Search

True mangroves and mangrove associates are salt‐tolerant trees and shrubs that serve a critical role in preserving the ecological balance of tropical and subtropical estuarine environments. However, they are not immune to the damage caused by fungal pathogens. In this study, leaves exhibiting leaf spot symptoms were gathered from mangrove estuary and forests in Prachuap Khiri Khan, Thailand. Through morphological and multilocus phylogenetic analyses (LSU, ITS, RPB2 and TUB2) along with genealogical concordance phylogenetic species recognition, we identified Allophoma acanthi sp. nov. from Acanthus ilicifolius. Additionally, A. minor was identified as the causative agent of leaf spots in true mangrove and mangrove associate species, namely, Acanthus ilicifolius, Combretum sp., Hibiscus tiliaceus, Intsia bijuga, Lumnitzera racemosa and Sonneratia alba. We also provide evidence to support the synonymization of A. thunbergiae with A. minor. All eight isolates of Allophoma species in this study demonstrated pathogenicity to their original hosts with varied virulence, confirming Koch's postulates. Our findings contribute to the understanding of fungal pathogens affecting true mangroves and mangrove associates. [ABSTRACT FROM AUTHOR]

Genotypic and virulence diversity of Neofusicoccum luteum and N. australe isolates recovered from grapevines displaying symptoms of dieback and decline in New Zealand were investigated. The universally primed PCR ( UP- PCR) method was used to investigate the genetic diversity of 40 isolates of N. luteum and 33 isolates of N. australe. Five UP- PCR primers produced a total of 51 loci from N. luteum and 57 from N. australe with a greater number of polymorphic loci produced in N. australe (86%) compared with N. luteum (69%). Analysis of UP- PCR data showed both species found in New Zealand vineyards were genetically diverse at both the inter- and intra-vineyard levels with only a single pair of clonal isolates in N. luteum. Cluster analysis of UP- PCR data produced four genetic groups in N. luteum and 10 in N. australe ( P < 0.05). For both species, there was no relationship between the genetic groups and the origin of isolates. The mean genetic diversity ( H) of N. luteum was less than for N. australe, being 0.1791 and 0.2417, respectively. Pathogenicity assays of both species using isolates from either the same or different genetic groups inoculated onto either green shoots or grapevine trunks, showed virulence diversity within the population; however, no correlation was identified between genetic groups and virulence. [ABSTRACT FROM AUTHOR]

A collection of isolates of the fungi Leptosphaeria maculans and L. biglobosa, which cause blackleg disease on Brassica napus (canola/oilseed rape) and other Brassicaceae species, was assembled to represent the global diversity of these pathogens and a resource for international research. The collection consists of 226 isolates (205 L. maculans and 21 L. biglobosa) from 11 countries. The genomes of all 205 L. maculans isolates were sequenced, and the distribution and identity of avirulence gene alleles were determined based on genotypic information and phenotypic reactions on B. napus lines that hosted specific resistance genes. Whilst the frequencies of some avirulence alleles were consistent across each of the regions, others differed dramatically, potentially reflecting the canola/oilseed rape cultivars grown in those countries. Analyses of the single‐nucleotide polymorphism (SNP) diversity within these L. maculans isolates revealed geographical separation of the populations. This "open access" resource provides a standardized set of isolates that can be used to define the basis for how these fungal pathogens cause disease, and as a tool for discovery of new resistance traits in Brassica species. [ABSTRACT FROM AUTHOR]

Bacterial canker of cherry, caused by Pseudomonas syringae pathovars, is a major constraint to cherry growing in New Zealand. The prevalence of strains from cherry orchards in Central Otago, the main growing area for cherries in New Zealand, was studied, to better understand the epidemiology of the disease. Pseudomonas spp. isolates were collected from symptomatic and asymptomatic cherry tissue from 23 commercial cherry orchards in 2015. Isolates were classified into strains belonging to three different taxonomic groups by determining their phylogeny using the gltA gene sequence for all the strains and multilocus sequence analysis (MLSA) of four housekeeping genes for 35 strains. Pathogenicity of all Central Otago strains was tested on immature cherry fruit to support the phylogenetic classification. The two main taxonomic groups were P. syringae pv. syringae (Pss) and P. syringae pv. morsprunorum race 1 (Psm1), in Phylogroup 2 (PG2) and Phylogroup 3 (PG3), respectively. The third group comprised nonpathogenic strains classified as Pseudomonas spp. Strains of Psm1 formed a monophyletic group, representing an almost clonal population. There was more variation detected within strains of Pss, although they were restricted to group PG2d. Nonpathogenic Pseudomonas spp. and pathogenic Pss and Psm1 strains coexisted in the same orchard. It was concluded that Pss is the predominant pathovar in Central Otago. This is the first detailed study of the P. syringae species complex in cherry orchards in New Zealand and provides the basis for future epidemiology studies. [ABSTRACT FROM AUTHOR]

