The predominant disease affecting oil palms in Colombia is bud rot, a decay of the growing leaf tissues that may eventually reach the meristem. Previous studies have suggested many biotic and abiotic ...causes, but Koch’s Postulates have recently confirmed Phytophthora palmivora as the primary pathogen of bud rot. In this paper, we describe the infection process in immature leaflets inoculated with zoospores of P. palmivora using light microscopy and scanning electron microscopy. Initially, zoospores were attracted primarily to leaf trichomes, where some developed appressorium-like structures and subsequently penetrated the tissue. Germinated zoospores were also observed penetrating the stomata or intercellular spaces. After penetration hyphae colonized the intercellular leaf spaces, followed by intracellular invasion, penetrating to the vascular bundles and then spreading throughout the host tissue. Between 12 and 24 h after inoculation, hyphae emerged from the surface of the leaflet through the stomata, trichomes and intercellular spaces. Within 36 and 48 h, sporangia, chlamydospores, and newly released zoospores were observed, starting a new cycle of secondary infections. This sequence was consistently observed in repeated experiments. We suggest that in the field collection of moisture at the base of emerging leaflets stimulates the release of zoospores and infection. Colonization is restricted once the leaflet emerges, leaving dormant chlamydospores and hyphae in small necrotic lesions. Successive rain events stimulate the formation of new generations of sporangia, zoospores and infections, which, if frequent enough, may completely colonize the bud area. Subsequent colonization of infected tissues by opportunistic bacteria and fungi increases the severity of bud rot symptoms. The information presented here provides an overview of histopathological aspects of the early infections process of P. palmivora in detached immature leaflets.
Novel species of microfungi described in the present study include the following from Australia: Phytophthora amnicola from still water, Gnomoniopsis smithogilvyi from Castanea sp., Pseudoplagiostoma ...corymbiae from Corymbia sp., Diaporthe eucalyptorum
from Eucalyptus sp., Sporisorium andrewmitchellii from Enneapogon aff. lindleyanus, Myrmecridium banksiae from Banksia, and Pilidiella wangiensis from Eucalyptus sp. Several species are also described from South Africa, namely: Gondwanamyces
wingfieldii from Protea caffra, Montagnula aloes from Aloe sp., Diaporthe canthii from Canthium inerne, Phyllosticta ericarum from Erica gracilis, Coleophoma proteae from Protea caffra, Toxicocladosporium strelitziae from Strelitzia reginae,
and Devriesia agapanthi from Agapanthus africanus. Other species include Phytophthora asparagi from Asparagus officinalis (USA), and Diaporthe passiflorae from Passiflora edulis (South America). Furthermore, novel genera of coelomycetes include Chrysocrypta
corymbiae from Corymbia sp. (Australia), Trinosporium guianense, isolated as a contaminant (French Guiana), and Xenosonderhenia syzygii, from Syzygium cordatum (South Africa). Pseudopenidiella piceae from Picea abies (Czech Republic),
and Phaeocercospora colophospermi from Colophospermum mopane (South Africa) represent novel genera of hyphomycetes. Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.
Chestnut rot is an important disease of chestnut trees in Oceania (Australia, New Zealand), and Europe (Italy, France, Switzerland, United Kingdom). The causal agent has been identified as the fungus
...Gnomoniopsis smithogilvyi
(
Gnomoniaceae
,
Diaporthales
). Koch’s Postulates was demonstrated on nuts from three Australian chestnut varieties with
G. smithogilvyi
from Australia, New Zealand and Italy. The Australian and New Zealand isolates were pathogenic on all three varieties, however the Italian isolate produced smaller lesions on all three, and was only mildly pathogenic on Decoppi Marone. Infection of chestnut floral and vegetative tissues was investigated during the chestnut phenological stages of flowering (sampled twice over two years), immature nuts and burrs, mature nuts and burrs, and tree dormancy (immature nuts and burrs, mature nuts and burrs, and tree dormancy were sampled once in one year).
Gnomoniopsis smithogilvyi
was present in all the sampled phenological stages, most frequently from female flowers during the flowering period. In the first year, the fungus infected 82% of female flowers, while in the second year only 10% were infected. Ascospore trapping in a laboratory chamber experiment confirmed ascopores are released in to the air from infected burrs. Ascospore trapping in an Australian chestnut orchard during the flowering period also showed ascospores are released in to the air, with peak trapping times at sunset and the hours following sunset (8-11 pm), and the hours following sunrise (7-9 am). These experiments support the hypothesis that ascospores of
G. smithogilvyi
infect chestnut trees, particularly the flowers. The fungus then exists as a latent pathogen in reproductive and vegetative tissues, leading to the development of the disease during nut maturity.
