Role of Fresh Dead Wood in the Epidemiology and the Biological Control of the Chestnut Blight Fungus

Abstract

The invasive fungus Cryphonectria parasitica, the causal agent of chestnut blight, is able to survive and sporulate on the bark of fresh dead Castanea sativa wood for at least 2 years. Here, we experimentally investigated the role of fresh dead wood in the epidemiology of chestnut blight, specifically in the spread of the hyperparasitic virus Cryphonectria hypovirus 1, which acts as biocontrol agent of C. parasitica. A total of 152 artificially initiated, virulent bark cankers in four chestnut stands were treated with virus-infected asexual spores originating either from sporulating dead wood or from a spore suspension. Molecular markers for both the virus and the fungal carrier were used to examine the spread of the applied biocontrol virus. Fourteen months after treatment, 42 to 76% of the conidial spray-treated cankers and 50 to 60% of the cankers exposed to a sporulating dead stem had been virus infected by the applied hypovirulent conidia in all four study sites. Virus infection reduced canker expansion and promoted canker healing (callusing). Thus, fresh chestnut dead wood may play an important role in supporting the successful spread of natural hypovirulence in chestnut forests. Further, combined with the application of virus-infected conidial suspensions, it may help promote the establishment of artificially released hypoviruses in chestnut stands to control chestnut blight.

Testing the Pathogenic Potential of Cryphonectria parasitica and Related Species on Three Common European Fagaceae

“…Considering the climatic changes predicted for European chestnut growing regions, like an increase of extreme weather events and of drought periods (Giorgi and Lionello, 2008;Mariotti et al, 2015), it would be worth to further investigate the effect of such tree stressors on the pathogenicity of these two Cryphonectria species. As observed in C. parasitica (Prospero et al, 2006;Meyer et al, 2019), the ability of C. naterciae and C. japonica to colonize and saprophytically grow on recently dead chestnut stems could contribute in building up a reservoir of inoculum. This could help both species to become successfully established and spread in European forests.…”

“…The inoculation points were sealed with tape and the developing lesions were measured every 2 weeks for 4 months. The length and the width were recorded, and lesion area was calculated with the formula for the ellipse area, since lesions had an approximately elliptical shape (Dennert et al, 2019;Meyer et al, 2019). At the end of the experiment, the final lesion area was recorded and used for further analysis.…”

“…By contrast, in Europe the C. parasitica epidemic on European chestnut (Castanea sativa) showed a milder course due to the appearance and spread in the C. parasitica population of a hyperparasitic mycovirus (CHV-1) that acts as biological control agent, and to higher resistance of C. castanea compared to C. dentata (Rigling and Prospero, 2018). The pathogen can also survive and readily sporulate on fresh dead wood, which is considered to have an important epidemiological role (Prospero et al, 2006;Meyer et al, 2019). Although C. parasitica is considered a primary pathogen only on C. dentata and C. sativa (Anagnostakis, 1987;Bragança et al, 2011), it has also been occasionally detected on various Quercus species in different European countries, such as Greece (Tziros et al, 2015), the Czech Republic (Haltofová et al, 2005), Italy (Biraghi, 1950;Dallavalle and Zambonelli, 1999) and Slovakia (Adamčíková et al, 2010).…”

Differing Responses to Cryphonectria parasitica at Two Indiana Locations

“…Alternative means used to investigate resistance levels have ranged from backcrossing [70] and interspecific crosses [43] to the generation of transgenics [71], genotyping [60] and genome editing [72]. New research published by Meyer et al [73] noted C. parasitica and the CpHV can survive on the bark of fresh dead chestnut for over two years. This suggests fresh dead wood could be used as a vector for transmission of both agents in the forest, recommendations for the removal of fresh dead chestnut from the forest may be detrimental if CpHV is present [73], and that time is a critical factor [74].…”

Testing the pathogenic potential ofCryphonectria parasiticaand related species on three common European Fagaceae

“…By contrast, in Europe the C. parasitica epidemic on European chestnut (Castanea sativa) showed a milder course due to the appearance and spread in the C. parasitica population of a hyperparasitic 63 mycovirus (CHV-1) that acts as biological control agent, and to higher resistance of C. castanea 64 compared to C. dentata (Rigling and Prospero, 2018). The pathogen can also survive and readily 65 sporulate on fresh dead wood, which is considered to have an important epidemiological role 66 (Prospero et al, 2006;Meyer et al, 2019). Although C. parasitica is considered a primary pathogen 67 only on C. dentata and C. sativa (Anagnostakis, 1987 In this study, we aimed to compare the parasitic and saprotrophic ability of the Asian C. japonica 81 with that of an invasive species already established in Europe (C. parasitica) and a native European 82 species (C. naterciae).…”