PHOMA BETAE ON THE LEAVES OF THE SUGAR BEET 



By Venus W. Pool, Assistant Pathologist, and M. B. McKay, Scientific Assistant, 

 Cotton- and Truck-Disease and Sugar-Plant Investigations, Bureau of Plant Industry 



INTRODUCTION 



Various names have been given at different times to the fungus caus- 

 ing a root-rot, a damping-off, and a leaf -spot of the sugar beet {Beta 

 vulgaris L.), and consequently their relationship to each other has not been 

 recognized. The leaf -spotting was attributed by Gudemans^ to Phyllo- 

 sticta hetae and later by Prillieux and Delacroix ^ to P. tabifica. Frank ^ 

 believed the latter organism to be identical with his root-rot fungus, 

 Phoma hetae, but on account of generic differences no combination of 

 names was made. Hedgcock* pointed out for the first time a definite 

 connection between Phyllosticta on the leaf and Phoma on the root. 

 Peters^ and Edson'' give evidence that the fungus which produces leaf- 

 spotting is also a cause of damping-off. The present investigation shows 

 that the leaf-spot and the root-rot organism are the same and points out 

 that the entire life cycle of the fungus must be considered in any inter- 

 pretation that is made of the disease phenomena. The name "Phoma 

 hetae (Cud.) Fr." is deemed by the writers and by Edson® to be correct and 

 inclusive; however, the generic name "Phyllosticta" is retained in this 

 paper for the organism isolated from leaves. 



SYMPTOMATOLOGY 



A mature, normally developed spot of Phoma hetae on the sugar-beet 

 leaf varies in size from i to 2 cm. in diameter and is usually light brown 

 in color. At times such spots show concentric rings of growth, the 

 different zones being outlined by pycnidia. There is no sharp differen- 

 tiation (PI. XXVII) between the infected area and the surrounding tis- 

 sue, owing to the lessened activity of the beet leaf at the time the organ- 

 ism is growing in the leaf tissue. This accounts for the comparatively 

 large size of the spot and its rather diffusive character. The spots which 



1 Oudemans, C. A. J. A. Aanwinsten voor de flora mycologica van Nederland van Juli 1875 tot Juli. 

 1876. /re Nederland. Kruidk. Arch., s. 2, deel 2, stuk 3, p. 181. 1877. 



2 Prillieux, E. E., and Delacroix, Georges. Compltment k I'ttude de la maladie du cocur de la 

 betterave. In Bui. Soc. Mycol. France, t. 7, p. 23-25, pi. 3. 1891. 



3 Frank, A. B. Phoma Betae, ein ncuer Rubenpilz. In Ztschr. Pflanzenkrank., Bd. 3, p. 90-92. 1893. 

 * Hedgcock, G. G. Proof of the identity of Phoma and Phyllosticta on the sugar beet. In Jour. Mycol., 



V. 10, p. 2-3. 1904. 



' Peters, Leo. Ueber die Erreger des Wurzelbrandes. In Arb. K. Biol. Anst. Land- u. Forstw., Bd. 8, 

 Heft 2, p. 229-239. 1911. 



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

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



Jotunal of Agricultural Research, Vol. IV, No. 2 



Dept. o Agriculture, Washington, D. C. May 15, 1915 



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