A method to detect and quantify Phaeomoniella chlamydospora and Phaeoacremonium aleophilum DNA in grapevine-wood samples.

Grapevines are sensitive to a wide range of fungal pathogens, including agents such as Phaeomoniella chlamydospora and Phaeoacremonium aleophilum that cause tracheomycosis. In the present study, a procedure for DNA extraction from grapevine woody tissue is first evaluated and shown to be suitable for quantitative analysis. Next, a multiplex real-time PCR method targeting the ß-tubulin gene of the pathogens and the actin gene of plant material is developed and its quantitative capability is verified. This protocol was evaluated in inoculated grapevine-wood samples and in young vines from a nursery and was found to be reliable and highly specific. Results obtained from inoculated cuttings show that the fungal colonization process must be considered regardless of the wood phenotype. An analysis of samples of young vines from the nursery shows that a high rate of contamination occurs at the basis of plants and that this contamination is associated with low quantitative values. This finding provides evidence that in vine nurseries, these fungi may be efficient soil-borne pathogens.

An Arabidopsis mutant with altered hypersensitive response to Xanthomonas campestris pv. campestris, hxc1, displays a complex pathophenotype.

SUMMARY The hxc1 mutant was identified by screening an EMS (ethylmethane sulphonate) mutagenized population of Arabidopsis Col-0 plants for an altered hypersensitive response (HR), after spray inoculation with an HR-inducing isolate of Xanthomonas campestris pv. campestris (Xcc) (strain 147). The hxc1 mutant shows a susceptible phenotype several days after initiation of the interaction with the avirulent strain. This macroscopically observed phenotype was confirmed by measurement of in planta bacterial growth and by microscopical analysis. Interestingly, the hxc1 mutation acts very specifically. Hxc1 displays a pathophenotype identical to that observed in the wild-type with several extensively characterized avirulent and virulent bacteria, except in response to Pseudomonas syringae pv. tomato strain DC3000/avrRpm1, for which a partial loss of resistance was observed. Finally, the mutation causes an attenuation of expression of several defence markers regulated through different signalling pathways. Together, these data underline the complexity of this novel defence mutant, and support the hypothesis of a mutation affecting a key component acting during the first steps of the plant defence response leading to resistance to Xcc147 and Pseudomonas syringae pv. tomato containing the avr gene, avrRpm1.