Showing papers in "Australasian Plant Pathology in 2008"
TL;DR: Issues that were addressed in establishing the DNA-based soil testing service in Australia are discussed and the training and accreditation programs that have been established are explained to ensure that results are interpreted adequately at the farm level.
Abstract: A DNA-based soil testing service operates in Australia to assist grain growers in predicting the likely extent of losses from various soilborne diseases well before a crop is planted. Growers, therefore, have the option of changing cultivars or modifying cropping programs in situations where the risk of crop loss is high. The service was launched in 1997 and although the initial focus was on wheat and barley, pathogens of rotation crops are now included. Key features of the service include a unique high-throughput DNA extraction system to process 500-g soil samples and a series of specific real-time PCR assays that allow a range of fungal and nematode pathogens to be quantified in a single soil sample. Tests for Heterodera avenae, Pratylenchus neglectus, P. thornei, Gaeumannomyces graminis var. tritici, G. graminis var. avenae, Rhizoctonia solani AG-8, Fusarium pseudograminearum, F. culmorum and the pea pathogens Mycosphaerella pinodes and Phoma medicaginis var. pinodella are available at present, while tests for Bipolaris sorokiniana, Ditylenchus dipsaci and Pratylenchus teres are in development. This paper discusses issues that were addressed in establishing the service (e.g. sampling strategies, extraction of DNA from soil, development of specific tests, disease risk categories) and explains the training and accreditation programs that have been established to ensure that results are interpreted adequately at the farm level. It also outlines research being conducted to extend the service to horticulture.
260 citations
TL;DR: The aim of this review is to summarise contemporary knowledge relating to the pitch canker pathogen, with a particular focus on its threat to plantation forestry.
Abstract: Pitch canker, caused by the fungus Fusarium circinatum, is one of the most important pathogens of Pinus species. Sporadic outbreaks and epidemics caused by this fungus have been reported from numerous countries. Symptoms differ depending on the host species, geographical region, climatic conditions and associated insects. Pitch canker represents a significant threat to countries where non-native and susceptible Pinus spp. are grown intensively in plantations.Athorough understanding of the ecology and epidemiology of the causal agent is an important prerequisite to managing this threat. The aim of this review is to summarise contemporary knowledge relating to the pitch canker pathogen, with a particular focus on its threat to plantation forestry.
228 citations
TL;DR: Cereal cyst nematode losses have declined significantly in the last 15 years due to more effective rotations and the widespread adoption of well adapted cereal cultivars with nematodes resistance, but a better-resourced plant breeding program is required to develop resistant cereal cultivar adapted to environmental conditions across the region.
Abstract: Both cereal cyst (Heterodera avenae) and root-lesion nematode (Pratylenchus spp. ) are associated with loss of grain yield in south-eastern and western Australia. Cereal cyst nematode has been a major pest since the 1930s but losses have declined significantly in the last 15 years due to more effective rotations and the widespread adoption of well adapted cereal cultivars with nematode resistance — strategies that were developed during several decades of research by pathologists, nematologists, agronomists and plant breeders. Research efforts are now focussed on reducing crop losses associated with root-lesion nematode. Rotations that minimise losses from the nematode have been identified, but a better-resourced plant breeding program is required to develop resistant cereal cultivars adapted to environmental conditions across the region. This paper reviews 40 years of research on the epidemiology and management of these two important pests.
120 citations
TL;DR: This review focuses on research which has led to the development of effective integrated management programs for two species of root-lesion nematode in Australia's northern grain belt and discusses how planned crop sequencing with tolerant and partially resistant wheat cultivars, together with crops such as sorghum, sunflower, millets and canaryseed, can be used to reduce nematodes populations and limit crop damage.
Abstract: Two species of root-lesion nematode (predominantly Pratylenchus thornei but also P. neglectus) are widespread pathogens of wheat and other crops in Australia's northern grain belt, a subtropical region with deep, fertile clay soils and a summer-dominant rainfall pattern. Losses in grain yield from P. thornei can be as high as 70% for intolerant wheat cultivars. This review focuses on research which has led to the development of effective integrated management programs for these nematodes. It highlights the importance of correct identification in managing Pratylenchus species, reviews the plant breeding work done in developing tolerant and resistant cultivars, outlines the methods used to screen for tolerance and resistance, and discusses how planned crop sequencing with tolerant and partially resistant wheat cultivars, together with crops such as sorghum, sunflower, millets and canaryseed, can be used to reduce nematode populations and limit crop damage. The declining levels of soil organic matter in cropped soils are also discussed with reference to their effect on soil health and biological suppression of root-lesion nematodes.
114 citations
TL;DR: Oaks and tanoaks in California and Oregon coastal forests are being ravaged by sudden oak death, and the continued spread of Phytophthora ramorum presents significant impetus for adjustments in the management and regulation of forest pathogens and nursery stock.