Fusarium oxysporum f. sp. cucumerinum is the fungal pathogen responsible for Fusarium vascular wilt of cucumber. In Australia, disease management in soilless greenhouse cucumbers is limited by the ...understanding of the disease cycle, in particular the risk associated with infection of pruning wounds by airborne propagules. Aerial dissemination of the pathogen in response to temperature and relative humidity was investigated using a specific and sensitive quantitative real-time PCR assay. Both macroconidia and microconidia were identified as airborne propagules and a potential relationship between fluctuation in relative humidity and spore release was found, however, it appears that crop disturbance may also influence conidia liberation. Experimental inoculation of stem wounds with conidia however, failed to establish infections. These results suggest that aerial inoculum propagates and disseminates the pathogen, however airborne spores are deposited on the substrate surface and infection occurs primarily through the root. We conclude that while airborne conidia are a risk to infection of cucumber plants in soilless greenhouse crops, resistant rootstocks are likely to provide good protection against this pathogen.
Phytophthora
wilt, caused by
Phytophthora capsici
Leon., is the most devastating disease of chilli in Bhutan. In this study, effects of bed heights to improve soil drainage, animal manures and ...fungicides on
Phytophthora
wilt on chilli were evaluated on naturally infested plots at the wet lowlands site of Bhur and in a farmer’s field at a drier, higher altitude site at Darachu in Bhutan. The experimental design was a split-plot arrangement of a randomised complete block. Bed height (flat or raised) was the main plot with amendments (poultry manure, cattle manure) or fungicide drenches (metalaxyl or potassium phosphonate) as subplot treatments. Aged manures (28,000 kg DW/ha) were applied to the field one week before planting. Chilli seedlings in the nursery bed were drenched with 1 g a.i./L potassium phosphonate or 10 mg a.i./L metalaxyl 24 hours prior to transplanting. Plant survival was significantly higher on raised beds than flat beds at Bhur (
p
= 0.0105), but not Darachu, although marketable yields were significantly higher on raised beds at both sites. At Darachu, poultry manure significantly improved plant survival (50%), as did cattle manure (41%) compared to unamended control plots (25%). Similar results were found at Bhur, with survival on poultry manure amended soils (40%) and cattle manure (34%), both significantly higher than on unamended soils (20%). Both fungicides significantly improved plant survival (
p
< 0.0001) and marketable yield (
p
< 0.0001) at both sites. Yields at the high-altitude, drier site at Darachu were generally higher than at the wet lowlands site at Bhur. Marketable yields on phosphonate-treated plots at both Bhur and Darachu, (16.8 and 19.1 tonnes/ha, respectively) and metalaxyl-treated plots (15.4 and 17.5 tonnes/ha) were significantly higher than on untreated plots (6.0 and 7.5 tonnes/ha). A highly significant (
p
= 0.0007) benefit of combining raised beds planting with manure and fungicide treatments on yield was observed at the wet lowlands site, but not at the drier site. Integrating raised bed planting with the application of poultry manure and fungicides is likely to significantly reduce yield losses of chilli due to
Phytophthora
wilt in different regions of Bhutan.
In Papua New Guinea (PNG) cocoa (Theobroma cacao) is one of the most important cash crops grown in the tropical lowland and island regions. As in most cocoa‐growing areas, phytophthora black pod and ...canker cause significant yield losses. Cocoa breeding activities in PNG are focused in East New Britain province where disease control recommendations are also developed. This study tested the hypothesis that there was no diversity in the Phytophthora palmivora population causing black pod on cocoa by characterizing the variation in pathogen populations within and between the five major cocoa‐growing areas. Diseased pods were sampled hierarchically from the five locations and additional isolates were collected from soil, stem and leaf lesions, or retrieved from culture collections. Morphological characters showed continuous variation within the range described for P. palmivora. Genetic analysis revealed that the isolates belonged to one dominant clonal lineage, with restricted distributions of several other subpopulations. Lowest diversities were found in the geographically isolated Karkar Island and East Sepik province. Soil isolates showed greater genetic diversity than isolates from cocoa lesions. Intra‐farm variation was as much as inter‐farm or inter‐province variation. Both mating types were detected, although no strong evidence of sexual recombination was observed. The analysis revealed limited geographic, temporal or host specialization, suggesting continuous selection for pathogenicity from a genetic pool of P. palmivora. These findings have significant implications on the deployment of cocoa genotypes, enforcement of inter‐province quarantine and sustainable disease management strategies.
