Australian Quarantine Review Secretariat Australian Quarantine a shared responsibility
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- 3.2 Forest Pathogens
- 3.3 Cost of Incursions of Plant Pathogens
3 PATHOGENS OF PLANTS3.1 Pathogens of Crop, Ornamental and Nursery PlantsThe report on recent incursions of plant pathogens was prepared by Dr D. Hanold of the Department of Crop Protection, Waite Campus, University of Adelaide, with input from other staff of the Department. It considered nematodes, fungi, bacteria and phytoplasmas, viruses and viroids of all the major species of crop, ornamental and nursery plants (excluding forest trees). This report covered probably the broadest range of host species and the largest combination of hosts and agents of the reports commissioned. The authors stressed that the report is not definitive, being compiled in a very short period from mainly published records and personal communication with plant pathologists in New South Wales, the Northern Territory, South Australia and Tasmania. The report examined 562 incidents involving plant pathogens during the study period — 143 detected in post-entry quarantine and 30 records of occurrences on new host species — representing a total of 389 incursions that led to the establishment of exotic plant pathogens in Australia. The data demonstrated that although the annual rate of incursions leading to establishment is high relative to other taxa of pests and pathogens of animals or plants, there was no significant change in the rate of incursions or establishment of plant pathogens during the study period (see Table 2). Table 2: Apparent rate of incursion and establishment of plant pathogens between 1971 and 1995
The report attributed a probable route of introduction to 306 (78.5%) of the pathogens that established during the study period — one could not be ascribed to 83 incidents (21.5%). The report concluded that the main routes of introduction appear to be plant materials (160 or 41%) and seeds (132 or 34%). Very few pathogens that established appeared to be associated with imports of whole plants (4 or 1%), imports of tissue culture materials (2 or 0.5%), wind (6 or 1.5%) or soil and other means (2 or 0.5%). The designation 'plant material' includes cuttings, budwood, fruit, leaf waste and dried materials. When analysed by host, exotic plant pathogens that apparently established in Australia during the study period were most commonly associated with fruits and vegetables (34.5%), nursery plants, ornamentals and flowers (22.5%), legumes (13%) cereals (11%) and other field crops and grasses (11%). When analysed by type of pathogen, fungi (42%) and viruses and viroids (39%) predominated over bacteria and mycoplasma-like organisms (18%) and nematodes (1%). The report provided some evidence of possible trends in the types of pathogen detected during the study period — there may be a trend towards more detections of viruses and viroids (and fewer of fungi) in recent years. However, these apparent trends may be confounded by factors such as the number of scientists working on different groups of pathogens during the period and different rates in the development and availability of diagnostic tests (e.g. the relatively recent availability of tests for viruses and viroids). 3.2 Forest PathogensTo ensure that forest pathogens were fully considered, the Review Committee commissioned a report on them as part of the report on forest pests and pathogens. The section in this report that dealt with forest pathogens was prepared by Drs Mark Dudzinski, Ken Old, Gary Johnson and Glen Kile of CSIRO Forestry and Forest Products. The report considered exotic invertebrate pests (insects) that entered Australia between 1971 and 1995 and established on native and naturalised (formerly exotic) trees. The report noted that some of the most serious forest pathogens rely on insect vectors for transmission over significant distances (e.g. pine wilt nematode and Dutch elm disease). Thus quarantine measures that are effective against insects will also protect against a range of pathogens. The report could not identify any documented examples of incursions by bacteria, nematodes, viruses or mycoplasma-like organisms that led to the establishment of a disease of forest trees in Australia between 1971 and 1995. Fungi provided the only unequivocal examples of the establishment of exotic pathogens of trees during the study period. Fungi, through their capacity to sporulate and release large numbers of spores into the atmosphere, are particularly well adapted for spread over long distances. The report noted that in comparison with agriculture or horticulture, incursions of forest pathogens are more difficult to detect because: · there is an incomplete knowledge of the range of pathogens currently present on woody vegetation in Australia, especially in regard to native forest vegetation; · although there were many new records for tree diseases between 1971 and 1995, only few could be identified as recent introductions; · recognition of incursions usually relies on opportunistic discovery; · even high value plantation forests may only be surveyed irregularly for growth and health, and native forests receive even less attention; and · diseases are rarely detected before reaching levels at which eradication is usually not feasible. The report identified nine pathogens that established on forest trees in Australia between 1971 and 1995. All occurred on naturalised (formerly exotic) species of trees and were pathogenic fungi causing foliar diseases (see Table 3). Table 3: Forest pathogens established in Australia between 1971 and 1995
3.3 Cost of Incursions of Plant PathogensThe commissioned reports on plant pathogens were able to identify little information on the economic effect of exotic pathogens that established in Australia during the past 25 years. Some information on costs associated with plant pathogens was provided to the Review Committee by AQIS, which prepared a background paper on costs of control and eradication funded through the Standing Committee on Agriculture and Resource Management (SCARM) process between 1977 and 1992. The paper was prepared as input to the deliberations of the SCARM Task Force on Incursion Management (see Section 10.1 of the Report). Approximate costs attributed to joint Commonwealth–State control and eradication of plant pathogens between 1977 and 1992 are shown in Table 4. Although incomplete, these data provide an indication of the costs to governments associated with the control and eradication of incursions of plant pathogens in Australia, excluding losses to producers. Table 4: Approximate costs attributed to joint Commonwealth–State control and eradication of plant pathogens between 1977 and 1992 (amounts in $000)
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