forest health news No. 153, July 2005 ISSN 1175-9755
ALBIZIA WILT – A NEW DISEASE IN NEW ZEALAND? Wilt of Albizia spp. caused by Fusarium oxysporum f. sp. perniciosum is well documented in the United States, where it is Albizia julibrissin, the Chinese silk tree, is prized in many urban referred to as “mimosa wilt”. It has also been recorded in Greece, gardens for its attractive shape, colourful flowers, and delicate Japan, Argentina, Puerto Rico, and in parts of the former USSR . foliage. It is also a popular street tree because of its rapid growth, In the United States it is reported as an extremely serious disease relatively small size at maturity, and adaptability to a wide range of A. julibrissin, with little chance of survival for most infected of sites. Recently, wilting and dying A. julibrissin were reported trees. Other closely related species, e.g., Paraserianthes lophantha in two Auckland locations (St Heliers and Swanson) by Vigil (formerly Albizia lophantha), are also affected but to a lesser Forest Health Advisor Chris Inglis. Dark staining observed within extent. Initial symptoms of mimosa wilt appear as yellowing and the growth rings in the stem was characteristic of a vascular wilt wilting of the foliage on one or more branches. Defoliation and disease. Previously, disease samples from A. julibrissin have been death of the affected branches soon follow. These symptoms rare, although samples from street trees in Mt Eden, Auckland, steadily progress through the crown, and death of the plant usually were sent in for diagnosis in 1996. The cause of the wilt, dieback, occurs within a year. Discolouration of the wood is most and resin bleed was determined as alcoholic flux. pronounced on the lower stems and roots.
Dying Albizia julibrissin street trees in Swanson. (Photo: C Inglis, Vigil)
Isolates taken from discoloured stem tissue (see illustration) and from fruiting bodies on branch material from Auckland samples have been identified as F. oxysporum by morphological and DNA analyses. The F. oxysporum complex contains around 150 formae speciales, or races, associated with specific hosts. Based on host association, the isolates collected from A. julibrissin in Auckland would be classified as F. oxysporum f. sp. perniciosum, but when the DNA sequence data were analysed, F. oxysporum f. sp. perniciosum was not the closest match. This is the first record of a Fusarium disease on silk trees in New Zealand and efforts are currently under way to determine exactly which member of the F. oxysporum complex is causing the disease in Auckland. Because of the taxonomic difficulties within F. oxysporum, MAF has funded Landcare Research to conduct an operational research project to resolve formae speciales identifications within this complex. Vascular stain in stem of infected Albizia julibrissin (Photo: C Inglis, Vigil) Margaret Dick and Tod Ramsfield (Ensis)
Newsletter of the Forest Biosecurity and Protection Unit, and the Forest Health Reference Laboratory (incorporating the Forest Research Mycological Herbarium (NZFRI-M), the Forest Research Culture Collection (NZFS), and the National Forest Insect Collection (FRNZ). Edited by John Bain, New Zealand Forest Research Institute Ltd, Private Bag 3020, Rotorua.
