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Use of Bicarbonates to Inhibit in vitro Colony Growth of Botrytis cinerea

Fungicide resistance in Botrytis cinerea has caused increased concerns about losses due to gray mold on many important agricultural and horticultural crops. Since bicarbonates have been reported to be an effective control of powdery mildew on greenhouse roses, the purpose of this research was to determine the effectiveness of bicarbonates against B. cinerea. Assessments were made of in vitro fungal colony growth in response to ammonium, potassium, and sodium bicarbonates. Bicarbonates inhibited colony growth at concentrations as low as 20 mM. In addition, comparisons of several ammonium, potassium, and sodium salts were conducted to determine whether cation or anion is the active moiety. Although the bicarbonate anion primarily affected growth, the ammonium cation also contributed greatly to fungal growth inhibition. With the exception of dibasic phosphate, only salts with high pK_a values or that are reducing agents, or both, decreased colony growth. The effect of pH on B. cinerea was then examined. Since bicarbonate anion concentration is related to pH, this parameter was examined in combination with several salts to separate pH effects from bicarbonate effects. As pH increased from 7.0 to 8.5, colony growth decreased with bicarbonates and phosphates, but not with ammonium sulfate. Since bicarbonates and phosphates decreased colony growth more than could be accounted for from pH alone, and since both have buffering characteristics, buffering capacity was examined and found to decrease colony growth but not as much as bicarbonate. Therefore, bicarbonates control B. cinerea colony growth in vitro, and both pH and buffering capacity contribute to, but are not solely responsible for, growth inhibition.