Diversity of Cryphonectria parasitica in callused chestnut blight cankers on European and American chestnut

Abstract

Infection of American and European chestnuts with the chestnut blight fungus Cryphonectria parasitica results in the formation of cankers, lesions caused by the growth of mycelia within bark tissue of the host plant. Infection of the fungus with Cryphonectria hypovirus 1 (CHV‐1) results in conversion of the mycelial phenotype from virulent to hypovirulent, thus allowing production of callus around cankers as a reaction by infected trees, rendering active into inactive cankers. In this study, we sampled one USA and six European chestnut stands and assessed frequency of hypovirulent C. parasitica and diversity of vegetative compatibility (vc) types present in calluses and randomly sampled cankers. Callused cankers on C. dentata at West Salem in the USA yielded significantly more hypovirulent C. parasitica isolates compared with four sampled populations on C. sativa, while all six sampled European populations did not show any statistically significant differences among themselves. We observed no correlation between hypovirulence frequencies in randomly sampled cankers and calluses, as well as no correlation of C. parasitica vc type diversity in calluses and residential populations of the fungus. Furthermore, even though we have observed calluses with more than one vc type, they do not occur regularly. Even when present in C. parasitica populations with high vc type diversity, no more than three different vc types were observed in a single callus.

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

“…The same authors reported 47.3% of C. parasitica hypovirulent isolates recovered in West Salem (USA) where hypovirulence had been artificially introduced. However, considering only all isolates of C. parasitica, the percentage of hypovirulent isolates in our study ranged from 88.9% in Valpaços to 82.9% in Vinhais, while the study of Ježić et al (2019) recorded on average more virulent isolates (64.7%) than hypovirulent isolates (35.3%). Studies performed by Shain and Miller (1992), where natural hypovirulence was established, show that CHV1 moves about 7.2 cm per week through the mycelium on the periphery of a virulent canker when the same vc type is present; however, it does not move extensively to the older parts in the centre of cankers.…”

“…C. parasitica virulent isolates were also isolated in a reduced percentage (0-11%), as well as a considerable percentage, of other non-C. parasitica species. Studies performed by Ježić et al (2019) to assess the abundance of hypovirulent C. parasitica strains from callused cankers revealed that the percentage of hypovirulent C. parasitica isolates recovered from healed cankers on C. sativa from different European countries, ranged from 9.47% to 51.6% where natural hypovirulence was established. The same authors reported 47.3% of C. parasitica hypovirulent isolates recovered in West Salem (USA) where hypovirulence had been artificially introduced.…”

Temporal changes in pathogen diversity in a perennial plant–pathogen–hyperparasite system

“…The difference may be due to the fact that most cankers sampled in 2019 were inactive (i.e., no fungal growth resulting in canker extension). Such cankers, although not lethal for the infected trees, are frequently CHV1‐free (Bryner et al, 2014; Ježić et al, 2019). CHV1 drastically slows down the metabolism of its fungal host, resulting in the inactivation of chestnut blight cankers.…”

“…Such cankers, although not lethal for the infected trees, are frequently CHV1-free (Bryner et al, 2014;Ježić et al, 2019). CHV1…”

Differing Responses to Cryphonectria parasitica at Two Indiana Locations

“…The C. parasitica fungus shows little genetic diversity, specifically within vegetative compatibility (vc) types, in studies from Azerbaijan [33], Spain [34], and Romania [35,36], but studies in Croatia and Slovenia report considerable diversity [37]. Increased diversity within vc types is often considered a negative outcome of sexual reproduction; however, these data may be misleading when natural populations rather than laboratory populations are examined [38][39][40][41][42][43][44].…”