engleski

In search for optimal virus strain for biological control of chestnut blight

Cryphonectria parasitica (Murr.) Barr is an introduced phytopathogenic fungus and causal agent of chestnut blight, a devastating disease of chestnut trees. Since its introduction into Europe in the first half of the 20th century it has caused serious damage in the stands of European chestnut (Castanea sativa Mill.). After initial disease outbreak chestnut populations started to recover due to the natural biocontrol of C. parasitica with cointroduced dsRNA virus Cryphonectria hypovirus 1 (CHV1). CHV1 reduces the virulence of C. parasitica, a phenomenon called hypovirulence, thus enabling the recovery of chestnuts. Based on the genetic variability of European populations five subtypes of CHV1 have been defined, differing in their virulence towards the fungal host. In several European countries chestnut blight biocontrol by application of selected hypoviulent C. parasitica strains on active cankers is implemented. The success of biocontrol is limited by high diversity of fungal vegetative (vc) types which impedes the spread of the virus through C. parasitica populations. Thus the best practice approach in the biocontrol has to take into account specificities of local C. parasitica and CHV1 populations. The aim of the work was to investigate the effect of Croatian virus strains on different Croatian C. parasitica isolates in order to find optimal virus candidate for use in biocontrol treatments of chestnut blight in Croatia. Virus isolates were characterised as “strong” or “weak” based on their impact on fungal growth on chestnut stems. Then they were transferred into three fungal isolates of the same vc type by hyphal anastomosis. The effect of the virus on fungal radial growth in vitro and on the activity of fungal stress response enzymes catalase, glutathione S-transferase and superoxide dismutase was measured. The presence of CHV-1 in the C. parasitica resulted in reduced fungal growth in most virus-fungus combinations. The activities of fungal stress enzymes were affected by the presence of CHV-1, but the direction and intensity of the effects depended on virus and fungus isolate and their combination. Therefore, the “strength” of the virus is not solely determined by its subtype but is very strongly affected by both host and pathogen genotypes. This further confirms that possible biocontrol efforts have to take into account local specificities of C. parasitica and CHV1 populations.

biocontrol ; chestnut blight ; hypovirulence

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