Apple host defence reactions as affected by cycloheximide,phosphonate, and citrus green mould, Penicillium digitatum

摘要

A host defence reaction was detected in apples which reduced decay development in fruit that had been challenged by the apple blue mould organism Penicillium expansum. It was found that this reaction could be negated by the application of the protein synthesis inhibitor cycloheximide, which when applied to inoculated fruit resulted in more than a 700% increase in decay. The defence response was temperature dependent and was optimised by holding damaged fruit at 22deg C for 48 hours before inoculation. Decay development under these conditions was reduced from 96% to37%. Application of potassium phosphonate after fruit injury reduced decay initially by over 60%,although this compound had no in vitro activity against the fungus. Inoculation of apples with the citrus green mould pathogen, Penicillium digitatum,normally does not result in decay in fresh apples. However, when the defence reaction was prevented by the application of cycloheximide, mould development occurred. It was also found that if mould resulting from P.digitatum infection progressed through an apple and came in contact with a previously damaged section, it progressed around that damaged site.,leaving a halo of uninfected tissue of up to 1 cm in diameter. It is proposed that this area is where the host defence reaction is occurring and it has been visualised by P.digitatum development. Gel electrophoresis of protein production in these areas showed that phosphonate increased production of proteins particularly in the 25 k Dalton range, whereas cycloheximide inhibited it.