A total of 57 Ilyonectria liriodendri isolates were identified by a combination of species-specific PCR and DNA sequencing from a collection of 174 Ilyonectria-like isolates recovered from 101 diseased grapevine samples. These samples were representative of the national vineyard, comprising material contributed by 49 grape growers across seven grape growing areas. This species was predominant, representing 33% of the recovered isolates, and has been reported as a major pathogen of grapevines in other countries. The genetic diversity of the 57 New Zealand isolates was compared to that of isolates from Australia and South Africa using universally primed polymerase chain reaction ( UP- PCR). A total of 66 informative loci distinguished 52 genotypes, of which five contained up to four clonal isolates. Four main clades were identified in a neighbour-joining ( NJ) tree. The international isolates (Australia and South Africa) were placed in a clade that did not include New Zealand isolates. There was a high level of intra- and inter-vineyard genetic variation indicating the free movement of isolates between regions. A subset of nine isolates from different branches of the NJ tree produced two vegetative compatibility groups and hyphal fusion was observed between non-self pairings. Pathogenicity tests using isolates from different genetic groups inoculated onto either detached roots or 1-year-old potted vines showed variability in virulence; however, no correlations were detected. [ABSTRACT FROM AUTHOR]

This study assessed the symptoms that developed when 114 Botryosphaeriaceae isolates from grapevine nursery plant materials were used to inoculate excised green shoots and 1-year-old rooted canes of Sauvignon blanc. The experiments showed that all isolates and species were able to produce lesions. Overall, the Neofusicoccum species were shown to be highly pathogenic in both tissue types while the Diplodia species were highly pathogenic on canes but not on green shoots. Isolates of the most prevalent species, N. luteum and N. parvum, showed varying lesion lengths on excised green shoots and canes. An evaluation of the factors associated with lengths of lesions showed that they were significantly affected by experimental batch which reflected inherent host and environmental factors over time. Reisolation from inoculated canes also indicated that most isolates of all species except D. seriata were able to spread internally beyond the lesions. Genetic variability analysis using UP- PCR showed that N. luteum isolates were genetically diverse but no association was observed between the phylogenetic group and degree of pathogenicity caused by the isolates. This study demonstrated that all Botryosphaeriaceae species from grapevine nurseries were pathogenic to grapevines and that the lesion lengths varied between species, among isolates within a species and among nursery sources, and was affected by the test method. [ABSTRACT FROM AUTHOR]

This study investigated the ability of Neofusicoccum luteum to infect wounded shoots, trunks, pruned cane ends, leaf surfaces, buds, berries and roots, and its further progression into stem tissues. All tissue types were susceptible to infection except roots, with highest incidences in trunks (100%), cane ends (100%), shoots (92%) and buds (88%), indicating that in New Zealand, N. luteum is primarily a trunk and shoot pathogen. In trunks, there were no external symptoms, although N. luteum could be reisolated from 60 to 70 cm acropetally from the inoculation site after 4 months, by which time the pathogen had progressed into side shoots which became necrotic. Wounded and non-wounded buds became infected; most were killed, with basipetal progression of the pathogen into the supporting shoots. Berries wounded and inoculated at the pre-bunch closure stage were susceptible to N. luteum infection, with isolation incidence increasing over the season and peaking at harvest, when infected berries became mummified and produced pycnidia with many conidia. The pathogen was also able to progress from berries into bunch stems and supporting canes. Results from this research have indicated that N. luteum infection can occur in all aerial grapevine tissues and progress to young stem tissues where it causes wood necrosis. Growers should remove mummified berries from vineyard trash to ensure that pruning and trimming times do not coincide with rainy periods when conidia are released and dispersed. Furthermore, the susceptibility of buds to N. luteum infection indicates the need for fungicide sprays before budburst in spring. [ABSTRACT FROM AUTHOR]

