Description of the fungus

• The perfect form (teleomorph), Eutypa lata , is characterized by perithecia developing into a stroma blackish visible on dead wood in areas where the bark is exfoliated (Figures 1 and 2). These globular perithecia (300 to 500 µm) with a fairly short neck give the surface of the colonized wood a bumpy appearance. They contain asci (separated by paraphyses) cylindro-claviform, rounded at the top, provided with a long pedicel (figure 3); their size is approximately 30-60 x 4-7 µm. Each ascus typically contains 8 ascospores that are arching (banana-shaped) pale yellow to light brown in color and measure 5-11 x 1.5-2 µm (Figure 4).

• The imperfect form (anamorph), Libertella blepharis. AL Smith, is characterized by pycnidia black (figure 5), sub-globose 200 to 300 µm, forming on wood generally in areas where perithecia will appear later. These pycnidia emit a cirrh (a sort of fine gelatinous cord) (figure 6) in which are embedded stylospores characteristic arcuate (pycniospores) measuring 18-25 x 1 µm (figure 7).

• Isolation, conservation on artificial medium : E. lata is easily isolated in dead wood or on the border with healthy wood and cultivable in the laboratory on a nutrient medium on which it develops a white mycelial colony, showing more or less abundant aerial filaments joining together in small cords. As they age, colonies turn gray or brown in color and pycnidia appear after 4 to 8 weeks of incubation (Figure 8). Like many mushrooms, its thermal optimum is between 20 ° C and 25 ° C. But it is also capable of germinating from 1 ° C and growing slowly at low temperatures of around 5 ° C.

Note that another species of Eutypa pathogenic on grapevine, E. leptoplaca (Mont.) Rappaz 1987, has been identified in California as well as two related species, Eutypella vitis Ellis & Everh. (1892), and Cryptovalsa ampelina (Nitschke) Fuckel 1870. The first is morphologically different, the second is quite similar in culture, the three seem secondary in France.