Search

Citrus tristeza virus was detected for the first time in the Lao People’s Democratic Republic. Samples were collected from citrus trees across the southern provinces for testing in Australia. RNA was extracted and tested using conventional and real-time reverse transcription polymerase chain reactions with the virus detected in 12 of 59 samples tested. Viral identities were confirmed by sequencing. Additional confirmation was obtained by an enzyme-linked immunosorbent assay. The implications of the presence of this virus for citrus production in Lao are discussed briefly.

Citrus exocortis viroid, citrus bent leaf viroid, hop stunt viroid and citrus dwarfing viroid were detected for the first time in Lao PDR. Samples were collected from citrus trees across southern Lao PDR for laboratory testing in Australia. RNA was extracted and amplified using quantitative reverse transcription polymerase chain reaction (qRT-PCR); viroid identities were confirmed by sequencing.

Fusarium is one of the most remarkable genera of the fungi. It is remarkable for it’s genetic and morphological diversity, it’s wide geographic distribution, the diversity of it’s relationships with plants, the diversity of plant diseases for which it is responsible, and its abundance and diversity in natural ecosystems. Evidence to support this contention is presented and discussed focusing on the author’s career-long and continuing research on the genus. The diversity and socio-economic importance of Fusarium diseases is illustrated by reference to diseases common in the Australasian region. Examples include the Fusarium wilts caused by formae speciales of F. oxysporum and the stalk and cob rots of maize and cereal head blights caused by F. graminearum. The importance of Fusarium mycotoxins is noted. Endophytic colonization of living plant tissue by Fusarium species remains a poorly understood and insidious phenomenon. Examples are provided in relation to crop plants and plants in natural ecosystems. The role of natural ecosystems as reservoirs of crop pathogens and potential emerging pathogens is discussed briefly in relation to disease management and biosecurity.

Phytophthora capsici is an economically significant pathogen of various important annual and perennial crops in temperate and tropical regions. Not much is known about the genetic diversity of this pathogen worldwide. In Vietnam it is the causal agent of devastating diseases on several hosts, including chilli and black pepper. Crossinfectivity of P. capsici isolates obtained from the two hosts was demonstrated. Analysis of forty-six P. capsici isolates based on Random Amplified Microsatellites (RAMS) and Repetitive Extragenic Palindromic (REP) fingerprinting revealed that isolates from black pepper were genetically distinct from isolates recovered from chilli. Twenty-two isolates from chilli clustered into two clonal groups at a DICE similarity level of >85%, whereas twenty-four isolates from black pepper were separated from these chilli isolates at a similarity level of

Indonesia is one of the world’s leading producers of vanilla, an important cash crop for smallholders. Stem rot disease is a major constraint to vanilla production in Indonesia and has caused significant economic losses over the last decade. Previous reports of vanilla stem rots in the Asia-Pacific region include those caused by Fusarium, Colletotrichum and Phytophthora species. In this paper, we report Fusarium species associated with the disease. Seven major vanilla-producing provinces were surveyed for disease incidence and 850 samples were collected. Isolates were recovered from diseased stem tissues using a selective medium. Pure cultures on carnation leaf-piece agar and potato dextrose agar were identified based on morphological criteria. Some ambiguous species were verified based on DNA sequences of the translation elongation factor gene.Atotal of 542 Fusarium isolates were recovered, comprising 12 species, namely F. decemcellulare, F. fujikuroi, F. graminearum, F. mangiferae, F. napiforme, F. oxysporum, F. polyphialidicum, F. proliferatum, F. pseudocircinatum, F. semitectum, F. solani and F. subglutinans. F. oxysporum was the most commonly isolated species from all areas surveyed, followed by F. solani and F. semitectum. F. oxysporum, F. solani and F. semitectum were tested for pathogenicity to vanilla but only F. oxysporum was shown to be pathogenic. The vanilla stem rot pathogen in Indonesia is verified to be F. oxysporum f. sp. vanillae.

The status of teaching and research in plant pathology in Vietnam in 1993 is summarised together with an outline of the key features of the climate. The four phases of a capacity building program in plant pathology from 1993 to 2009 are then described and discussed. The program was concerned mainly, but not exclusively, with the insidious diseases caused by soilborne fungal pathogens. They have emerged as a major cause of yield loss, particularly over the past decade, presumably as a consequence of changed cropping practices and movement of infected planting material. Their socioeconomic impact has been considerable. The program involved development activities at national level and more recently at provincial level. The importance of integrating English-in-context training with diagnostic training at provincial level is highlighted.

