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The toxicity of cultures of Fusarium species and subspecies in section Gibbosum from soils from locations in various climatic regions of Australia was determined using a chick bioassay. Most cultures of F. compactum and F. acuminatum subsp. armeniacum were found to be highly toxic irrespective of geographical origin. The other species and subspecies in section Gibbosum viz; F. acuminatum subsp. acuminatum, F. equiseti, F. scirpi , and F. longipes , were shown to be non-toxic or of low toxicity. Selected culture extracts of F. compactum, F. acuminatum armeniacum and F. acuminatum acuminatum were analysed by gas chromatography after clean up and hydrolysis for the four main trichothecene families, namely; nivalenol (NIV), deoxynivalenol (DON), scirpentriol (Sctol) and T-2 tetraol (T-2tol). Some cultures of F. compactum were found to produce high levels of T-2tol derivatives while others produced high levels of Sctol derivatives. Cultures of F. acuminatum armeniacum produced high levels of T-2tol derivatives and trace levels of Sctol derivatives. In contrast, only trace levels of T-2tol and Sctol were detected in hydrolysed culture extracts of F. acuminatum acuminatum . GC/MS analysis of individual trichothecene derivatives in culture extracts of F. compactum indicated that the main trichothecenes produced were either acuminatin or diacetoxyscirpenol respectively, while F. acuminatum armeniacum was found to produce mainly T-2 toxin and neosolaniol.

Soil samples were collected along two transects in relatively undisturbed forest and woodland areas in north-eastern Queensland, Australia. One transact was between Cairns (on the east coast) and Chillagoe (approximately 200 km inland), and the other between Mossman (on the east coast) and Mt. Lewis, (approximately 18 km inland). Fusarium species were isolated using the soil dilution plate technique and by plating soil debris, predominantly root material. Thirteen species, F. beomiforme, F. chlamydosporum, F. compactum, F. equiseti, F. longipes, F. moniliforme, F. nygamai, F. oxysporum, F. proliferatum, F. scirpi, F. semitectum, F. solani and F. subglutinans and one undescribed population of Fusarium were isolated. There was no marked difference between the Fusarium species recovered by the two isolation techniques. F. semitectum and F. moniliforme were only recovered from sites having high rainfall. F. oxysporum and F. solani were isolated from the majority of the soils being most abundant in sites having higher rainfall. Fusarium species in the section Gibbosum and F. nygamai were isolated only in those areas with relatively lower rainfall.

Fusarium acuminatum Ellis & Everh. sensu Gordon (section Gibbosum) subspecies armeniacum subsp. nov. is described. Hawksworth's (4) guidelines were adopted as the basis for assigning this infraspecies population to the rank of subspecies. Fusarium acuminatum subsp. armeniacum was differentiated first from typical isolates of F. acuminatum in Minnesota recorded under the name F. roseum (Lk.). emend. Snyder & Hansen 'Gibbosum' (5; Windels, unpubl). It also was recovered in eastern Australia and described informally by Forbes (3) and Burgess et al. (1). Cultures of this subspecies were isolated in South Africa by Marasas et al. (7), Rabie et al. (9), and Van Wyk et al. (10) who referred to them as atypical isolates of F. acuminatum. Rabie et al. (9) reported that some of these isolates produced high levels of T-2 toxin. These populations exhibiting this phenotype are designated as a sub

Fusarium species were isolated from grassland soil samples from four areas located along the Tropic of Capricorn between Rockhampton on the east coast and Boulia on the margin of the Simpson Desert in Queensland, Australia. Fusarium species were isolated by plating root debris on Selective Fusarium Agar, and by the dilution plate technique on peptone PCNB agar. The five most frequently isolated species were F. chlamydosporum, F. compactum, F. equiseti, F. nygamai and F. solani, all of which were isolated from each sampling area. F. chalmydosporum, F. compactum and F. equiseti were isolated more frequently from the drier sampling areas. F. solani was isolated more frequently from Rockhampton, a wetter, subtropical area. F. longipes was only isolated from the Rockhampton area. F. beomiforme was isolated frequently from the Rockhampton area, one culture was obtained from the Emerald area, and it was not isolated from the two driest areas. Five species. F. moniliforme, F. napiforme, F. oxysporum, F. scirpi and F. semitectum, and the undescribed population were isolated infrequently.

