 specimen deposited in the Herbarium of the Department of Botany, Michigan 

 State College, from a published record by Coons (20). Study of this material 

 showed that the organism is Alternaria dianthi which was described seven years 

 later (62) on the basis of material found in Raleigh, North Carolina. In the 

 meantime, Clinton (14) reported a serious occurrence of the Alternaria disease 

 on carnations in a greenhouse at Greenfield Hill, Connecticut; and Woods (82) 

 reported that the disease was especially destructive to the varieties Enchantress 

 and Lawson, designated the "softer types." The plants acquired the disease 

 during their growing period in the field and were damaged seriously after bench- 

 ing. 



More recenth-, the disease has been epidemic in the Northeastern States, 

 notably New York, New Jersey, Pennsylvania (49), Virginia, Connecticut, 

 Massachusetts, New Hampshire, and Maine. In this general area frequent 

 serious instances of the disease and plant failures have occurred. Less frequent 

 occurrences of the disease are recorded from Colorado, Indiana, Michigan, 

 Missouri, Texas, and Wisconsin, and it was reported in 1932 to be a limiting 

 factor in the production of light-colored varieties grown under lath near Los 

 Angeles, California. The disease has been serious on carnations in certain por- 

 tions of Canada, notably in St. Anne, Quebec; Lincoln, Middlesex, and Cobourg 

 counties of Ontario; and also in garden patches of Dianthus throughout the prov- 

 ince of New Brunswick, especially in the vicinity of Fredericton (16, 45). It has 

 been reported on Dianthus sp. from Puerto Rico (54). 



