476 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY 



THE POSSIBLE SOURCE OF ORIGIN OF THE LEAF- 

 SPOT DISEASE OF CULTIVATED CELERY, 



By Geo. H. Pethybridge, B.Sc, Ph.D., F.R.H.S. 



The presence of the leaf-spot disease of celery, caused by the parasitic 

 fungus Septoria Petroselini var. Apii, was first announced in England * 

 and in Ireland f in the autumn of igo6, although on the Continent 

 and in the United States of America the disease has been known for 

 more than twenty years. 



There is no doubt that during recent years it has become widely 

 spread in the British Isles, and that where no preventive means are 

 taken serious losses occur. Leaflets deahng with the disease have 

 been pubhshed both by the Department of Agriculture and Technical 

 Instruction for Ireland (No. 5) and by the Board of Agriculture and 

 Fisheries in England (No. 238). An excellent illustrated account of 

 the disease, with very full references to the earlier literature, was 

 published in a previous volume of this Journal, | and more recently 

 another one has appeared in the Gardeners' Chronicle.^ 



As to the means by which the disease has become spread through 

 the country, there can be but little doubt that this has occurred mainly 

 through the employment for sowing purposes of celery " seed " 

 bearing the spore-containing fructifications (pycnidia) of the fungus 

 partially embedded in the pericarp. 



Klebahn,|| apparently, was the first to call attention to the 

 possibihty of the spread of this disease by means of affected " seed," 

 although he did not actually prove that such affected " seed " gave 

 rise to diseased seedhngs. Recently, however, it has been fully 

 estabhshed both by Chittenden ^ and by the present author ** that 

 celery seed " bearing the fructifications and spores of the parasite 

 (and such affected " seed " is abundant in commerce) may and does 

 produce diseased seedhngs. Further, it has been shown that by 

 steeping such " seed " in appropriate germicides such as hydrogen 

 peroxide or dilute formaldehyde, the disease-producing parasite upon 



* Gard. Chron. xl. 1906, p. 378, and Journal R.H.S. xxxii. 1907, p. xciii. 

 f Irish Naturalist, xv. 1906, p. 271. 



I Chittenden, F. J,, " Leaf-spot of Celery," Journ. R.H.S. xxxvii. 1911, 

 p. 115. 



§ Salmon, E. S., " Celery ' Blight ' or ' Rust ' [Septoria Petroselini var. Apii) 

 and its Prevention," Gard. Chron. liii. 1913, p. 414, and liv. 1913, p. 3. 



|j Klebahn, H., " Krankheiten des Selleries," Zeitschr. f. Pflanzenkrank. 

 XX. 1910, p. I. 



^ Chittenden, F. J., "A Note on Celery Leaf -spot Disease," Ann. of 

 Applied Biol. i. 1914, p. 204. 



** Pethybridge, G. H., " The Spread of the Celery Leaf-spot Disease by the 

 Use of Affected Seed, and its Prevention," Journ. Dep. oj Agric. and Tech, 

 Inst, for Ireland, xiv. 1914, p. 687. 



