Overview of 20 years of work on apples

Control of storage rot by post-harvest hot water treatment

Hot water treatment (HWT) is now considered to be an alternative technique effective in controlling storage rot in apples. Yet this control method is not particularly recent since Gilles Bompeix, professor of plant pathology at the University of Paris VI, was already testing it in the 1970s. At that time, the arrival of synthetic fungicides quickly put an end to this area of experimentation. However, by the end of the 1990s, growers practising agrobiology had reclaimed the principle and in 1999, the first trials on apples were carried out in the laboratory at the La Morinière research centre, and then within the CTIFL/CEFEL/La Morinière national conservation network. In the early 2000s, XEDA, a forerunner in France, proposed an automated bulk bin immersion system. Today, there are industrial machines with treatment rates that are adapted to current fruit packhouses. This technique is now also being developed for other uses, such as for peaches, pears, young plants, etc. Why, when and how should apples be treated with hot water immersion? This article summarises the knowledge acquired by the national conservation network over the last 20 years.

Claude COUREAU , CTIFL

Pascale WESTERCAMP , CTIFL

Published 01/12/2023

Hot water treatment, dual action against rot

The primary aim of hot water treatment is to control fungal diseases that affect the storage of apples. The hot water applied directly to the fruit disrupts the development of pathogenic fungi: it inhibits the germination of spores, blocks the elongation of the germ tube and deteriorates the spores. Biochemical studies of fruit compounds have also revealed a defence reaction in the fruit, which is initiated in the epidermis. Several teams have demonstrated the activation of the plant's defence mechanisms via the synthesis of certain enzymes, including heat shock proteins. HWT therefore has a dual mode of action.

The main rots observed on fruit after leaving storage and packaging are lenticel rot, known as Gloeosporium rot, and rots caused by the genus Phytophthora. These are followed by Nectria canker, depending on the geographical area, and wound rots caused by several species such as Penicillium, Botrytis and Monilia. In conditions that are adapted to apples, the technique is not very effective against these wound rots. Scientific articles cite the effectiveness of the technique against Penicillium at a temperature of 55°C for 2 minutes. But at these temperatures, the majority of apple varieties show burns on the epidermis. On the other hand, HWT has proved effective against Gloeosporium rot and Phytophthora spp1 . Most of the trials carried out within the network concerned these diseases, and the application of hot water was always carried out by dipping.

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