Defence mechanisms of a resistant monocot model to phytophthora cinnamomi

The plant pathogen Phytophthora cinnamomi causes devastating disease in natural and agricultural systems worldwide. While some plants can survive, little is known about the underlying mechanisms of resistance. This research used histochemical and genome-wide analysis to identify key cellular and molecular defence mechanisms within the resistant plant Zea mays.

Defining plant resistance to Phytophthora cinnamomi : a standardized approach to assessment

Phytophthora cinnamomi is a soil-borne plant pathogen that causes devastating disease in agricultural and natural systems worldwide. While a small number of species survive infection by the pathogen without producing disease symptoms, the nature of resistance, especially under controlled conditions, remains poorly understood. At present, there are no standardized criteria by which resistance or susceptibility to P. cinnamomi can be assessed, and we have used five parameters consisting of plant fresh weight, root growth, lesion length, relative chlorophyll content of leaves and pathogen colonization of roots to analyse responses to the pathogen. The parameters were tested using two plant species, Zea mays and Lupinus angustifolius, through a time course study of the interactions and resistance and susceptibility defined 7days after inoculation. A scoring system was devised to enable differentiation of these responses. In the resistant interaction with Z. mays, there was no significant difference in fresh weight, root length and relative chlorophyll content in inoculated compared with control plants. Both lesion size and pathogen colonization of root tissues were limited to the site of inoculation. Following inoculation L. angustifolius showed a significant reduction in plant fresh weight and relative leaf chlorophyll content, cessation of root growth and increased lesion lengths and pathogen colonization. We propose that this technique provides a standardized method for plant-P. cinnamomi interactions that could be widely used to differentiate resistant from susceptible species.

Profiling of secondary metabolites in blue lupin inoculated with Phytophthora cinnamomi following phosphite treatment

In order to discover phytochemicals that are potentially bioactive against Phytophthora cinnamomi, (a soil-borne plant pathogen) a metabolite profiling protocol for investigation of metabolic changes in Lupinus angustifolius L. plant roots in response to pathogen challenge has been established. Analysis of the metabolic profiles from healthy and P. cinnamomi-inoculated root tissue with high resolution mass spectrometry and nuclear magnetic resonance spectroscopy confirmed that although susceptible, L. angustifolius upregulated a defence associated genistein and 2′-hydroxygenistein-based isoflavonoid and a soyasapogenol saponin at 12h post inoculation which increased in concentration at 72h post inoculation. In contrast to the typical susceptible interaction, the application of a phosphorous-based treatment to L. angustifolius foliage 48h before P. cinnamomi challenge negated the ability of the pathogen to colonise the root tissue and cause disease. Importantly, although the root profiles of water-treated and phosphite-treated plants post pathogen inoculation contained the same secondary metabolites, concentration variations were observed. Accumulation of secondary metabolites within the P. cinnamomi-inoculated plants confirms that pathogen ingress of the root interstitially occurs in phosphite-treated plants, confirming a direct mode of action against the pathogen upon breaching the root cells.

Characterisation of accessions and species of Macadamia to stem infection by Phytophthora cinnamomi

Phytophthora cinnamomi is a major pathogen in most macadamia plantations worldwide. Due to stem lesions, stem cankers and leaf defoliation it results in loss of productivity and tree death. In this study we examined accessions of the four Macadamia species and their hybrids, produced via rooted stem cuttings or germinated seeds, for susceptibility to stem canker and necrotic lesion caused by P. cinnamomi. Plants were wound-inoculated with agar containing P. cinnamomi. The symptoms produced in inoculated plants were used to characterize host susceptibility variation within and among the population. Lesion lengths and severity of stem canker were recorded. The four species and hybrids differed significantly in stem canker severity (P < 0.001) and lesion length (P = 0.04). M. integrifolia and M. tetraphylla hybrids were the most susceptible. M. integrifolia had the greatest stem canker severity and the most extensive lesions above and below the site of inoculation. Restricted lesion sizes were observed in M. ternifolia and M. jansenii. The effects of basal stem diameter and the method of propagation either from cuttings or seed were not significant. The genetic variation in the reactions of macadamia accessions to stem infection by P. cinnamomi is discussed.

