CARNATION WILT DISEASES 7 



The disease can be recognized by the slow wilting and withering of the indi- 

 vidual branches accompanied by changes in color from normal to dull green, 

 then to yellow or straw. There is a progressive discoloration of the vascular or 

 conductive tissue from the normal pale green to a yellowish, reddish, and brown- 

 ish color. Infection is established in the roots, in the stem, or in the branches. 

 Wilting does not appear until the disease has advanced considerably around the 

 periphery of the branch or stem above and below the point of infection. The 

 branches are progressively invaded by the fungus through the conducting tissue 

 from the stem, and the brown color and dry rot spread radially and vertically. 

 Frequently only the branches on the rotted side of the stem wilt and change 

 color. Ultimately, the entire plant succumbs. Plants may live harboring in- 

 fection for a long time without showing symptoms of disease. Pinkish spore 

 masses of the fungus are usually evident on the surface of the stem and in the 

 base of the branches at the level of the soil. The fungus is essentially a vascular 

 parasite causing a typical wilting of the branches and subsequently a dry rot of 

 the stem and branches. The disease may appear at any stage in the culture of 

 carnations, but the losses are most significant in the summer and fall months. 

 In 1914 Peltier (53) proposed the name "branch rot" for this Fusarium wilt 

 disease, and this name is generally used by the growers. It is also called Fusarium 

 wilt (5, 78), which appears to be a more appropriate name. The causal fungus 

 has more recently been designated Fusarium oxysporum Schl. f. dianthi (Prill. & 

 Delacr.) Snyder and Hansen (56). 



Stem Rot 



This disease, caused by the fungus Rhizoctonia solani Kiihn, is characterized 

 by a progressive wilting, collapse, and browning of the entire plant, associated 

 with a soft decay of the stem at the soil line. The foliage acquires a pale or dull 

 greenish color. The leaves wilt slightly at first, then more generally, and finally 

 the entire plant collapses. The stem at the soil level is soft and moist and the 

 bark is easily rubbed off with the fingers. The wood beneath the decayed bark 

 at first remains firm. The roots remain intact and attached to the stem. The 

 stem of the dead plant becomes fibrous as disintegration continues. Compact 

 brownish clumps or sclerotia of the fungus are present on the decayed bark, and 

 the mycelium of the fungus is present about the stem and adjacent soil. 



This fungus is an omnipresent inhabitant of soil. It attacks cuttings in the 

 sand bench and propagating house; rooted plants in the flats (Fig. 7), where 

 it causes a troublesome basal rot; and all subsequent stages of the plant in the 

 field and in the greenhouse. The association of the Rhizoctonia fungus with the 

 stem rot disease of carnations was established in 1899 (25), but even before that 

 time the disease was widely distributed on carnations throughout the United 

 States. Its occurrence in Massachusetts was reported in 1902 (64). The fungus 

 attacks all kinds of plants and it has been the subject of extensive research 

 (52, 53). 



TEMPERATURE RELATIONS OF THE PATHOGENES CAUSING WILT 



The optimum temperature for growth and for spore germination of the patho- 

 genic organisms considered in this paper lies in a range of 75° to 88° F. The 

 optimum and highest temperatures of the year prevail in the greenhouse in 

 July and August, and after the benches are newly planted. 



The optimum temperature for spore germination and growth of AUernaria 

 dianthi is about 75° F., and at 40° and 90° growth is almost completely inhibited. 



Fusarium avenaceum and F. culmorum, the root-rotting organisms, grow best 

 at temperatures around 80° F. Dowson (24) reported that the optimum growth 



