News from the 8th International Congress of Plant Pathology
The 8th International Congress of Plant Pathology took place on the 2003-02-02/07, at Christchurch, New Zealand, where a very large number of presentations were made. The EPPO Secretariat has extracted the following information.
In Iran, samples of ornamental and other crops were tested in 2000 for the presence of 5 tospoviruses: Tomato spotted wilt tospovirus (TSWV – EPPO A2 quarantine pest), Tomato chlorotic spot tospovirus (TCSV), Impatiens necrotic spot tospovirus (INSV – EPPO A2 quarantine pest), Iris yellow spot tospovirus (IYSV – EPPO Alert List), and a newly observed virus tentatively named Tomato Varamin tospovirus (ToVV). ToVV, TSWV and INSV were frequently detected from ornamentals. ToVV and TSWV were found in potato, tomato and soybeans; TCSV and ToVV in Alstoemeria; IYSV and ToVV in one sample of Cycas. The EPPO Secretariat had no data on the occurrence of IYSV in Iran (Shahraeen & Ghotbi, 2003).
Chrysanthemum stem necrosis tospovirus (EPPO Alert List) is reported for the first time from Slovenia. It was detected on chrysanthemum (Ravnikar et al., 2003).
The strain of Parietaria mottle ilarvirus which infects tomato was detected in Spain in 2001 (Aramburu & Ariño, 2003). Since then, the virus has spread especially in outdoor tomato crops in the province of Barcelona. This virus had already been observed in France and Italy on tomato crops (see EPPO RS 2000/081).
Xanthomonas arboricola pv. corylina (EPPO A2 quarantine pest) is reported for the first time in New Zealand (Braithwaite & Eade, 2003).
In Australia, Mycosphaerella fijiensis (Black Sigatoka) is considered as a major threat to banana production. Since 1981, 8 incursions have been recorded in the Cape York area, Queensland. All outbreaks were eradicated by destruction of infected plants and use of resistant cultivars. In April 2001, the most serious incursion was observed at Tully (commercial production area). Molecular diagnostic techniques (PCR) are being developed to survey the disease and detect all future incursions (Henderson et al., 2003).
In New Zealand, Potato spindle tuber pospiviroid (PSTVd - EPPO A2 quarantine pest) was detected in 3 commercial tomato glasshouses in the Auckland region (north Island) and at 1 site in Nelson (South Island) in May 2000 (see EPPO RS 2001/061). In April-June 2002, further surveys were carried out. 59 tomato and 41 capsicum glasshouses were inspected and random samples were collected. PSTVd was not found in tomato glasshouses (except in one already found in 2000) but was detected in 3 cultivars of capsicum growing in Warkworth (north of Auckland). This is the first report of PSTVd on capsicum (Lebas et al., 2003).
Lime witches’ broom, caused by Candidatus Phytoplasma aurantifoliae (EU Annexes) was first observed in Oman in the mid 1970s. The disease has now spread to almost 100% of the lime producing areas of the country. The disease has also recently spread to neighbouring countries including United Arab Emirates, Iran and India. Control methods including rotation, adequate nutrition, tree injections, use of resistant rootstocks are envisaged (Al Busaidi et al., 2003).
Biology, epidemiology, detection
A PCR-based molecular diagnostic technique is being developed in New Zealand to enable rapid detection of fungal mycelium of Endocronartium harknessii (EPPO A1 quarantine pest) within non-sporulating galls (Ramsfield, 2003).
Lime witches’ broom (Candidatus Phytoplasma aurantifoliae – EU Annexes) is graft-transmissible and insect vectors are suspected. In earlier studies, seed transmission had been suggested. Preliminary results of ongoing studies are also in favour of seed transmission (Khan et al., 2003).
