Apfip Ltd has been using the heat treatment process for over five years to eliminate viruses of economic concern from fruit tree propagating material for the betterment of the Australian Pome Fruit Industry.

Heat treatment of pome fruit planting material has been somewhat of a mythical subject in Australia with a low understanding of what it means, how it is carried out and what are its benefits. In most industry circles the urban myth has been "that heat treatment makes red apples green". The practical reality is that nothing could be further form the truth. Heat treatment has been standard procedure for virus elimination in Europe and North America for the past 30 years. It was adopted to eliminate the viruses of economic significance. Research in this area showed that there were significant improvement to orchard yields if trees were not infected. The certification systems that were setup to assure the virus status of planting material are still in operation and widely supported. Like all specialised operations there needs to be careful control of the process to ensure that mistakes are not made. There is now a large volume of evidence that shows that no detrimental pomological changes occur to the rootstocks and varieties that are heat-treated.

Heat treatment is a fairly straightforward process. It is conducted as follows; the infected rootstock or variety is propagated onto a vigorous rootstock (usually seedling) and growth established in a hot house. The tree is then introduced into a growth cabinet where temperature and light are controlled. After a period of acclimatisation the temperature is increased so that it averages 37 degrees Celsius for a minimum of 70 consecutive days with light for around 16 hours per day. In this environment the ability of the viruses to develop is hindered to the point that they are unable to spread to the growing tips on the tree. The result is the growing tips are potentially uninfected by the viruses. A number of tips are removed and shoot tip grafted onto virus-tested rootstocks (usually seedlings) and grown in a hot house. Once established these new trees are tested to see if the viruses have been removed. Several trees of each variety or rootstock are heat treated to ensure that there are plenty of tips to test as some may still be infected. From there the trees are planted in the field and encourage to crop to check trueness to type.

Click here to view the heat treatment flow chart.