No abstract

Eradication of plant pathogen incursions is very important for the protection of plant industries, managed gardens and natural environments worldwide. The consequence of a pathogen becoming endemic can be serious, in some cases having an impact on the national economy. The current strategy for eradication of a pathogen relies on techniques for the treatment, removal and disposal of affected host plants. There are many examples where these techniques have been successful but many where they have not. Success relies on a sound understanding of the biology and epidemiology of the pathogen and its interaction with the host. Removal and disposal of infected plant material for eradication and containment of plant and soil inhabiting fungal, bacterial and viral pathogens are reviewed by considering black Sigatoka of banana, apple scab, maize smut, fireblight, citrus canker and sharka disease of stone-fruit crops. In examining examples of dealing with plant pathogens and diseased host material around the world, particularly Australasia, various techniques including burning, burying, pruning, composting, soil-and biofumigation, solarization, steam sterilization and biological vector control are discussed. Gaps in the literature are identified and emphasize the insufficient detail of information available from past eradications. More effort is required to produce and publish scientific evidence to support the success or otherwise of techniques and suggestions for future research are proposed.

Disease severity keys are described and illustrated for powdery mildew (Erysiphe pisi DC.) and downy mildew (Peronospora viciae (Berk.) Caspary) of pea (Pisum sativum L.), and powdery scab (Spongospora subterranea (Wallr.) Lagerh. f. sp. subterranea Tomlinson) of potato (Solanum tuberosum L.). The keys consist of illustrations of pea leaves or potato tubers in 11-point (0-10) severity scales of arbitrary proportions of surface areas diseased. The keys were constructed from hand drawings of pea leaflets or potato tubers, with colonies or lesions drawn to resemble typical infections of the respective diseases. Proportions of surface area of plant parts "diseased" on drawings were confirmed using computer-assisted image analysis. The drawings were then scanned into computer storage for manipulation into illustrated keys for publication. The complete keys, or abbreviated versions, have been used for assessing severity of the diseases in recent research on crop loss assessment, disease control, susceptibility assessment, and disease epidemiology. They also provide bases for accurate disease severity assessment in commercial pea and potato crops.

Myrtle rust (caused by Austropuccinia psidii) affects more than 500 known host species in the Myrtaceae family. Three different modelling approaches (CLIMEX, MaxEnt and Multi‐Model Framework) were used to project the habitat suitability for myrtle rust at both global and local scales. Current data on the global occurrence of myrtle rust were collected from online literature and expert solicitation. Long‐term averages of climate data (1960–1990) were sourced from WorldClim and CliMond websites. Recent reports of myrtle rust in New Zealand were used for validation of model outputs but not in model training and testing. The model outputs were combined into a consensus model to identify localities projected to be suitable for myrtle rust according to two or three models (hotspots). In addition to the locations where the pathogen is currently present, all models successfully projected independent occurrence data in New Zealand suitable for establishment of the pathogen. Climate suitability for the pathogen was primarily related to temperature followed by rainfall in MaxEnt and the CLIMEX model. The results confirmed the optimum temperature range of this pathogen in the literature (15–25 °C). Additional analysis of the precipitation variables indicated that excessive rain (more than 2000 mm in warmest quarter of the year) combined with high temperatures (>30 °C) constrain pathogen establishment. The results of the current study can be useful for countries such as New Zealand, China, South Africa and Singapore where the pathogen has not fully spread or established.

Components of quantitative resistance in pea (Pisum sativum) to Erysiphe pisi, the pathogen causing powdery mildew, were investigated. Conidium germination, infection efficiency, latent period and conidium production dynamics on cv. Quantum (quantitatively resistant) were compared with those on Pania and Bolero (susceptible). There was an additional comparison in conidium germination experiments with the resistant cv. Resal. Quantitative resistance in Quantum did not affect conidium germination, but infection efficiency of conidia on this cultivar was 34% less than on the susceptible Pania. More conidia germinated on 5-day-old leaflets than on 15-day-old leaflets but the age of the plant did not affect percentage germination or infection efficiency. The length of the latent period did not differ between cultivars. Total conidium production (AUC) per unit leaflet area on Quantum was 25% less than on Pania. The maximum conidium production per day (CMAX) per unit leaflet area on Quantum was 33% less than on Pania. The time to maximum conidium production per day (TMAX) was 10% longer on Quantum than on Pania. The cv. Bolero, reported to be susceptible, also showed some degree of quantitative resistance, but this differed from that of Quantum. Total conidium production was less on Bolero than on Quantum, but the conidia on Bolero were produced sooner, and for a shorter period, than on Quantum. The stability of these responses was tested by analysing components in three different temperature regimes and testing for interactions with temperature, and with leaflet age. Temperature affected all conidium production variables. AUC per leaflet area was nearly seven times as great and CMAX nearly 15 times greater at 23ЊC than at 13ЊC. TMAX increased by 1·5 times when temperature increased from 13ЊC to 18ЊC or 23ЊC. Several interactions occurred and these are described.