SUvSCKPTlBILlTY OF THE DIFFERENT Vx\RIETIES OF 

 SWEET POTATOES TO DECAY BY RHIZOPUS NIGRI- 

 CANS AND RHIZOPUS TRITICI 



By L. L. Harter. Pathologist, and J. I,. Weimer, Pathologist, Office of Cotton, Truck, 

 and Forage Crop Disease Investigations, Bureau of Plant Industry, 'United States 

 Departinent of Agriculture 



INTRODUCTION 



Although Rhizopus yiigricans Ehrb. has generally been regarded as 

 the cause of the softrot of the sweet potato (Ipomoea batatas Lam.), 

 Harter, Weimer, and Lauritzen^ have shown by recent experiments that 

 a similar decay may be caused by the following additional species of the 

 genus: tritici Saito, nodosus Namysl, reflexns Bainier, delemar (Boid), 

 Wehmer and Hanzawa, oryzae, Went and Pr. Geerligs, maydis Bruderl., 

 arrhizus Fischer, and artocarpi Racib. Their investigations showed that 

 in order to obtain infection with the dififerent species it was necessary to 

 incubate the potatoes at a temperature suited to the growth of the par- 

 ticular species of Rhizopus with which they were inoculated. They group 

 the different species into high, intermediate, and low temperature forms, 

 R. nigricans Ehrb. and R. tritici, the two species concerned in the 

 present investigations, belonging to the low and intermediate forms, 

 respectively. 



The parasitism of the dififerent species of Rhizopus was determined by 

 them for the Yellow Jersey variety of sweet potatoes only. Although 

 softrot occurs on all the varieties, it is the general belief that some of 

 them are more resistant to decay than others. The Jersey type of sweet 

 potatoes, for example, is recognized as a poor keeper, while some of the 

 varieties grown in the South are thought to keep well in storage. The 

 present investigations were conducted in order to throw more light on 

 the relative susceptibility of a number of the commercial varieties to 

 infection and decay by R. nigricans and R. tritici. 



R. nigricans was employed for the major portion of the inoculations 

 because it is the species commonly found under storage-house conditions 

 and seems to be responsible for most of the loss. R. tritici although not 

 so common as R. nigricans is a very parasitic species, especially under 

 artificial conditions. A comparison of these two species gives some idea 

 of the results that may be expected from them, one requiring relatively 

 low and the other one an intermediate temperature, or at least a tem- 

 perature considerably above that recommended for the storage of sweet 

 potatoes. 



METHODS OF EXPERIMENTATION 



The susceptibility to infection and decay by R. nigricans was deter- 

 mined for the following varieties of sweet potatoes: Big Stem Jersey, 

 Little Stem Jersey, Southern Queen, Porto Rico, Dooley, Georgia, Pierson, 

 Dahomey, Triumph, Gold Skin, Haiti, Nancy Hall, Early CaroHna, Yellow 



1 Harter. L. L., Weimer, J. L., and Lauritzen, J. I. the decay of sweet potatoes (ipomoea 

 batatas) produced by different species of rhizopus. In Phytopathology, v. ii, no. 7, p. 279-284. 

 Literature cited, p. 2S4. 1921. 



Journal of Agricultural Research. Vol. XXII, No. 9 



Washington, D. C. Nov. 26, igar 



aas Key No. 0-258 



(511'; 



