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August / September 2022

6 Viruses and a Viroid

SA Fruit Journal: August / September 2022

The essentials explained for pome- and stone-fruit growers seeking to prevent losses. By Anna Mouton

The first thing to realise about viruses and viroids is that signs of infection in fruit trees show up most clearly in financial statements. South African stone-fruit growers were recently reminded of this with the emergence of plum marbling. Plum marbling is caused by a viroid that renders fruit unmarketable due to its impact on external appearance and internal quality.

Viral infections are associated with reduced growth and yields in both pome- and stone-fruit trees. Researchers in New Zealand and Germany found growth reductions of about 40% in apple trees infected with apple mosaic virus compared to non-infected trees. A South African study showed that yields in apple trees infected with apple mosaic virus were reduced by a third. Similar – and worse – outcomes have been reported for some viral infections of stone fruit.

So what exactly are viruses and viroids? And what can growers do to protect their orchards?

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