Recent insights into the pandemic disease butternut canker caused by the invasive pathogen Ophiognomonia clavigignenti‐juglandacearum

Abstract

In the 25 years following the initial 1967 report of the disease, butternut canker was able to quickly spread throughout the entire range of butternut (Juglans cinerea) in North America, from Minnesota in the upper Midwest to Tennessee in the south and Quebec in the northeast. The speed of this dispersal is notable as butternut trees do not make up a significant proportion of any single forest type. Instead, they are usually found sparingly in most mixed hardwood forests. In this review, we synthesize the current knowledge of the invasion process of the butternut canker pathogen, Ophiognomonia clavigignenti-juglandacearum, an invasive fungal pathogen, that as its emergence has spread across North America and is now found wherever butternut naturally occurs. Taxonomic studies have determined that the fungus belongs in the genus Ophiognomonia, which includes a number of saprophytes, endophytes and pathogens of members of the Fagales, rather than the genus Sirococcus, which includes several important pine pathogens. The ability of fungus to be dispersed by rain splash, transported on and in beetle vectors, transmitted by infected seed and successfully colonized several species of Juglans and Carya have all likely contributed to the rapid increase in abundance and severity of disease and tree mortality in the invaded forest ecosystems. Recent genomic and population genetic analyses have determined that there were at least three emergence events. A less virulent strain of the fungus likely has been present in the north eastern United States for over a century, but it was the emergence of a more virulent strain of the fungus in Minnesota and Wisconsin in the 1960s that resulted in range-wide mortality and pushed butternut to be listed as an endangered species in Canada and a number of states in the United States.

Effects of Host Variability on the Spread of Invasive Forest Diseases

“…Nair, Kostichka & J.E. Kuntze) Broders & Boland, which was dispersed over longer distances by beetle vectors and infected seeds [74]. Similarly, a fragmented distribution of some white pines (e.g., Pinus strobiformis Engelm.)…”

Estimating heritability of disease resistance and factors that contribute to long-term survival in butternut (Juglans cinerea L.)

“…A stem canker disease of butternut caused by the ascomycete fungus Ophiognomonia clavigignenti-juglandacearum (Oc-j) (=Sirococcus clavigignenti-juglandacearum) (Broders and Boland 2011) was first reported in the late 1960s (Renlund 1971), although it was most likely introduced decades prior in some areas (Broders et al 2012(Broders et al , 2014. Cankers generally initiate in small crown branches, spreading to main limbs and the trunk (Nair et al 1979;Ostry and Woeste 2004) and causing mortality either when cankers coalesce to girdle the stem or when secondary decay results in breakage or windfall.…”

qPCR quantification of Ophiognomonia clavigignenti‐juglandacearum from infected butternut trees under different release treatments

“…It is interesting to note that Broders et al. confirmed in 2015 (Broders, Boraks, Barbison, Brown, & Boland, ) that another Asian species, an endophyte isolated from Acer truncatum (Sun, Guo, & Hyde, ), appears to be the closest relative of O. c‐j . The assay that we described in this study was generally able to discriminate O. c‐j from its sister taxa but, we cannot entirely rule out cross‐reactivity with cryptic species closely related to O. c‐j .…”