Biocontrol introduction
Target pest: Clematis vitalba (Ranunculales: Ranunculaceae), old man's beard
Agent introduced: Longididymella clematidis (Pleosporales: Didymellaceae) = Didymella clematidis, Phoma clematidina, old man's beard leaf fungus
Imported:
1990
Import source:
Washington, USA
Import notes:
Gourlay et al. (2000) - after extensive laboratory tests for virulence and host specificity to C. vitalba, a single isolate of L. clematidis [as Phoma clematidina, subsequently reclassified as Didymella clematidis and then Longididymella clematidis - see Woudenberg et al. (2009) and Hou et al. (2020) entries in 'General comments' section] from Clematis ligusticifolia, that was collected in Washington State, USA, was selected for release in New Zealand. A weakly pathogenic form of L. clematidis was already present in New Zealand. An application for release of the fungus was made in 1996 and approved, and the fungus introduced in that year.
Gourlay (2008) - a selected strain of this fungus was introduced from USA as a biocontrol agent; other less virulent strains were already present in the country.
Released:
1996
Release details:
Gourlay et al. (2000) - the new virulent strain of L. clematidis was introduced in 1996; it has now been released at 23 sites in New Zealand.
Gourlay (2008) - first releases were in summer of 1996; widespread releases began in spring 1997.
Establishment:
Gourlay et al. (2000) - establishment of the virulent strain L. clematidis has been confirmed at 11 of the 23 release sites and this strain has spread rapidly throughout the country.
Gourlay (2008) - there is no evidence the deliberately released strain is still present in New Zealand.
Landcare Research (2021b) - the deliberately released strain did not persist and is believed to have been outcompeted by native fungi.
Impacts on target:
Gourlay et al. (2000) - at several of the release sites, L. clematidis has caused extensive leaf necrosis, leaf fall, and stem dieback of C. vitalba.
Gourlay (2008) - initially caused considerable damage, but has since become rare and has probably died out. Minor damage caused by the less virulent strains is commonly seen.
Landcare Research (2016d) - it is possible that the released strain was outcompeted by other fungi on old man's beard, some of which studies have shown occur as symptomless endophytes that may confer disease resistance to the plant.
Impacts on non-targets:
Gourlay et al. (2000) - in initial host range tests carried out prior to the application to release L. clematidis, small lesions were formed on petioles of Clematis paniculata and C. quadribracteolata [both endemic species], leaf spots on C. montana [an exotic ornamental species] and necrotic spots on three weed Ranunculus species. Further tests were carried out against 16 endemic Clematis species and 16 endemic Ranunculus species; minor spotting occurred on leaves of some plants but no pycnidia were formed on any species.
General comments:
Woudenberg et al. (2009) - multiple taxa are present within the morphological variation understood to represent Phoma clematidina. A study to assess the diversity of P. clematidina by means of DNA sequence comparisons showed three distinct groups which are elevated to species level. One of these is described as Didymella clematidis. Due to the presence of only two-celled conidia both in vitro and in vivo, the anamorph [asexual] stage of D. clematidis (previously considered to be Phoma clematidina) is classified in the genus Ascochyta. This species has been released in New Zealand as a biological control agent of Clematis vitalba.
Hou et al. (2020) - Didymella clematidis is shown to be part of a fully supported clade that is distant from Didymella and distinct from other known genera in family Didymellaceae and is consequently reclassified in a newly introduced genus as Longididymella clematidis.
References
Gourlay AH, Wittenberg R, Hill RL, Spiers AG, Fowler SV (2000). The biological control programme against Clematis vitalba in New Zealand. In Proceedings of the X international symposium on biological control of weeds 2000 (pp. 799-806). Montana State University Bozeman, Montana, USA. https://bugwoodcloud.org/ibiocontrol/proceedings/pdf/10_709-718.pdf
Gourlay H (2008). Old Man's Beard Leaf Fungus. In The Biological Control of weeds Book (Landcare Research) https://www.landcareresearch.co.nz/discover-our-research/biosecurity/weed-management/using-biocontrol/the-biological-control-of-weeds-book/
Hou LW, Groenewald JZ, Pfenning LH, Yarden O, Crous PW, Cai L (2020). The phoma-like dilemma. Studies in Mycology 96: 309-396 https://doi.org/10.1016/j.simyco.2020.05.001
Landcare Research (2016d). What's happening with old man's beard? Weed Biocontrol: What's New? 76: 4-5 http://www.landcareresearch.co.nz/publications/newsletters/biological-control-of-weeds/issue-76
Landcare Research (2021b). Old man's beard agents show promise. Weed Biocontrol: What's New? 95, Feb 2021 https://www.landcareresearch.co.nz/publications/weed-biocontrol/weed-biocontrol-articles/old-mans-beard-agents-show-promise
Woudenberg JHC, Aveskamp MM, de Gruyter J, Spiers AG, Crous PW (2009). Multiple Didymella teleomorphs are linked to the Phoma clematidina morphotype. Persoonia - Molecular Phylogeny and Evolution of Fungi 22: 56-62
