Variations in the pathogenicity of Apiognomonia quercina isolates from different hosts.

The pathogenic specialization of Apiognomonia quercina isolates from different hosts was determined on a wide range of target host species. Isolates were taken from 3-cm-diameter twigs of declining Quercus cerris, Q. frainetto, Q. pubescens and Q. robur, growing in eight regions of Italy: Abruzzo, Campania, Emilia-Romagna, Liguria, Marche, Toscana and Umbria. Isolates were also collected from Castanea sativa and Fagus sylvatica. Eighteen 2-year-old seedlings from each of these species were inoculated by placing a 0.5-cm-diameter plug of mycelium from 10-day-old colonies on the wood of each seedling. The length of visible lesions was measured at 7, 14, 21, 35, 42, 49 and 56 days after inoculation. With only two exceptions, isolates from all host species caused infections on all the target hosts, though with different mortality rates. The exceptions that did not produce infections were isolates from F. sylvatica inoculated on C sativa, and vice versa, Q. cerris was the most susceptible to A. quercina infection. Differences in susceptibility between the target oak species was highly significant at P < 0.05 and P < 0.01. The most clear-cut finding was that isolates were most virulent when the source species was the same as the target host.