10 MASS. EXPERIMENT STATION BULLETIN 427 



soil about injured roots and the plants cared for in the ordinary way, no disease 

 s>'mptoms developed. 



Fusarium Branch Rot 



Peltier (53) reported that the branch rot fungus infects carnation plants through 

 wounds. Wickens (78) showed that cuttings planted in contaminated sand or 

 inoculated at wounds were a total loss. Infection was established at the cut 

 surface at the base of the cutting. Inoculations were usually successful through 

 wounds but never through unwounded tissue. Wight (79) reported that soil 

 contamination with the fungus was not likely to cause disease in sound plants. 

 Van der Bijl (67) obtained successful infections by inserting pieces of cultures 

 of the fungus into needle pricks in the stems below the natural soil level. Bicker- 

 ton (5) reported successful infections of young rooted plants by inserting inocu- 

 lum of the pathogen into wounds at the base of the stem and by dipping the 

 roots into a water suspension of spores. It appeared to him that the large major- 

 ity of infections are initiated in the roots. Similar evidence was secured by the 

 writer. 



Pure culture material of Fusarium dianthi containing an abundance of spores 

 was macerated and added to sterile water. Forty rooted cuttings of each of 

 eighteen varieties were washed free of sand and then immersed in the water 

 suspension of spores and planted in steam-sterilized soil in flats. Within a 

 month most of the plants of some varieties were totally destroyed; others showed 

 symptoms of infection. The fungus was easily isolated from both the roots and 

 stems, and the path of the fungus high up in the shoots was recognized by the 

 discoloration of the water-conducting tissue. Obviously the roots were injured 

 in lifting the plants from the sand, thus assisting the fungus in its infection process. 



In the general area of New England the branch rot disease appears throughout 

 the year among established plants and is usually most prominent after the bench- 

 ing season, 5 to 8 months from propagation. At this time the temperatures are 

 excessive, frequent watering is required, and the plants have experienced con- 

 siderable injury from handling and transplanting. As the plants resume growth 

 and the weather becomes colder, the disease progresses more slowly and is masked 

 by the fresh green growth, but it becomes important again in the warm months 

 after winter. The disease is especially troublesome m certain varieties and 

 among some classes of stock, indicating that the continuity of the disease is 

 closely bound up with cuttings from contaminated stock plants. 



In the writer's experiments, 12 transfers from a culture of the fungus 

 into incisions In the stems and branches on well-established plants 10 months 

 from the cutting stage were all positively successful as against 6 similar inocula- 

 tions made without incisions, of which 5 were negative and 1 positive. In another 

 instance in June, 1 1 months after benching, plants of Nina Brener were inoculated 

 by placing bits of a culture of Fusarium dianthi in the axils of the leaves and then 

 swabbing the points of inoculation with moist cotton. Infections were positive 

 only when the inoculum was placed in an axil from which a cutting or axillary 

 branch had been torn out. 



It appears definitely that injuries are necessary for infection. Natural check- 

 ing of the base of the stems of the cuttings during and after rooting is a common 

 phenomenon. These openings provide favorable infection courts for the fungus 

 (24, 79). Injuries to the plants in transplanting into the field and back into the 

 greenhouse contribute greatly to the disease, but this seems almost unavoidable 

 if the plants are grown outside. 



