Disease resistance in sucrose polyester coated conference pears inoculated with Penicillium expansum and Monilinia fructigena
The objectives of this research were to examine the effect of the sucrose polyester coating Semperfresh® on the physiology and biochemistry of ‘Conference’ pear tissues; to determine how Semperfresh® affects the rate of tissue invasion by Penicillium expansum and Monilinia fructigena; and to determine the physiological basis for any such effect. ‘Conference’ pears coated with 0.5 or 1% Semperfresh® and sampled after 0, 2, 4, and 5 months storage at 0°C showed signs of delayed ripening as indicated by the recorded firmness, sugar contents, starch contents, and colour data. Additional information indicated that Semperfresh® had a greater effect on firmness when compared to other quality attributes such as colour and starch conversion. Semperfresh® (1%) significantly reduced the external and internal lesion dimensions recorded after artificial inoculation with P. expansum and M. fructigena, having a greater effect on the rate of growth of Monilinia fructigena in comparison to Penicillium expansum. When fruits were exposed to controlled atmosphere (CA) environments to generate a similar internal gas atmosphere (IGA) to that induced by coating there was a decrease in the rate of lesion growth for P. expansum and M. fructigena. Generally the magnitude of the effect varied accordingly to the extent of IGA modification in the same way for fruit which are coated and those in CA. The gas atmosphere developing in 1% Semperfresh® coated fruit was reproduced using 8% CO2 combined with 7% O2. Coated and CA stored ‘Conference’ pears inoculated with M. fructigena presented similar lesion dimensions which were significantly reduced in comparison to non-coated material. Submitting the fruits to 10% CO2 + 5% O2 for four days before and one day after inoculation delays the progression of the rot. However, when the fruits were returned to air, the rate of growth of M. fructigena resumed at a similar rate to the control.