CARNATION WILT DISEASES 9 



Fusarium Root and Crown Rot 



The generalized rotting of carnation roots, stems, and branches due to several 

 distinct species of Fusarium is well known. Starkey (58, 59, 60, 61) traced the 

 development of the disease from the fine roots in the remote parts of the root 

 system to the crown and into the stem. The roots decay and slough off and 

 infection spreads from root to root in the soil. Plants with sound roots were 

 not infected in soil inoculated with spores of F. culmoruni or in contaminated 

 soil 'under conditions favorable for good root action (71, 72, 74, 76, 78), but 

 cuttings planted in contaminated sand readily succumbed. Spores or pieces of 

 culture of F. culmorum applied to stabs in the stems and to wounds at the nodes 

 or to the cut ends of stems caused rotting at the point of inoculation and dying- 

 back of the branches. Dowson (24) reported that infection occurs only through 

 wounds in the presence of high temperature and high soil and atmospheric 

 moisture. 



Both Fusarium culmorum and F. avenaceum are associated with a devastating 

 basal rot of cuttings in sand and of the roots of plants in subsequent stages of 

 growth. These organisms are active pathogenes, but well-established uninjured 

 plants growing under favorable cultural conditions are never affected. In a 

 few instances devastating cases of root rot have been noted in association with 

 both a heavy soil infestation of garden symphylids and poor growing conditions — • 

 essentially wet soil and the absence of good drainage — and the latter factor 

 appeared more significant than the small amount of root injury caused by the 

 symphylids. Nevertheless, these creatures are general feeders and destroy the 

 fine roots, and consequently can be regarded as a contributing factor. White 

 (74, 76) stated that injuries to the roots by wireworms and wood lice contributed 

 to root rot infection after planting. Severe damage from F. culmorum has been 

 noted after the flowering stock had been mulched with manure; in other instances 

 following applications of concentrated chemical fertilizers, and also following 

 the use of cuttings from stock plants showing a prevalent rotting about the nodes 

 and snags in the branches. 



The importance of injuries in relation to infection was confirmed by a series 

 of demonstrations. Bits of inoculum from authentic cultures of F. avenaceum. 

 and F. culmorum, were transferred to axils of flowering shoots of Nina Brener 

 carnations in June, twelve months after benching. The points of inoculation 

 were wrapped in moist cotton. Rotting followed only where the cutting in the 

 axil had been removed. Transfers of similar inoculum into incisions in the stem 

 were successful; without incisions infection failed. With an authentic culture 

 of F. culmorum from England, eleven inoculations through injuries in the stems 

 of young potted plants yielded positive infections; without injuries five stem 

 inoculations were negative and three were positive. With an authentic culture 

 of F. poae from Germany, eight of the nine inoculations at injuries in the stems 

 developed active cankers and nine inoculations made without injuries failed to 

 cause infection. With a culture from England designated F. herbarum (Corda) 

 Fr. = F. avenaceum (Fr.) Sacc, nine inoculations yielded six positive infections 

 when the inoculum was applied to injuries and only negative results when the 

 inoculum was applied to the stem without injuries. With an authentic culture 

 of F. avenaceum from Germany, decay and dying back of the branches followed 

 nine inoculations at injuries; inoculum applied to stems not injured at the point 

 of inoculation also yielded positive Infections. With F. sporotrichioides Sherb. 

 from Germany, six inoculations at injuries were positive and three were negative; 

 without injury all were negative. In these tests infection following inoculations 

 with F. poae, F. avenaceum, and F. culmorum were particularly devastating. 

 When the inoculum from pure cultures of these organisms was buried in the 



