246 EXPERIMENT STATION" EECOED. 



Some potato tuber rots caused by species of Fusarium, C. W. Cabpentee 

 {U. S. Dept. Agr., Jour. Agr. Research, 5 (1915), No. 5, pp. 183-210, pis 8).— 

 The object of this paper is to demonstrate tlie parasitic nature of certain species 

 of Fusarium, the tuber rots considered being all of the stem-end and wound- 

 parasitic type. 



A new stem-end and wound-invading dry rot that is said to be the cause of 

 serious damage in Pennsylvania is attributed to F. eumartii n. sp. Anotlier 

 widely prevalent dry rot similar to the above is referred to F. radicicola. This 

 latter species and F. oxysporum are associated with the so-called jelly end rot, 

 a serious trouble in the tule lands of California. Experimental inoculations 

 show that F. oxysporum and F. hyperoxysporum, species of the section Elegans, 

 which has been reported as containing purely vascular parasites, are capable of 

 entirely destroying potato tubers. F. oxysporum is also said to be the cause 

 of certain types of tuber rot. F. radicicola will cause no rot at temperatures of 

 12° C, and constant storage temperatures below 50° F., it is said, will prevent 

 the action of F. radicicola, F. eumartii, and F. oxysporum. It is claimed that 

 the following species of Fusarium are added to those known to be tiie cause of 

 tiiber rot through wound infection : F. radicicola, F. eumartii, F. oxysporum. and 

 F. hyperoxysporum. 



A bibliography of cited literature is given. 



Germination and infection with the fungus of the late blight of potato 

 (Phytophtbora infestans), I. E. Melhus {Wisconsin Sta. Research Bui. 37 

 (1915), pp. 64, figs. 8). — The author presents the results of a study of external 

 influences on spore germination and a study of the infection of potato foliage 

 with Phytophthora. 



The spores were found to germinate either directly by germ tubes or indirectly 

 by the production of zoospores, the type of germination being determined by 

 temperature, moisture, and medium. The spores were killetl in from 6 to 24 

 hours when exposed to dry atmospheric conditions such as exist in an ordinary 

 room, and by frost which is suflicient to kill the host plant. Leaf juices result- 

 ing from the softening of diseased tissues were found to have an inhibiting 

 effect on germination, but light did not hinder germination so long as the tem- 

 perature was not above the optimum. Indirect or zoospore germination was 

 found to take place in dew or rain in the open under field conditions, while direct 

 germination was not observed on foliage in the open. 



The toxicity of various salts to P. infestans, and also Pla^mopara riticola, 

 was tested by the glass slide method, and it was found that, when subjected to 

 optimum temperature conditions for indirect germination, 0.0159 per cent of 

 corner was necessary to prevent germination. Slight changes in the amount of 

 calcium oxid in Bordeaux mixture were not found to change its toxicity mate- 

 rially, and Bordeaux mixture made by the so-called Woburn formula was not 

 more toxic than one high in lime. The spores of Plasmopara were found slightly 

 more resistant to the polysulphids than those of Phytophthora. 



In connection with studies on infection of potato foilago, it was found that 

 plants chilled for periods of from 12 to 24 hours at 10 to 13° C. showed a greater 

 iimount of infection than controls held at higher temperatures. This is be- 

 lieved to be due to the effect on the fungus rather than on the host, as chilling 

 had no tendency to increase susceptibility. Infection becomes visible in two 

 to three days at temperatures between 23 and 27°, and it may take place on 

 foliage only when direct germination occurs, and through either the upper or 

 lower surface of the leaf. The difference in susceptibility of the upper and 

 lower surfaces is attributed to the difference in the relative number of stuin.'ita. 



A bibliography is appended. 



