Diversity of Cryphonectria parasitica, hypovirulence, and possibilities for biocontrol of chestnut canker in Albania

Abstract

Since 1967 when chestnut blight (Cryphonectria parasitica) was observed for the first time in Albania
several field surveys have been carried out in chestnut (Castanea sativa) stands and have emphasized
the widespread presence of the disease. About 30% of surveyed trees showed different stages of
decline. Different proportions of C. parasitica morphotypes (normal/orange, intermediate, white) were
detected when isolates were grown on agar media in the laboratory. About 57% of isolates showed
normal pigmentation suggesting virulence, while 42% showed intermediate morphology. Less than 1%
(or five isolates) was identified as hypovirulent based on detection of dsRNA of virus. Five European
vegetative compatibility (vc) groups, EU-1, EU-2, EU-3, EU-10 and EU-12 were identified in four districts
(Pogradec, Tropoje, Tirana and Elbasan) with dominant chestnut forests. EU-12 was the dominant vc
type making up 39% of isolates studied. Transmission of dsRNA between virulent and hypovirulent
isolates was successful in laboratory conditions. Biological control using hypovirulent strains to
inoculate virulent cankers on chestnut trees in the field yielded between 46 and 84% of heavily
calloused cankers, while around 30% of healthy trees that had not been inoculated produced heavily
calloused cankers, suggesting natural spread of hypovirulence.