Minimizing Crop Damage Through Understanding Relationships Between Pyrethrum Phenology and Ray Blight Disease Severity

The most damaging foliar disease of pyrethrum in Australia is ray blight caused by Stagonosporopsis tanaceti. The probability of growers incurring economic losses caused by this disease has been substantially reduced by the implementation of a prophylactically applied spring fungicide program. This has been traditionally initiated when 50% of the stems have reached between 5 and 10 cm in height. Data collected on the emergence of stems from semidormant plants over late winter from 27 fields across northern Tasmania from 2009 to 2011 were used to develop a degree-day model to assist with initiation of the fungicide program. Temporal changes in cumulative proportion of plants with elongated stems were well described by a logistic growth model (R² ≥ 0.97 across all fields). These models were used to calculate the number of days until 50% of the sampling units had at least one elongated stem for the calculation of simple degree-days, assuming a nominal biofix date of the austral winter solstice. The median date for 50% stem elongation was estimated as 30 August in these data sets. Mean error and root mean square error of degree-day models were minimized when a base of 0°C was selected. Mixed-model analysis found prediction errors to be significantly affected by geographic region, requiring the use of scalar correction factors for specific production regions. In the Western region, 50% stem emergence was predicted at 590.3 degree-days (mean prediction error = 0.7 days), compared with 644.6 (mean prediction error = 7.7 days) in the Coastal region and 684.7 (mean prediction error = 0.7 days) degree-days in the Inland region. The importance of fungicide timing for initiation of the spring disease management program in minimizing losses (expressed as percent disease control in October) was also quantified. This relationship was best explained by a split-line regression with a significant break-point of 513.8 degree-days, which corresponded to 10.7% of sampling units with elongated stems. Overall, this research indicated that disease management may be improved by applying the first fungicide of the program substantially earlier in phenological development of the stems than currently recommended

Estimation of Pyrethrum Flower Number Using Digital Imagery

Flower number is the primary determinant of yield in pyrethrum (Tanacetum cineariifolium). Traditional estimates of flower numbers use physical harvesting of flowers, which is time consuming, destructive, and complicated. The precision of flower number estimates may be highly influenced by spatial heterogeneity of plant density and vigor. Here, we examined the potential for digital image analysis to enable rapid, nondestructive assessment of flower number. This technique involved removal of pixels with color profiles not typical of the disc florets of pyrethrum. Particle counting was then performed using defined size and shape parameters to estimate flower numbers. Estimates of flower number based on image analyses were correlated with physical harvests of flowers, with estimates representing about an average of 32% of total flower numbers present within a sampling unit. This relationship was consistent across all observed flower densities. Covariate analysis indicated that occurrences of crop lodging and over mature flower canopies had significant, detrimental effects on system predictions. Pyrethrum flowers were spatially aggregated within fields with the degree of aggregation greatest at the lowest flower densities. Based on modeled flower distributions, eight quadrats (0.49-m² sampling unit) were sufficient to achieve a cv of 0.1 in a 600-m² plot area in all but the lowest flower densities. The utility of this approach for biomass assessment in pyrethrum and other Compositae is discussed.This is the publisher’s final pdf. The published article is copyrighted by the American Society for Horticultural Science and can be found at: http://horttech.ashspublications.org/Keywords: Tanacetum cinerariifolium, spatial variability, remote sensing, image analysis, yield estimation, sample siz

Phylogenetic and population genetic analyses of Stagonosporopsis tanaceti, the cause of ray blight of pyrethrum in Australia

Ray blight is a destructive fungal disease of pyrethrum (Tanacetum cinerariifolium) and a major threat to the Australian pyrethrum industry; the largest producer of pyrethrum worldwide. Multi-gene phylogenies and morphological studies resulted in the recognition of three Stagonosporopsis species as the cause of ray blight on Asteraceae. Stagonosporopsis tanacetiwas described as a new species and the cause of ray blight of pyrethrum in Australia. A de novo genome assembly of paired-end Illumina reads was used to develop a multiplex set of microsatellite markers, which was further employed for temporal and geographical genetic structure analyses of S. tanaceti populations in Australia. Identification of only one mating type gene in the population, high levels of clonality and significant linkage disequilibrium suggested sexual reproduction is absent or infrequent in the Australian pyrethrum fields. Discriminant analysis of principal components (DAPC) and minimum spanning networks detected two distinct clonal lineages in the older populations; each consisting of one dominant multilocus genotype (MLG) and multiple closely-related MLGs at low frequencies. This may be indicative of introduction of two clonal lineages; which have diversified independently in the apparent absence of a sexual stage in the field. Low geographical differentiation among fields in the absence of airborne sexual spores suggests that human-mediated movement of infected seed may be a major source of long distance dispersal. A significant change in the genetic composition of the recent populations of S. tanaceti was detected, which is unlikely to be the result of mutation or recombination, and is subject to further investigation