The susceptibility of grain sorghum (Sorghum bicolor) to infection and colonisation by Fusarium pseudograminearum and Gibberella zeae was assessed by isolation studies involving plants grown in field plots and commercial fields in New South Wales. F. pseudograminearum was isolated at a low frequency from plants sampled from an experimental trial site at Livingston Farm, Moree where five different residue management practices had been implemented. In this trial site, 1000 plants were analysed at the pre- and post-senescence stages from four replicate plots in each of five residue management treatments. There was an insignificant level of recovery of F. pseudograminearum from sorghum from the different treatments and inoculum levels. No G. zeae was isolated from this trial site. The effect of agro-climate factors on the occurrence of F. pseudograminearum and G. zeae in mature sorghum stems was assessed from 31 commercial sites representing two climatic regions, Goondiwindi/Moree and the Liverpool Plains. F. pseudograminearum was rarely isolated from the commercial crops that were from two different climatic regions. In contrast, G. zeae was isolated at low to medium levels from the Liverpool Plains region as this region has been identified as suitable for survival of this pathogen. The result also indicated that infection and colonisation of G. zeae was dependent on inoculum levels present in the residues of the preceding crop in the field and in the presence of medium to high rainfall distribution in areas that were detrimental to dispersal and initiation of infection. However, G. zeae was not isolated from sorghum stalks from the Goondiwindi/Moree region. In addition, G. zeae was more frequently isolated from sorghum crops where the wheat residues were known to be infested with G. zeae.

Recent revisions in taxonomy have led to significant changes in our understanding of the Fusarium species associated with sorghum worldwide. To reassess the Fusarium species associated with stalk rot of grain sorghum in Australia, a survey was conducted in two different agroclimatic areas in the northern grain belt of eastern Australia (Goondiwindi and Quirindi). Across three sites in each of the two areas, 288 grain sorghum stalks were sampled from which a total of 324 Fusarium isolates were recovered. Species diversity and eveness was higher in the Goondiwindi area, which is hotter and dryer than the Quirindi area. Fusarium andiyazi and F. thapsinum were the most frequently isolated species overall, comprising 61% and 82% of the isolates from the Goondiwindi and Quirindi areas, respectively. The dominance and relative abundance of these species was associated with agroclimatic areas, with F. thapsinum more abundant in the Goondiwindi area and F. andiyazi more abundant in the Quirindi area. This study represents the first formal report of F. andiyazi and F. thapsinum in Australia.

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.

Little information is available on Fusarium associations with non-crop hosts in grasslands despite extensive studies on Fusarium species in agricultural systems. The Fusarium species associated with the Australian indigenous grass, Austrostipa aristiglumis, including the key pathogenic species Fusarium pseudograminearum, F. thapsinum and Gibberella zeae, in addition to several saprobic Fusarium species, are reported.

The effects of stubble management and crop rotation on suppression of soilborne pathogens was studied in wheat cropping soils taken from established trials at Moree, Warialda and Croppa Creek in northern New South Wales, Australia. Biological resilience was evaluated in two ways: by measuring severity of take-all when the pathogen (Gaeumannomyces graminis var. tritici) was introduced to soil, and by assessing displacement of Fusarium pseudograminearum, the cause of crown rot of wheat, from buried straw pieces. No effects of stubble management or rotation with sorghum were found on suppression of either the introduced or resident pathogens at the Moree site. At Warialda and Croppa Creek, the severity of take-all in pot bioassays was significantly lower in soils from zero-tillage plots with stubble retained than in cultivated plots where the stubble was burnt. This effect was seen in soils from both continuous wheat and wheat-chickpe a rotation treatments. There were no consistent differences between treatments in soil microbial biomass or respiration, or in soil carbon contents. Stubble retention also significantly increased the rate of displacement of F. pseudograminearum from infested straw at Croppa Creek, but not at Warialda. The results showed that, at two out of three sites, retention of crop residues increased the ability of the soil to resist the effects of introduction of a major plant disease.

