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Rapid Bioassay for Inhibitory Rhizobacteria Using Digital Image Analysis

Dep. of Natural Resources, Preble Hall, 39 High St., Univ. of Maine, Farmington, ME 04938-1987

A. C. Kennedy^*

USDA-ARS, Land Management and Conservation Research, 215 Johnson Hall, Washington State Univ., Pullman, WA 99164-6421

W. L. Pan

Washington State Univ., Pullman, WA 99164-6420

* Corresponding author ( kennedy{at}wsuvml.csc.wsu.edu).

ABSTRACT

Current methods for assaying the potential effects of rhizobacteria on plant growth are tedious and time consuming. A rapid, automated bioassay has been developed using a flatbed scanner and digital image analysis. Comparisons were made between manual measurements of root length and computed values based on an edge discrimination image analysis procedure. The assay consisted of bacterial cultures of filtrates added to 18 mL of 0.9% agar in square petri plates. Seeds were planted along a marked axis and incubated for 4 d at 15°C, and then the roots were measured. Total root length measurements for the two methods, manual and image analysis, were well correlated (r² = 0.94), and both were equally able to identify bacteria inhibitory to plant growth. Root measurements by the scan method were five times faster than the manual method. Each sample required 53 s to read with the scan method vs. 250 s with the manual method. The scan method provides a quick and accurate method for screening inhibitory activity of rhizobacteria based on seedling root length and has potential in the screening of toxic substances of other origin.

Contribution no. 9312-57 from the USDA-ARS in cooperation with the College of Agriculture, Washington State Univ., Pullman.

Received for publication December 16, 1993.