Spatiotemporal Characterization of Sclerotinia Crown Rot Epidemics in Pyrethrum

Sclerotinia crown rot, caused by Sclerotinia minor and S. sclerotiorum, is a disease of pyrethrum in Australia that may cause substantial decline in plant density. The spatiotemporal characteristics of the disease were quantified in 14 fields during three growing seasons. Fitting the binary power law to disease incidence provided slope (b = 1.063) and intercept (ln(A[subscript p]) = 0.669) estimates significantly (P ≤ 0.0001) greater than 1 and 0, respectively, indicating spatial aggregation at the sampling unit scale that was dependent upon disease incidence. Covariate analyses indicated that application of fungicides did not significantly influence these estimates. Spatial autocorrelation and spatial analysis by distance indices indicated that spatial aggregation above the sampling unit scale was limited to 20 and 17% of transects analyzed, respectively. The range of significant aggregation was limited primarily to neighboring sampling units only. Simple temporal disease models failed to adequately describe disease progress, due to a decline in disease incidence in spring. The relationships between disease incidence at the scales of individual plants within quadrats and quadrats within a field was modeled using four predictors of sample size. The choice of the specific incidence–incidence relationship influenced the classification of disease incidence as greater than or less than 2% of plants, a provisional commercial threshold for fungicide application. Together, these studies indicated that epidemics of Sclerotinia crown rot were dominated by small-scale aggregation of disease. Larger scale patterns of diseased plants, when present, were associated with severe disease outbreaks. The spatial and temporal analyses were suggestive of disease epidemics being associated with localized primary inoculum and other factors that favor disease development at a small scale

Changes in Distribution and Frequency of Fungi Associated With a Foliar Disease Complex of Pyrethrum in Australia

In Australia, pyrethrum (Tanacetum cinerariifolium) is affected by a foliar disease complex that can substantially reduce green leaf area and yield. Historically, the most important foliar disease of pyrethrum in Australia has been ray blight, caused by Stagonosporopsis tanaceti, and other fungi generally of minor importance. Temporal fluctuations in the frequency of fungi associated with foliar disease were quantified in each of 83 fields in northern Tasmania, Australia, during 2012 and 2013. Sampling was conducted throughout winter (April to July), spring (August to September), and summer (November) representing different phenological stages. Microsphaeropsis tanaceti, the cause of tan spot, was the pathogen most prevalent and isolated at the highest frequency, irrespective of sampling period. The next most common species was S. tanaceti, whose isolation frequency was low in winter and increased in spring and summer. Known pathogens of pyrethrum, Alternaria tenuissima, Colletotrichum tanaceti, and Stemphylium botryosum were recovered sporadically and at low frequency. Two species of potential importance, Paraphoma chrysanthemicola and Itersonilia perplexans, were also found at low frequency. This finding suggests a substantial shift in the dominant pathogen associated with foliar disease, from S. tanaceti to M. tanaceti, and coincides with an increase in defoliation severity in winter, and control failures of the spring fungicide program. Factors associated with this finding were also investigated. Sensitivity of M. tanaceti and S. tanaceti populations to the fungicides boscalid and cyprodinil collected prior to and following disease control failures in the field were tested under in vitro conditions. A high proportion (60%) of the M. tanaceti isolates obtained from fields in which no response to the spring fungicide program was found were insensitive to 50 µg a.i./ml boscalid. This represented a 4.2-fold increase in the frequency of this phenotype within the M. tanaceti population over 2 years. No shifts in sensitivities to cyprodinil of M. tanaceti and S. tanaceti, or S. tanaceti to boscalid, were observed. Considering the increase in defoliation severity over winter, the benefits of applying fungicides in autumn, in addition to the commercial standard (spring only), were quantified in 14 individual field trials conducted in 2011 and 2012. Mixed-model analysis suggested fungicide application in autumn may improve pyrethrum growth during late winter and early spring, although effects on defoliation and yield were minimal. The increasing prevalence and isolation frequency of M. tanaceti and boscalid resistance within the population is of concern and highlights the urgent need for adoption of nonchemical methods for disease management in Australian pyrethrum fields.This is the publisher’s final pdf. The published article is copyrighted by American Phytopathological Society and can be found at: http://apsjournals.apsnet.org/loi/pdi

