JOIME OF AGKICDlTim RESEARCH 



Vol. X Washington, D. C, July 23, 1917 No. 4 



A COLLETOTRICHUM LEAFSPOT OF TURNIPS •-»^''^»<' 



By B. B. HiGGiNS, ^^^ ^'*'^ 



Botanist, Georgia Agricultural Experiment Station **** A** * • 



DESCRIPTION OF THE LEAFSPOT 



During August, 1914, young turnip plants {Brassica rapa) with leaves 

 badly affected by a leafspot disease were brought to this Station from 

 near Macon, Ga. The grower stated that during two previous 

 seasons the disease had been very destructive to young turnips, but 

 observations on specimens sent from this field indicate that' the greater 

 part of damage was probably due to a bacterial softrot of the roots. 

 Since that time the diseased plants have been collected locally several 

 times. The disease rarely killed the plants or proved very serious, other 

 than in disfiguring and occasionally killing the tops. 



The spots are small (X inch or less in diameter), circular in outline, 

 and of a pale-gray or straw color. Usually no sign of a parasite can be 

 seen with the unaided eye or even with a good hand lens; but, if the spot 

 has developed under very moist conditions, both surfaces are covered 

 with a salmon-pink layer of spores, a condition which is evident to the 

 unaided eye. Under the microscope this layer is found to be composed 

 of small, rod-shaped, i-ceUed spores which singly appear colorless. They 

 are borne on short sporophores which arise in small clusters from a 

 delicate stroma in the surface of tne leaf. Intermixed with these sporo- 

 phores are prominent, long, black setae, indicating at once the affinity of 

 the fungus to the genus Colletotrichum. 



Cultures of the fungus were readily obtained by sowing the spores in 

 an agar plate. The mycelial growth was rather inconspicuous on all 

 media, much more so than that from a culture of Glomerella cingulata 

 from a decaying pear. Green bean pods, steamed in an autoclave and 

 inoculated with the fungus from turnips, were covered in a few days with 

 a thick layer of salmon-colored spores. On corn-meal agar ^ tfee acervuli, 

 instead of being scattered evenly over the surface as on bean pods, were 

 grouped in clusters. In old cultures on various media black structures 

 having the appearance of perithecia were produced in abundance; but, 

 when examined under the microscope, these were found to be only^iense 

 clusters of setae. No perithecia were ever found either in cultures or 

 cr> on the infected leaves. 



CD 



1 Shear C. L., and Wood, Anna K.- studies op fungus parasites bei-onging to the genus 

 GLOMERELLA. U. S. Dept. Agr. Bur. Plant Indus. Bui. 232. P- iS- i9i3- 



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



CD Washington, D. C. Ju'v 23, 1917 



— ■> it (157) KeyNo. Ga.— 2 



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