Brown Rot/Calcium

Plant Pathology Research at The Kearneysville Tree Fruit Research and Education Center

Effect of Calcium Salts on Growth, Polygalacturonase Activity, and Infection of Peach Fruit by Monilinia fructicola

Brown rot on peach Brown rot is one of the most important fungal diseases of stone fruit in the world's fruit-growing regions. Field losses of peaches, plums and prunes, sweet and tart cherries, and apricots can be extensive if conditions are favorable for disease development either during the blossom period, following shuck fall, or during the preharvest and harvest period. Disease control is achieved primarily through the use of fungicides to protect blossoms and ripening fruits, although orchard sanitation is an integral part of the disease management program. Postharvest losses of stone fruit due to brown rot may be significant in some years, and fungicide treatment of fruit after harvest is routine, especially if fruit are to be stored and/or shipped long distances. Increasing the calcium content of other fruits and vegetables with calcium salts has been shown to increase storage life, mainly due to the role of calcium in physiological and pathological disorders. In this study, we investigated the effect of several calcium salts on growth and polygalacturonase activity, and infection of harvested peach fruit by brown rot. All salts except calcium formate, calcium pantothenate, and dibasic calcium phosphate reduced fungal growth on amended potato dextrose agar (PDA) after 7 days. Minimal growth occurred on PDA amended with calcium propionate. Calcium hydroxide, calcium oxide, calcium silicate, and calcium pyrophosphate reduced growth by ca. 65% of the control. Substances that were inhibitory in amended PDA also were inhibitory in potato dextrose broth (PDB), but varied in effectiveness depending on whether PDB or PDA was used. Fungal polygalacturonase (PG) activity was inhibited by all salts used in this study, except dibasic calcium phosphate and calcium tartrate. Greatest inhibition of PG was associated with calcium propionate, followed by calcium sulfate, tribasic calcium phosphate, calcium gluconate, and calcium succinate. When inoculum was sprayed on detached fruit, the incidence and severity of brown rot was least on fruit that had been dipped in solutions of calcium propionate or calcium silicate. When inoculum was applied as a localized drop to wounded fruit that had been dipped in 1,200 mg/L calcium, brown rot severity was least for fruit treated with calcium oxide and calcium hydroxide. For nonwounded fruit and drop inoculations, calcium hydroxide was the most effective in reducing brown rot incidence, and all salts reduced rot severity similarly. Activity of calcium salts was not affected by pH. PG activity was correlated with growth on PDA, but was not correlated with growth in PDB. There were significant correlations between growth in PDB and disease incidence and severity after 4 days at both levels of calcium. Furthermore, disease incidence and severity after 4 days at both levels of calcium also were correlated significantly with PG activity. Future investigations on brown rot and calcium salts should utilize PDB for in vitro investigations and spray mist inoculations for fruit studies.

A. R. Biggs and R. Nickerson (October, 1996)

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Biggs, A.R., M. El-Kholi, S. El-Neshawy, and R. Nickerson. 1997. Effect of calcium salts on growth, polygalacturonase activity, and colonization of peach fruit by Monilinia fructicola. Plant Disease 81:399-403.

01/30/2008 09:15:17 AM