GETTING OFF TO A HEALTHY START “Physiological needle blight”. The Australian physiologists are also working on growth loss associated with foliar pathogens. All of the newly formed groups within Ensis are faced with the Knowledge of the pathogen, combined with understanding of the getting-to-know-you phase that forms the basis of trans-Tasman tree, will enable us to better understand the underlying causes of teamwork. As part of this process, forest pathologists Lindsay growth loss resulting from interactions between the fungus and Bulman and Tod Ramsfield from Rotorua recently visited Australia the host and to devise cost-effective methods of management. to find out what their colleagues are up to. After spending a week with Dr Caroline Mohammed’s team in Hobart, Lindsay was very Tod Ramsfield visited 2 weeks after Lindsay and met up with positive about the combined strength of their new team. New colleague Morag Glen. Until recently, Morag was based in Perth, Zealand has a lot of expertise in the biological aspects of forest Western Australia, where she worked with Dr Inez Tommerup on health, whereas the Australian team has strengths in modelling the development of DNA-based diagnostics for forest pathogens. and remote sensing. He considers there is a lot of scope for us to While Tod was in Tasmania, he and Morag compared notes on bring these skills together in a way that will help us understand their independently developed identification systems for the pitch more about the behaviour of pests. canker pathogen Fusarium circinatum, and discussed how to further the collaboration between the two groups. Collaboration These complementary skill sets can be used to study a serious with Morag actually preceded the initiation of the Ensis JV; she disease of radiata pine in both countries. In Tasmania, this disease has been studying Cyclaneusma isolates from New Zealand to is known as spring needle cast, whereas in New Zealand it is determine if the simile and verum varieties can be distinguished referred to as Cyclaneusma. Lindsay spent a few days looking at using DNA markers. Tod and Morag have been communicating sites suitable for setting up a range of different studies. One aim for some time, and meeting in person, allowing a face to be put is to develop remote-sensing methods that will be able to improve with a name, was an extremely beneficial exercise. Now that Tod our ability to monitor pine diseases in the field. The ability to and Morag are part of the same unit, collaboration will be closer, superimpose information from remote sensing technology with thereby strengthening the development of DNA-based diagnostics other environmental layers in a GIS will enable us to better for forest pathogens of concern in New Zealand and Australia. understand the influence of non-biological factors, such as climate and site. Lindsay Bulman and Tod Ramsfield (Ensis)
WILLOW SAWFLY IN AUSTRALIA Nematus oligospilus (willow sawfly), a Northern Hemisphere species, was first found in New Zealand in 1997 in Auckland. It has subsequently spread throughout the country. It is now present in parts of the Australian Capital Territory, New South Wales, and South Australia. The sawfly was initially detected in Canberra and its identity was confirmed in February 2005. A decision to not attempt eradication of the sawfly from Australia was made at a Consultative Committee on Emergency Plant Pests meeting held in March 2005. This decision was made after surveys for the sawfly found that it was too widespread to eradicate, and because of the presence of large numbers of host plants in southern Australia. For further information see: Lindsay Bulman with Tim Wardlaw (of Forestry Tasmania) in Tasmania http://www.hortnet.co.nz/publications/guides/willow_sawfly/ wsawfly.htm Another area of strength in the Australian team is tree physiology, http://www.ento.csiro.au/about_insects/willow_sawfly.html and Lindsay questioned the physiologists at length on possible approaches to study the episodic defoliation now known as John Bain (Ensis)
NEW RECORDS
New to New Zealand record – Fungus: Fusarium oxysporum; New distribution record for New Zealand – Fungus: Bioregion: Auckland; Host: Albizia julibrissin; Coll: C Inglis, Hapalopilus nidulans; Bioregion: Gisborne; Host: Pinus radiata; 25/04/2005; Ident: T Ramsfield, 17/06/2005; Comments: See Coll: B Rogan, 24/03/2005; Ident: I Hood, 21/07/2005; article in this issue of FH News. Comments: This wood-decay fungus is found on dead standing or fallen trees or wood and branch debris. It is widely distributed New host record and distribution record for New Zealand – in the Northern Hemisphere and some other parts of the world. In Fungus: Rhizosphaera pini; Bioregion: Taupo; Host: New Zealand it has been recorded on Pinus radiata, P. contorta, Pseudotsuga menziesii; Coll: T Merriman, 23/06/2005; Ident: Elaeocarpus dentatus, and Eucalyptus pulchella. It has previously K Dobbie, 20/07/2005; Comments: This species was confirmed been recorded in Northland, Taupo, Wellington, and North and as present in New Zealand in 2003 when it was found on unthrifty Mid Canterbury. and dying needles of Picea pungens in Taranaki. It has also been (John Bain, Ensis) found on casting Picea sitchensis foliage in Buller. Overseas it is often considered to be a weak pathogen taking advantage of stressed or dying foliage. ERRATUM FHNews 149: 2. New Records, New distribution record for New Zealand, Stigemella microtheriella (Nepticulidae). This stated that the species was first found here in the 1950s. That should read the 1850s. 2