EFFECT OF CALCIUM SALTS ON GROWTH, PECTIC ENZYME-ACTIVITY, AND COLONIZATION OF PEACH TWIGS BY LEUCOSTOMA-PERSOONII

The effects of several calcium salts on in vitro growth, pectic enzyme activity, and colonization of excised peach twigs by the peach canker fungus, Leucostoma persoonii, were investigated. Fungal growth was determined on potato-dextrose agar amended with various calcium salts. The greatest growth reduction (85%) was caused by calcium propionate, followed by calcium hydroxide (76%) and calcium silicate (73%). The fungicides captan, iprodione, and thiophanate-methyl completely inhibited fungal growth. Lesion length was reduced when excised peach twigs were wounded with a cork borer, dipped for 15 or 60 min in the various calcium solutions, and inoculated with L. persoonii. For 15-min dips, lesion length was reduced more than 70% by calcium silicate, iprodione, and calcium propionate. After 15 min, calcium in the bark was not greater than that in the distilled, deionized water control. When twig segments were dipped for 60 min, lesion length was reduced more than 70% by calcium acetate, calcium sulfate, calcium heptagluconate, calcium oxide, calcium succinate, calcium chloride, calcium hydroxide, and the fungicide iprodione. No lesions occurred when twigs were treated with calcium propionate, captan, and thiophanate-methyl After 60 min, only twigs dipped in calcium sulfate showed significantly elevated levels of bark Ca2+. Canker length and calcium content of bark were negatively correlated (r = -0.26, P less than or equal to 0.05) after the 15-min treatment. No correlation was found with the 60-min dip, even though calcium content of the bark had increased significantly. When L. persoonii was grown on Ca2+ -amended media, pectin lyase activity was not reduced significantly by any treatment. Calcium oxide and calcium propionate, and calcium silicate treatments reduced polygalacturonase activity after 7 and 15 days, respectively.