Diseases in natural and agricultural systems have been linked to species of the Oomycete genus
Phytophthora
, around the world. Direct detection of the pathogen requires sampling of soil or plant ...material, which can be expensive, difficult to obtain and error-prone. As an alternative, reflectance spectroscopy provides a potential indirect method for detecting symptoms of infection by
P. cinnamomi
. Here we evaluate the use of reflectance spectroscopy to detect physiological changes associated with infection in host plants using spectral indices designed to quantify changes in plant pigments (pigment indices), leaf water content (water indices) and fluorescence (fluorescence indices). Two grasses and two tree species with different susceptibilities to
P. cinnamomi
were inoculated and/or exposed to water stress in a glasshouse experiment. Inoculated plants were detected using pigment and fluorescence indices, which also had the capacity to separate inoculated plants from water stressed uninoculated plants. While inoculation may have caused an opposing spectral response to water stress in some indices, plants that were both water stressed and inoculated then demonstrated an intermediate response. Water stress was detected using the water indices in all four species, and spectroscopic changes associated with inoculation were often greater in the susceptible species. Our results indicate that reflectance spectroscopy at the leaf scale detects the effects of
P. cinnamomi
infection in native vegetation. Extending these results has the potential to improve early detection of disease in natural vegetation and avoiding manual sampling, thus improving management of the disease.
Chestnut rot of
Castanea sativa
(European chestnut) and
C
.
crenata
(Japanese chestnut) ×
C
.
sativa
hybrids is a significant problem facing the Australian chestnut industry. It affects the chestnut ...kernel, symptoms occur as pale, medium and dark brown lesions occurring on the endosperm and embryo. Twenty-two orchards in Victoria and New South Wales were surveyed in 2008, and 21 of these were again surveyed in 2009. All 22 orchards were affected by chestnut rot. Incidence at individual orchards up to 72 % was found in 2008, and 35 % in 2009. Incidence varied widely between orchards and within individual orchards between the 2 years. All varieties were affected, including Decoppi Marone, Purton’s Pride and Red Spanish, displaying examples of both high incidence (>1 %) and industry acceptable incidence (0–1 %) depending on orchard and year. In 2008 and 2009, surveys of Sydney Markets showed incidence of >1 % (2008: varieties Decoppi Marone, Purton’s Pride; and in 2009: varieties Purton’s Pride, Red Spanish). The early December flowering Red Spanish had significantly higher average incidence than the early to mid December flowering Decoppi Marone and Purton’s Pride, suggesting that the timing of flowering may be an important factor affecting incidence. There was a mild positive correlation between orchard incidence and December rainfall of the previous year (r
2
= 0.4), indicating rainfall during the chestnut flowering period had a mild effect on incidence.
A “broadbeam” facility is demonstrated for the vertical microbeam at Surrey’s Ion Beam Centre, validating the new technique used by Barazzuol et al. (Radiat Res 177:651–662,
2012
). Here, droplets ...with a diameter of about 4 mm of 15,000 mammalian cells in suspension were pipetted onto defined locations on a 42-mm-diameter cell dish with each droplet individually irradiated in “broadbeam” mode with 2 MeV protons and 4 MeV alpha particles and assayed for clonogenicity. This method enables multiple experimental data points to be rapidly collected from the same cell dish. Initially, the Surrey vertical beamline was designed for the targeted irradiation of single cells with single counted ions. Here, the benefits of both targeted single-cell and broadbeam irradiations being available at the same facility are discussed: in particular, high-throughput cell irradiation experiments can be conducted on the same system as time-intensive focused-beam experiments with the added benefits of fluorescent microscopy, cell recognition and time-lapse capabilities. The limitations of the system based on a 2 MV tandem accelerator are also discussed, including the uncertainties associated with particle Poisson counting statistics, spread of linear energy transfer in the nucleus and a timed dose delivery. These uncertainties are calculated with Monte Carlo methods. An analysis of how this uncertainty affects relative biological effect measurements is made and discussed.
In the late 1990’s a decline syndrome emerged in jackfruit orchards in the Eastern Visayas region of the Philippines. Symptoms included trunk cankers, wilting and dieback of the canopy and, in many ...cases, tree death. The decline resulted in significant yield losses for farmers. A survey was conducted to assess disease incidence and to identify the causal organism. Fifty two percent of farms surveyed had a disease incidence greater than 50 %. On some farms 100 % of trees were affected. While
Fusarium
,
Pythium
,
Colletotrichum
and
Phytophthora
species were isolated during disease surveys only
Phytophthora
was shown to consistently cause decline symptoms in artificially inoculated jackfruit. Healthy jackfruit seedlings, detached leaves and fruit inoculated with
Phytophthora
isolates expressed similar symptoms to those observed in the field. Based on morphological and molecular characteristics the pathogen was identified as
Phytophthora palmivora
.
PDF