The effects of different inocula of the mycoparasiteConiothyrium minitanson carpogenic germination of sclerotia ofSclerotinia sclerotiorumat different times of year were assessed. A series of three glasshouse box bioassays was used to compare the effect of five spore-suspension inocula ofC. minitans, including three different isolates (Conio, IVT1 and Contans), with a standard maizemeal–perlite inoculum. Apothecial production, as well as viability andC. minitansinfection ofS. sclerotiorumsclerotia buried in treated soil, were assessed. Maizemeal–perlite inoculum at 107 CFU per cm3 soil reduced sclerotial germination and apothecial production in all three box bioassays, decreasing sclerotial recovery and viability in the second bioassay and increasingC. minitansinfection of sclerotia in the first bioassay. Spore-suspension inocula applied at a lower concentration (104 CFU per cm3 soil) were inconsistent in their effects on sclerotial germination in the three box bioassays. Temperature was an important factor influencing apothecial production. Sclerotial germination was delayed or inhibited when bioassays were made in the summer. High temperatures also inhibited infection of sclerotia byC. minitans.Coniothyrium minitanssurvived these high temperatures, however, and infected the sclerotia once the temperature decreased to a lower level. Inoculum level ofC. minitanswas an important factor in reducing apothecial production by sclerotia. The effects of temperature on both carpogenic germination of sclerotia and parasitism of sclerotia byC. minitansare discussed. [ABSTRACT FROM AUTHOR]

The effects ofConiothyrium minitansinoculum quality and an 8-week interval between inoculum application and crop planting on sclerotinia (Sclerotinia sclerotiorum) disease in three successive lettuce crops were investigated in a glasshouse trial. Spore suspensions of three isolates ofC. minitans(Conio, IVT1 and Contans) applied at 108 CFU m−2 and a standard Conio maizemeal–perlite application (06 L m−2, 1011 CFU m−2) were assessed for their ability to controlS. sclerotiorum. Only the maizemeal–perlite inoculum (isolate Conio) consistently reduced sclerotinia disease. In the third lettuce crop only, isolates IVT1 and Contans formulated by Prophyta and isolate IVT as an oil–water formulation, all applied as spore suspensions, reduced disease at harvest compared with the untreated control. Recovery, viability andC. minitansinfection of sclerotia buried during the 8-week period prior to each of the three lettuce crops, and of sclerotia formed on the crop, were tested. Only the maizemeal–perlite inoculum (isolate Conio) reduced the recovery of sclerotia buried in soil for weeks between inoculum application and crop planting, reducing their viability and increasing infection byC. minitans. Eight weeks was sufficient to enableC. minitansto infect sclerotia ofS. sclerotiorum, and may account for disease control. After harvest of the second and third crops, maizemeal–perlite treatment (isolate Conio) reduced the number and viability of sclerotia recovered on the soil surface and increased infection byC. minitanscompared with spore-suspension treatments. The effect of inoculum concentration and the influence of soil temperature (varying with time of year) on infection of sclerotia byC. minitansare discussed. [ABSTRACT FROM AUTHOR]

Inoculation of plants by spraying with a suspension of zoospores (released from sporangia of Sclerospora graminicola) induced immediate encystment of the zoospores and drastically reduced their ability to cause disease. The incidence of infection in spray-inoculated pearl millet seedlings was reduced from 90% when sporangia were sprayed, to less than 30% when zoospores were sprayed. Rapid encystment was observed when zoospores were sprayed from both a hand-pumped sprayer and a compressed-gas sprayer and was probably caused by shearing forces. Chilling suspensions of sporangia prior to spraying delayed zoospore release and was an effective method for maintaining infection potential. Disease incidence was higher when sporangia were chilled to 0·2°C rather than to 4°C. Chilling resulted in some abnormal zoospore structures being released from sporangia when suspensions were returned to 20°C. The frequency of these structures increased with increasing chilling time. For seedlings sprayed with sporangia before zoospore release, a small reduction in disease incidence was observed when chilled inoculum was used, probably due to cold disruption of zoosporogenesis. For large-scale disease resistance screening, this reduction is outweighed by the benefit of a uniform and adequately high disease pressure that can be obtained over many hours using chilled spore suspensions. [ABSTRACT FROM AUTHOR]

