Dec. io, 1913 
Foot-Rot of the Sweet Potato 
273 
SUMMARY 
(1) The foot-rot has been hitherto unknown on the sweet potato 
(.Ipomoea batatas). It is caused by the fungus Plenodomus destruens , 
(2) The organism is a very destructive wound parasite of the sweet 
potato in the vicinity of the Dismal Swamp, Va., and occurs at Cape 
Charles and Keller, Va. 
(3) It kills the plant by the destruction of the cortex of the stem 
near the ground. 
(4) Pycnidia are abundantly formed on the diseased area of the stem 
about the time the plant dies, or soon thereafter. 
(5) The disease, while primarily found on the stem, invades the roots 
and vines also. 
(6) The fungus is cultivable on most artificial media, but gives the 
highest development on com meal, rice, and stems of the sweet potato. 
(7) The parasitism of the organism has been proved by numerous 
inoculations of plants grown on the Potomac Flats and in the green¬ 
house. 
(8) Successful infection experiments were carried out with reisolations 
of the fungus from inoculated plants. 
(9) The organism is parasitic on Ipomoea coccinea , but not on /. pur¬ 
purea and /. hederacea . 
(10) Sweet potatoes from storage are decayed by the fungus when 
inoculated under sterile conditions and kept moist in light. 
(n) Light has no apparent effect on the production of fruiting bodies 
in pure cultures of rice. 
(12) The fungus makes its best growth, as measured by abundance 
and rapidity of sporulation, in rice cultures at an average temperature of 
about 21.9 0 C. 
(13) The fungus can live through the winter on dead vines of the 
sweet potato. 
(14) The disease is probably disseminated principally by means of 
“seed roots” and the slips produced therefrom. 
(15) Seed beds should be sterilized, and potatoes to be used for seed 
should be carefully selected. 
