Hola Susana,
you are right, your fungus is likely around E. leptoplaca and E. lejoplaca. Eutypa maura can be ruled out because it is distinctive in having more immersed perithecia and the wood markedly blackened beneath the surface between the necks.
The most reliable difference between the two species is the reaction of the apical apparatus to iodine.
I suggest you follow Rappaz's procedure with a short pretreatment of perithecial content in 3% KOH and mounting in Melzer's reagent. This leads to a more drastic retraction of the ascal content than IKI and makes the apical apparatus easier to make out. Remember it is in fact subapical, at the bottom of a shallow tubular structure. The thing is to work on a very small amount of material in order to make a very thin slide, otherwise interpreting the iodine reaction is most often tricky, especially in species where the apical apparatus is very small. This applies to all species of Diatrypaceae since the character of reaction to iodine is crucial.
Come back with a clear result, whatever how long it takes!
Cheers,
Jacques

Salut Jacques

¿C'est la réaction tout aussi intense avec KOH + Melzer, qui KOH + IKI?

J'ai fait quelques préparations KOH + IKI (je n'ai pas de Melzer) et pense que c'est positif, j'observe dans les asques un couple de très petits points que je dirais sont bleus.

Que pensez-vous?

Saludos

Susana

Hola Susana,
ton excellente photo montre bien une réaction positive, amyloide. Tu peux donc écarter lejoplaca.
E. leptoplaca est beaucoup plus fréquente sur Fraxinus, tu devrais la trouver facilement sur des petites branches tombées récemment avec le vent et tu pourras ainsi lui comparer ta récolte.
Amitiés,
Jacques

Muchas gracias Jacques

Saludos.
Susana