Distributions of phytoplankton carbohydrate, protein and lipid in the world oceans from satellite ocean colour

Energy value of phytoplankton regulates the growth of higher trophic species, affecting the tropic balance and sustainability of marine food webs. Therefore, developing our capability to estimate and monitor, on a global scale, the concentrations of macromolecules that determine phytoplankton energy value, would be invaluable. Reported here are the first estimates of carbohydrate, protein, lipid, and overall energy value of phytoplankton in the world oceans, using ocean-colour data from satellites. The estimates are based on a novel bio-optical method that utilises satellite-derived bio-optical fingerprints of living phytoplankton combined with allometric relationships between phytoplankton cells and cellular macromolecular contents. The annually-averaged phytoplankton energy value, per cubic meter of sub-surface ocean, varied from less than 0.1 kJ in subtropical gyres, to 0.5–1.0 kJ in parts of the equatorial, northern and southern latitudes, and rising to more than 10 kJ in certain coastal and optically complex waters. The annually-averaged global stocks of carbohydrate, protein and lipid were 0.044, 0.17 and 0.108 gigatonnes, respectively, with monthly stocks highest in September and lowest in June, over 1997-2013. The fractional contributions of phytoplankton size classes e.g., picoplankton, nanoplankton and microplankton to surface concentrations and global stocks of macromolecules varied considerably across marine biomes classified as Longhurst provinces. Among these provinces, the highest annually-averaged surface concentrations of carbohydrate, protein, and lipid were in North-East Atlantic Coastal Shelves, whereas, the lowest concentration of carbohydrate or lipid were in North Atlantic Tropical Gyral, and that of protein was in North Pacific Subtropical Gyre West. The regional accuracy of the estimates and their sensitivity to satellite inputs are quantified from the bio-optical model, which show promise for possible operational monitoring of phytoplankton energy value from satellite ocean colour. Adequate in situ measurements of macromolecules and improved retrievals of inherent optical properties from high-resolution satellite images, would be required to validate these estimates at local sites, and to further improve their accuracy in the world oceans

Carpogenic germination of sclerotia of Sclerotinia minor and ascosporic infection of pyrethrum flowers

Carpogenic germination of sclerotia and infection of flowers by ascospores of Sclerotinia minor is rare and seldom documented in most hosts. During 2007–2009, S. minor isolates were obtained from surface-sterilized pyrethrum flowers collected from fields in Australia. The isolation frequency of S. minor from flowers in 2007, 2008 and 2009 was 15.8%, 5% and 1.4%, respectively. During these years, the prevalence of S. minor in flowers amongst pyrethrum fields varied between 10.3% and 60%. Sclerotia with apothecia, consistent in size with S. minor, were collected in one field. Colonies from individual ascospores from this isolate were identified as S. minor. A subsample of 10 S. minor isolates was selected for further studies. Phylogenetic analysis based on the internal transcribed spacer region grouped these isolates with S. minor, and distinct from published sequences of other Sclerotinia spp. Species-specific primers developed previously to differentiate the four major Sclerotinia spp. (S. sclerotiorum, S. minor, S. homoeocarpa and S. trifoliorum) were used to confirm identity. Of the 10 S. minor isolates, eight were able to carpogenically germinate in vitro. Pathogenicity of S. minor to flowers was confirmed in the greenhouse using ascospores. This study is one of the few instances documenting the ability of S. minor to infect floral tissues and the first documentation of S. minor causing flower disease of pyrethrum. These findings serve as a scaffold for further investigations into the mechanisms of flower infection by S. minor and have implications for the management of the Sclerotinia disease complex affecting pyrethrum in Australia.This is the publisher’s final pdf. The article is copyrighted by Canadian Phytopathological Society (Société Canadienne de Phytopathologie) and published by Taylor & Francis. It can be found at: http://www.tandfonline.com/toc/tcjp20/currentKeywords: pyrethrum, Sclerotinia flower blight, Sclerotinia minor, Sclerotinia sclerotiorum, carpogenic germinationKeywords: pyrethrum, Sclerotinia flower blight, Sclerotinia minor, Sclerotinia sclerotiorum, carpogenic germinatio