Pythium aphanidermaturn antagonized several other fungi after hyphal contact on films of water agar, recorded by video microscopy. It sometimes coiled round, penetrated and caused cytoplasmic coagulation of hyphae of the mycoparasites P. oligandrum, P. acanthophoron, P. mycoparasiticum and P. periplocum, but was not affected by them. It also coiled round, penetrated and coagulated P. ultimum, P. vexans, P. catenulatum, P. dissotocum and (infrequently) P. graminicola. It caused cytoplasmic coagulation of Fusarium oxysporum and Trichoderma aureoviride after contact, but without coiling. Six isolates of P. aphanidermatum behaved similarly, with a mode of action like that of the mycoparasite F. oligandrum but less rapid and consistent than this species. The results are discussed in relation to possible ecological roles of P. aphanidermatum. [ABSTRACT FROM AUTHOR]

Species of Botryosphaeriaceae are important wound pathogens of grapevines as causal agents of botryosphaeria dieback, but the behaviour of their conidia pre-infection is unknown and may be important for disease development. Adhesion properties of conidia were investigated for Botryosphaeria dothidea, Neofusicoccum luteum and N. parvum on substrata with different affinities for water. Greatest adhesion on any surface was reached after 5 min for isolates N. luteum MM558, B. dothidea 007 and N. parvum G652 (53·1, 54·0 and 50·6%, respectively) and for N. luteum isolate CC445 after 20 min (61·4%). As conidia adhered well to all artificial substrata, it appeared as if the attachment process was nonspecific. Overall, surface wettability did not play a major role in the adhesion of conidia. Spore surface proteins appeared to play a role in the adhesion process because treatment of conidia of N. luteum MM558 with a protease completely prevented adhesion. Histochemical labelling of conidia and germlings with Coomassie brilliant blue (specific for proteins) was positive for all isolates, with a blue 'halo' often seen surrounding conidia or near the germ tube emergence point after incubation times conducive to germination. Alcian blue also stained material surrounding conidia after longer incubation times, which indicated that mucopolysaccharide and protein production may be involved in a second phase of adhesion. [ABSTRACT FROM AUTHOR]

Unique bands were identified in single isolates of Neofusicoccum parvum and Neofusicoccum luteum using universally primed polymerase chain reaction (UP-PCR) analysis of isolates obtained from grapevines and non-grapevine hosts in New Zealand, Australia, South Africa and the USA. Primers were designed to amplify a 1550 bp portion of the 1573 bp marker band from N. parvum isolate B2141 and a 510 bp portion of the 524 bp marker band from N. luteum isolate G51a2. A PCR-RFLP assay was developed to distinguish the N. parvum isolate B2141 from other N. parvum isolates, based on a polymorphism found in the marker band using the TaqI restriction endonuclease. For N. luteum isolate G51a2, the designed primers were specific at an annealing temperature of 63°C in the PCR. The sensitivity threshold of the N. parvum and N. luteum isolate-specific markers was 50 pg and 5 pg, respectively, when used in standard PCR with purified genomic DNA. The sensitivity of the N. parvum isolate-specific marker was increased to 0·5 pg by nested PCR. The specificity test of both isolate-specific markers with six other Botryosphaeriaceae spp. showed that they were specific to their respective species and isolates. Both markers were able to detect the conidia of N. parvum and N. luteum marker isolates in rainwater samples collected at different distances from an inoculation point in the vineyard. The results showed that rain splash could disperse the conidia of both of these species up to 2 m from the inoculum point in a single rainfall event. [ABSTRACT FROM AUTHOR]

