118 I. WAHL 



germination; the mode of action of these substances is not 

 clear. Your second question is rather difficult to answer, since 

 different fungi are capable of producing sclerotia as a result of 

 diverse stimuH. It is assumed that in many instances sclerotia 

 formation is induced by inimical environmental factors. 

 Sclerotia resist adverse conditions, for example Avizohar- 

 Hershenzon (personal communication) demonstrated that 

 sclerotia of Sclerotium rolfsii are tolerant of relatively high 

 temperatures prevailing in alimentary tract of cows, but lose 

 to a considerable degree their viability in compost heaps. 

 Lavee'^ reported that coumarin, maleic hydrazide, and trietha- 

 nolamine bring about pronounced inhibition in sclerotia 

 germination of Sclerotium rolfsii and reduce the number of 

 sclerotia per culture. 



Keynan: It is well known that the soil contains a large 

 number of spores of fungi which will only germinate under 

 favourable conditions. Inhibitors have been shown to exist in 

 the soil, is anything known about these? 



Wahl: I presume that you have in mind the phenomenon 

 referred to as fungistasis. Investigations in various countries 

 proved that spores of many fungi rest dormant in soil but 

 germinate readily when placed in distilled water. 



Dobbs and Hinson^ postulated the widespread existence of 

 fungistasis in soil. The nature of the germination inhibitors is 

 obscure. The inhibitory effect can be removed by specific 

 organic soil amendments, by soil heating, or prolonged soil 

 desiccation. Fungistatic substances can be neutralized by root 

 exudates of certain plants. Buxton^' ^ found that exudates from 

 the roots of pea varieties stimulate germination of spores 

 belonging to fusariuni oxysporum /. pisi to which the varieties 

 are vulnerable and depress that of races to which they are 

 resistant. 



Chinn and Ledingham^ suggested that successful control of 

 some root diseases attained by green manures application is 



