DEVELOPMENT OF A PRACTICAL METHOD TO EVALUATE THE EFFICACY OF POTASSIUM SORBATE AS A GERMINATION INHIBITOR OF PENICILLIUM DIGITATUM CONIDIA FOR POTENTIAL USE IN THE CITRUS SUPPLY CHAIN

Penicillium digitatum is the most serious citrus pathogen and the disease is currently controlled using conventional fungicides.
Risk of increased pathogen resistance, withdrawal of chemicals, residue levels of chemicals on fruit and the disposal of fungicide solutions are major problems. ‘Generally Recognized as Safe’ (GRAS) chemical alternatives are being researched for controlling P. digitatum, including the food additive potassium sorbate (KS). Initially a practical, laboratory method was developed to induce conidial germination.
Combinations of various fruit sugars with citric acid did not induce conidial germination.
Three orange juices were trialled at 0.625% concentration with Minute Maid^® and fresh ‘Navel’ orange juice inducing conidia germination after 8 h.
With the germination medium established this was then amended with KS concentrations of 0.003, 0.005 and 0.050% w/v, buffered at pH 4.5 and 5.5, and 1.18×10⁶ conidia/ml.
After 9 h at 25°C all three KS concentrations gave EC95 concentrations at pH 4.5. At pH 5.5, 0.005 and 0.050% KS gave EC₉₅ concentrations.
The effect of pH on KS dissociation was evident.
Germ tube measurement was difficult compared to recording the percentage germination.
The combination of 0.050% KS, buffered to pH 4.5 with 0.0625% Minute Maid^® gave significant inhibition of conidia germination.
The method developed combines the chosen components in solution, in reusable containers, to then give a visual indication of pathogen presence and germination inhibition results in approximately 9 h.
This technique provides a test kit which may be of potential use in the citrus supply chain.

XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Postharvest Technology in the Global Market

S. Potton , J. Cullum

GRAS, food additive, orange juice, Minute Maid^®, test kit

https://doi.org/10.17660/ActaHortic.2012.934.41