Short and long term efficacy and prevalence of Cryphonectria parasitica hypovirulent strains released as biocontrol agents of chestnut blight

Abstract

Chestnut blight, Cryphonectria parasitica (Murrill) Barr, was reported in Portugal in 1989. The disease rapidly spread within the chestnut region of the Trás-os-Montes (the Northeast of Portugal). Eradication and mechanical/burning exclusion failed to control the disease and natural hypovirulence is still absent or of very low incidence. The introduction of human-assisted therapeutic hypovirulence is therefore required to control the disease. We presente here the efficacy of field applications (short and long term) of a locally characterized hypovirulent strain (CHV1-RBB111), by the punch method in two chestnut orchards (Valpaços and Vinhais). The Valpaços disease incidence was 68% (65 out of 96 trees) and in Vinhais it was 46% (78 out of 169 trees). In both locations, diversity of vegetative incompatibility (vc type) was low and largely dominated (> 85%) by a single vc type (EU11). In Valpaços, all cankers of the orchard were treated (63 cankers) and in Vinhais 31 trees (cankers) were treated. One year after application, field efficacy was very high with 93.8% of healed cankers in Valpaços and 90.3% in Vinhais, these values increased to 100% and 93.5% (respectively) after four years. The persistence of the introduced CHV1-RBB 111 strain was high and present in almost all treated cankers and it was dominant both inwards and on the application site revealing an endophytic behavior. The non-C. parasitica microfungi were abundant with 14 different species. Biscogniauxia mediterranea (De Not.) Kuntze was the most abundant in both orchards. Treatment with the introduced hypovirulent strain (CHV1-RBB111) was found to be effective in controlling chestnut blight with regeneration of cortical tissues and recovery of treated trees.

Molecular genetic variability of Cryphonectria hypovirus 1 associated with Cryphonectria parasitica in South Tyrol (northern Italy)

“…The low level of hypovirulence occurrence in South Tyrol could also be influenced by the current control strategies of chestnut blight that rely exclusively on sanitation and pruning of infected chestnut trees. In contrast to South Tyrol, many other European regions successfully use the artificial application of hypovirulent fungal strains as biocontrol agents against chestnut blight (Heiniger and Rigling, 1994 , 2009 ; Robin et al, 2000 ; Prospero and Rigling, 2016 ; Coelho et al, 2021 ). Although artificial inoculation of hypovirulent strains of C. parasitica was performed in South Tyrol in the 1990s (Maresi et al, 1993 ), more than 25 years have passed since the last application.…”

Various Population Structures of Cryphonectria parasitica in Cáceres (Spain) Determine the Feasibility of the Biological Control of Chestnut Blight with Hypovirulent Strains

“…Complementary DNA (cDNA) was generated using the High capacity cDNA Reverse Transcription Kit (Thermo Fisher) according to the manufacturer's protocol. A PCR test was conducted using primers EP 713-5 and R2280 [26] to amplify a 1439 bp region of open reading frame A (ORF-A) and primers ORF B-12F and ORF B-12R to amplify a 780 bp region of open reading frame B (ORF B) [32]. A PCR test was performed on a final volume of 20 µL, containing 1 µL of the cDNA, 0.2 µL each primer (10 pmol) and 2X PCR SuperMix (Genedirex).…”

“…In areas where no natural hypovirulence is present or it is low, the hypovirus (CHV-1) can be artificially introduced by field application of hypovirulent strains, which, by hyphal anastomosis, will transmit the hypovirus to the virulent C. parasitica population. Based on the transmission of hypovirulence, biological control programmes for chestnut blight have been implemented in France, Italy, Switzerland, Greece, Spain and Portugal [21][22][23][24][25][26]. In Europe, several molecularly identifiable subtypes of CHV-1 have been described, i.e., subtype I, F1, F2, E, D and G [27][28][29].…”

<i>Arcopilus aureus</i>: a valuable endophytic associate of hazelnut

“…Arcopilus aureus is also part of the endophytic communities of trees of notable economic importance, such as olive (Olea europaea) (Nicoletti et al, 2020) and chestnut (Castanea sativa) (Nicoletti et al, 2021). An endophytic strain from the latter plant has been identified in Portugal as a prospective antagonist in the control of bark canker caused by Cryphonectria parasitica (Coelho et al, 2022). Moreover, an endophytic isolate from P. nigra reduced the disease progress resulting aer inoculation of the canker agent Fusarium circinatum on Pinus radiata seedlings, indicating that it can find application in biological control of this pathogen (Martínez-Álvarez et al, 2016).…”