May 1, 19:6 Effect of FusaHum spp. on Potato Tubers 195 



rotting them. The brownrot fungus of peaches reduces the sugar 

 content of that fruit. The presence of the enzyms sucrase and maltase 

 in fungi has frequently been recorded. 



The starch content of the potato makes up the greater part of its dry 

 weight and may be regarded as stored food material. That the fungi 

 which so efficiently utilize the monosaccharids and disaccharids of the 

 potato tuber are unable, apparently, to affect this polysaccahrid is of 

 considerable interest. The fungi grow for the most part in the cell walls 

 and thus are not closely in contact with the starch grains. This might 

 retard the action because of the low rate of diffusion of the diastase but 

 could hardly inhibit it entirely. The fact that the diastases of these fungi 

 had no apparent effect on unbroken starch grains in vitro during the 

 time of the experiment, while potato starch when gelatinized was readily 

 hydrolyzed by these enzyms, indicates that the rate of action under 

 what are usually favorable conditions for such reaction is to say the 

 least very low. The experiments seem to show that enzymic studies 

 are of doubtful value in determining the effect of the parasite on the host 

 plant unless corroborated in a study of the physiological relations existing 

 between the two organisms. The effect of the fungi on the pentosan and 

 galactan content of the potato shows that they can break down at least 

 some of the constituents of the cell wall. Now, when a parasitic fungus 

 such as those used in this study enters a cell of its host plant, it must 

 either force its way in mechanically by exerting sufficient pressure to 

 rupture the cell wall or a portion of the cell wall must be dissolved. 

 Likewise, in growing between the cells of the host plant where no appreci- 

 able intercellular spaces exist, the cells must be forced apart mechanically 

 or some parts of the cell walls dissolved. It is evident from their effect 

 on the pentosans that these fungi are able to dissolve at least some portions 

 of the cell wall. That they secrete enzyms which can hydrolyze xylan is 

 more evidence on this point. The crude-fiber content of the potato was 

 increased in rotting owing to the formation in the fungi of some sub- 

 stances which were not broken down by the acid or alkali treatment in 

 the crude-fiber determinations. Therefore it was impossible to obtain 

 evidence as to the effect of the fungi upon the crude fiber. As shown in 

 the tables the crude-fiber content of the inner portion of the potato is 

 not high. It is noticeable that throughout this study the different 

 species of Fusariura had practically the same effect on the potato. 



CONCLUSION 



In conclusion, it has been shown in this study that the fungi in the 

 potato reduced the content of sugar, both sucrose and reducing sugar, 

 pentosans, galactans, and dry matter. The starch and methyl pentosans 

 are apparently not affected appreciably, and the crude-fiber content was 

 not reduced. It was shown that these two species of fungi secrete 

 sucrase, maltase, xylanase, and diastase; the last-mentioned enzyra is 

 apparently incapable of acting on the ungelatinized potato starch. 



