605 Postharvest Fungicide Treatments in Mango Fruits according to the Level of Quiescent Infection of Pathogens at Harvest D. Prusky, Y. Shalom, I. Kobiler, M. Akerman and Y. Fuchs Department of Postharvest Science of Fresh Produce, The Volcani Center Bet Dagan, 50250 Israel E-mail: dovprusk@volcani.agri.gov.il Keywords: Disease control; quiescent infections, plant protection Abstract The effectiveness of different postharvest treatments to control different levels of quiescent infections of Alternaria alternata causing Alternaria rot in mango fruits during storage was compared. A combined hot water spray and fruit brushing (hot water brushing - HWB) treatment for 15 - 20 s with 225 µg ml -1 prochloraz was the most effective treatment to control Alternaria rot in fruits with a high relative quiescent infected surface (RQIS) rating of 36 at harvest. Comparable control was obtained with the commercially used treatment of 900 µg ml -1 prochloraz spray. However Alternaria rot in mango fruits with intermediate levels of RQIS rating of 25 was controlled by HWB treatment alone or HWB with chlorine (300 µg ml -1 Troclosene Na). HWB alone was effective enough to control postharvest decay in fruits with a RQIS of 5. Present results have indicated that effectiveness of postharvest HWB and prochloraz applications, are dependent on the quiescent infected area of the fruit by A. alternata at harvest. A RQIS rating, before harvest, has resulted in the use of effective, mild, fungicides as a single postharvest treatment thus avoiding wide use of less friendly synthetic fungicides INTRODUCTION Susceptibility of mango fruits to postharvest diseases increases after harvest during prolonged storage as a result of senescence and physiological changes occurring in the fruits that enable pathogen development (Prusky and Keen, 1993). Mango fruit in Israel is susceptible to two types of diseases that have a different way of infection: i. Alternaria rot caused by Alternaria alternata (FR.:Fr) Keissel that infect the fruit mainly through lenticels and produces rot predominantly on the side of the fruit and and ii. stem- end rots, which are caused by A. alternata, Phomopsis spp. or Lasiodiplodia spp. attacking at the stem-end. Recently a new postharvest treatment of a 15 - 20 s combined hot water spray and fruit brushing was developed by our group to reduce the incidence of Alternaria rot and improve mango fruit keeping quality (Prusky et al. 1999). Differences in Alternaria rot incidence among stored mango fruits from various regions in Israel have been closely correlated to differences in the relative quiescent infected surface area of fruits at harvest from those locations (Prusky et al. 1983). A. alternata infection is highly depended on relative humidity and moisture at the orchard location (Prusky et al., 1992). As a consequence a highly significant correlation exists between values of the maximal relative humidity and the relative quiescent infected surface of the fruit (Prusky et al., 1983, 1992). Regions with the highest potential for disease incidence are located close to the isolines of 85% to 90% RH, the intermediate regions are between 75% and 85% RH and the lowest potential risk regions are in the dry area, with RH lower than 75% (Prusky et al., 1992). This has resulted in three clear regions of differential occurrence of Alternaria rot after harvest: i. a highly infested region at the southern coastal plain, ii. a medium infested region at the central coastal plain and iii. a low infested region at the northern inner valleys of Israel. The above findings brought up the question whether the same postharvest treatments should be used for fruits from all the orchards in Israel. This particular point is very important since significant limitations regarding fungicide treated fruit are being imposed recently at local and international markets (Droby et al., 2000). Proc. VII th IS on Mango Eds. A.C.Q. Pinto et al. Acta Hort 645, ISHS 2004