Abstract: Oaks and tanoaks in California and Oregon coastal forests are being ravaged by sudden oak death. The exotic causal agent, Phytophthora ramorum, is an oomycete in the Straminipile group, a relative of diatoms and algae. P. ramorum also infects many popular horticultural plants (i.e. camellia and rhododendron), causing ramorum blight, with symptoms expressed as leaf spots, twig blight and shoot dieback. P. ramorum has raised important biosecurity issues, which continue to reverberate through the agriculture, forestry and horticulture industries as well as associated government management, regulatory and scientific agencies. The continued spread of this and other new Phytophthora spp. presents significant impetus for adjustments in the management and regulation of forest pathogens and nursery stock.
96 citations
TL;DR: The use of bio-primed seeds might be considered as a safe, cheap and easily applied biocontrol method against these soilborne plant pathogens.
Abstract: The long-term activity of some antagonistic fungal and bacterial agents against the incidence of faba bean root rot incidence was evaluated when applied as a bio-priming seed treatment. The inhibitory effect of antagonistic fungi and bacteria against the linear growth of root rot pathogenic fungi was evaluated in vitro. The tested inhibitor factor in this study was the antagonistic agents applied as either growth culture discs or bio-primed faba bean seeds. The inhibitor effect of Trichoderma viride, T. harzianum, Bacillus subtilis and Pseudomonas fluorescens was significantly higher than T. hamatum and B. cereus, respectively. Similar results were also obtained when the antagonistic agents were applied as bio-primed seeds. Under greenhouse conditions, all the tested fresh and 2 months-stored, bio-primed faba bean seeds showed a highly significant effect causing complete reduction of root rot incidence at both pre — and post-emergence stages of plant growth compared with the control treatment. Stored seeds at 4 and 6 months showed a less protective effect against the incidence of disease. After 3 months of storage under field conditions, the antagonistic agents could protect seeds against infection by root rot pathogens at both pre- and post-emergence stages. However, after 6 months of storage, a lower protective effect was observed. No significance was observed between seeds primed only with adhesive agents and the untreated control. Promising applicable techniques could be suggested in light of the results obtained in the present study. The use of bio-primed seeds might be considered as a safe, cheap and easily applied biocontrol method against these soilborne plant pathogens.
69 citations
TL;DR: It is believed that this is the first report demonstrating that a cotyledon assay can be successfully applied to rapidly differentiate the reactions of B. napus genotypes against S. sclerotiorum.
Abstract: Sclerotinia sclerotiorum is a major pathogen of many crops, including oilseed rape (Brassica napus), and there is keen interest worldwide to identify Brassica genotypes with resistance to this pathogen. However, field testing to identify resistance in B. napus germplasm is expensive, time-consuming and at times unreliable due to variability in field environmental conditions and plant architecture. To address this, we aimed to examine the feasibility of utilising for B. napus a cotyledon test already developed for Sclerotinia disease on legumes. Initially, cotyledons of 32 B. napus genotypes were drop-inoculated using macerated mycelium (104 mycelial fragments/mL) under controlled environmental conditions. Significant differences were recorded between B. napus genotypes, and the experiment was repeated twice using genotypes selected from the first experiment. Certain genotypes responded with a distinct hypersensitive reaction (lesions <1 mm diameter), either always (cv. Mystic) or frequently (cv. Charlton), which is the first report of this phenomenon in the B. napus-S. sclerotiorum pathosystem. Responses of genotypes between the three screening experiments were significantly and positively correlated. Results obtained in the first experiment were compared with those from our earlier field screening for stem rot that utilised the same strain of S. sclerotiorum and the same B. napus genotypes. In particular, there was a significant positive correlation (r=0.62, P < 0.01) between published field data for stem rot and our cotyledon test results across genotypes in common. This indicates the usefulness of this cotyledon assay to provide a relatively reliable indication of field performance of genotypes. We believe that this is the first report demonstrating that a cotyledon assay can be successfully applied to rapidly differentiate the reactions of B. napus genotypes against S. sclerotiorum.
61 citations
TL;DR: Several of the atypical strains proved highly virulent on both tubers and stems of potato, suggesting that a variety of novel species or subspecies are responsible for soft rot of potatoes in New Zealand, including Pectobacterium wasabiae.
Abstract: The diversity of 89 pectolytic enterobacteria collected from potatoes in New Zealand was investigated by comparing their physiological, biochemical and genetic characteristics with those of type strains of Pectobacterium and strains previously identified as isolates of the genus Dickeya. Biochemical and physiological analyses demonstrated that the predominant pectolytic enterobacterium present in New Zealand is Pectobacterium carotovorum subspecies carotovorum. Isolates of Pectobacterium atrosepticum and strains closely related to Dickeya were also detected. Species and subspeciesspecific PCR confirmed the identity of the majority of the P. carotovorum subsp. carotovorum and P. atrosepticum strains. However, several atypical isolates classified by Biolog as P. carotovorum subsp. carotovorum failed to grow at 37C or to amplify the pectate lyase-encoding gene (pel gene) characteristic of this subspecies. Restriction fragment length polymorphism (RFLP) analyses of the 16S–23S intergenic transcribed spacer (ITS) also identified atypical isolates with unique ITS-RFLP profiles. Further characterisation of the atypical strains, by phylogenetic analysis of their 16S rRNA sequences, clustered them into four groups distinct from pectolytic enterobacteria previously found on potato. Several of the atypical strains proved highly virulent on both tubers and stems of potato, suggesting that a variety of novel species or subspecies are responsible for soft rot of potatoes in New Zealand, including Pectobacterium wasabiae.
