INFLUENCE OF NITROGEN NUTRITION ON THE FRUIT QUALITY OF VIRUS-FREE AND VIRUS-INFECTED APPLE TREES

Over a period of three years virus-free and virus-infected (i.e. with latent viruses, apple mosaic virus, rubbery wood) apple trees (Cox’s Orange Pippin/M.9) were investigated.
Trials were conducted using 50 litre containers and a flooding method.
During this period the trees received three different nitrate nitrogen levels (4,8 and 12 mmol NO₃-l^-1). Virus-free trees flowered better in the third year than virus-infected ones.

Fruits were harvested in September 1978 and analysed for components such as carbohydrates, malic acid and mineral elements.
The rest of the fruits were stored at low temperature for investigations of bitter pit.
The analyses showed the following results: fruits taken from apple mosaic virus-infected trees showed higher contents of glucose and fructose independent of their nitrogen nutrition.

Virus-infected trees had the highest sucrose content.
The starch content was lowest in trees infected with apple mosaic virus.
There appeared to be an inverse relationship between the contents of sugars and starch, i.e. a low glucose and fructose content corresponded to a high starch content and vice versa.

No differences were observed in the malic acid content.
In spite of this, due to differing sugar contents, differing sugar/acid ratios were obtained for fruits of virus-free and virus-infected trees.

Changes in mineral content were found both with the nature of viral infection and the level of applied nitrogen.

Symposium on Mineral Nutrition and Fruit Quality of Temperate Zone Fruit Trees

H. HELM

https://doi.org/10.17660/ActaHortic.1980.92.41