The first global deep-sea stable isotope assessment reveals the unique trophic ecology of Vampire Squid Vampyroteuthis infernalis (Cephalopoda)

Vampyroteuthis infernalis Chun, 1903, is a widely distributed deepwater cephalopod with unique morphology and phylogenetic position. We assessed its habitat and trophic ecology on a global scale via stable isotope analyses of a unique collection of beaks from 104 specimens from the Atlantic, Pacific and Indian Oceans. Cephalopods typically are active predators occupying a high trophic level (TL) and exhibit an ontogenetic increase in δ15N and TL. Our results, presenting the first global comparison for a deep-sea invertebrate, demonstrate that V. infernalis has an ontogenetic decrease in δ15N and TL, coupled with niche broadening. Juveniles are mobile zooplanktivores, while larger Vampyroteuthis are slow-swimming opportunistic consumers and ingest particulate organic matter. Vampyroteuthis infernalis occupies the same TL (3.0–4.3) over its global range and has a unique niche in deep-sea ecosystems. These traits have enabled the success and abundance of this relict species inhabiting the largest ecological realm on the planet.Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. The attached file is the published pdf

A global perspective on the trophic geography of sharks

Sharks are a diverse group of mobile predators that forage across varied spatial scales and have the potential to influence food web dynamics. The ecological consequences of recent declines in shark biomass may extend across broader geographic ranges if shark taxa display common behavioural traits. By tracking the original site of photosynthetic fixation of carbon atoms that were ultimately assimilated into muscle tissues of 5,394 sharks from 114 species, we identify globally consistent biogeographic traits in trophic interactions between sharks found in different habitats. We show that populations of shelf-dwelling sharks derive a substantial proportion of their carbon from regional pelagic sources, but contain individuals that forage within additional isotopically diverse local food webs, such as those supported by terrestrial plant sources, benthic production and macrophytes. In contrast, oceanic sharks seem to use carbon derived from between 30° and 50° of latitude. Global-scale compilations of stable isotope data combined with biogeochemical modelling generate hypotheses regarding animal behaviours that can be tested with other methodological approaches.This research was conducted as part of C.S.B.’s Ph.D dissertation, which was funded by the University of Southampton and NERC (NE/L50161X/1), and through a NERC Grant-in-Kind from the Life Sciences Mass Spectrometry Facility (LSMSF; EK267-03/16). We thank A. Bates, D. Sims, F. Neat, R. McGill and J. Newton for their analytical contributions and comments on the manuscripts.Peer reviewe

The Ascomycete Verticillium longisporum Is a Hybrid and a Plant Pathogen with an Expanded Host Range

Hybridization plays a central role in plant evolution, but its overall importance in fungi is unknown. New plant pathogens are thought to arise by hybridization between formerly separated fungal species. Evolution of hybrid plant pathogens from non-pathogenic ancestors in the fungal-like protist Phytophthora has been demonstrated, but in fungi, the most important group of plant pathogens, there are few well-characterized examples of hybrids. We focused our attention on the hybrid and plant pathogen Verticillium longisporum, the causal agent of the Verticillium wilt disease in crucifer crops. In order to address questions related to the evolutionary origin of V. longisporum, we used phylogenetic analyses of seven nuclear loci and a dataset of 203 isolates of V. longisporum, V. dahliae and related species. We confirmed that V. longisporum was diploid, and originated three different times, involving four different lineages and three different parental species. All hybrids shared a common parent, species A1, that hybridized respectively with species D1, V. dahliae lineage D2 and V. dahliae lineage D3, to give rise to three different lineages of V. longisporum. Species A1 and species D1 constituted as yet unknown taxa. Verticillium longisporum likely originated recently, as each V. longisporum lineage was genetically homogenous, and comprised species A1 alleles that were identical across lineages