Lecanosticta acicola: A growing threat to expanding global pine forests and plantations

Abstract

Lecanosticta acicola causes brown spot needle blight (BSNB) of Pinus species. The pathogen occurs mostly in the Northern Hemisphere but has also been reported in Central America and Colombia. BSNB can lead to stunted growth and tree mortality, and has resulted in severe damage to pine plantations in the past. There have been increasingly frequent new reports of this pathogen in Europe and in North America during the course of the past 10 years. This is despite the fact that quarantine practices and eradication protocols are in place to prevent its spread.

Taxonomy: Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Dothideomycetes; Subclass Dothideomycetidae; Order Capniodales; Family Mycosphaerellaceae; Genus Lecanosticta.

Host range and distribution: Lecanosticta spp. occur on various Pinus species and are found in North America, Central America, South America (Colombia), Europe as well as Asia.

Disease symptoms: Small yellow irregular spots appear on the infected pine needles that become brown over time. They can be surrounded by a yellow halo. These characteristic brown spots develop to form narrow brown bands that result in needle death from the tips down to the point of infection. Needles are prematurely shed, leaving bare branches with tufts of new needles at the branch tips. Infection is usually most severe in the lower parts of the trees and progresses upwards into the canopies.

Useful websites: The EPPO global database providing information on L. acicola (https://gd.eppo.int/taxon/SCIRAC) Reference genome of L. acicola available on GenBank (https://www.ncbi.nlm.nih.gov/genome/?term=Lecanosticta+acicola) JGI Gold Genome database information sheet of L. acicola sequenced genome (https://gold.jgi.doe.gov/organism?xml:id=Go0047147).

Keywords: Lecanosticta acicola; Mycosphaerella dearnessii; Lecanosticta species; Pinus spp; brown spot needle blight; pine pathogen.

Figure 1

Life cycle of Lecanosticta acicola on Pinus spp. (A) Asexual state: acervuli (a) develop on attached needles and needle debris and release conidia (b). Infection occurs through the stomata of new season needles (c), resulting in brown spot symptoms (d). (B) Sexual state: ascostromata develop on dead needles associated with previous season infections (a) and release ascospores in spring (b). Infection occurs through the stomata of new season needles (c), resulting in brown spot symptoms (d).

Figure 2

Symptoms of Lecanosticta acicola. (A) Pinus mugo in Austria displaying symptoms of both brown spot needle blight (BSNB) and Dothistroma needle blight (DNB) on the same branches. (B) Both the characteristic brown spots associated with BSNB (black arrow) and the red banding associated with DNB (white arrow) can be observed. (C)–(E) Symptoms of BSNB vary from only brown spots as observed on P. mugo (C) to distinct brown bands as observed on P. radiata (D) to irregular mosaic spots as observed on P. palustris (E). (F) Lecanosticta acicola conidiogenous cells giving rise to conidia on malt extract agar. (G) Lecanosticta acicola septate conidia with verruculose surfaces and truncate bases.

Figure 3

Maximum likelihood (ML) tree representing the nine known species of Lecanosticta as well as the three lineages of L. acicola generated from the translation elongation 1‐α region. ML bootstrap support (>70%) are indicated first, followed by maximum parsimony (MP) bootstrap support values (ML/MP, * = insignificant value). Phaeophleospora gregaria was used as the outgroup taxa. All represented type species are indicated in bold.