57 citations
TL;DR: The paper argues the case for developing minimum tillage practices for vegetable production and integrating them into the sugarcane farming system, and concludes that a farming system of this nature would improve profitability in both industries, produce better environmental outcomes at a landscape level and provide more sustainable solutions to nematode and soilborne disease problems.
Abstract: A sugarcane farming system based on residue retention, minimum tillage, a leguminous rotation crop and controlled traffic using global positioning system guidance is currently being adopted by the Australian sugar industry because it improves sugar yields, reduces costs and provides additional income from crops such as soybean and peanut. This paper discusses the soil health improvements that are being obtained with this new farming system, particularly its beneficial effects on soil carbon levels and soil biological properties. It also summarises research showing that breaking the sugarcane monoculture with a soybean or peanut crop reduces populations of lesion nematode (Pratylenchus zeae) and root-knot nematode (Meloidogyne javanica), the two most important nematode pests of sugarcane. The role of minimum tillage and inputs of organic matter in enhancing the natural biological control mechanisms that suppress these nematodes is also discussed. The paper then considers the farming system currently used for vegetable crops such as tomato, capsicum and rockmelon, where inadequate crop rotation, excessive tillage, low organic inputs and the fallowing and solarisation effect of covering beds with plastic leads to a situation where soil fumigation is seen as the only option for reducing losses from soilborne pests and pathogens. Since the sugar industry coexists with the vegetable industry in some areas of Australia, the paper argues the case for developing minimum tillage practices for vegetable production and integrating them into the sugarcane farming system. It concludes that a farming system of this nature would improve profitability in both industries, produce better environmental outcomes at a landscape level and provide more sustainable solutions to nematode and soilborne disease problems.
49 citations
TL;DR: Two reliable small-plant bioassays were developed using tissue-cultured banana, resulting in consistent symptom expression and infection by Fusarium oxysporum f.
Abstract: Two reliable small-plant bioassays were developed using tissue-cultured banana, resulting in consistent symptom expression and infection by Fusarium oxysporum f. sp. cubense (Foc). One bioassay was based on providing a constant watertable within a closed pot and the second used free-draining pots. Culture medium for spore generation influenced infectivity of Foc. Inoculation of potted banana by drenching potting mix with a conidial suspension, consisting mostly of microconidia, few macroconidia and no chlamydospores, generated from one-quarter-strength potato dextrose agar + streptomycin sulfate, resulted in inconsistent infection. When a conidial suspension that consisted of all three spore types, microconidia, macroconidia and chlamydospores, prepared from spores generated on carnation leaf agar was used, all plants became infected, indicating that the spore type present in conidial suspensions may contribute to inconsistency of infection. Inconsistency of infection was not due to loss of virulence of the pathogen in culture. Millet grain precolonised by Foc as a source of inoculum resulted in consistent infection between replicate plants. Sorghum was not a suitable grain for preparation of inoculum as it was observed to discolour roots and has the potential to stunt root growth, possibly due to the release of phytotoxins. For the modified closed-pot system, a pasteurised potting mix consisting of equal parts of bedding sand, perlite and vermiculite plus 1 g/L Triabon slow release fertiliser was suitable for plant growth and promoted capillary movement of water through the potting mix profile. A suitable potting mix for the free-draining pot system was also developed.
46 citations
TL;DR: Regression analysis demonstrated that disease incidence, disease severity and disease index were negatively correlated with both the number of pods or seeds per bean plant, whereas there was a positive correlation between the disease and 100-seed weight.
Abstract: In 2007, prevalence of root rot pathogens and disease yield losses were studied under prevailing environmental conditions in common bean fields at Zanjan. Root rot disease incidence varied by sampling time and location of a field. In the majority of fields, Fusarium solani was the predominant fungus, being isolated from 2.8 to 96% of root samples over the sampling time, followed by Rhizoctonia solani, Macrophomina phaseolina and F. oxysporum. At pod maturity, the mean values for investigated factors were: disease incidence, 4.7–95%; disease severity, 0.1–2; disease index, 0.1–29%; number of seeds, 3.3–19; number of pods per plant, 8.3–62; and 100-seed weight, 19–53 g. Regression analysis demonstrated that disease incidence, disease severity and disease index were negatively correlated with both the number of pods or seeds per bean plant, whereas there was a positive correlation between the disease and 100-seed weight. If the indicative relations obtained between the disease and yield components are confirmed by further studies, then findings may contribute to the future estimation of bean yield losses to root rots and selection for resistant cultivars.
TL;DR: Phylogenetic analyses of selected regions of these sequences indicated that Pineapple mealybug wilt-associated virus 5 is a distinct species and most closely related to PMWaV-1, which was the most commonly found of the four viruses and conversely PM WaV-5 was only occasionally found.
