257 Short-Term CO 2 Exposure at Curing Temperature to Control Postharvest Green Mold of Mandarins L. Palou, C. Montesinos-Herrero and M.Á. del Río Centre de Tecnologia Postcollita Institut Valencià d’Investigacions Agràries (IVIA) Montcada, València Spain Keywords: carbon dioxide, citrus, Penicillium digitatum, postharvest fungicide alternatives Abstract Alternatives to synthetic fungicides are needed worldwide to control citrus postharvest diseases. Curing of citrus fruit at 30-37°C and 90-98% RH for 65-72h has been repeatedly reported as an effective method to control green mold caused by Penicillium digitatum. However, commercial adoption of this practice is limited because of the length of treatment and risks of negative impact on fruit quality. Exposure to CO 2 -enriched atmospheres is known to provide fungistatic effects and, in some cases, to induce resistance in fresh fruit against major postharvest pathogens. To improve curing treatments against citrus postharvest green mold, work is in progress to determine if short treatments with CO 2 at curing temperature can control established infections and/or induce fruit resistance. Mandarins ‘Nadorcott’ and ‘Ortanique’ were artificially inoculated with P. digitatum and 24h later, were exposed to air (control) or 15, 30 and 50 kPa CO 2 at 20 or 33°C for 8 or 24h. Number of decayed fruit was counted after 4 and 7 d incubation at 20°C. To assess potential induction of resistance and time of induction, the same treatments were applied to another set of non-inoculated fruit. Treated fruit were kept at 20°C for 1, 2 or 5 d, at which time mandarins were wound inoculated with the pathogen. Lesion diameter was then measured after 3 and 6 d at 20°C. For both cultivars, only treatments at 33°C for 24h reduced the incidence of disease significantly after 4 d incubation, with 15 kPa CO 2 slightly superior to other gas concentrations used. Regardless of time between treatment and inoculation and incubation period, all treatments were ineffective in reducing disease severity and, therefore, in inducing any kind of fruit resistance. It is planned to evaluate longer exposure times (maximum of 48h) to 15 kPa CO 2 at 33°C. INTRODUCTION Synthetic fungicides have been widely used for treatment of mandarins against postharvest diseases and particularly against green mold caused by Penicillium digitatum (Pers.:Fr.) Sacc., a pathogenic fungi that causes serious economic losses during post- harvest storage and distribution of citrus fruit (Eckert and Eaks, 1989). However, massive use of these fungicides has induced proliferation of resistant pathogen strains with a consequent loss of treatment efficacy. Furthermore, use of chemical fungicides involves potential risks for nature and human health due to accumulation of toxic residues in the environment and on fruit surface. For the above reasons, there is a need to develop new alternatives to conventional fungicides to control postharvest decay of citrus fruit. Several treatments have been studied in order to substitute fungicides. Curing of citrus fruit consists in holding fruit at 30-37ºC and 90-98% relative humidity (RH) for 65- 72h. Methods based on curing treatments have been evaluated to control green mold on citrus fruit (Ben-Yehoshua et al., 1989; Lanza and Di Martino Aleppo, 1996; Plaza et al., 2003). Satisfactory results have been obtained for disease control but the length of treat- ment is not convenient commercially because of high costs and possible adverse effects on fruit quality. Exposure of fruit to CO 2 -enriched atmospheres has been effective for the control of diseases caused by fungi, by either a direct fungistatic effect or induction in fresh fruit of some kind of resistance against pathogens (Kader, 1986; Prusky et al., 1993). Proc. XXVII IHC-S8 Role of Postharv. Technol. in Global. of Hort. Eds.-in-Chief: E.W. Hewett et al. Acta Hort. 768, ISHS 2008