Modified Nash and Snyder's medium (MNSM) has been used to study soil populations of the fungus Fusarium solani f. sp. glycines, the causal agent of sudden death syndrome (SDS) of soybean. However, no studies have been conducted to confirm the accuracy of this technique in enumerating the SDS pathogen. To determine what portion of the colonies enumerated on MNSM are the SDS pathogen, 282 isolates resembling F. solani f. sp. glycines were collected from soil of two fields with a history of SDS in Arkansas using a soil dilution method with MNSM. The colony morphology of these isolates was compared on MNSM and on potato dextrose agar (PDA). Of these isolates, 112 were tested for pathogenicity on soybean in the greenhouse. In addition to fungi that produced colonies typical of F. solani f. sp. glycines on MNSM, 5 isolates each of four common colony types on MNSM were collected from each field for a total of 40 isolates. These isolates were compared to F. solani f. sp. glycines for colony morphology on PDA and for pathogenicity. Isolates that had colonies on MNSM that resembled F. solani f. sp. glycines had colony morphologies on PDA similar to this pathogen and produced SDS-like foliar symptoms in greenhouse inoculations of soybean. There was a significant quadratic relationship between foliar symptom severity and plant fresh weight. None of the other isolates tested resembled F. solani f. sp. glycines on either MNSM or PDA or produced SDS-foliar symptoms in greenhouse inoculations. These non-SDS isolates were F. solani, F. merismoides, a Pythium sp., and a Paecilomyces sp. All of these isolates produced some root rot, but significantly less than the F. solani f. sp. glycines reference isolate. The results of this study established that soil populations of F. solani f. sp. glycines can be accurately enumerated using MNSM. It should be noted that, on both MNSM and PDA, F. solani f. sp. glycines can resemble some isolates of F. solani f. sp. phaseoli, so pathogenicity tests of random isolates may be required to confirm the forma specialis especially in fields that have a history of both Glycines max and Phaseolus vulgaris.

Knowledge of solute distribution is required for improved understanding of double‐diffusive phenomena in which transports of heat and species occur simultaneously. The present paper describes an experimental technique to monitor the local composition of an aqueous copper sulfate solution without resort to a sampling procedure. The method is based on the principles of electrochemistry and employs a copper electrode as a sensing probe. Calibration experiments were conducted with the concentration and temperature of a reference solution fixed at 5 wt% and 25°C, respectively. The regressed equation empirically relates the electric potential difference between working and reference electrodes to the concentration and temperature of the solution that contacts the working electrode. During a double‐diffusion experiment, liquid composition can be determined from the measured values of local temperature and cell potential, with the uncertainty smaller than 0.85 mV for the confidence interval of 99.7%. A series of experiments to determine the best method of preparing the copper electrode has also been performed. For the tested diameter of the electrode (0.75 mm), a constant current of 0.4 mA and plating time of 450 s yield minimum offset in electrode potential. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 367–378, 1999

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