Activity of calcium salts in controlling Phytophthora root rot of citrus

The effect of 10 calcium salts in controlling Phytophthora root rot of citrus was evaluated both in vitro, on agar and liquid media, and in vivo, on sour orange citrus seedlings. In vitro, calcium salts were applied at 300, 600, and 1200 ppm. Calcium oxide and calcium carbonate significantly reduced the growth of P. nicotianae, in comparison with the control; minimum dry weight of the mycelium. was observed with calcium oxide; moreover, this salt significantly reduced zoospore production and their viability. In vivo, calcium salts were applied at 1200 ppm on 4-month old sour orange seedlings. Calcium propionate and calcium lactate significantly reduced the inoculum density of the pathogen in the soil, whereas all the,other calcium salts-except nitrate, pantothenate and gluconate-significantly reduced root infections in comparison with the control. Phytotoxicity symptoms on sour orange seedlings were induced only by calcium chloride. (C) 2002 Elsevier Science Ltd. All rights reserved.