VIEW ARTICLE

Techniques

In Situ Observations of Phymatotrichum omnivorum with a Borescope Mini-Rhizotron System. C. M. Rush, Texas Agricultural Experiment Station, Blackland Research Center, Post Office Box 748, Temple 76503; D. R. Upchurch(2), and T. J. Gerik(3). (2)Grassland Soil and Water Research Laboratory, USDA/ARS, Post Office Box 748, Temple, TX 76503; (3)Texas Agricultural Experiment Station, Blackland Research Center, Post Office Box 748, Temple 76503. Phytopathology 74:104-105. Accepted for publication 20 July 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-104.

A new application of the borescope mini-rhizotron system is described. It was evaluated as a method for observing Phymatotrichum omnivorum in situ in field and greenhouse situations. At 31 mm from the objective being viewed, the borescope provides a 1-1 image and a field of view of 2 cm. Objects 50 μm and larger were easily resolved. Fungal strands of P. omnivorum were observed on cotton roots in the field 14 days before any aboveground symptoms appeared. This is the first reported indication made by nondestructive means of when the primary inoculum of P. omnivorum becomes active. The borescope was also used in a greenhouse study to determine how the presence or absence of a host affected sclerotial germination. In all treatments, sclerotia germinated regardless of the presence or absence of a host. The borescope mini-rhizotron is potentially a valuable tool for ecological and epidemiological studies of certain soilborne plant pathogens.