The Dry Root-Rot of the Bean 1017 



pathogenicity 

 Inoculation experiments with the bean plant 



Many hundreds of inoculations have been made from time to time 

 with Fusarium martii phaseoli on the roots of bean plants. In approx- 

 imately one hundred per cent of the tests, infections occurred. These 

 experiments were conducted both in the greenhouse and in experimental 

 gardens. Infection takes place readily when the soil is contaminated 

 before the seed is planted, when the seeds are dipped in suspensions of 

 spores from a pure culture and planted in sterilized soil, and when inocu- 

 lations are made with the pathogene after the plants are above ground. 

 The incubation period under favorable conditions is about five days to 

 a week. The spores used in these experiments were taken from pure 

 cultures and alwaS s showed a high percentage of germination. The age 

 of the cultures varied greatly; this factor, however, is unimportant, since 

 the spores do not lose their viability very early. 



Inoculation experiments were conducted to determine other important 

 points respecting the pathogenicity of the fungus. The length of the 

 period of susceptibility in the bean plant was thought to be worthy of 

 consideration. It was believed that if it were found that infection takes 

 place only in the seedling stage, a basis for controlling the disease would 

 be available. It might be possible to protect the bean roots from the 

 pathogene for a short time. On the other hand, the extermination of 

 the fungus in the soil is exceedingly difficult without injury to the host 

 plant or without too great expense. It was found, however, that the 

 bean plants were susceptible over a greater period than the seedling 

 stage. The results of the experiment to determine this point are set 

 forth in table 1. The seeds used in the experiment were of the White 

 Marrow variety. 



The plants inoculated thirty-one days after planting became infected 

 as readily as did those inoculated at the time of planting. From this 

 it is evident that the period of infection does not extend over the seedling 

 stage only, but on toward the maturity of the plant. It is possible that 

 the plants arc susceptible throughout their period of life. Early infec- 

 tion, however, would be more severe, as the fungus grows but slowly in 

 the host. 



