Effect of volatile citral on the development of blue mould, green mould and sour rot on navel orange

Abstract

The essential oil, citral, has potential for non-conventional control of postharvest diseases of citrus caused by Penicillium digitatum, Penicillium italicum and Geotrichum citri-aurantii. Citral in volatile phase has been shown to inhibit the three pathogens in vitro. The effect of citral applied as a fumigant on the incidence of disease on navel oranges (Citrus sinensis) was therefore studied. Fumigation of oranges with citral (20, 60 or 150 mL L−1 in absorbent pads) in a closed system, following application of conidia (20 μL of 106 conidia mL−1) to puncture wounds, delayed the onset of sour rot at room temperature by 7–10 days and at 5 °C, by 13–30 days, but had limited effect on blue and green mould. Blue and green mould developed faster on oranges wounded by puncture than by abrasion and volatile citral delayed the development of blue mould in abraded, but not punctured, oranges stored at 5 °C. Phytotoxicity symptoms were observed on the upper surface of some fruit close to or in direct contact with citral-soaked pads at concentrations of 60 and 150 mL L−1. Citral residue was not detected in the rind of fumigated oranges. Volatile citral applied at 60 mL L−1 appeared to have potential for the control of sour rot, although phytotoxicity was associated with high concentrations of volatile citral.