Strains of Rhizoctonia Solani Ki'thn 205 



be di\'ided into three groups. The most rapid growers were 

 E, PO, PE, S and /; the slowest were .4 and B. The fungus W 

 took an intennediate position between the above two groups. 

 At this temperature and normal room temperatures / con- 

 sistently fomied sclerotia quicker than the others. The observa- 

 tions were made with cultures from mycelia which had been 

 isolated from a common host (cress seedlings) . 



Effect of Light. A series of cultures of all the forms was made 

 in Petri dishes and placed under a blackened sheet of tin so that 

 only one half was exposed to the light. None of the forms showed 

 any reaction to hght. 



Pathogenicity. 



The following experiments were carried out with a \-iew to 

 ascertaining whether there was any difference in the parasitism 

 of the forms on the same host under the same conditions. 



Experiment I. The fungi used in this experiment were E, I, 

 S, A and B on broad bean and garden pea. The experiment 

 comprised ten lots of five flowerpots (3 in. diam.) which were 

 filled with sand and treated as follows: 



1. Three seeds of broad bean sown in each of the five pots. 

 A piece of potato on which the fungus was gro\\ing Wcis placed 

 in contact N\ith the seed in three of the pots. Seed and fungus 

 were then co\-ered with sand and watered with tap water. In 

 the other two pots no fungus was placed with the seed (controls). 



2. As for I, but three seeds of garden pea sown in place of 

 broad bean. 



3 and 4, 5 and 6, 7 and S, 9 and 10 w^ere similar to i and 2, 

 but fungi /, S, A and B respectively were used. 



All were treated on ^larch 26th and placed together in a 

 greenhouse. The week following the date of sowing was bright 

 and sunny with the result that no marked difference could be 

 seen between the controls and infected in any series. It should 

 be pointed out that the soil temperature was not sufficiently high 

 to inhibit the growth of the fungi, but acted indirectly by 

 hastening the growth of the seedhngs and increasing the rate 

 of evaporation from the pots. 



Experiment II. This was a repetition of Experiment I, except 

 that six-inch pots and distilled water were used instead of 

 three-inch pots and tap water. The date of sowing was April nth ; 

 the plants were examined on May 14th. As in Experiment I 

 no difference w^as observed between the controls and infected in 

 the pots containing garden peas. The results for the broad beans 

 series w'ere as follows: 



Seedlings infected with fungus E gave (i) two healthy, one 

 diseased, (2) one killed, two attacked at hypocotyl, and (3) three 

 attacked at hypocotyl. 



M s. 14 



