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Effect of Relative Humidity During Mango Growth on the Incidence of Quiescent Infections of Alternaria alternata. D. Prusky, Department of Fruit and Vegetable Storage, Agricultural Research Organization, The Volcani Center, P.O.B. 6, Bet Dagan, Israel 50250. Z. Gat, and P. Burd. Division of Agricultural Meteorology, Israel Meteorological Service, Bet Dagan 50250. Plant Dis. 77:249-252. Accepted for publication 22 June 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0249.

The quiescent infected area of Alternaria alternata on mango fruit at harvest was closely related to the number of hours of relative humidity (RH) ≥80% during a 52-day period of fruit development. At least 350 hr of RH ≥80% were needed for a significant quiescent infected area in fruits at harvest. Disease incidence increased as the number of hours of RH ≥80% over 320 increased. In some groves climatic parameters other than RH appeared to affect disease incidence. A map of average daily maximum RH during fruit growth can be used as a basis for predicting the incidence of black spot in Israel.