Crown rot, caused by the fungus Fusarium pseudograminearum (teleomorph Gibberella coronicola) is a major disease of wheat in the Australian grain belt. However, there is little information available on the population structure of this pathogen. We measured genetic diversity as assessed with amplified fragment length polymorphism (AFLP) analysis within and between populations of F. pseudograminearum from northeastern, south central, and southwestern regions of the Australian grain belt. Amongst the 217 isolates, 176 haplotypes were identified and grouped into two main clusters. One cluster contained isolates from populations in northeastern Australia, and the other cluster contained isolates from populations in south central and southwestern Australia. The southern populations were distinguished from the northeastern populations by higher levels of population differentiation (Gst) between them and genetic identity amongst the regional populations. We hypothesize that the F. pseudograminearum populations from northeastern and southern Australia are independent, which could result from different founding events or from geographic isolation and the accumulation of genetic differences due to genetic drift and/or selection.

Temperature and osmotic potential had a significant effect on linear growth of Fusarium oxysporum, Fusarium species in section Liseola, and three recently described species. Linear growth was greatest at 25 C for all species except F. beomiforme for which maximum linear growth occurred at 30 C. Osmotic potentials of -0.4 MPa, -1.0 MPa, and -2.2 MPa were favorable for growth of all Fusarium species tested, with maximum linear growth recorded at ?1.0 MPa. Linear growth was reduced sig? nificantly at osmotic potentials of -4.8 MPa and -9.9 MPa. Osmotic potential also influenced for? mation of sporodochia, microconidia, and chlamydospores on both carnation leaf agar and soil agar. Some implications of these findings for the activity and survival of Fusarium species are discussed.

The herbicides atrazine, chlorsulfuron and glyphosate were added to potato dextrose agar (PDA), PDA with TES buffer [ N -tris(hydroxymethyl) methylaminoethanesulfonic acid] (PDAT) and Defined Buffered Agar with TES (DBAT) with unamended controls for each medium and herbicide. Fusarium graminearum Schwabe Group 1 was grown on the media at 25° C and colony growth rates were estimated for 3 days. The fungus was also grown on DBAT amended with the herbicides at five temperatures, and on DBAT adjusted to five osmotic potentials with Nad at 15 or 25°C. Atrazine significantly reduced growth rates on PDA and PDAT at 50 μg ml −1 , a concentration equivalent to field rates used with sorghum. Temperatures between 10 and 30°C and osmotic potentials between −0.5 and −4.5 MPa at 25°C did not modify the response of the fungus to atrazine (1, 5, 10 or 50 μg ml −1 ). Colony pigmentation was generally reduced and margins tended to become more irregular with increased amounts of atrazine. Chlorsulfuron did not affect growth rates on any medium or between 10 and 30° C on DBAT, except at amounts well above field rates (0.5μg ml −1 ). Glyphosate did not affect growth rate at any temperature or osmotic potential. The results indicate that it is unlikely that the herbicides will have a significant direct effect on parasitic growth of F. graminearum Group 1 under field conditions. The influence of unbuffered media and the amounts of nutrients on the significance of such studies is discussed.

The toxicity of cultures of Fusarium acuminatum subsp. acuminatum and Fusarium acuminatum subsp. armeniacum grown on Weet-Bix® medium was assessed using a chick bioassay. Thirty-nine of 45 cultures of F. a. armeniacum tested produced at least 50% mortality in the chick bioassay. In contrast, of the 26 cultures of F. a. acuminatum tested, only nine produced at least 50% mortality. Selected extracts of both subspecies were analyzed by gas chromatography after clean-up and hydrolysis for the four main trichothecene families, namely; nivalenol (NIV), deoxynivalenol (DON), scirpentriol (Sctol), and T-2 tetraol (T-2tol). Levels of up to 500 μg/g and 7 μg/g of T-2tol were detected in F. a. armeniacum and F. a. acuminatum extracts respectively. Four cultures each of F. a. armeniacum and F. a. acuminatum were also grown on two solid media (Weet-Bix® and Vermiculite) and two liquid media (MYRO and GYEP). Culture extracts were again tested for toxicity and analyzed for trichothecene production. Cultures of F. a. armeniacum grown on the solid media and on MYRO produced the highest toxicity. Levels of up to 168, 129, 150, and 8 μg/g of T-2tol were detected in cultures of F. a. armeniacum on Weet-Bix®, Vermiculite, MYRO, and GYEP respectively. In contrast, only trace amounts of T-2tol were detected in extracts of F. a. acuminatum on all media. Sctol levels of less than 0.5 μg/g were also detected in some cultures of both subspecies on solid media, but only F. a. armeniacum produced trace levels of Sctol on liquid media. Analysis without hydrolysis of F. a. armeniacum extracts revealed that the most common trichothecenes produced were T-2 toxin and neosolaniol. These data indicate that F. a. armeniacum is a highly toxigenic fungus. © 1992 Wiley-Liss, Inc.

