VIEW ARTICLE

Etiology

Role of Soil Microflora and Pratylenchus penetrans in an Apple Replant Disease. B. A. Jaffee, Department of Plant Pathology, Cornell University, Ithaca, NY 14853, Present address: Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29631; G. S. Abawi(2), and W. F. Mai(3). (2)Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva, 14456; (3)Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 72:247-251. Accepted for publication 9 June 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-247.

Consistent reproduction of apple replant disease (ARD) was developed under controlled conditions. A small quantity of untreated field soil (FS) obtained from an orchard with a history of ARD was incorporated into a steamed (75 C for 30 min) portion of the same soil (SS). Ten-day-old apple seedlings (Northern Spy) were transplanted into SS or 5% FS (5 parts FS + 95 parts SS) and maintained for 6 wk in a growth chamber. The addition of 5% FS reduced plant dry weight by 50% and induced orange and black root discoloration. Treatment of the FS (prior to incorporation in SS) with gamma radiation, broad-spectrum fumigants, and heating (60 C or higher for 30 min) eliminated the stunting and root discoloration. Pratylenchus penetrans was the most abundant parasitic nematode, but its highest density in 5% FS was only four per 100 cm³ soil. This density was considered to be below the damaging level. Addition of 140 or more P. penetrans per 100 cm³ SS resulted in significant stunting and root necrosis. Our data suggest that at least two agents contribute to the ARD occurring in the field: an unknown organism(s) inducing stunting and root discoloration in 5% FS, and P. penetrans.