A combination of cuminaldehyde with citral- / trans-2-hexen-1-al alleviates green mold disease in citrus fruit

Management of Penicillium digitatum requires use of highly effective fungicides that are not prone to drug resistance and are safe to humans and the environment. This study examined the fungicidal potential of combinations of cuminaldehyde (CA) + trans-2-hexen-1-al (TH) and CA + Citral. Both CA + TH and CA + Citral exhibited enhanced fungitoxicity against P. digitatum than CA, citral or TH alone. The minimum inhibitory concentration (MIC) of CA + Citral consisted of 0.13 ml/L CA and 0.3 ml/L citral, representing a synergistic interaction. MIC of CA + TH consisted of 0.12 ml/L CA and 0.15 ml/L TH, representing an additive interaction. The minimum fungicidal concentration (MFC) of CA + Citral and of CA + TH consisted of 0.26 ml/L CA and 0.6 ml/L citral, and 0.18 ml/L CA and 0.24 ml/L TH, respectively. 10×MFC CA + Citral in Tween-80 (WCI) delayed onset of hyphal growth in fruits inoculated with P. digitatum to day 5 compared to day 4 in the 10×MFC CA + TH in Tween-80 (WCT) treatment, and day 3 for the control samples. Daily green mold disease incidence and disease severity were much lower in WCI and WCT treatments than in the 10×MFC CA in Tween-80 (WCA) treatment and in control samples. Our results show that WCI was much fungitoxic against P. digitatum than WCT and WCA, its effect being comparable to that of imazalil. Additionally, at 25 ± 2 °C and 85–90% relative humidity, both WCI and WCT markedly preserved fruit quality by day 6 of treatment. WCI and WCT are thus, safe, cheap and highly effective alternatives to chemical fungicides being used to control postharvest green mold in citrus fruits.