Pythium oligandrum: a biological agent to control Esca disease?

Since the 2001 ban on using sodium arsenite in France, no chemical solution has been able to control the damage caused by the pathogens responsible for Esca. Researchers in the INRA Joint Research Unit for Vine Health and Agroecology (SAVE) in Bordeaux have studied the potential of Pythium oligandrum as a biological agent in the context of an Esca control strategy.

Esca may be present in two forms: a chronic, slow-developing form, which causes discoloration between the nerves of leaves ("stripy" symptoms), and an apoplectic or severe form, characterised by the rapid die-back of some or all of the stock. Several pathogenic agents are responsible for vine stock blight, the best known being: Phaeomoniella chlamydospora, Phaeoacremonium aleophilum, Botryosphaeria spp and Fomitiporia mediterranea.

In this present case, the scientists assessed the potential of Pythium oligandrum to endow the vine stock with resistance against attack by P. chlamydospora (Pch). P. oligandrum is an oomycete already known as a biological control agent, and has two modes of action: it exerts an indirect effect by inducing resistance in plants, and a direct effect by controlling the development of rhizosphere pathogens (via mycoparasitism, antibiosis and nutrient competition).

The study was carried out in the Bordeaux region: twelve different vineyards, aged between 20 and 25 years and planted with the same variety (Cabernet Sauvignon) were selected. They presented three different soil textures: silty clay, sandy clay and gravel. In each vineyard, root samples were collected at a depth of 30 centimetres from 10 plants chosen at random.

Whatever the soil type, the scientists were able to isolate more than 40 oomycete strains from the rhizosphere around the vine plants. After 10 days of incubation in the dark at 25°C, 35 of them were identified as belonging to the P. oligandrum species. The DNA of each purified strain was then extracted from the mycelium using a CTAB (Cetyl Trimethyl Ammonium Bromide)-based method, and amplified by PCR. The DNA sequences thus obtained were analysed using the GenBank database, which enabled the detection of some genes implicated in eliciting the defences of plants: the "oligandrine" and "POD1" genes.

Experimental system

The Cabernet Sauvignon stocks were planted in a greenhouse, 2 months before the fungi were introduced onto the plants. The experiment was performed according to a randomised 3-block system, with 30 plants under each mode. The experimental conditions applied to each batch of 30 plants were as follows: batch 1 was inoculated at the level of the roots with P. oligandrum strain 1; batch 2 was inoculated at the level of the roots with P. oligandrum strain 2; batch 3 was infected by P. chlamydospora (Pch) on the trunk; batch 4 was inoculated with P. oligandrum strain 1 and then, a week later, inoculated with Pch; batch 5 was inoculated with P. oligandrum strain 2 and then, a week later, inoculated with Pch; batch 6 were control plants with a hole in the stem and the roots of batch 7 were not inoculated with either P. oligandrum or Pch.

The course of root colonisation by P. oligandrum was followed by sampling 270 root fragments between August and December 2010. Damage due to Pch was assessed at the end of the 4-month trial period by sectioning the trunks of 30 plants from each batch. The number of plants affected by necrosis was calculated by observing the length of the brownish lesions.

This study demonstrated for the first time that P. oligandrum frequently colonises the roots of vine stock. It is therefore well-suited ecologically to the conditions prevailing in Bordeaux vineyards. It can improve the protection of these vines against a fungus implicated in vine trunk diseases, as testified by the induction of resistance in plants against Pch attack.

This research was carried out in partnership with the Biovitis in Saint-Etienne de Chomeil (15) and the CNRS Joint Research Unit for the Environment and Microbiology in Pau (Université de Pau et des Pays de l'Adour).

Contact(s)
Scientific contact(s):

  • Jonathan GERBORE (+335 57 12 26 39) UMR1065 SAVE Santé et Agroécologie du Vignoble INRA Domaine de la Grande Ferrade 71 avenue Edouard Bourlaux 33883 VILLENAVE D'ORNON CEDEX
  • Patrice REY (+335 57 12 26 14)

For further information

  • Jonathan Gerbore, Emilie Bruez, Jessica Vallance, Damien Grizard, Catherine Regnault-Roger, Patrice Rey, “Protection against a vine trunk attack by Phaeomoniella chlamydospora is concomitant with root colonization by oomycete Pythium oligandrum”, Multitrophic Interactions in soil, IOBC/wprs, Bulletin Vol. 71, 2011, pp. 31-35.