Investigating the control of the green mould Penicillium digitatum on sweet oranges subjected to steam treatment
Steam treatment of 'Amber' sweet orange (Citrus sinensis) fruit prior to storage at tropical ambient temperature controlled Penicillium digitatum infection. To investigate the basis of decay control by steam in this cultivar, an equal number of fruit was treated as follows: wound-inoculated with the pathogen and exposed to steam at 50°C; unwounded, uninoculated but heated by steam; unwounded, uninoculated and unheated; wounded and steam treated; wounded and unheated. Control fruit were wound-inoculated but not exposed to steam. All fruit were stored at 28°C and 95% relative humidity. All control fruit decayed. Dichloromethane extracts of flavedo tissue from fruit that remained healthy were fractionated and tested for biological activity. Fractions from all treatments showed inhibition of fungal spore germination, indicating the presence of antifungal compounds. Gas chromatography-mass spectrometry analysis of the active fractions revealed that hydrocarbons (substituted and unsubstituted aliphatic, aromatic and alicyclic), esters and terpenes were some of the components common to all fruit. Several of them are known for antioxidant, antibacterial or antifungal action: carveol, an oxidation product of limonene; trans-p-mentha-1(7), 8-dien-2-ol, an oxygenated monoterpene; and 9, 12, 15-octadecatrienoic acid, 2-(acetyloxy)-1-[(acetyloxy) methyl] ethyl ester, (Z,Z,Z)-. However, they were present only in the wound-inoculated steam treated fruit, suggesting that they were produced in response to infection. Carveol, being antifungal itself, possibly synergized other components of the essential oil to further antifungal action in addition to the spore killing effect of steam treatment. The results suggest the presence of both preformed and induced antifungal compounds in inoculated fruit.
Aborisade, A.T. and Akomolafe, O.M. (2016). Investigating the control of the green mould Penicillium digitatum on sweet oranges subjected to steam treatment. Acta Hortic. 1144, 303-308
steam treatment, antifungal, sweet orange, green mould control