AIR AND WIND DISSEMINATION OF ASCOPORES OF 

 THE CHESTNUT-BLIGHT FUNGUS 



By F. D. Heald, M. VV. Gardner, and R. A. Studhalter, Agents, Investigations in 

 Forest Pathology, Bureau of Plant Industry^ 



HISTORICAL INTRODUCTION 



Wind dissemination of the chestnut-blight fungus {Endothia parasitica 

 (Murr.) And.) was first suggested by Murrill (13) ^ in 1906, although he 

 apparently had only the pycnospores in mind", as is shown by the follow- 

 ing quotation: 



Later the fruiting pustules push up through the lenticels and give the bark a rough, 

 warty appearance; and from these numerous yeIlowish-bro\vn pustules millions of 

 minute summer spores emerge from day to day in elongated reddish-brown masses to 

 be disseminated by the wind and other agencies, such as insects, birds, squirrels, etc. 



A few years later, in a discussion of the means of spreading the disease, 

 Hodson (9) says: 



Wind is probably the principal agency, but the spores are no doubt carried by ani- 

 mals, birds, insects, and by shipment of infected material. 



He also cited some observations to substantiate the wind-dissemination 

 theory, but it was not brought out clearly whether he had in mind the 

 ascopores or the pycnospores only. A similar opinion is expressed by 

 Mickleborough (12) a little later. After speaking of both the ascopores 

 and the conidal, or summer, spores, he states: 



The minute spores are carried by the wind, on the feathers of birds, and the fur of 

 squirrels. 



Referring to the spore horns, Mickleborough writes: 



These threads are dissolved and washed away by the rain and the spores are blown 

 about by the wind. ° 



There are two possible ways in which pycnospores might be dissem- 

 inated by the wind: First, by the direct transport of spore horns or small 

 fragments of these structures; second, by the transport of dust particles 

 bearing spores previously washed down by rains. 



Fulton (4) reports experiments which indicate that the former method 

 of transport of pycnospores is of little importance in the spread of the 

 disease. He concludes his discussion of this topic with the following 

 statement : 



It seems likely the detachment was largely of small bits of the tendrils made up of 

 large numbers of spores, and that these are too heavy to be carried great distances; 



' The writers received valuable assistance in this work from Mr. R. C. Walton, also an agent. Investi- 

 gations in Forest Pathology. 

 3 Reference is made by number to "Literature cited." p. 525-526. 



Journal of Agricultural Research, Vol. III. No. 6 



Dept. of Agriculture, Washington. D. C. Mar. 25. 1915 



G— 41 

 (493) 