Abstract: Pineapple mealybug wilt-associated virus 1 (PMWaV-1), 2 (PMWaV-2) and 3 (PMWaV-3) have been detected in Australian commercial pineapple crops, along with a previously undescribed ampelovirus, forwhich the name Pineapple mealybug wilt-associated virus 5 (PMWaV-5) is proposed Partial sequences extending from open reading frame 1 b through to the heat shock protein homologue were obtained for PMWaV-1, -3 and -5 Phylogenetic analyses of selected regions of these sequences indicated that PMWaV-5 is a distinct species and most closely related to PMWaV-1 The amino acid sequence variation observed in the RNA-dependent RNA polymerase region of PMWaV-1 isolates was 958–984% and of PMWaV-3 isolates was 922–995% p ]In surveys of mealybug wilt disease (MWD) affected crops, none of the four viruses was clearly associated with the disease at all survey sites A statistically significant association (P <0001) between the presence of PMWaV-2 and symptoms was observed at one survey site (site 3), but the virus was at a low incidence at the remaining three survey sites By contrast, although PMWaV-1 and −3 were equally distributed between symptomless and MWD-affected plants at site 3, there was a statistically significant (P < 0001) association between each of these two viruses and MWD at sites 1 and 4 At site 2, there was a statistically significant (P < 0001) association only between PMWaV-3 and MWD PMWaV-1 was the most commonly found of the four viruses and conversely PMWaV-5 was only occasionally found Australian isolates of PMWaV-1, -2 and -3 were transmitted by the mealybug species Dysmicoccus brevipes
TL;DR: Geographic isolation and relatively recent arrivals of agricultural materials from the rest of the world have given Australia, New Zealand and Papua New Guinea a plant-associated nematode fauna substantially different from other countries, and many of the major cosmopolitan species of plant-pathogenic nematodes are now present.
Abstract: Geographic isolation and relatively recent arrivals of agricultural materials from the rest of the world have given Australia, New Zealand and Papua New Guinea a plant-associated nematode fauna substantially different from other countries. Although many of the major cosmopolitan species of plant-pathogenic nematodes are now present, several remain absent, particularly those with more restricted host, geographic or ecological ranges. There is a substantial indigenous plant-feeding native fauna associated with the native vegetation, but this is concentrated in a few families and genera, and few native species have become pathogenic to recently introduced commercial crops. Grasslands of both native and introduced species, as well as coastal habitats (dunes, beaches and mangroves) have been widely studied. Many plant-feeding and free-living nematodes from these habitats are from cosmopolitan taxa, but there are also endemic species and genera. Notable are the many species from otherwise terrestrial taxa in the coastal habitats. Geographic isolation has played a substantial role in evolution and radiation of many of the new taxa, as well as perhaps in the lack of many plant-parasitic nematode taxa.
TL;DR: Sugarcane smut, caused by the fungus Ustilago scitaminea, was reported for the first time in Queensland on 8 June 2006 and was subsequently identified in the Mackay region on 6 November 2006 and in the Herbert River region on 15 December 2006.
Abstract: Sugarcane smut, caused by the fungus Ustilago scitaminea, was reported for the first time in Queensland on 8 June 2006. The initial finding was near Childers in the cultivar Q205. Sugarcane smut was found in Western Australia in 1998, but was contained in that state and was considered to be eligible for inclusion as a pest under the Government and Plant Industry Cost Sharing Deed in Respect of Emergency Plant Pest Responses (EPP deed). The emergency response to the incursion was coordinated by the Queensland Department of Primary Industries and Fisheries, CANEGROWERS and BSES Limited and followed the PLANTPLAN generic emergency response plan. The eligibility of the incursion for funding under the arrangements of the EPP deed was considered by the National Management Group, who met several times, but in August 2006 they failed to agree that the incursion was eligible for funding. The delay in coming to this decision left growers and industry in doubt about the funding available for activities such as the destruction of infested fields.
TL;DR: It is demonstrated that exogenous SA treatment of rice could increase production of the enzymes implicated in resistance to oxidative stresses and antifungal compounds, which appear to play a significant role in rice resistance to the invasion of blast fungal pathogens.
Abstract: Salicylic acid (SA) may play an important role in induced disease resistance in rice but its mode of action in plant defence remains unclear. In this study,we examined the effect of exogenous SA treatment on host resistance and biochemistry of four near-isogenic lines of rice to the blast fungus Magnaporthe grisea. Host resistance, as indicated by suppressed blast lesion formation, was enhanced following foliar application of 8 mM SA in the two isogenic lines susceptible to the pathogen. Exogenous SA treatment increased the enzyme activity of peroxidase and polyphenol oxidase in all isogenic lines. Chemical analysis of crude leaf extracts detected higher concentrations of four rice phytoalexins (oryzalexin A, C and F and momilactone A) following root application of SA treatment. Furthermore, the hydrolysates of conjugated antifungal compounds from the SA-treated rice showed a much more potent inhibitory effect on the spore germination of M. grisea than the controls from the untreated plants, suggesting the existence of inducible conjugated antifungal compounds. Taken together, these data demonstrate that exogenous SA treatment of rice could increase production of the enzymes implicated in resistance to oxidative stresses and antifungal compounds, which appear to play a significant role in rice resistance to the invasion of blast fungal pathogens.