Variation in susceptibility among macadamia genotypes and species to Phytophthora root decay caused by Phytophthora cinnamomi

Phytophthora cinnamomi is a major pathogen of cultivated macadamia (Macadamia integrifolia, Macadamia tetraphylla and their hybrids) worldwide. The susceptibility of the two non-edible Macadamia species (Macadamia ternifolia and Macadamia jansenii) to P. cinnamomi is not well-understood. Commercial macadamia trees are established on grafted seedling (seed propagation) or own-rooted cutting (vegetative propagation) rootstocks of hybrids of the cultivated species. There is little information to support the preferential use of rootstock propagated by either seedling or own-rooted cutting methods in macadamia. In this study we assessed roots of macadamia plants of the four species and their hybrids, derived from the two methods of propagation, for their susceptibility to P. cinnamomi infection. The roots of inoculated plant from which P. cinnamomi was recovered showed blackening symptoms. The non-cultivated species, M. ternifolia and M. jansenii and their hybrids were the most susceptible germplasm compared with M. tetraphylla and M. integrifolia. Of these two species, M. tetraphylla was less susceptible than M. integrifolia. Significant differences were observed among the accessions of their hybrids. A strong association (R2 > 0.75) was recorded between symptomatic roots and disease severity. Root density reduced with increasing disease severity rating in both own-rooted cuttings (R2 = 0.65) and germinated seedlings (R2 = 0.55). P. cinnamomi severity data were not significantly (P > 0.05) different between the two methods of plant propagation. The significance of this study to macadamia breeding and selection of disease resistant rootstocks is discussed.

Silencing the gip gene of Phytophthora cinnamomi by iRNA and studying the subcellular localization of GIP and NPP1 proteins

Ink Disease is considered one of the most important causes of the decline of chestnut orchards. The break in yield of Castanea sativa Mill is caused by two species: Phytophthora cinnamomi and Phytophthora cambivora, being the first one the foremost pathogen of ink disease in Portugal. P. cinnamomi is one of the most aggressive and widespread plant pathogen with nearly 1,000 host species. This oomycete causes enormous economic losses and it is responsible for the decline of many plant species in Europe and worldwide. Up to now no efficient treatments are available to fight these pathogens. Because of the importance of chestnut at economical and ecological levels, especially in Portugal, it becomes essential to explore the molecular mechanisms that determine the interaction between Phytophthora species and host plants through the study of proteins GIP (glucanase inhibitor protein) and NPP1 (necrosis-inducing Phytophthora protein 1) produced by P. cinnamomi during the infection. The technique of RNA interference was used to knockdown the gip gene of P. cinnamomi. Transformants obtained with the silenced gene have been used to infect C. sativa, in order to determine the effect of gene silencing on the plant phenotype. To know more about the function of GIP and NPP1 involved in the mechanism of infection, the ORF’s of gip and npp1 genes have been cloned to the pTOR-eGFP vector for a future observation of P. cinnamomi transformants with fluorescent microscopy and determination of the subcellular localization. Moreover the prediction by bioinformatics tools indicates that both GIP and NPP1 proteins are secreted. The results allow to predict the secretory destination of both GIP and NPP1 proteins and confirm RNAi as a potential alternative biological tool in the control and management of P. cinnamomi. Keywords:

Genes found in partial sequencing od Phytophthora cinnamomi

Members of the oomycete cause extensive losses in agriculture and widespread degradation in natural plant communities, being responsible for the death of thousands of trees every year. Two of the representative species are Phytophthora infestans, which causes late blight of potato, and Phytophthora cinnamomi, which causes chestnut ink disease, responsible for losses on sweet chestnut production in Europe. Genome sequencing efforts have been focused on the study of three species: P. infestans, P. sojae and P. ramorum. Phytophthora infestans has been developed as the model specie for the genus, possessing excellent genetic and genomics resources including genetic maps, BAC libraries, and EST sequences. Our research team is trying to sequence the genome of P. cinnamomi in order to gain a better understanding of this oomycete, to study changes in plant-pathogen relationships including those resulting from climate change and trying to decrease the pathogen’s impact on crops and plants in natural ecosystems worldwide. We present here a preliminary report of partially sequenced genomic DNA from P. cinnamomi encoding putative protein-coding sequences and tRNAs. Database analysis reveals the presence of genes conserved in oomycetes.

