1 66 



Journal of Agricultural Research 



Vol. X, No. 4 



stromata of X. hypoxylon (L.) Grev. appeared at the base of a dead apple 

 tree at Blacksburg (Pi. 17, A). These had produced but few spores at 

 the time of collection (January), but sporulated abundantly after being 

 placed in moist chamber for a month (PI. 17, F)- Carpophores of Clito- 

 cyhe monadelpha (Morgan) Sacc. were found at the base of several trees 

 in one orchard at Middletown, but the relation of this fungus to the 

 rootrot problem has not been determined. Affected roots brought to 

 the labors tory and placed in moist chamber have developed conidial 

 stromata of X. hypoxylon in a few cases (PI. 15, D). 



Isolation studies from roots in various stages of attack have been 

 carried on during the past two growing seasons (1915 and 1916) in con- 

 tinuation of pre\nous studies 

 by Reed and Crabill. Cra- 

 bill ( I ) reported the isolation 

 of Trichodernia koningi Oud. 

 in culture 72 times in 116 

 trials, using apple roots from 

 seven sources, and concluded 

 that this fungus is probably 

 the cause of rootrot. No 

 experimental proof of its 

 pathogenicity was given. 

 Jensen (9),Werkenthin (13), 

 and Waksman (12) have 

 found T. koningi commonly 

 present in various types of 

 soil, and the writers have 

 found it common on decay- 

 ing wood. Although we 

 have also frequently isolated 

 this fungus from diseased 

 apple roots, we are convinced from inoculation studies that it exists in 

 them as a saprophyte in tissue killed by other agencies. 



In our isolations we have plated fragments of diseased roots on agar 

 media. In the early part of the work the tissue fragments were taken 

 from various parts of roots and a number of species of fungi were obtained, 

 with Trichoderma koningi predominating. Later, the fragments were 

 taken only from the margins of the lesions. A considerable number of 

 these have yielded cultures of a species of Xylaria,^ often uncontaminated 

 with T. koningi, the most common accompaniment, and occasional 

 species of Fusarium, unidentified fungi, and bacteria. Physalospora 

 cydoniae Amaud {Sphaeropsis malorum Peck) was obtained from the 



Fig. I. — Root system of a 7-year-old apple tree affected with 

 rootrot. The infected parts are shaded. Infection v/as pro- 

 gressing outward on the sound roots. The initial infection 

 probably took place on the side marked X. Drawn from a 

 photograph. 



' At first assigned to the genus Stilbella. A culture bearing conidial stromata was submitted to Dr. C. I«. 

 Shear, of the Bureau of Plant Industry, who stated that the fungus was probably Xylaria hypoxylon. 



