Informative value of canker morphology on the presence or absence of virus infection in chestnut blight cankers

Abstract

Summary Chestnut blight destroyed the native chestnut forests in North America and also severely affected the European chestnut trees after its introduction in the 20th century. The ascomycete fungus Cryphonectria parasitica is responsible for this serious disease and causes lethal bark cankers on susceptible chestnut trees. In Europe, however, an infection of C. parasitica with Cryphonectria hypovirus 1 (CHV‐1) causes hypovirulence in C. parasitica and reduces the severity of the disease. Hypovirulence biologically controls chestnut blight in many regions to date. In this study, our goal was to determine morphological canker characteristics that are indicative of virus presence or absence in C. parasitica. We investigated 677 chestnut blight cankers from seven different geographic locations across Europe. For each canker, we assessed canker length, stem encircling, canker depth, presence of sporulation, canker activity and virus infection. We statistically analysed the informative value of these morphological characteristics for the presence or absence of CHV‐1. However, we did not find reliable indicators. Our logistic regression analysis revealed that virus infection of C. parasitica is not clearly related to canker morphology. This implies that fungal isolations from chestnut blight cankers and assessments in the laboratory are required to determine infection with CHV‐1 unequivocally.

Cryphonectria hypovirus 1 (CHV‐1) survey reveals low occurrence and diversity of subtypes in NE Spain

“…Thus, we targeted healed and healing cankers, perhaps limiting our sample base. As later reported by Bryner et al (2013), canker morphology does not always reflect hypovirus infection. Canker morphology may also be influenced by host ontogenic factors or environmental conditions (Bazzigher 1980), or by the partial blight resistance of European chestnut (Graves 1950;Berry 1960).…”

“…In addition, the incomplete movement of hypovirus within fungal mycelium or the possible disappearance of CHV‐1 in healed cankers (Bryner et al. ) may also explain the low presence of CHV‐1 among our sampled cankers. Thus, our sampling design could have only detected a part of the hypovirus population.…”

“…Canker morphology may also be influenced by host ontogenic factors or environmental conditions (Bazzigher 1980), or by the partial blight resistance of European chestnut (Graves 1950;Berry 1960). In addition, the incomplete movement of hypovirus within fungal mycelium or the possible disappearance of CHV-1 in healed cankers (Bryner et al 2013) may also explain the low presence of CHV-1 among our sampled cankers. Thus, our sampling design could have only detected a part of the hypovirus population.…”

“…CHV is a non-encapsidated cytoplasmatic virus that belongs to the Hypoviridae family (Dolja and Koonin 2012). CHV-1 infection leads to superficial, swollen cankers with reduced growth and less sporulation compared with active cankers (Heiniger and Rigling 1994), although the lack of a clear relation between canker morphology and virus infection of C. parasitica has been recently reported (Bryner et al 2013). Hypovirus-infected C. parasitica isolates often show white colour and reduced sporulation on PDA growth medium, compared with non-infected isolates (Peever et al 2000).…”

Toxicity of plant essential oils to Cryphonectria parasitica (Murr.) barr, the causal agent of chestnut blight

“…The tree may react to canker by producing epicormic shoots below it. Non-lethal, superficial or callusing cankers on susceptible host trees are usually associated with mycovirus-induced hypovirulence (Bryner et al, 2013).…”