
Pest/Pathogen of the Month: February
Scientific name: Elsinoe necatrix
Common name: Eucalyptus scab and shoot malformation
Elsinoe was introduced by Raciborski (1900) to accommodate a fungus that caused scab-like lesions on plant tissue. The genus name Elsinoe, interestingly, was taken from the name of the heroine in the play Iridion by the Polish poet and dramatist Zygmunt Krasiński.
The serious disease, recently named as Eucalyptus scab and shoot malformation, was first observed in North Sumatra, Indonesia in 2014. However, the causal agent was discovered only recently as a novel species of Elsinoe. The name of the pathogen is derived from the Latin word “necatrix” (killer, murderess) to refer to the destructive impact that the disease has on its Eucalyptus hosts.
The disease is characterized by black necrotic spots that initially appear on young leaves and petioles, which become scab‐like as the lesions age. Infected trees respond to infection by producing shoots with small leaves that commonly appear feathered. Severely affected clones usually die after a number of successive infection cycles, generally over a period of two to three years.
The origin of Elsinoe necatrix is unknown, but evidence suggests that this is likely from an area where its Eucalyptus species are native. The pathogen would then have been accidentally introduced into North Sumatra where it has encountered susceptible host trees and an environment conducive to infection. In this regard, it should be considered as a high-risk pathogen and efforts should be made to prevent its spread to new environments.
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Pest/Pathogen of the Month: December
Scientific name: Approximately 1300 species distributed among five plant families e.g. Arceuthobium spp., Viscum spp., Phoradendron spp.
Common name: Mistletoe
In Nordic mythology the goddess of love and fertility, Frigg, had a premonition that her son Baldur would be killed. She went forth to obtain an oath from all object in the nine realms that they would avoid harming her son, but she overlooked mistletoe due to its small and innocent demeanour. Even though Baldur was invincible, a mistletoe dart created by the god of mischief, Loki, killed him where he stood. Today, mistletoe is considered an obligate aerial parasite of several cornerstone tree species in forestry. Berries of mistletoes are eaten by herbivores that spread the seeds through defecation, especially birds. Seeds may also be disseminated by wind or hydrostatic pressure. The seed of mistletoe is coated by a sticky substance called viscin that cements the seed and ensures the seed is not disturbed. In spring, the seed will germinate and produce a haustorium that penetrates the vascular tissues of the host plant to syphon water and photosynthetic metabolites. Leaves of the mistletoe are dark green, oval and rigid and flowers in summer may be white, yellow or red. White berries produced by this plant contain toxic compounds that are poisonous to humans and some animals. Mistletoe has been reported as a serious parasite of conifers, especially in Northern America and Europe. Infection leads to weakened trees which reduces growth and timber quality, allows for attack by insects and bole swelling at the base provides a home for decaying fungi. Infection at the crown may also impact the soil ecosystem and the optimal functioning of the ectomycorrhizal community of the tree. In the end, the tree may succumb to the combined damage of the different factors and this may lead to extensive yield losses. Mistletoes are distributed across several different plant families, however, in the Southern Hemisphere most of the species belong to the Loranthaceae and Viscaceae. Despite their fragile exterior, the oath of the mistletoe should never be treated as superfluous.

Pest/Pathogen of the Month: January
Scientific name: Pewenomyces kutranfy
Pewenomyces kutranfy is a recently-discovered fungal pathogen with the ability to girdle branches and trunks of the symbolic Araucaria araucana in Chile. This tree is of sacred importance to the indigenous Mapuche people in Chile, and from whose language, Mapudungun, the pathogen’s name was derived: Pewen being the name for A. araucaria, and kutran, meaning disease.
Pewenomyces is a monotypic genus inside the Coryneliaceae. This family contains other emergent canker pathogens including Caliciopsis pinea and C. Moriondi on Pinus species in North America and Europe respectively, and Hypsotheca pleomorpha on Eucalyptus spp. in Australia. Although Pewenomyces resembles these species morphologically, it is distinctly adapted to cold temperatures and, so far, has only been recorded from A. araucana. Research is still needed to disclose the rest of the story regarding P. kutranfy, although, the current hypothesis points to a native pathogen causing uncharacteristic disease epidemics as a result of climate change.
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Pest/Pathogen of the Month: November
Scientific name: Berkeleyomyces basciola and B. rouxiae
Common names: Black root rot
Black root rot is a fungal disease caused by two species from the genus Berkeleyomyces. These species are hemibiotrophic pathogens that penetrate living root tissue before killing them to obtain nutrients. Coalescing necrotic lesions lead to black discolouration of the roots, the character to which the disease attributes its name. Thus far, black root rot has been reported on more than 170 agricultural and ornamental plant species.
For nearly 100 years, the disease was thought to be caused by a single fungal species, Thielaviopsis basicola. However, in 2018 researchers at FABI showed that black root rot is caused by two cryptic sister species in a distinct generic lineage of the Ceratocystidaceae. Unfortunately, for most of the reported cases, the species responsible for the disease is unclear as identification relied on morphology rather than DNA evidence. With so little known regarding the true host range and distribution of these two species, concerns arise regarding their quarantine status and regulations surrounding their movement.
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