This is the first report of Pythium root rot of chrysanthemum, and the pathogen responsible, Pythium aphanidermatum, from Quang Nam and TT Hue Provinces in Vietnam. The typical symptoms included stunting, wilting, and necrosis of the main, lateral and feeder rootlets. A black necrotic lesion girdling the lower stem was present in some diseased plants. The root rot commonly caused death of diseased plants and affected plants at all growth stages. The pathogen was also isolated from transplants affected by root rot, and sampled directly from boxes transported from Dalat, Lam Dong Province, the source of most transplants used in Quang Nam. Metalaxyl was shown to provide effective control of Pythium root rot in a field trial when used to dip transplants before planting, and as a regular drench. Metalaxyl also provided effective control of the disease in commercial crops on the farm where the field was located.

The occurrence of Neocosmospora vasinfecta is reported for the first time from Vietnam where it was found in association with peanut roots affected by root rot. It was isolated from diseased roots from peanut crops in Nghe An Province in March 2007 but perithecia were not observed on the diseased roots. However, characteristic perithecia were produced abundantly in pure cultures on potato dextrose agar and carnation leaf-piece agar. Subsequently, perithecia were observed on diseased peanut roots in Thua Thien Hue Province. Representative cultures from Nghe An were confirmed as Neocosmospora vasinfecta by the Centraalbureau voor Schimmelcultures (CBS).

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.

Sclerotinia blight, caused by Sclerotinia sclerotiorum is reported from Quang Nam Province, Vietnam, for the first time. The disease is common in cool wet winter and spring seasons on dwarf and climbing beans, peanuts and occasionally on chilli plants. A serious epidemic occurred in peanuts in some communes in spring 2008, following a period of cool wet weather after the crop canopy had closed and when flowering was well advanced.

Fusarium wilt of watermelon caused by Fusarium oxysporum f. sp. niveum caused seedling losses in nurseries, as well as severe losses in many crops in Nghe An province, Vietnam, in 2008. Isolates of the fungus were shown to be pathogenic. All 20 cultivars grown in the province in 2008 were susceptible. This is the first formal report of this disease in Vietnam.

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.

Severe losses of plants in crops of Telosma cordata occurred in Nam Dan District, Nghe An Province, Vietnam, following prolonged wet weather in September 2007. Phytophthora palmivora was isolated consistently from the margin of diseased and healthy tissue in underground stems. Koch’s Postulates were fulfilled. This is the first report of this disease.

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.

Fusarium proliferatum (Matsushima) Nirenberg (teleomorph = Gibberella intermedia) is a member of a group of closely related and agriculturally important fungal plant pathogens known as the 'Gibberella fujikuroi species complex'. The genetic structure of populations of F. proliferatum in non-agricultural soils collected from Finke Gorge National Park, Northern Territory, Australia, was investigated. F. proliferatum was isolated from soils from the root zone of Livistona mariae palms. Amplified fragment length polymorphism (AFLP) analysis of 77 isolates distinguished 73 unique haplotypes with an overall genetic similarity of 0.94. Cluster and bootstrap analysis indicated the population was composed of two well supported groups, possibly of clonal origin. Statistical analysis of the distribution of genotypes in the study area showed there were clear spatial subdivisions of genotypic diversity (P < 0.001) indicating limited mixing of genotypes.

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.

The influence of surface soil moisture and stubble management practices on the progress of infection of wheat by Fusarium pseudograminearum, the cause of crown rot, was assessed in a field trial at Moree in northern New South Wales during the growing seasons of 1994, 1995 and 1996 by analysis of infection progress curves. During the dry season of 1994, wheat was sown into dry surface soil. Increases in incidence of infection followed rainfall events that raised the water content of the surface soil above the equivalent of a water potential of –1.5 MPa. The rate of increase in incidence of infection was more uniform in the 1995 and 1996 seasons, which had more regular rainfall. The area under the infection progress curve (AUIPC) was consistently greater when stubble was retained on the surface compared with incorporation with a disc plough, and this difference was significant in 2 out of 3 years. Comparison of AUIPCs indicated greater epidemiological differences between stubble management treatments than did comparisons of incidence of infection at single points during the season.

