engleski

Biological control of chestnut blight: effect of host diversity on the prevalence of biocontrol agent – Cryphonectria hypovirus 1

The term “biological control” and its abbreviated synonym “biocontrol” describe the use of pathogen antagonists in suppression of diseases. Biocontrol of a dangerous plant disease, chestnut blight, which is caused by a highly pathogenic fungus Cryphonectria parasitica is enabled by naturally-occurring virus Cryphonectria hypovirus 1 (CHV 1). CHV 1 reduces fungal virulence and reproductive capacities. The fact that this virus attacks only one host species makes it a perfect biocontrol agent. Unfortunately, the spread of this virus is limited by the vegetative (in)compatibility (vc) system of the fungal host. The first comprehensive research of C. parasitica in Croatia started ten years ago and revealed considerably higher populations’ vc type diversity than in southeastern Europe and slightly lower than in western Europe. The same study also showed high proportion of hypovirulent (CHV 1 – infected) isolates in many tested populations, indicating that CHV 1, responsible for the natural biocontrol of the chestnut blight disease, is widely spread in C. parasitica populations. One population from Ozalj, which was included in that study, was observed through the period of ten years. A decade ago, the research showed dominance of a single vc type, EU1, which accounted for more than 60% of all analyzed fungal isolates from that population. Furthermore, little less than half of all analyzed isolates were infected with CHV 1, implying successful natural biocontrol of the disease in this population. However, our recent study in 2014 showed that the EU1 vc type hegemony in Ozalj slowly waned and currently this particular vc type accounts for less than 30% of analyzed isolates. Other vc types’ frequencies – most notably EU2 and EU5 increased, while some new, previously unreported vc types emerged. This new genotypes might have migrated from nearby populations or have emerged as a result of sexual reproduction. The most concerning finding of our study was a decrease in percentage of hypovirulent isolates in Ozalj. The obvious reason for that is the fact that the transmission of virus between different vc types is usually difficult or impossible while it occurs with high frequency between the isolates of the same vc type. Therefore, with the increase of fungal vc type diversity, human-mediated biocontrol using well defined CHV 1 isolates (strong and moderate) might be needed to complement naturally-occurring hypovirulence in chestnut protection attempts.

biocontrol; Cryphonectria parasitica; diversity; CHV1

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