Pak. J. Bot., 44(2): 831-836, 2012. INFLUENCE OF STORAGE TEMPERATURE ON FUNGAL PREVALENCE AND QUALITY OF CITRUS FRUIT (CV. BLOOD RED) ABDUR RAB*, MUHAMMAD SAJID, NAQIB ULLAH KHAN, KHALID NAWAB, MUHAMMAD ARIF AND MANSOOR KHAN KHATTAK Khyber Pakhtunkhwa Agricultural University, Peshawar 25130, Pakistan *Corresponding author email: abdurrabaup@gmail.com Abstract The influence of storage temperature on post storage fungal prevalence and quality of citrus fruit (sweet orange cv. Blood Red) was investigated at the Horticultural Laboratory of Khyber Pakhtunkhwa Agricultural University, Peshawar. The fruits were exposed to 5, 10 and 20 °C for 45 days and then kept at ambient temperature for 25 days. The fruits were evaluated for disease incidence and other quality attributes at 5 days incubation to the maximum of 25 days. Results indicated that disease incidence and prevalence of Penecillium itallicum and Penecillium digitatum were higher in fruits stored at 5 and 20°C and were lower at 10°C. Weight loss was higher in the fruits stored at 20°C followed by 5°C and was lower at 10°C Ascorbic acid was higher in fruits stored at 10°C followed by 5 and was lower at 20°C. Disease incidence and prevalence of Penecillium itallicum and Penecillium digitatum and weight loss increased while ascorbic acid decreased with increase in post storage incubation from 0 to 25 days. It is concluded that storage of citrus fruits at 10°C performed better in terms of fight against disease and fungal prevalence and perseverance of quality. Introduction Sweet orange is a high value fruit due to its taste and nutrition throughout the world. Among the sweet orange, cultivars Blood Red is generally preferred because of its red flesh caused by anthocyanins (Dougo et al., 2003) and possibly its therapeutic properties (Sajia, 1994). Citrus species is however susceptible to both pre and post- harvest pathogens (Pienar, 1969) that limit its export (Mahmood et al., 2008). Post harvest quality losses in citrus fruits have been commonly observed (Tariq et al., 2001a). Chemical (Smilanick et al., 2003; Palou et al., 2004). Biological (Kinay et al., 2001) and physical measures are usually adopted to remove spores from the surface of fruits and these are effective methods to decrease disease incidence (Abdel-El-Aziz & Mansour, 2006; Smilanick et al., 2003). Post-harvest diseases destroy 10-30% of the total yield of crops but in perishable crops, especially in developing countries, they destroy more than 30% of the crop yield (Kader, 2002). The fungal pathogens, Penicillium digitatum and Penicillium italicum, are the predominant pathogens of citrus fruits (Snowdon, 1990, Brown & Eckert, 1988). Disease incidence in storage of sweet orange fruit increases with increasing storage duration (D’ hallewin and Schirra, 2000) which could be as high as 50% (Abd-El-Aziz & Mansour, 2006). Infection of oranges by Penicillium digitatum results in green mold, a predominant post-harvest disease of citrus (Brown & Eckert, 1988). Initial infection of the fruit occurs prior to or after harvest via wounds in the fruit peel (Snowdon, 1990). Another common fungal disease of oranges is the blue mold, caused by the fungus Penicillium italicum which can be decreased by storage at low but non-chilling temperatures. However, chilling for prolong duration may actually damage the tissue to the level where it may become highly sensitive to fungal infections (Ritenour et al., 2004). Both the fungi grow best at a temperature of 75 o F (23.8°C) and their development is slowed by lower temperatures. While fungicides can be used to decrease diseases on citrus fruit (Agostini et al., 2006) but chemical residues limits their application. Thus, non-chemical measures of disease control are generally preferred in postharvest disease suppression (Al-Obeed & Harhash, 2006). Therefore, cooling citrus fruit at optimal temperature during storage may be effective to decrease blue mold. But exposure to suboptimal low chilling temperatures may cause chilling injury, which may favor the decay causing organisms (Kader, 2002, Arpaia & Kader, 2009). Thus long term low temperature storage of citrus fruits is limited by their sensitivity to chilling (Arpaia & Kader, 2009) that may enhance susceptibility to decay causing organisms (Chalutz et al., 1985). The objective of this experiment was to investigate the influence of storage temperature on fungal and disease prevalence and citrus fruit quality during 25 days post-storage period. Materials and Methods To study the influence of storage temperature on fungal and disease prevalence and quality of citrus fruits, an experiment was carried out at Khyber Pakhtunkhwa Agricultural University, Peshawar. The sweet orange fruits cv. Blood Red with about similar size and maturity and free from bruises and other mechanical injuries were procured from an orchard in Rustum, Mardan. The fruits were immediately transported to the laboratory and were carefully washed with distilled water and dried with a blower before allotting to designed storage conditions. The experiment was laid out in randomized complete block (RCB) design with three replications. The treatments consisted of three storage temperatures (5, 10 and 20°C) and post-storage incubation (0-25 days). There were 20 fruits per treatment. The fruits were stored at 5, 10 and 20°C for 45 days and then incubated at ambient temperature for 0-25 days. The fruits were evaluated for fungal prevalence and disease incidence and other quality attributes at 5 days interval to the maximum of 25 days. Data were recorded on the following parameters. Disease incidence (%): Total disease incidence was recorded at each post-storage interval by visual