1544 



DISEASES OF VARIOUS CROPS 



1 129- Effect of Certain Species of Fusarium on the Composition of the Potato Tu- 

 ber. — Hawkins, 1,. A. in the Journal 0/ A'^riculliiral Kcscarcli, N'ol. VI, Xo. 5, pp. 183- 

 196. Washint'toK, D. C, i()i6. 



Potato tubers are subject to the attacks of various parasitic fungi. 

 vSome of these invade the tuber, kill the cells, break down the cell walls, and 

 cause,directly or indirectly, a more or less complete disorganisation of the 

 host tissues. In the present paper the writer has given the result of a se- 

 ries of researches on the modifications that are produced in the potato by 

 Fusarium coendenm (Lib.) vSacc, F. oxysporum Schlecht and F. radicicola 

 Wollenw. Kach tuber is cut in four and each quarter is placed in a culture 

 tube stoppered with sterile cotton wool. Of the four preparations, two act 

 as control. This method gives results which are much more directly com- 

 parable than those that would be obtained if different tubers were used ra- 

 ther than parts of the same tuber, because the amount of sugar, starch and 

 pentosan contained varies very much in different tubers. The most im- 

 portant conclusions can be summarised as follows : 



Table I. — Reducinj^ Sugar and Sucrose Content of the Sound and Rotted 

 Quarters of Potatoes. Expressed as percentages of the oaiginal wet weights). 



As is seen in the table all three species of Fusarium use the sugars wlricli 

 in most cases disappear almost completely. The fungi secrete two enzymes, 

 sucrase and maltase, which hydrolized the saccarose and maltose. The 

 effect of the fungi on the starch is in marked contrast to their action on the 

 sugars. The amount of starch is undiminished, a"nd there may even appeal 

 to be an increase due to the fact that the fungi build up material in the 

 course of the examination. Fusarium consumes a considerable quantity 

 of pentosans while leaving the methylpentosans untouched. 