Rotational effects of chickpea, an important N2-fixing pulse legume of the northern grains region, on subsequent wheat require quantification of the contribution of the legume to soil N and the N status of the wheat, and of suppression of soil and stubble-borne pathogens, such as crown rot (Fusarium graminearum Schwabe Group 1). Results from selected treatments of 10 experiments in northern New South Wales in which chickpea and wheat in one season were followed by wheat in following seasons indicated generally higher dry matter (DM) and grain yields of wheat after chickpea than after wheat. Responses to chickpea were -0·8 to 3·3 t/ha (shoot DM) and -3 to 39 kg N/ha (shoot N). Responses in wheat grain yields were -0·1 to 1·7 t/ha (mean 0·85 t/ha); grain N responses were -2 to 33 kg/ha (mean 19 kg/ha). Grain protein responses were small (0·6%) and variable. Although these productivity responses could be explained largely in terms of additional nitrate-N following chickpea, we measured reduced incidences of crown rot in wheat after chickpea (range 1-36%, mean of 12%), compared with wheat after wheat (range 5-52%, mean 30%). Modelling the incidence of crown rot indicated highly significant interactions between prior crop and total water (pre-plant soil water plus in-crop rainfall). When wheat followed chickpea, incidence of the disease declined sharply with increasing water. When wheat followed wheat, there was a marginal decline in disease incidence with increasing water. Our results support the strategy of using legumes in rotation with wheat in the northern grains region for enhanced soil-N supply and disease-break effects.

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 effect of 3 stubble management regimes (burning after harvest, incorporation with a disc plough, retention on the surface) on the incidence of infection of wheat with Fusarium graminearum Schw. Group 1 was studied for 5 seasons at 2 sites at Moree, New South Wales. One site had high initial incidence (site A) and the other low initial incidence (site B). There were no differences in incidence of infection between retained and incorporated treatments. Stubble burning reduced the increase in incidence of infection in 2 of 5 years at site A and 3 of 4 years at site B. Failure of control in other years was attributed to susceptible weed hosts and poor burns. When stubble was retained on the plots at site B that had been burnt, incidence of infection in the next season increased to a level not significantly different from the retained or incorporated treatments. Incidence of infection at the fourth consecutive wheat crop at both sites was close to the maximum recorded, which was 92% at site A and 65% at site B. There was no evidence of a decline in incidence by the time of the most recent season assessed (eighth year of continuous wheat cultivation at site A, and sixth year at site B). In most years, the differences in yield between treatments were not significant.

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.

The influence of temperature and external water potential on mycelial growth, production of pseudothecia and maturation of ascospores by P. tritici-repentis was examined. In the range 10°–30 °C, mycelial growth was optimal at 20°–25°, but pseudothecial production was not temperature dependent. Ascospores developed most quickly at 15°. Mycelial growth and pseudothecial numbers declined as the external water potential decreased. Pseudothecia were not produced at water potentials lower than −1.7 MPa. Ascospores did not develop when the external water potential was less than −2.8 MPa. The production of pseudothecia on naturally infected wheat, barley and oat straw also was examined. Pseudothecia developed on all straw types in equivalent numbers, and production was not correlated with the reaction of the living host to infection.

The influence of environment, management practices and cultivar on the rate of cereal straw decomposition was assessed in laboratory and field studies. Decomposition was measured using the reduction in dry wt as an indicator of decomposition. The rate of straw decomposition decreased with reductions in water potential at potentials below − 0.1 MPa. The decomposition rate at−0.01 MPa was lower than at −0.1 MPa. The rate of straw decomposition increased with increasing temperature over the range measured (5–35°C). Buried straw decomposed more rapidly than surface straw in all treatments except at −0.01 and −5.0 MPa. The influence of three stubble management practices on the rate of decomposition of straw of two wheat cultivars, Suneca and Kite, was assessed in field experiments lasting 2 yr. The rate of decomposition was greatest following the partial incorporation and burial of wheat residues. The retention of residues on the soil surface retarded decomposition. The straw of wheat and barley cultivars tested in the laboratory varied significantly in respect of the rate of decomposition. The straw of barley cultivars decomposed more rapidly than straw of the wheat cultivars tested. In the field studies there was no significant difference in the rate of decomposition of straw of the two cultivars. The percentage of hot water-soluble components, hemicellulose and cellulose decreased, while the proportion of lignin increased as the straw decomposed. Total N increased in buried straw, but decreased in the straw retained on the soil surface. There was no relationship between the amount of a chemical component and the rate of straw decomposition other than the higher percentage of hot water-soluble components found initially in barley straw.

Fusarium crookwellense is described and illustrated. Initial isolates were from potato tubers from the Crookwell area of New South Wales, Australia. Additional isolates have been recovered from wheat, corn, barley, Paspalum sp., Pinus sp. and debris from temperate and tropical pasture soils from various locations in Eastern Australia. Isolates from a variety of host plants and debris from soil have been obtained from the U.S.A., South Africa, France, Colombia, and China. Descriptions of the sporodochial cultures and macroconidia are given and compared to F. sambucinum, F. culmorum, F. robustum , and F. graminearum. F. crookwellense is generally more abundant in temperate high rainfall or irrigated areas.

Fusarium nygamai is described and illustrated. The key features of this species are the formation of microconidia in relatively short chains as well as false heads and the production of rough-walle...