TL;DR: The results indicated that the time of application of BABA and the susceptibility of the cultivars affect both the protection against late blight and the expression of defence molecules like glucanases, chitinases and phenolic compounds.
Abstract: The protective effect of β-aminobutyric acid (BABA) on two potato cultivars (Bintje and Pampeana) with different levels of horizontal resistance against Phytophthora infestans was investigated during the crop cycle. Plants were treated with BABA16, 23, 30, 38, 44, 51, 61 or 75 days after emergence. After each application, the percentage of protection and the content of glucanases, chitinases and phenolic compounds were determined in detached leaves. The foliar pretreatment with BABA up to 30 days after emergence showed a 60% protection percentage against P. infestans in cv. Pampeana, while cv. Bintje almost reached 20%. The results indicated that the time of application of BABA and the susceptibility of the cultivars affect both the protection against late blight and the expression of defence molecules like glucanases, chitinases and phenolic compounds.
TL;DR: Latent period response to temperature was independent of cultivar resistance, however, cultivar×temperature interactions were evident for disease incidence, sporulation incidence and lesion severity responses.
Abstract: The impact of temperature was assessed on mycelial growth of Colletotrichum lupini on agar and on anthracnose expression in lupin cultivars with varying degrees of resistance. Growth rate of C. lupini was determined at temperatures from 5 to 3°C. Fungal growth was observed at temperatures from 10 to 30°C with maximum growth rate occurring at 25°C. In growth cabinet experiments, the impact of temperatures ranging from 10 to 26°C was observed on anthracnose development in the Lupinus angustifolius cultivars Myallie (susceptible), Merrit (moderately susceptible) and Wonga (resistant) and the L. albus cultivar Kiev Mutant (extremely susceptible). At 10°C, disease incidence was very low (0–12%) in all cultivars, reflecting the slow in vitro growth of the fungus at this temperature. Increasing temperature from 12 to 26°C reduced the latent period by more than 50% and increased disease incidence, sporulation incidence and lesion severity. Latent period response to temperature was independent of cultivar resistance. However, cultivar×temperature interactionswere evident for disease incidence, sporulation incidence and lesion severity responses. Anthracnose resistance in cv.Wonga was temperature sensitive. At 12 and 18°C, disease incidence and severity inWonga were significantly lower than other L. angustifolius cultivars tested but at 26°C disease incidence and severity were similar to other cultivars.
TL;DR: In this article, the authors compared a range of fungicides and found that chlorothalonil was superior to mancozeb and carbendazim in controlling ascochyta blight in all varieties.
Abstract: Ascochyta blight has constrained chickpea production in Australia. Therefore, control strategies are required to prevent major crop losses. Field experiments in 1998 and 1999 showed that all the chickpea varieties grown commercially in Australia at that time were very susceptible to the disease. Fortnightly sprays with the fungicide chlorothalonil could effectively control epidemics but the additional cost significantly reduced profitability. The kabuli variety Kaniva was still profitable to grow but desi varieties were less profitable than alternative crops. Further experiments were conducted throughout Australia in 1999, 2000 and 2001 to compare a range of fungicides and to determine the optimum rates and frequency of fungicide sprays. Chlorothalonil was superior to mancozeb and carbendazim. Fortnightly sprays of chlorothalonil controlled ascochyta blight in all varieties; sprays every 3 weeks did not eliminate yield losses due to ascochyta blight in susceptible varieties under high disease pressure.Lowfungicide rates were less effective than maximum recommended rates when conditions favoured a severe epidemic. Several newvarieties with improved resistance to ascochyta blight have been released and arenowgrown commercially in Australia. Field experiments were established in 2002 and 2005 to compare these new varieties with the older, susceptible varieties. The new varieties had significantly less disease than the older varieties and did not require fortnightly sprays. The best new varieties required fungicide sprays only at the podding stage in order to prevent pod and seed infection. As more varieties with greater resistance become available, growers will need to apply fewer fungicides and the consequences of missing a fungicide spray will be less serious. However, variety specific management strategies still need to be developed to enable growers to tailor their control strategy to each variety’s susceptibility in order to minimise fungicide usage and maximise profits.
TL;DR: It is suggested that sizeselection of seed is not an option for growers to eliminate WSMV infected seed from seed lot, and seed transmission was shown to occur at very low levels in infected commercial wheat crops of New South Wales, Australia.
Abstract: Wheat streak mosaic, caused by Wheat streak mosaic virus (WMSV), is a recent disease of wheat in Australia. This study was conducted to investigate seed transmission of WSMV and is the first publication to report on the rate of WSMV seed transmission in artificially inoculated wheat cultivars (0.4%). Furthermore, seed transmission was shown to occur at very low levels (with a maximum of 0.22%) in infected commercial wheat crops of New South Wales, Australia. Seed infection was shown not to be correlated with seed size, and no relationship was determined between seed size and transmission. These results confirm the recent discovery that WSMV is a seedborne disease, and suggest that sizeselection of seed is not an option for growers to eliminate WSMV infected seed from seed lot.
