PECTIN RELATIONS OF SCLEROTINIA CINEREA 1 



J. J. W ILL AM AN 



The pectic substances which constitute the middle lamellae of 

 fleshy fruits, and thus serve as the cementing material between cells, 

 are of great interest to the plant pathologist because of the fact 

 that if an invading organism is to make its way into a tissue, it 

 must either pass along the line of the middle lamella between the 

 cells, or it must bore through the cells. In the first case a pectic 

 enzyme at the hands of the parasite may be presupposed, and in 

 the second case a cellulose enzyme. 



The mechanism of infection by Sclerotinia cinerea has received 

 particular attention recently by Cooley (4) and by Valleau (8). 

 Cooley maintains that its hyphae in plum tissue are mainly 

 intracellular; while Valleau finds them to be entirely intercellu- 

 lar, and produces photomicrographs to prove it. Cooley could 

 not demonstrate the presence of an enzyme which would dissolve 

 the calcium pectate of the middle lamella. He also failed to find 

 any evidence of a softening of the tissue in advance of penetra- 

 tion. Valleau, by more careful methods, noticed a marked 

 separation of the cells in rotted tissue, and demonstrated that an 

 extract of rotted apple would bring this about. The agent in this 

 case is the enzyme designated by Valleau "pectinase," but more 

 correctly called u pectosinase " according to the terminology of its 

 discovery (3, 10), and of Atkins (2). Valleau's illustrations 

 show that it is secreted considerably in advance of the penetrating 

 hyphae. The question of oxalic acid being the solvent was con- 

 sidered by both writers. Cooley found appreciable amounts of 

 the acid in rotted peaches and plums, but was not convinced that 

 it was the middle lamella solvent. Valleau demonstrated that 

 dilute solutions of oxalic acid would soften the tissues of these 

 fruits, but not of potato, which facts convinced him that this acid 

 is not the only factor involved in the disintegration of the middle 



1 Published with the approval of the Director as Paper no. 186, Journal Series, 

 Minnesota Agricultural Experiment Station. 



221] 



[Botanical Gazette, vol. 70 