Several Fusarium species are associated with wheat stems in New Zealand, but there are no detailed reports on the relative abundance and distribution of these species. Hence, a survey was conducted on the South Island of New Zealand to assess the frequency of isolation of Fusarium species associated with randomly collected wheat stem bases and seven grass species. A total of 11 Fusarium species were isolated from wheat stem bases, six of which were also isolated from the other grasses. Putative isolates of the known wheat pathogens F. culmorum and F. pseudograminearum were recovered from wheat and grass stem bases. Fusarium culmorum was isolated from 16% of all wheat stems compared with F. pseudograminearum which was only isolated from 1.5% of the wheat stems. Amplified fragment length polymorphism analysis revealed five distinct clusters among the isolates analysed. These clusters correspond to four pathogenic species, F. pseudograminearum, F. culmorum, F. crookwellense and F. graminearum, based on the sequence of the Tef-1 (translation elongation factor-1a) gene. Isolates from the grass Chionochloa rubra ssp. cuprea which were putatively identified as F. pseudograminearum based on morphological features were found to be isolates of F. graminearum that could not formperithecia homothallically under laboratory conditions. Molecular characterisation confirmed the association of F. pseudograminearum with wheat stem bases, and indicated that there is some genetic divergence between isolates of this important pathogen recovered on the North and the South Islands of New Zealand.

Fusarium wilt of basil, caused by Fusarium oxysporum f. sp. basilici, occurs worldwide but has not been officially recorded in Australia. Fourteen isolates of F. oxysporum were collected from diseased basil from a number of locations in Australia. A PCR diagnostic test previously shown to react only with isolates of F. oxysporum f. sp. basilici was used to identify the isolates and Koch’s postulates were performed for a subset of isolates to confirm pathogenicity. Two techniques, vegetative compatibility grouping and DNA fingerprinting using enterobacterial repetitive intergenic consensus (ERIC) targeted primers, were used to analyse all isolates. Diagnostic PCR confirmed that 11 of the isolates were F. oxysporum f. sp. basilici and they were shown to belong to a single VCG and to have a single ERIC profile, indicating that the population is essentially clonal. This is the first report of this pathogen in Australia.

Fusarium species associated with crown rot were isolated and identified from 409 wheat, barley or durum wheat crops from the eastern Australian grain belt between 1996 and 1999. Fusarium pseudograminearum was almost the only species isolated from crops in Queensland and New South Wales. F pseudograminearum was also the most common species in Victoria and South Australia, but F. culmorum was frequently isolated in these states. F. culmorum accounted for more than 70% of isolates from the Victorian high-rainfall (> 500 mm) region and the South-East region of South Australia. F culmorum comprised 18% of isolates from the Victorian medium-rainfall (350–500 mm) region, and 7% of isolates from each of the Victorian low-rainfall region and the Mid-North region of South Australia. F avenaceum, F crookwellense and F. graminearum were isolated very infrequently. The proportion of F. culmorum among isolates of Fusarium from districts in Victoria and South Australia was strongly correlated with climatic conditions around the end of the growing season, especially with rainfall in November.

A specific molecular diagnostic test was developed to aid in the identification of Australian Armillaria species. The test involves polymerase chain reaction (PCR) amplification using the primer pair A1F and A2R followed by restriction cleavage by Taq 1. Sample populations of the four predominant Australian species, A. luteobubalina, A. hinnulea, A. fumosa and A. novae-zelandiae were collected in the form of basidiome tissue, diploid vegetative culture or infected root material. All samples were correctly identified as Armillaria using the test and subsequently identified to species level by comparing the Taq 1 restriction patterns. Variation was observed within A. luteobubalina Taq 1 restriction patterns, which suggested the presence of sexual recombination within the population. This procedure will assist in the diagnosis of Armillaria root rot and enable an accurate species identification to be made from infected root material or basidiome tissue.