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

Experiments were conducted on olive plants in controlled environments to determine the effect of conidial concentration, leaf age, temperature, continuous and interrupted leaf wetness periods, and relative humidity (RH) during the drier periods that interrupted wet periods, on olive leaf spot (OLS) severity. As inoculum concentration increased from 1·0 × 10 to 2·5 × 10 conidia mL, the severity of OLS increased at all five temperatures (5, 10, 15, 20 and 25°C). A simple polynomial model satisfactorily described the relationship between the inoculum concentration at the upper asymptote (maximum number of lesions) and temperature. The results showed that for the three leaf age groups tested (2-4, 6-8 and 10-12 weeks old) OLS severity decreased significantly ( P < 0·001) with increasing leaf age at the time of inoculation. Overall, temperature also affected ( P < 0·001) OLS severity, with the lesion numbers increasing gradually from 5°C to a maximum at 15°C, and then declining to a minimum at 25°C. When nine leaf wetness periods (0, 6, 12, 18, 24, 36, 48, 72 and 96 h) were tested at the same temperatures, the numbers of lesions increased with increasing leaf wetness period at all temperatures tested. The minimum leaf wetness periods for infection at 5, 10, 15, 20 and 25°C were 18, 12, 12, 12 and 24 h, respectively. The wet periods during early infection processes were interrupted with drying periods (0, 3, 6, 12, 18 and 24 h) at two levels of RH (70 and 100%). The length of drying period had a significant ( P < 0·001) effect on disease severity, the effect depending on the RH during the interruption. High RH (100%) resulted in greater disease severity than low RH (70%). A polynomial equation with linear and quadratic terms of temperature, wetness and leaf age was developed to describe the effects of temperature, wetness and leaf age on OLS infection, which could be incorporated as a forecasting component of an integrated system for the control of OLS. [ABSTRACT FROM AUTHOR]

Botryosphaeriaceous species are significant grapevine trunk pathogens worldwide, which can be difficult to identify to species level using conventional morphological methods. This study developed and optimized a quick, reliable molecular identification method that could facilitate investigations into the epidemiology of these diseases in vineyards. The multi-species primers, BOT100F and BOT472R, amplified a 371-372 bp portion of the rRNA gene region from the six botryosphaeriaceous species commonly found in New Zealand vineyards. In silico analysis indicated that they would amplify DNA from six of the 12 lineages of the Botryosphaeriaceae, including all of the main species pathogenic to grapevines. A detection sensitivity of 1 and 0·1 pg DNA in standard and nested PCR, respectively, was achieved and this was calculated as equivalent to 2·5 conidia. Validation of the primers for environmental samples showed that their specificity was not compromized by the presence of competing DNA templates extracted from wood and soil. Single stranded conformational polymorphism (SSCP) analysis of the amplicons could resolve Neofusicoccum australe, N. luteum, Diplodia mutila and D. seriata, but did not differentiate between N. parvum and N. ribis. The optimized PCR-SSCP was used to identify botryosphaeriaceous species present in rainwater traps collected over 1 year in a vineyard known to contain infected vines. It could detect multiple species in individual samples and demonstrated differences in the dispersal patterns of conidia from different species. Given the specificity and sensitivity of this method it could prove useful in epidemiology studies involving the numerous botryosphaeriaceous species that infect a wide range of host species. [ABSTRACT FROM AUTHOR]

Crown rust (caused by Puccinia coronata f. sp. lolii) is a serious foliar disease of the pasture and turfgrass perennial ryegrass ( Lolium perenne). Previous genetic studies have detected both qualitative and quantitative resistance mechanisms, and interpretation of the genetic system is complicated by variation within the sexually reproducing pathogen. Resistant and susceptible parental genotypes of ryegrass were identified using a composite urediniospore population collected from three geographically distinct locations. A two-way pseudo-testcross mapping population was obtained as the F1 progeny of the pair-cross between ryegrass parental genotypes Vedette6 and Victorian9. Both parents showed intermediate resistance against a pathogen population collected in a single geographical zone (Hamilton, Victoria), but in the F1 population, significant variation for a range of resistance-associated characters was detected. Statistical analysis of phenotypic data suggested a major gene effect, hence bulked segregant analysis with map-assigned simple sequence repeat (SSR) markers was used to scan the genome. A marker showing strong association with resistance was assigned to linkage group (LG) 2 of perennial ryegrass. Analysis of 11 LG2 SSR markers defined an interval between loci xlpssrh03f03 and xlpssrk02e02 as containing the gene or genes ( LpPc1) conferring crown rust resistance. Resistance gene determinants were inherited from both parents, with up to 80% of the total phenotypic variation explained by markers segregating from Vedette6 and up to 26% of the variation explained by markers segregating from Victorian9. The two contributions together resulted in an additive increase in effect, with fully resistant individuals requiring determinants from both parents. A conserved syntenic relationship was observed with linkage group B of Avena strigosa, which is the location of a cluster of resistance genes to the oat form of crown rust. The implications of this study for marker-assisted selection of disease resistance in perennial ryegrass are discussed. [ABSTRACT FROM AUTHOR]