Aspectos da interacção entre Phytophthora cinnamomi e a doença do declínio em Q. suber e Q. rotundifolia

Faculdade de Engenharia de Recursos Naturais, Univ. do Algarve, 2001

Effects of vegetation, fire and other disturbance factors on small mammal ecology and conservation

The relationship of vegetation and disturbance factors to the distribution, abundance and diversity of small mammals in the eastern Otway region, Victoria were investigated. Antechinus stuartii, Rattus fuscipes and Rattus lutreolus were widely distributed and occurred in the majority of the eleven floristic vegetation groups identified. Antechinus minimus, Antechinus swainsonnii and Pseudomys novaehollandiae had restricted distributions and were recorded in only two or three vegetation groups. New information on the distribution of the rare species P. novaehollandiae, was obtained and two floristically rich vegetation groups that it preferred were identified. Species-rich small mammal communities occurred in vegetation communities with high numbers of sclerophyll plant species and high structural diversity. Maximum food resources were considered to be provided in these communities. Local habitat diversity was also correlated with species-richness. Small mammal abundance was maximum in non-sclerophyllous canmunities, where high plant productivity was considered to be important. For the first time, the presence of the plant pathogen Phytophthora cinnamomi was shown to affect small mammals. It was associated with small mammal communities of low species richness and abundance, Recovery of small mammal populations after wildfire was slow until the fourth year. Mus musculus reached peak abundance from 2-3 years and then declined rapidly. P. novaehollandiae was the only native species that achieved maximum abundance early in the succession. A. stuartii, R. fuscipes and R. lutreolus approached maximum abundance in mid-succession, while Isoodon obesulus was a mid- to late-successional species. A. minimus survived the fire, but did not persist after one year. The pattern of succession was influenced by attributes of species, such as survival after fire, their ability to disperse and reproduce.

Phytophthora, avocado root rot /

Mode of access: Internet.

Seasonal effects of foliar application of phosphonate on phosphonate translocation, in vitro pollen viability and pollen germination in `Hass' avocado (Persea americana Mill.)

Phosphonate fungicides are used widely in the control of diseases caused by Phytophthora cinnamomi Rands. For the most part phosphonate is seen as a safe to use on crops with phytotoxicity rare. However, recent research has shown that phosphonate has detrimental effects on the floral biology of some indigenous Australian plants. Since phosphonate fungicides are regularly used for the control of Phytophthora root rot in avocados, research was carried out to study the translocation of phosphonate fungicide in 'Hass' trees and any effects on their floral biology. Field-grown trees were sprayed with 0, 0.06 or 0.12 M mono-dipotassium phosphonate (pH 7.2) at summer flush maturity, floral bud break or anthesis. Following treatment, phosphonic acid concentrations were determined in leaves, roots, inflorescence rachi and flowers and in vitro pollen germination and pollen tube growth studied. Phosphonic acid concentration in the roots and floral parts was related to their sink strength at the respective times of application with concentration in roots highest (36.9.mg g±1) after treatment at summer flush maturity and in flowers (234.7 mg g±1) after treatment during early anthesis. Phosphonate at >0.03 M was found to be significantly phytotoxic to in vitro pollen germination and pollen tube growth. However, this rate gave a concentration far in excess of that measured in plant tissues following standard commercial applications of mono-dipotassium phosphonate fungicide. There was a small effect on pollen germination and pollen tube growth when 0.06 and 0.12 M mono-dipotassium phosphonate was applied during early anthesis. However, under favourable pollination and fruit set conditions it is not expected to have commercial impact on tree yield. However, there may be detrimental commercial implications from phosphonate sprays at early anthesis if unfavourable climatic conditions for pollination and fruit set subsequently occur. A commercial implication from this study is that phosphonic acid root concentrations can be elevated and maintained with strategic foliar applications of phosphonate fungicide timed to coincide with peaks in root sink strength. These occur at the end of the spring and summer flushes when shoot growth is relatively quiescent. Additional foliar applications may be advantageous in under high disease-pressure situations but where possible should be timed to minimize overlap with other significant growth events in the tree such as rapid inflorescence, and fruit development and major vegetative flushing.