The distributions of Fusarium graminearum (Gibberella zeae), F. pseudograminearum (F. graminearum Group 1) and F. culmorum from cereals in Australia were determined from published survey data and accessions to culture collections. The distributions were analysed in terms of climate, using the climate matching system BIOCLIM. F. graminearum was found mostly in warm temperate to subtropical areas with moderate to high summer rainfall, where mean temperature of the warmest quarter was greater than 18.7°C and rainfall of the warmest quarter was greater than 195 mm. This appeared to be due to the effect of climate on production of maize, the host from which most records were obtained. F. pseudograminearum occurred throughout the main cereal growing areas and its occurrence did not appear to be limited by climate within the Australian grain belt. The distribution of F. culmorum on cereals was more limited than that of F. pseudograminearum. In the southern winter rainfall zone, F. culmorum was restricted to sites with mean summer temperatures less than about 22°C and annual rainfall greater than about 350 mm, whereas in the northern summer rainfall zone F. culmorum was restricted to areas with mean summer temperatures less than about 24.5°C and annual rainfall greater than about 625 mm.

Peronophythora litchii has been recorded on litchi (lychee) in Thanh Ha district, Hai Duong Province, Vietnam causing downy blight of fruit.

Fusarium solani, F. proliferatum, F. oxysporum and F. subglutinans were isolated from the roots of diseased orchids in the genera Coelogyne, Stanhopea and Cymbidium. The pathogenicity of these fungi to Cymbidium orchids was assessed. All four fungi were associated with an increase in root necrosis and were reisolated from diseased roots.

The effects of late (autumn) burning of stubble, and of rotation with sorghum, on the incidence of infection of wheat with Fusarium graminearum Group 1 were studied under conditions simulating commercial practice. Late stubble burning was effective in maintaining a low incidence of infection over four seasons, compared with stubble retention. This did not result in increased yield, possibly because of deleterious agronomic effects of removing residue. Incidence of infection was significantly lower in wheat rotated with sorghum than in continuous wheat, over three complete rotation cycles.

Isolates of Fusariurn graminum from heads of Paspalum dilatatum infected with Claviceps paspali were compared with isolates from soil which had been identified as F. graminum or F. heterosporum on the basis of conidial characters in an earlier study. Differences between isolates were found only in the degree of pigmentation and in the length of macroconidia. Colony morphology, growth rates, and responses of growth to temperature and osmotic potential were similar in all isolates. It was concluded that all isolates belonged to a single species, F. heterosporum. Crossing experiments indicated that the fungus may be homothallic, although ascospores were rare under the conditions used. None of the isolates tested was toxigenic.

The comparative pathogenicity of Fusarium graminearum Group 1 and Fusarium crookwellense to the durum wheat cv. Yallaroi was studied in the greenhouse. F. graminearum Group 1 was shown to cause more severe above ground symptoms of crow rot and a higher incidence of infection than F. crookwellense at all the sampling dates. F. crookwellense did, however, cause some root and crow necrosis.

The identity and abundance of Fusarium species in soils from Palm Valley in the central arid ranges of Australia were assessed in two successive years. This location enabled a comparison of Fusarium species in soils from within the valley where soil moisture is more readily available and the dominant plants are shallow rooted palms, with Fusarium species in soils from the arid rim characterised by spinifex grasses and xeric shrubs. Sixteen sites were sampled. Of the sites within the valley, four were dominated by palms, three by cycads, and four by endemic grasses. The five arid habitats sampled from the rim were dominated by grasses. Twelve Fusarium species and one subspecies were isolated using the dilution plate technique and peptone-PCNB agar. Fusarium oxysporum was recovered from all sites in both years irrespective of vegetation or moisture availability. Fusarium compactum, F. solani and F. scirpi were recovered from most sites. The greatest range of species was recovered from grassed sites, with fewest species being recovered from cycad sites. Taxonomic characteristics of the isolates of F. polyphialidicum are described in detail because they expand the boundaries of the published description.

The effectiveness of three media, peptone-PCNB agar (PPA), dichloran-chloramphenicol agar (DCPA) and modified potato-dextrose agar (MPDA) for the recovery of Fusarium, Alternaria and other fungi from sorghum grain was evaluated using three grain samples. One sample appeared free of mould damage on visual inspection whereas the other two samples had obvious mould damage and were discoloured. PPA was the most effective medium for the recovery of Fusarium spp. while DCPA was most effective in recovering Alternaria spp. MPDA proved useful for the recovery of Phoma sorghina and a number of dematiaceous fungal species. A. alternata was frequently recovered from the clean sorghum sample but rarely recovered from the two mouldy samples. F. moniliforme, F. equiseti, F. chlamydosporum and F. semitectum were all isolated at relatively high frequencies from the two mouldy sorghum samples but only F. moniliforme was recovered from the clean sample. P. sorghina was recovered at high frequencies from the two mouldy samples but not from the clean sample. Thirty species of fungi, including 13 species of Fusarium, were isolated from the two mouldy sorghum samples.

