Preharvest environmental conditions influence fatty acid metabolism and chilling-injury during postharvest cold storage of citrus fruits

Fatty acid (FA) metabolism, particularly changes in unsaturation levels in response to low-temperature stress, has been suggested to play a key role in fruit tolerance to postharvest chilling injury (CI), a major physiological disorder in citrus. Although preharvest environmental conditions are known to influence CI incidence during cold storage, the relationship between preharvest variability, FA metabolism and CI remain still unclear. Therefore, in this study we investigated FA metabolism in the peel of three citrus genotypes harvested from locations with contrasting agroclimatic conditions. Fruit of Tango and Nadorcott mandarins and Valencia orange exposed in the field to a higher number of hours of cold (<5 °C) or at low relative humidity (<30%) developed higher CI index during storage at 2 °C. In CI-sensitive fruit, FA metabolism genes were upregulated at harvest and further stimulated in response to cold storage. The expression of specific genes involved in FA desaturation (oleate desaturase, FAD2.1 ) as well as in lipoxygenation ( LOX2 ) presented strong positive correlations with preharvest cold and dehydration stress, respectively, and specially with CI. The stress-induced or postharvest modifications in FA content were genotype-dependent, although the FA unsaturation ratio also correlated positively with CI index. These results suggest that exposure of citrus fruits to preharvest environmental stress conditions modulates the expression of FA metabolism genes already in the field and enhances CI sensitivity, thereby determining its postharvest responses. • Preharvest cold and low relative humidity influence postharvest CI susceptibility • Preharvest conditions modulate the expression of fatty acid metabolism genes • Fatty acid unsaturation ratio positively correlates with CI incidence • Expression of oleate desaturase ( FAD2.1 ) and lipoxygenase ( LOX2 ) genes strongly correlate with CI