The application of DArTseq technology to pineapple

DArTseq technology is potentially the most appropriate system to discover hundreds of polymorphic genomic loci, scoring thousands of unique genomic-wide DNA fragments in one single experiment, without requiring existing DNA sequence information. The DArT complexity reduction approach in combination with Illumina short read sequencing (Hiseq2000) was applied. To test the application of DArTseq technology in pineapple, a reference population of 13 Ananas genotypes from primitive wild accessions to modern cultivars was used. In a comparison of 3 systems, the combination of restriction enzymes PstI and MseI performed the best producing 18,900 DArT markers and close to 20,000 SNPs. Based on these markers genetic relationships between the samples were identified and a dendrogram was generated. The topography of the tree corresponds with our understanding of the genetic relationships between the genotypes. Importantly, the replicated samples of all genotypes have a dissimilarity of close to 0.0 and occupy the same positions on the tree, confirming high reproducibility of the markers detected. Eventually it is planned that molecular markers will be identified that are associated with resistance to Phytophthora cinnamomi (Pc), the most economically important pathogen of pineapple in Australia, as genetic resistance is known to exist within the Ananas. Marker assisted selection can then be utilized in a pineapple breeding program to develop cultivars resistant to Pc.

Factores asociados a la mortalidad de encinos (Quercus spp.) en la Reserva natural Cerro Tomabú, Estelí, Nicaragua

Con el objetivo de estudiar los factores asociados a la mortalidad de los encinos (Quercus spp), en la Reserva Natural Cerro Tomabú, Estelí; se establecieron seis parcelas de estudio de 0.1 ha, durante los meses de Febrero – Mayo y Junio – Octubre 2014. En cada una se colectaron insectos, suelo y tejido vegetal enfermo; estimación de incidencia y severidad de la marchitez de los encinos; datos dasométricos y antropogénico. Para la identificación de patógenos, se utilizaron medios generales (Papa Dextrosa Agar, Agar Nutritivo y Agar Agua) y selectivos (Caldo V8, agar V8, y Harina de maíz -agar más antibióticos: Piramicina, Ampicillina, Rifampicina, Vancomycina y Benomyl) y caracterización macro morfométrica, con claves taxonómicas. Los datos fueron analizados de manera descriptiva. La población de árboles muestreados fue de 298 Q. segoviensis y Q. sapotifolia son las especies, que predominan en un 58 % y 42 % respectivamente. En el mes de septiembrese registró el mayor porcentaje de incidencia de marchitez en ramas con 88.3 % y 99 % de incidencia por especie en árboles jóvenes de Q. sapotifolia. La severidad con 29.2 %. Phytophthora cinnamomi, se aisló de suelo y tejido vegetal, constituyendo el patógeno que se asocia a la marchitez de ramas, chancros con exudados negros en fuste y muerte en los encinos. Las pocas lluvias y el despale ocasionado por los pobladores participan como factores de estrés en la mortalidad de los encinos. Los insectos colectados se consideran de naturaleza benéfica y constituyen parte de la diversidad de insectos de la reserva.

The Top 10 Oomycete Pathogens in Molecular Plant Pathology

Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens that threaten natural and managed ecosystems. We undertook a survey to query the community for their ranking of plant pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) Pythium ultimum; and (10) Albugo candida. The article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.