414 



SPORE GERMINATION 



interactions of spore populations are formally analogous to the self- 

 inhibition of growth reported in species of actinomycetes (207, 290) 

 and inhibition of spore germination in Phycomyces blakesleeanus by 

 products of mycelial growth (249). However, we may anticipate that 

 these reactions of growing mycelium are more complex and more de- 

 pendent on the environment than is self-inhibition in spores. Bacillus 

 globigii endospores produce a substance, antagonized by alanine, which 

 inhibits germination of fresh endospores of the same species (265). 



Self-inhibition has been most clearly demonstrated in studies of rusts, 

 Uromyces phaseoli (313, 314), Puccinia graminis tritici (2), and P. he- 

 lianthi (315). The inhibitory effect of a dense concentration has been 

 demonstrated in vivo, on the host plant, as well as in vitro (Figure 9); 

 most of our information indicates that the active material is volatile. 



Allen (2) has determined several characteristics of the substance — 

 possibly substances — responsible for self-inhibition of Puccinia grami- 

 nis tritici uredospores. The active material is stable to heat, is inacti- 

 vated or removed from solution by glass surfaces, and is more effective 

 at high pH than at low. The inhibitor is a spore metabolite produced 

 under aerobic conditions. This differs somewhat from the situation 



0.4 0.8 1.2 1.6 



Weight of spores, mg per ml 



2.0 



Figure 9. The effect of uredospore concentration on germination in Puccinia 

 graminis tritici. Curve 1, spores in open vessels; curve 2, spores in sealed vessels. 

 Redrawn from Allen (2), by permission of Phytopathology . 



