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Querina (R) florina, apple variety resistant to apple scab. © INRA, LE LEZEC Marcel

Novel mechanisms for more sustainable resistance to disease

Plum pox virus: rolling out resistant varieties wisely

INRA has developed a range of apricot trees that are resistant to plum pox, and recommends caution in implementing them. The Institute is also pursuing research to combine several sources of resistance.

By Pascale Mollier, translated by Inge Laino
Updated on 05/20/2015
Published on 01/26/2015

Symptoms of plum pox virus in peach.. © INRA, DUNEZ Jean
Symptoms of plum pox virus in peach. © INRA, DUNEZ Jean

Plum pox virus is a quarantine disease that affects fruit trees of the Prunus genus (peach, plum, apricot), making fruit unfit for consumption without, however, presenting a health risk. The disease is linked to a virus transmitted by aphids. It was introduced in France in the 1970s by trees imported from the Netherlands, and spread significantly in the 1980s, when the virus was identified in peach orchards.

Since then, research carried out by INRA in confined enclosures in Bordeaux and Avignon has resulted in several findings: the development of particularly accurate diagnostic methods, and the identification of a source of resistance in apricot trees. Within the Prunus genus, with the exception of cherry trees - of which all local varieties are resistant - apricot is the only tree endowed with resistance to the disease. All cultivated peach and plum trees are susceptible.

An imperfectly-characterised resistance

Researchers have identified a QTL (region of the genome consisting of several genes that play a role in resistance) linked to three markers that allow them to track resistance in pant varieties. However, while this QTL (called PPVres for Plum Pox Virus resistance) is necessary for resistance, it alone does not suffice. More specifically, among varieties that have this QTL, some are resistant while others are merely tolerant, which means they present symptoms of the disease when exposed to high doses of the virus. For now, the only way to differentiate between these two types of varieties is to subject them to an inoculation test in confined greenhouses where there is a strong presence of the virus. Further research aims to characterise the additional genetic factors that bestow resistance.

Resistant varieties: use with caution

A range of resistant apricot trees has been available on the market since 2013. Nevertheless, INRA recommends that these varieties be used with caution, and this for several reasons.

Firstly, propagating tolerant varieties is something to be avoided, because it can lead to the reproduction and adaptation of the virus, which can in turn put resistant varieties at risk.

Secondly, fruit trees consist of the combination of rootstock and a variety. In resistant varieties, only the graft is resistant, while the rootstock is susceptible to the virus. That is why it is preferable to use scions (1) to create plantations, as opposed to grafting with dormant buds (2). It is also important to keep an eye on the health of both rootstock and grafts. Lastly, regrowth of rootstock should be avoided and orchards closely monitored hand in hand with plant health authorities such as Fredon (3), SRAL (4) and INRA.

Forging ahead with research

Several programmes aim to better combat Plum Pox Virus:

  • Research for markers that are complementary to QTL PPVres, to better differentiate between the properties of resistance and tolerance (European programme KBBE Mars)
  • Research for new sources of resistance (inactivation of features in host that are essential to the virus (European programme KBBE Cobra)
  • Introgression of almond resistance in peach trees (European programme KBBE Cobra, FAM Sharka2 programme).

(1) Scion: one year-old grafted plant.
(2) Dormant buds: grafted rootstock whose scion shield bud has not yet developed.
(3) Fredon: Fédérations gionales de Défense contre les Organismes Nuisibles. French association that works with the State within the framework of the French rural Code to monitor plant health and combat pests.
(4) SRAL: service régional de l’alimentation, a branch of the French regional directorate for food, agriculture and forestry.

Scientific contact(s):

Associated Division(s):
Plant Biology and Breeding
Associated Centre(s):
Provence-Alpes-Côte d'Azur