TL;DR: Results indicate that organic amendments and mulches have the potential to reduce losses from soilborne diseases in vegetable crops, provided plant nutrition can be managed satisfactorily when beds are mulched with organic matter.
Abstract: Modifications to the capsicum farming system (adding an organic amendment and replacing the standard plastic mulch with a layer of plant residue) were assessed for their potential to reduce losses from soilborne diseases. An amendment of sugarcane residue (12.5 t dry matter/ha) plus ammonium nitrate (100 kg N/ha) incorporated 4 months before planting capsicum enhanced microbial activity, increased numbers of free-living nematodes, decreased populations of rootknot nematode (Meloidogyne incognita) and reduced the severity of galling caused by the nematode. The amendment also reduced the severity of Pythium root rot caused by Pythium aphanidermatum, while a similar effect was obtained in a pot experiment with Pythium myriotylum. Damage from Pythium root rot was more severe in plastic-covered beds than in beds mulched with plant residue, probably because the organic mulch reduced soil temperatures by as much as 12°C. Mulching with plant residue also changed the pest and disease spectrum because it increased losses from cutworms (larvae of Agrostis sp.) and the severity of a leaf spot disease caused by Xanthomonas campestris pv. vesicatoria. The organic mulch also reduced fruit yield, largely because heavy rainfall leached nutrients (particularly N, K, Ca and Mg) from beds that were not covered with plastic. These results indicate that organic amendments and mulches have the potential to reduce losses from soilborne diseases in vegetable crops, provided plant nutrition can be managed satisfactorily when beds are mulched with organic matter.
TL;DR: Various components of current integrated pest management programs, including crop rotation, nematode monitoring, clean planting material, organic amendments, farming systems to enhance biological suppression of nematodes and judicious use of nematicides are discussed.
Abstract: Plant-parasitic nematodes are important pests of horticultural crops grown in tropical and subtropical regions of Australia. Burrowing nematode (Radopholus similis) is a major impediment to banana production and root-knot nematodes (predominantly Meloidogyne javanica and M. incognita) cause problems on pineapple and a range of annual vegetables, including tomato, capsicum, zucchini, watermelon, rockmelon, potato and sweet potato. In the early 1990s, nematode control in these industries was largely achieved with chemicals, with methyl bromide widely used on some subtropical vegetable crops, ethylene dibromide applied routinely to pineapples and non-volatile nematicides such as fenamiphos applied up to four times a year in banana plantations. This paper discusses the research and extension work done over the last 15 years to introduce an integrated pest management approach to nematode control in tropical and subtropical horticulture. It then discusses various components of current integrated pest management programs, including crop rotation, nematode monitoring, clean planting material, organic amendments, farming systems to enhance biological suppression of nematodes and judicious use of nematicides. Finally, options for improving current management practices are considered.
TL;DR: The race delineations of these strains from the WA grainbelt are expected to be helpful for selecting appropriate genotype resistance(s) for sowing in relation to the planned expansion of the B. juncea industry and also if there is future development of alternative cruciferous oilseed industries in WA.
Abstract: White rust caused by Albugo candida is a serious pathogen of Brassica juncea (Indian mustard) and one posing a potential hazard to the presently developing canola-quality B. juncea industry in Australia. The varieties of B. juncea available in Australia are known to be susceptible to attack by race 2 of A. candida, a race that is known to have two pathotypes, 2A and 2V. Two isolates of A. candida, representing strains collected from B. juncea and Raphanus raphanistrum (wild radish) from two sites in Western Australia (WA) were tested on cruciferous host differentials to characterise their pathogenic behaviour. The results clearly showthat the strains obtained from B. juncea and R. raphanistrum are different in their host range. The isolate from B. juncea showed significant levels of sporulation on both differential cultivars of B. juncea, Vulcan and Commercial Brown, used for differentiating pathotype 2A from 2V, confirming the presence of pathotype 2V in WA. This is the first report of pathotype 2V in Australia. This same isolate was able to infect Brassica napus from China (FAN 189), B. tournefortii (wild turnip) B. nigra and R. sativus. This serves as a caution to breeders when sourcing resistance against A. candida from B. napus germplasm. The isolate from R. raphanistrum, tested against the same set of cruciferous host differentials, caused significant sporulation on B. juncea differential Commercial Brown, B. napus (FAN 189), B. nigra (90745), R. raphanistrum and R. sativus (White Icicle). Our strain from R. raphanistrum, while being a direct threat to B. juncea, may be a hazard, not only to any B. napus germplasm developed from B. napus breeding lines from China, but also to B. nigra and R. sativus, should these species be utilised commercially in Australia. The race delineations of these strains from the WA grainbelt are expected to be helpful for selecting appropriate genotype resistance(s) for sowing in relation to the planned expansion of the B. juncea industry and also if there is future development of alternative cruciferous oilseed industries in WA.
TL;DR: Thyophthora capsici was determined as the main pathogen causing Phytophthora foot rot of black pepper in Vietnam based on disease symptoms, morphological characteristics, pathogenicity and ITS-RFLP analysis.