In 2001, a series of inoculation tests on fresh cut logs was initiated in UK to assess the risk presented by Phytophthora ramorum (EPPO Alert List) to European oaks and other trees and to compare European/US fungal populations. Preliminary results showed that bark of Quercus robur (European) may be more resistant than that of Q. rubra (American), and that bark of Castanea sativa was more resistant, but that bark of Fagus sativa was more susceptible (both European). On average, it appears that European and American isolates of P. ramorum differ in aggressiveness on both Q. rubra and Q. robur (Brasier et al., 2003)
A PCR assay has been developed to detect Puccinia psidii (EPPO Alert List). The rust could be detected in eucalyptus seeds and pollen. In the laboratory, PCR-positive pollen material incited typical rust symptoms on young eucalyptus leaves. The fungus was also detected from washings from surfaces of footwear, wristwatches, spectacles, camera bags and non-porous clothing items of personnel following visits to infected plantation sites. Contaminated pollen, seed and personal items could ensure long distance dissemination of the fungus (Langrell et al., 2003).
European wheat cultivars (15 winter, 15 spring and 11 durum) were tested in the laboratory for their susceptibility to Tilletia indica (EPPO A1 quarantine pest). Results showed that European wheat cultivars are as susceptible to T. indica as cultivars planted in countries where the disease occurs, thus indicating their potential to support establishment of the pathogen if introduced into Europe (Porta-Puglia et al., 2003).
New pests and new possible risks
In Vietnam (Lam Dong province), pine wilt symptoms and dead Pinus kesiya trees have been found in several locations and associated with a Bursaphelenchus species. A systematic survey was carried out. Disease incidence in 4 locations in Lam Dong province varied from 36% to 48%, and 38 symptomatic trees from these stands were sampled for the presence of the nematode. All were positive. The rate of pine mortality increased annually. Nematodes extracted from wood samples were identified as Bursaphelenchus sp. The species found in Vietnam is morphologically distinct from B. xylophilus (EPPO A1 quarantine pest) but shares the same vector Monochamus alternatus. Artificial inoculation of three-year old P. kesiya demonstrated the pathogenicity of this Bursaphelenchus species (Thu, 2003).
In Australia, a new tospovirus tentatively called Capsicum chlorosis tospovirus was found. It was first detected in 1999 and has been observed in all capsicum production areas in Queensland (except of high altitude summer-production area). The percentage of infected plants is commonly 1 to 5 %, but could reach up to 40% with unmarketable fruits. This virus is serologically related to Watermelon silver mottle tospovirus (Persley et al. 2003).
Citrus sudden death is a new disease of unknown aetiology which affects sweet orange grafted on Rangpur lime in Brazil. Spatial and temporal analyses of the disease suggest that a pathogen is associated with it, and that it might be a virus vectored by insects such as aphids (Bassanezi et al., 2003).
Cylindrocladium buxicola is a newly described fungus which causes leaf and twig blight on Buxus species. It is widespread in the UK and has also been detected in other countries of Western Europe and New Zealand (Henricot, 2003)
In Japan, a new bacterial disease of strawberry was observed in Tochigi and Fukushima Prefectures (Honshu) in 2000. Symptoms appear as tiny white rusty spots on the underside of the leaves. They enlarged to form angular brown white spots, then becoming reddish brown. Lesions are not water-soaked. A bacterium was consistently isolated from diseased plants and tentatively identified as a new and distinct Herbaspirillum species. So far, Herbaspirillum species had only been found on Poaceae (Takikawa et al., 2003)
As reported in EPPO RS 2002/174, mango decline is causing serious losses in Oman. Al Adawi et al. (2003) proposed different explanations on the possible causes of this new devastating disease. Two fungi were isolated and both fulfilled Koch’s postulates when healthy trees were artificially inoculated: Botryodiplodia theobromae and Ceratocystis fimbriata. Damage caused by a bark beetle (Cryphalus scabrecollis, Coleoptera: Scolytidae) was usually associated with the disease, and B. theobromae was isolated from this insect.
Pantoea ananatis has several host plants including pineapples, melons, sudangrass, sugarcane, maize and onions. It was recently found on Eucalyptus causing bacterial blight and die-back, and serious losses to the forest industry in South Africa. It is widespread in South Africa in all areas where eucalypts are planted commercially. It has recently been found in Uganda. Seed transmission is known in certain hosts (onions and sudangrass) and is suspected in eucalyptus. The authors felt that P. ananatis should be considered as a quarantine pest (Coutinho et al., 2003).
