First Report of an Apple Root Rot Caused by Botryodiplodia theobromae in the United States. A. J. Latham, Alabama Agricultural Experiment Station, Auburn University, AL 36849. W. A. Dozier, Jr., Alabama Agricultural Experiment Station, Auburn University, AL 36849. Plant Dis. 73:1020. Accepted for publication 18 July 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-1020A.
A root rot (1) was found in apple rootstock evaluations on the Piedmont Substation, Camp Hill, affecting 4% of the trees. Roots of diseased trees were dull black and tough, unlike the brittle rotted wood associated with black root rot, caused by Xylaria mali Fromme. Cortical cells were rotted away from the main rOOI, leaving the hard, black, woody xylem core. Some rOOl5 we~ covered by the remnants of epidermal tissues that appeared like a sleeve draping the central woody core. 8otryodiplodia theobromae Pat. was isolated from the diseased apple roots and cultured on sterile oats. The soil around potted, 1-yr-old Red Delicious apple trees was infested with the oat-fungus inoculum at 4% v/v; 56% of the trees died within 30 days after inoculation. The dead trees showed root rot similar to that observed in the field. Trees exposed to sterile oats remained healthy. The fungus sporulated profusely on necrotic apple tree shoots and was reisolated from roots.