Abstract: Black pepper is a high value export crop in Vietnam. The production of black pepper, however, is reduced remarkably by Phytophthora foot rot disease. Although the disease was first reported in 1952, the identity of the causal organism has never been conclusively determined. Hence, the aim of this study was to identify the causal agent associated with Phytophthora foot rot epidemics in black pepper. A national survey of the disease and collection of samples were conducted in four major black pepper growing provinces. Phytophthora isolates obtained from the diseased roots, collars and leaves as well as the root-zone soil were identified by morphological characteristics and verified by ITS-RFLP analysis. Phytophthora capsici was determined as the main pathogen causing Phytophthora foot rot of black pepper in Vietnam based on disease symptoms, morphological characteristics, pathogenicity and ITS-RFLP analysis.
TL;DR: Exogenous application of silicon dioxide through seed priming enhanced the germination and vigour of seed quality parameters and was effective at protecting pearl millet plants against downy mildew and reduced disease by 78% compared with the control.
Abstract: Conclusive evidence is presented here for the implication of silicon in the enhanced resistance of pearl millet to Sclerospora graminicola. Exogenous application of silicon dioxide through seed priming enhanced the germination and vigour of seed quality parameters. Further, with optimised conditions, seed priming in combination with SiO2 soil drenching and foliar spray was effective at protecting pearl millet plants against downy mildew and reduced disease by 78% compared with the control. There is a positive relationship between silicon level in tissues of pearl millet of various cultivars and their degree of downy mildew resistance; for example, resistant cultivar IP19892 had 82 mg/gDWof silicon and highly susceptible cultivar 7042S had 31 mg/g DW of silicon. Exogenous application of silicon was found to augment the silicon level and resistance of the susceptible cultivar. Histological observation of leaves showed higher silicon accumulation in the resistant cultivar compared with the susceptible cultivar. During resistance development in plants treated with silicon, the structural fortification with hydroxyproline-rich glycoprotein was observed and this was relatively and directly proportional to the level of silicon deposition.
TL;DR: The sympatry of foliar hosts with high infectivity and of highly susceptible stem hosts was identified: these areas may be at risk for the development of a forest epidemic and these species are suitable candidates for targeted surveillance programs in high-risk incursion areas of New Zealand.
Abstract: Phytophthora ramorum, the cause of sudden oak death in the westernUSAand a damaging pathogen in Europe, is a biosecurity threat of unknown magnitude to New Zealand and Australasia because of its presence in traded ornamental plants. Knowledge of potential hosts acting as carriers and of symptoms caused by the pathogen on such hosts will strengthen precautionary quarantine regulations to prevent inadvertent introductions of P. ramorum into the region. Also, the identification of potential hosts will permit determination of areas at risk within countries that do not have P. ramorum. Susceptibility of New Zealand plants, including 17 endemic and three commercial species (Eucalyptus globulus, Pinus radiata and Acacia melanoxylon), as well as two known Rhododendron cultivar hosts, was determined by analysing the size of lesions on inoculated excised leaves and branches, while infectivity was determined by counting sporangia produced on leaves. In order to identify extremely susceptible hosts, seven species were inoculated using three concentrations of zoospores ranging from low (1×102 zoospores/mL) to high (5×103 zoospores/mL). In branch inoculations, P. radiata and Nothofagus fusca were as susceptible as the Rhododendron cultivars. Pseudopanax arboreus, Fuchsia excorticata and one Rhododendron cultivar were equally susceptible in leaf inoculations. However, F. excorticata was the only species with 100% infected leaves, high foliar sporulation and was highly susceptible at all three zoospore concentrations. Leptospermum scoparium was the only asymptomatic foliar host that had high reisolations of the pathogen. F. excorticata, P. radiata, N. fusca, P. arboreus and L. scoparium should be added to the potential host list for P. ramorum and monitored for symptoms and sporulation in gardens and nurseries in theUSAand Europe. As part of a precautionary strategy, these species are suitable candidates for targeted surveillance programs in high-risk incursion areas of New Zealand. Furthermore, the sympatry of foliar hosts with high infectivity and of highly susceptible stem hosts was identified: these areas may be at risk for the development of a forest epidemic.
TL;DR: Data indicated that populations of P. oryzae in Argentina are genetically simple and predominantly clonal yet have a high pathotype diversity, revealing 41 pathotypes and 24 international races.
Abstract: The genetic diversity of the rice blast pathogen, Pyricularia oryzae, was analysed in rice-growing provinces of Argentina. A total of 161 isolates of the fungus was collected from 15 rice cultivars at nine locations during 2000-05 and characterised using Pot2-DNA fingerprinting. Based on DNA analysis (isolates with ≥70% band similarity), five lineages were identified and designated A, B, C,Dand E, with 11, 22, 4, 1 and 4 haplotypes identified, respectively. The predominant lineage, B, representing 38% of the collected isolates, was recovered from four cultivars in five locations. In contrast to lineages A and B, which did not contain a dominant haplotype, a single haplotype predominated in lineages C and E. Isolates representing all haplotypes were examined for virulence on a set of differential rice cultivars, near-isogenic lines and commercial cultivars commonly grown in Argentina, revealing 41 pathotypes and 24 international races. There was no significant association between DNA fingerprint similarities and pathotypes. Overall, these data indicated that populations of P. oryzae in Argentina are genetically simple and predominantly clonal yet have a high pathotype diversity.
