The Botrytis Blight of Tulips 341 



Conidia were isolated in several ways. Sometimes they were blown 

 over the surface of the agar from the bent end of a platinum needle. The 

 needle was attached to a piece of glass tubing which served as a blowpipe. 

 The tendency, at first was to gather too many spores on the needle, but 

 with practice a sparse sowing was readily made and transfers were then 

 obtained from the resulting colonies. Another method was to pick off, 

 with sharp-pointed forceps, a single conidiophore, under a binocular 

 microscope if possible, and then touch it to an agar plate in several places. 

 Pure cultures usually resulted from some of these plantings, and often 

 all the cultures were pure. 



Pure line cultures were obtained in two ways: first, by planting the 

 fungus on a poured plate of plain agar and water, which caused the 

 mycelium to spread out in its growth so that a single mycelial tip could 

 be marked under the low power, cut off, and transferred; secondly, by 

 the isolation of a single spore. In the latter method, which was the one 

 most frequently employed, care was necessary lest more than a single 

 spore should be obtained. A thin layer of agar containing a few conidia 

 was poured into a petri dish and the spores were allowed to germinate 

 slightly. After a conidium was marked and transferred to a poured 

 plate, a microscopical examination was always made to ascertain positively 

 that not more than one spore had been cut out. The growth of these 

 cultures on potato agar is characteristic and is described under Physiology 

 (page 355). 



Both mycelium and conidia were used as inoculum. The mycelium 

 inoculum was prepared by growing the fungus in a petri-dish culture 

 until the colony had reached the size of an inch or so in diameter. Small 

 cubes of agar containing mycelium were then cut with a sterile scalpel 

 from the edge of the colony and placed on the plant part to be inoculated, 

 with the side containing the mycelium against the host. To prevent 

 the inoculum from drying out, the plants were either placed in a large, 

 moist chamber or covered with a bell glass or a lamp chimney. When 

 it was desired to injure the inoculated parts, this was done by pricking 

 a sterile, sharp-pointed scalpel through the agar block into the host tissue. 



In using conidia, difficulty was at first experienced in attempting to 

 spray the plants with spore suspensions in water. No infections resulted. 

 As already mentioned, this is explained by the fact that the conidia are 



