Genetically modified plums in Europe

Plum pox virus (PPV) causes severe disease in plums and other stone fruit trees throughout Europe, and more recently the Americas. Transmitted by aphids and spread long distances by transferring infected plant material to new locations, the only defence against the disease is to destroy all infected trees.

The EU-funded 'Intercontinental and temporal research studies on transgene engineered in plums' (INTEREST) project is characterising a GM plum tree as a potential PPV-resistant cultivar. The GM cultivar, HoneySweet, contains a gene from the virus that protects the plant through acquired immunity, much like vaccination in animals.

In over 13 years of field testing in the Czech Republic, researchers have shown that HoneySweet is highly resistant to PPV and could benefit European agriculture. INTEREST is therefore evaluating HoneySweet's potential as a model GM fruit tree, particularly to address concerns about introducing this technology into the European environment.

Researchers first studied the resistance mechanism and durability of HoneySweet plants grown in different agro-climatic conditions in the Czech Republic and the United States and in a greenhouse controlled condition in France. They also looked at different virus exposure levels in the EU.

INTEREST tested virus resistance using both artificial graft inoculation, where an infected part of a susceptible plant is grafted onto virus-free rootstocks, and natural aphid transmission. Importantly, through these artificial conditions, they detected PPV only in leaves situated close to the inoculation point, indicating that the virus could not spread to other tissues.

HoneySweet's fruit quality and quantity was not affected by PPV infection, even when researchers added other severe plum viruses to increase the viral load.

While researchers are still collecting data on the PPV resistance mechanism, including how the GM-derived gene interacts with natural plant genes, INTEREST is showing great promise in terms of virus resistance and safety. In addition to economic benefits gained from combating PPV, the environment should benefit through reduced use of the insecticides normally required to kill aphids.