Abstracts of papers presented at the 8th International Congress of Plant Pathology, Christchurch, New Zealand (2003-02-02/07).
Al Adawi, A.; Deadman, M.; Khan, A.; Al Rawahi, A.; Al Maqbali, Y. (2003) Mango decline in Oman: a devastating new disease in the Sultanate (abst. 19.7)
Al Busaidi, R.; El Mardi, M.; Khan, I.; Al Maqbali, Y.; Deadman, M. (2003) Management of witches’broom disease of lime in the Sultanate of Oman (abst. 21.1)
Aramburu, J.; Ariño, J. (2003) Epidemiological aspects of a tomato strain of paretaria mottle virus (PMoV-T) present in Spain (abst. 23.35).
Bassanezi, R.B.; Bergamin Fihlo, A.; Amorim, L.; Gimenes-Fernandes, N.; Gottwald, T.R. (2003) Spacial and temporal analyses of citrus sudden death as a tool to elucidate its etiology (abst. 8.63).
Brasier, C.; Rose, J.; Kirk, S.; Webber, J. (2003) Pathogenicity of Phytophthora ramorum isolates from USA and Europe to bark of European forest trees (abst. 11.23).
Braithwaite, M.; Eade, K. (2003) Identification of Xanthomonas arboricola pv. corylina on hazel nut in New Zealand (abst. 7.52).
Coutinho, T.A.; Venter, S.N.; Mergaert, J.; Sings, J. ; Wingfield, M.J. (2003) Is Pantoea ananatis a high risk, quarantine pathogen ? (abst. 5.1).
Henderson, J.; Porchun, S.; Pattermore, J.; Grice, K.; Peterson, R. (2003) Molecular diagnosis of Sigatoka leaf spot disease in Australian banana crops. (abst. 7.7).
Henricot, B. (2003) Cylindrocladium buxicola, a new fungal species causing blight on Buxus spp. and its phylogenetic status (abst. 19.21).
Khan, I.A.; Lee, R.F.; Hartung, J. (2003) Confirming seed transmission of witches’ broom disease of lime (abst. 21.2).
Langrell, S.R.H.; Tommerup, I.C.; Zauza, E.A.V.; Alfenas, A.C. (2003) PCR based detection of Puccinia psidii from contaminated Eucalyptus germplasm-implications for global biosecurity and safeguarding commercial resources (abst. 5.3).
Lebas, B.S.M.; Elliott, D.R.; Ochoa-Corona, F.M.; Tang, J.; Alexander, B.J.R. (2003) Delimiting survey for Potato spindle tuber viroid on tomato and capsicum in New Zealand greenhouses (abst. 1943).
Persley, D.; Sharman, M.; McMichael, L.; Thomas, T. (2003) Tospoviruses infecting capsicums and tomatoes in Australia (abst. 23.13).
Porta-Puglia, A.; Inman, A.; Riccioni, L.; Valvassori, M.; Hughes, K.; Bowyer, R.; Barnes, A.; Magnus, H.; Peterson, G. (2003) Physiological susceptibility of European wheat cultivars to infection and development of Karnal bunt. (abst. 5.11).
Ramsfield, T.D. (2003) Molecular detection of Endocronartium harknessii (abst. 7.79).
Ravnikar, M.; Vozelj, N.; Mavric, S.D.; Zupancic, M.; Petrovic, N. (2003) Detection of Chrysanthemum stem necrosis virus and Tomato spotted wilt tospovirus in chrysanthemum (abst. 23.21).
Shahraeen, N.; Ghotbi, T. (2003) Natural occurrence of different Tospovirus species infecting ornamentals and other agricultural crops in Iran (abst. 23.26).
Takikawa, Y.; Kusumoto, S.; Tairako, K.; Kijima, T. (2003) Herbaspirillum sp. causing brown spot on strawberry leaves (abst. 2.17).
Thu, P.Q. (2003) The status of pine wilt nematode in Vietnam (abst. 11.27).