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Physiology and Biochemistry

Macromolecular Plant-Wilting Toxins: Artifacts of the Bioassay Method?. Neal K. Van Alfen, Associate professor, Department of Biology, Utah State University, Logan 84322; Brent D. McMillan, research technician, Department of Biology, Utah State University, Logan 84322. Phytopathology 72:132-135. Accepted for publication 18 May 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-132.

The use of plant cuttings to assay the wilt-inducing ability of potential phytotoxins is subject to misinterpretation. If the molecule being assayed has a molecular weight greater than ~20,000 daltons, it will physically induce wilt. Such a wilt response indicates only the plant’s susceptibility to disruption of water movement by macromolecules and should not be confused with any toxic properties of the molecule. Quantitation of the wilt bioassay by visually assessing when wilting occurs is not reliable. Measurement of transpiration of the cuttings is a better method of quantitation, but this also lacks precision. In evaluations of the wilt bioassay, no correlation was found between resistance in alfalfa to Corynebacterium insidiosum and wilt induced by the large glycopeptide isolated from cultures of this bacterium.