Xylella fastidiosa subsp. fastidiosa Wells et al., 1987

Pierce's disease

This bacterium, very polyphagous and classified as a pest *, has been reported on many plant species on the American continent, from Argentina to Ontario (in Canada), but also in Asia (in Taiwan only), and more recently in Italy. It was first described on vines in the USA in 1892 by Newton Pierce. It caused considerable losses for example in Southern California, destroying more than 35,000 hectares of vines, causing the displacement of the production towards the north. It is also reported in Venezuela on this plant. X. fastidiosa seems capable of affecting several species of the genus Vitis **: V. vinifera , as well as the American species V. labrusca and V. riparia . The other American species used as rootstocks ( V. aestivalis , V. berlandieri , V. candidans , V. rupestris ), as well as the hybrids derived from them, are resistant, as is V. rotundifolia .

This bacterium has not yet attacked European vineyards to date.

It is also found naturally in the coastal plains of the Gulf of Mexico, where V. vinifera and V. lambrusca cannot be cultivated due to their sensitivity and the high parasitic pressure exerted by this bacterium. The situation is roughly comparable in California where it is difficult to grow vines in rather warm climatic zones. On the other hand, it does not seem to spread easily to other cultivated areas

Classification : Bacteria, Proteobacteria, Xanthomonadaceae

English name  : Pierce's disease , California vine disease, etc.

* Alert

A strain of X. fastidiosa appeared from 2013 in Italy on olive, oleander, almond and oak. Laboratory investigations in this country reveal that the strain detected is X. fastidiosa subsp. paucane and that it would act in complex with parasitic fungi belonging to the genera Phaeoacremonium and Phaeomoniella . Note that this subspecies is not aggressive on the vine.

Until now, the main factor conditioning the spread of this bacterium in a given area was the climate, this bacterium especially appreciating sub-tropical conditions, as well as its potential vectors. Also, the establishment in Europe of X. fastidiosa should concern warmer areas such as southern Spain, the Italian peninsula and the low plains of Greece, which have winter temperatures approaching those of the southern United States. United. But be careful, the biologies of potential European vectors could foil these estimates.

It should be noted that this bacterium has been reported twice in France recently: in the Paris region (in Rungis on a coffee plant) and in July 2015 in Corsica on myrtle leaf polygale (P olygala myrtifolia plants ) in the Propriano region, and on Spartium junceum . The subspecies prevalent in France and different from that operating in Italy. This is X. fastidiosa subsp. multiplex that also does not attack the vine.

** Morphology and known strains

X. fastidiosa is a rod-shaped, Gram-negative, xylem-confined bacterium. It reveals rather characteristic wavy cell walls, is not flagellated, and does not form spores.

It should be noted that at present many uncertainties remain concerning the diversity of strains of X. fastidiosa , their host ranges and their distribution in the world. Although X. fastidiosa is considered a single species, there is a complex and ill-defined relationship between hosts and strains in the field.

Currently, four subspecies are generally recognized by the scientific community, differing in their host range:

- X. fastidiosa subsp. fastidiosa (vine, almond, alfalfa, and coffee);

- X. fastidiosa subsp. multiplex (almond, plum, peach, several species of hardwoods and other ornamental species);

- X. fastidiosa subsp. pauca (especially citrus, orange, coffee);

- X. fastidiosa subsp. sandyi (laurier rose, hémérocalle, jacaranda, magnolia).

This host specificity observed in the preceding subspecies appears to be relatively reliable. In fact, strains capable of attacking the vine have been observed in several of these subspecies, with different aggressiveness.