5.2.51
EFFECT OF PRE-HARVEST FACTORS AND HARVEST TIME ON BIOLOGICAL CONTROL OF PENICILLIUM EXPANSUM ON GOLDEN DELICIOUS APPLES

J USALL1; E GARZ1, J SI2 and I VINAS1

1Postharvest Unit, CERTA, Centre UDL-IRTA, and ; 2Agricultural Service, DARP, Catalonia Goverment, 177 Ave Rovira Roure, 25198 Lleida, Catalonia, Spain

Background and objectives
Post-harvest fruit diseases cause significant worldwide losses. Blue mould caused by Penicillium expansum is the most important post-harvest disease of pome fruits. Synthetic fungicides are the predominant means being used for controlling these diseases. The development of resistance to many fungicides by major post-harvest pathogens [1], and concern for public safety have combined to increase interest in alternative methods to fungicidal treatment. Biological control using microbial antagonists has been considered as a desirable alternative, and several new biocontrol agents have been demostrated to have potential. However, these antagonists have often not had a uniform and consistent efficacy at various maturity stages, or in different qualities of fruits. Candida sake (strain CPA-1) has been demonstrated to have antagonistic activity against the major post-harvest pathogens on pome fruits [2]. The objective of this work was to determine the effect of pre-harvest factors and harvest time on biocontrol of P. expansum on Golden Delicious apples with C. sake.

Materials and methods
During 1996 four commercial orchards were selected and apples were harvested at weekly intervals from 5 August to 30 September. Apples were wounded and inoculated with 7x10S or 2x106 cfu/ml of C. sake and 104 conidia/ml of P. expansum. A set of fruits were stored for 12 days at 20C and 85% relative humidity and the other set at 1C and 95% RH for 3 months. Apples were rated for decay severity by measuring the lesion diameter. Fruit quality was evaluated on 15-18 kg fruit samples in each orchard and harvest time. Firmness, soluble solids, acidity, colour, mineral content and loss of weight were determined. Management practices and yield were recorded from every orchard.

Results and conclusions
Significant differences were found in susceptibility to P. expansum in the four selected orchards. Fruits harvested until 19 August had low susceptibility to rot decay and the natural resistance decreased at advanced maturity stages. C. sake strongly reduced development of blue mould in all orchards at 2x106 cfu/ml . Antagonist efficacy decreased on fruits collected in the last two harvest periods of the experiment when inoculated with 7x105 cfu/ml, especially in the orchards which had more susceptibility to P. expansum decay. Significant correlation between susceptibility to rot decay and biocontrol effect was found. This suggests that for successful biological control, application of antagonists must be integrated with the management of the natural resistance of fruits.

References
1. Bertrand PF, Saulie-Carter, 1978. Plant Disease Reporter 62, 305-320.
2. Vinas I, Usall J, Teixide N, Sanchis V, 1998. International Journal of Food Microbiology (in press).