''Rhabdocline laricis'', also known as ''Meria laricis'', is a

hyphomycete Hyphomycetes are a form classification of fungi, part of what has often been referred to as fungi imperfecti, Deuteromycota, or anamorphic fungi. Hyphomycetes lack closed fruit bodies, and are often referred to as moulds (or molds). Most hyphom ...

fungus in the family Cenangiaceae. In

larch Larches are deciduous conifers in the genus ''Larix'', of the family Pinaceae (subfamily Laricoideae). Growing from tall, they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains furt ...

conifer trees (''Larix''), it causes the plant disease larch needle cast, also known as meria needle blight. It is generally harmless in older trees. However, it causes browning of needles, which can slow growth, weaken overall resistance to opportunistic pathogens, and can sometimes outright kill seedlings, making ''Rhabdocline laricis'' a threat in tree nurseries. The fungus is sometimes confused with the similar ''Hypodermella laricis'', which causes larch needle blight. Both fungi can infest the same larch for a more virulent effect.

Taxonomy and nomenclature

The species is traditionally known as ''Meria laricis''. ''Meria'' was first described by

Jean Paul Vuillemin Jean Paul Vuillemin (13 February 1861 – 25 September 1932 in Malzéville) was a French mycology, mycologist born in Docelles. He studied at the University of Nancy, earning his medical doctorate in 1884. In 1892 he obtained his doctorate in sc ...

(Vuill.) in France in 1896. DNA analysis in the 1990s indicated its closest ancestor was the ''

Rhabdocline ''Rhabdocline'' is a genus of fungi in the family Hemiphacidiaceae. In 2010, the genus contained 3 species. ''Meria'' and ''Rhabdogloeum'' are anamorphs. Species * '' Rhabdocline laricis'' * ''Rhabdocline pseudotsugae'' * ''Rhabdocline weiri ...

'' genus, with the similarity significant enough for the genera of ''Meria'', ''Hartigiella'', and ''Rhabdocline'' to be combined as synonyms, with ''Rhabdocline'' chosen as the name of the merged genus.

Plant pathology

The needle cast and needle blight affects all species of larch, although it has been speculated that Japanese larches handle it better. It is detected by an appearance of yellow or brown spots on needles during or after wet weather. If moist conditions continue, colorless

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

develop on the lower surface of needles in clusters, and

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s begin to grow, appearing as white spots. Browned needles consumed by ''Rhabdocline laricis'' eventually wither and drop off the larch. The fungus is native to Europe, but has since spread elsewhere. Its first reported appearance in North America was in 1942, but probably spread there much earlier.

Disease cycle

''Rhabdocline laricis'' overwinters in the dead terminal tufts of fallen needles that adhere to twigs as well as fallen needles in general. Spores splashed up from these can activate an infection in spring. Dry weather suppresses ''Rhabdocline laricis'', and moist weather favors it. Experiments suggest that it grows the most at 10–25°C; slight infection can occur from 0–5°C; and none at all over 30 °C.

Control

''Rhabdocline laricis'' is a threat to tree nurseries that are attempting to grow larches such as the

Western larch The western larch (''Larix occidentalis'') is a species of larch native to the mountains of western North America (Pacific Northwest, Inland Northwest); in Canada in southeastern British Columbia and southwestern Alberta, and in the United States ...

. Even if the infected tree ultimately survives, it may have reduced DBH (diameter) leading to culling by the maintainer for failing to meet the expected size.

Fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

can be used in nurseries, although control in a wider natural forest setting is generally not practical. Damage from ''Rhabdocline laricis'' is not always recognized as such, as the results can be confused with damage from insects or from

frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) ...

Interaction with ''Hypodermella laricis''

The species becomes substantially more problematic when paired with ''Hypodermella laricis'', an ascomycete fungus that lives on ''Larix'', and can produce ill effects more substantial than either plant pathogen alone.

References

{{Taxonbar, from=Q108316656 Helotiales Fungal conifer pathogens and diseases Fungus species