Infection Risk and Critical Period for the Postharvest Control of Gray Mold (Botrytis cinerea) on Blueberry in Chile

Rivera, S. A., Zoffoli, J. P., and Latorre, B. A. 2013. Infection risk and critical period for the postharvest control of gray mold (Botrytis cinerea) on blueberry in Chile. Plant Dis. 97:1069-1074. Gray mold (Botrytis cinerea) is a major disease of blueberries (Vaccinium spp.), which require more than 15 days of shipment at 0°C to reach international markets. The aims of this study were (i) to determine the relative susceptibility of the flowering and fruiting stages, (ii) to determine the critical blueberry growth stages for postharvest gray mold control, and (iii) to determine the infection risks on the basis of weather conditions. The epiphytic colonization of B. cinerea of flowers and fruits was demonstrated in blueberry ‘Brigitta’ and ‘Duke’ in Antuco and Virquenco. In inoculated flowers and fruits in humid chambers at 20°C, full bloom and mature fruit stages were the most susceptible stages. Fungicide applications at the mature fruit stage appeared as the most critical period for gray mold control in stored fruits. The algorithm proposed, which was based on >6 h of wetness between 14 and 25°C, allowed the estimation of the periods of B. cinerea infection risk. A significant correlation between the B. cinerea infection risk and gray mold incidence in stored fruits was obtained (r = 0.96, P < 0.0001). Therefore, this algorithm has the potential to optimize fungicide applications under field conditions, but field validation of this algorithm remains to be determined. Highbush blueberry (Vaccinium spp.) is a high-value export crop cultivated on over 8,400 ha across a range of diverse soil conditions and climate zones in Chile (www.odepa.cl). The commercial plantings in Chile extend from latitude 29° to 42° south, with harvesting from October to April (1). The blueberries are exported mainly to the United States (3), but markets in Europe and Asia are increasing. Blueberry flowers and fruits can be affected by several fungal diseases (5,16,23,24), with the gray mold caused by Botrytis cinerea Pers. ex Fr. (teleomorph Botryotinia fuckeliana (de Bary) Whetzel) being one of the most frequent and severe diseases. Gray mold commonly occurs in blueberry plantings in Chile (31) when favorable weather conditions prevail during the growing season and causes blossom and twig blights and a soft decay in mature fruits at harvest time and during storage (2,5,29,30,32). Furthermore, although the blueberries are transported at near 0°C, the Chilean blueberry transport to market requires more than 15 days by sea, with severe losses often occurring (3). As proposed for other fruit crops (10,13,18,21), it is postulated that the postharvest gray mold decay of blueberry can be initiated at flowering or during the early stages of fruit development, remaining latent until harvest and postharvest. Therefore, to prevent severe losses due to gray mold during storage and transportation, fungicide treatments have been proposed between flowering and fruit maturity, and several fungicides have been registered in Chile, including anilinopyrimidines (e.g., cyprodinil) and anhydroxanilide (e.g., fenhexamid) (www.sag.gob.cl). Recently, sulfur dioxide (SO2) treatments applied to packed fruits just after harvest have been advocated to prevent gray mold decay during storage and transportation (8,27). However, further studies are needed to establish the critical growth stages for gray mold control in the current blueberry cultivars planted at a relatively high density in Chile. This information would be valuable for the timing of fungicide treatments. Although such weather conditions as the temperature and duration of free moisture have been previously related to B. cinerea infection in table grapes (6,20) and strawberries (7), the effect of such factors has yet to be studied with regard to gray mold in blueberries. Therefore, this study was conducted (i) to determine the relative susceptibility of the flowering and fruiting stages to B. cinerea, (ii) to determine the critical blueberry growth stages for postharvest gray mold control, and (iii) to determine the infection risks on the basis of weather conditions.