JOMAL OF AGKIOJITIML RESEARCH 



DEPARTMENT OF AGRICULTURE 



Vol. IV Washington, D. C, July 15, 191 5 No. 4 



RHEOSPORANGIUM APHANIDERMATUS, A NEW GENUS 

 AND SPECIES OF FUNGUS PARASITIC ON SUGAR 

 BEETS AND RADISHES 



By H. A. Edson, 



Physiologist, Cotton and Truck-Disease and Sugar-Plant Investigations, 



Bureau of Plant Industry 



INTRODUCTION 



The fungus to be described in this paper was originally secured from 

 damped-off seedlings of sugar beets {Beta vulgaris) which were grown in 

 soil that had previously produced the black-root of the radish (Raphanus 

 sativus). It was at first mistaken for Aphanomyces laevis De Bary and 

 was so considered in a preliminary note.^ The organism stands in a 

 causal relation to both of the diseases mentioned, and recent trials have 

 shown that it retains its virulence after a continuance of 30 months in 

 artificial culture. The pathogenic relations of the organism were dis- 

 cussed in a recent paper,^ but the fungus was not named or treated in 

 its taxonomic relations. The present paper deals with the results of 

 such further studies involving the morphology, cytology, and taxonomy 

 of the organism as were found necessary to establish its identity and 

 relationships and to make clear the various stages of its life history. 



LIFE HISTORY AND GROSS MORPHOLOGY OF THE ORGANISM 



In the general character of the disease produced in seedlings and in 

 its appearance in cultures the organism resembles Pythium debaryanum 

 so closely as to be readily confused with it, except in the asexual fruiting 

 stage. The vegetative mycelium consists of nonseptate hyphae which 

 develop a profuse white aerial growth on suitable solid media, such as 

 string-bean or oatmeal agar and certain cooked vegetables, of which the 

 string bean is one of the most satisfactory. Oospores are formed in 



' Edson, H. A. Damping-off and root rot parasites of sugar beets. In Phytopathology, v. 3, no. i, 

 p. 76. 1913. 



2 Edson, H. A. Seedling diseases of sugar beets and their relation to root-rot and crown-rot. In Jour. 

 Agr. Research, v. 4, no. 2, p. 135-168, pi. i6-j6. 1915. 



Journal of Agricultural Research, Vol. IV, No. 4 



^JT) Dept. of Agriculture, Washington, D. C. July 15, 1915 



$^ (279) 



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