TL;DR: This paper provides a brief overview of the Australian grape industry and discusses the distribution and economic importance of its main nematode pests and outlines the management practices that are currently used to minimise losses from nematodes.
Abstract: This paper provides a brief overview of the Australian grape industry and discusses the distribution and economic importance of its main nematode pests and outlines the management practices (hot water treatment of planting material, nematode-resistant rootstocks and nematicides) that are currently used to minimise losses from nematodes. However, the main focus of the paper is the research that will be required to improve current practices for managing nematodes. Topics covered include: (i) methods of producing nematode-free planting material; (ii) breeding programs to develop rootstock material suitable for local conditions; (iii) the use of molecular-assisted selection and genetic modification to develop transgenic grapevines and rootstocks with resistance to several nematode species; (iv) options for enhancing naturally occurring biological controls; (v) the introduction of agronomic practices that improve the capacity of grapevines to withstand attack from nematodes; and (vi) the development of farming systems that improve soil physical, chemical and biological properties and enhance the suppressiveness of soil to nematodes.
TL;DR: A new species of Pesotum is described here as P. australi sp.
Abstract: Pesotum accommodates synnematal anamorphs of Ophiostoma spp. with sympodially proliferating conidiogenous cells. These fungi are usually closely associated with wounds on trees and the insects that visit them. During tree disease surveys in Uganda, as well as studies of fungi infecting wounds on Acacia mearnsii trees in Uganda and Australia, many isolates resembling species of Pesotum were collected. The aim of this study was to identify these fungi using both morphological and DNA sequence comparisons. The Pesotum, anamorph of O. quercus was the only species collected from multiple collections in Uganda. Collections from Australia represent a new species of Pesotum described here as P. australi sp. nov.
TL;DR: This is the first report on the characterisation of a PVYNP strain infecting eggplant in Iran, and sequence information identified the virus as a strain of Potato virus Y, designated eggplant strain of PVY (PVY-Eg), with a somewhat lower homology to an Indian isolate of Eggplant mottle virus belonging to the PVYO subgroup.
Abstract: Mosaic disease of eggplant (Solanum melongena L.) iscommonin many fields of southern Iran.Avirus isolated from diseased plants in the Boushehr Province was characterised by biological, serological, physiochemical and molecular studies. The virus was mechanically transmissible to Nicotiana tabacum cv. Turkish and several other solanaceous species and to Chenopodium amaranticolor and C. quinoa. Purified preparations of the virus contained flexuous rod-shaped particles. Two aphid species, Myzus persicae and Aphis gossypii, transmitted the virus between Turkish tobacco plants. An antiserum raised against purified virus preparation was used in the detection of the virus. Molecular weights of the virus genome and the coat protein (CP) were estimated at 3.1–3.2×106 and 36×103 Da, respectively. The 3′ region of the virus genome, including the CP and the untranslated region (UTR), was amplified using two pairs of general primers of the family Potyviridae. Sequence information identified the virus as a strain of Potato virus Y (PVY), designated eggplant strain of PVY (PVY-Eg), with the highest sequence homology to a tomato strain of PVY (PVY-LY84.2) from Spain, and a somewhat lower homology to an Indian isolate of Eggplant mottle virus belonging to the PVYO subgroup. Cluster dendrograms based on CP amino acid and 3′UTR sequences placed PVY-Eg within the PVYNP subgroup. This is the first report on the characterisation of a PVYNP strain infecting eggplant in Iran.
TL;DR: In the black spot experiments, difenoconazole, pyraclostrobin and chlorothalonil used alone or in spray programs were as effective as, or better than, the industry standards, mancozeb and tebuconazole.
Abstract: Several chemicals including strobilurins (pyraclostrobin and azoxystrobin), triazoles (difenoconazole and tebuconazole), dithiocarbamates (propineb, metiram, ziram and mancozeb) and the phthalimide chlorothalonil were evaluated in three field experiments in north Queensland, Australia, for the control of brown spot (caused by Corynespora cassiicola) and black spot (caused by Asperisporium caricae) of papaya. Chlorothalonil and pyraclostrobin were shown to be more effective than the industry standard, mancozeb, for the control of brown spot. In the black spot experiments, difenoconazole, pyraclostrobin and chlorothalonil used alone or in spray programs were as effective as, or better than, the industry standards, mancozeb and tebuconazole. Plants treated with pyraclostrobin and difenoconazole had more fruit unaffected by black spot (97% and 99% respectively) than plants treated with tebuconazole (51%), mancozeb (20%) and the untreated controls (1%). Laboratory tests also showed that A. caricae was more sensitive to difenoconazole (EC50 of 2 ppm) than tebuconazole (EC50 of 14 ppm). In 2007, off-label permits were obtained for chlorothalonil for control of brown spot and difenoconazole and chlorothalonil for the control of black spot of papaya.