Carnation-leaf agar (CLA), low-nutrient agar (LNA) and dichloran-chloramphenicol-peptone agar (DCPA) were compared for their usefulness in the identification of Fusarium species in section Liseola and the species F. oxysporum, F. solani, F. nygamai, F. napiforme and F. beomiforme. Typical macroconidia, microconidia and chlamydospores were produced consistently on CLA which was the most suitable medium for Fusarium identification. The production of typical microconidia and chlamydospores was consistent on LNA, but sporodochia did not form and only a few macroconidia were produced in the aerial mycelium. On DCPA, formation of microconidia was not consistent, sporodochia were not formed, and only distorted macroconidia were formed in the aerial mycelium. Chlamydospores were slow to form and difficult to detect. This medium was not suitable for the reliable differentiation of the species examined. All isolates of F. oxysporum, F. solani, F. beomiforme, F. napiforme and F. nygamai produced chlamydospores after 2 weeks on soil agar (SA), a medium used solely to enhance chlamydospore formation. nt]mis|Contribution No. 1742, Fusarium Research Center, Department of Plant Pathology, The Pennsylvania State University Agricultural Experiment Station. Authorised for publication 4 May 1989 as Journal Series Paper No. 8174.

High concentrations of V8 Juice and dextrose reduced the number of pseudothecia and inhibited production of ascospores by Pyrenophora tritici-repentis. The production of conidia by the fungus was greatest on filter paper soaked in 20% V8 Juice and transferred toV8-Juice agar. Conidial production was lower on V8-Juice agar, potato-dextrose agar and PDA amended with V8 Juice, and on filter paper soaked in potato-dextrose solution or potato-dextrose solution amended with V8 Juice. Cutting fungal colonies had no significant effect on production of conidia. The production of conidia on V8-Juice-treated filter paper appeared to be an effective method of generating inoculum of P. tritici-repentis.

Cylindrocarpon destructans was isolated from seedling and advanced waratahs with disease symptoms which included stem and lignotuber necrosis, wilting and subsequent death. Cream-coloured sporodochia were produced by C. destructans on the crown and lower stem of both seedling and advanced plants. The pathogenicity of the fungus was tested on seedling plants with chaff inoculum. Symptoms typical of those described above were recorded in the majority of plants inoculated, and C. destructans was recovered from the roots and stems of 87% of inoculated plants.

Fenarimol and triadimefon caused significant (P

The influence of stubble management practices on survival of Fusarium graminearum Group 1 in wheat stubble residues of cultivars Kite and Suneca was examined over a two-year period. Stubble was retained on the soil surface at two rates, incorporated by a rotary hoe or buried in nylon bags. F. graminearum Group 1 was recovered after 104 weeks from stubble which was retained or incorporated. In contrast, burial of the stubble residues was inimical to survival of the fungus which was recovered at very low levels from buried stubble after only 8 weeks and not recovered at all after 104 weeks. Survival of the fungus was closely correlated with decomposition rate of the wheat stubble. There was a tendency for the decline in the recovery of F. graminearum Group 1 to be more rapid in buried stubble of cultivar Kite than in buried stubble of cultivar Suneca.

Head blight (scab) of wheat caused by Fusarium graminearum Group 1 was detected in some crops in the northern wheat belt of New South Wales in 1983. The pathogen was isolated from up to 38.2% of grains from crops affected by head blight. However, it was isolated only from a low proportion (max. 1.6%) of grains of various grades from silos of the Grain Handling Authority of New South Wales. The frequency of isolation of other Fusarium spp. was also quite low despite wet preharvest conditions. F. graminearum Group 1 was isolated from 38.2% of the grains of one sample harvested from a crop with approximately 50% of the heads affected by blight. The trichothecene mycotoxin, 4-deoxynivalenol, was detected (0.6 ppm) in this sample. This is the first record of the production of 4-deoxynivalenol by F. graminearum Group 1 in grain grown under field conditions. 4-Deoxynivalenol was not detected in grain samples from Grain Handling Authority silos.