VOTilT.ME VT DeCEMBKR, 1010 NOS. 2 AND 3 



A PHYTOPHTHORA ROT OF PEARS AND APPLES. 

 By H. WOEMALD, D.Sc. (Lond.), A.R.C.Sc. 



{Mycological Department, South-Eastern Agricultural College, Wye, 



Kent.) 



(With 2 Text-figures and Plate III.) 



The Rot on Pears. 



In September, 1912, two pears affected with a soft rot were received at 

 Wye from a garden in Hertfordshire. The sender stated that the dis- 

 ease started at the stalk end of the pears and caused them to fall before 

 they reached maturity. The appearance at the surface of the affected 

 pears was different from that produced by the rots commonly met with, 

 in that there were present numerous glistening points which were evi- 

 dently highly refractive granules, bearing a striking resemblance to 

 hoar-frost. On microscopic examination these particles proved to be 

 clusters of sporangia borne on short unbranched sporangiophores pro- 

 jecting in tufts through the ruptured epidermis, each sporangiophore 

 bearing a terminal sporangium. 



The rather coarse non-septate mycelium present in the discoloured 

 tissues, and the type of sporangia found on the surface were typical of 

 those of the Peronosporaceae, and as no record could be found of the 

 occurrence of a member of this family on pears in this country further 

 investigation was made. 



Reference to foreign literature revealed the fact that a similar disease 

 had been observed on apples and pears on the Continent, and on apples 

 in America. The earliest record appears to be that of Osterwalder(4) 

 who in the summer of 1904 found numerous fallen fruit under cordon 

 apple trees in Switzerland. When these apples were placed in a moist 

 chamber numerous oospores developed; on immersing the apples in 

 water sporangia were also formed and Osterwalder was able to identify 

 the fungus as Phytophthora Cactorum (Lebert et Cohn) Schroter = P. 

 omnivora de Bary. In 1908 Marchal(3) described the same fungus as 

 producing a rot of pears in Belgium, the disease causing the fruit to 

 fall prematurely. Two years later a similar rot, also on pears, was 



Ann. Biol, vx 7 



