Comparative Biochemistry of the Oxidative Burst Produced by Rose and French Bean Cells Reveals Two Distinct Mechanisms1

Cultured cells of rose (Rosa damascena) treated with an elicitor derived from Phytophthora spp. and suspension-cultured cells of French bean (Phaseolus vulgaris) treated with an elicitor derived from the cell walls of Colletotrichum lindemuthianum both produced H2O2. It has been hypothesized that in rose cells H2O2 is produced by a plasma membrane NAD(P)H oxidase (superoxide synthase), whereas in bean cells H2O2 is derived directly from cell wall peroxidases following extracellular alkalinization and the appearance of a reductant. In the rose/Phytophthora spp. system treated with N,N-diethyldithiocarbamate, superoxide was detected by a N,N′-dimethyl-9,9′-biacridium dinitrate-dependent chemiluminescence; in contrast, in the bean/C. lindemuthianum system, no superoxide was detected, with or without N,N-diethyldithiocarbamate. When rose cells were washed free of medium (containing cell wall peroxidase) and then treated with Phytophthora spp. elicitor, they accumulated a higher maximum concentration of H2O2 than when treated without the washing procedure. In contrast, a washing treatment reduced the H2O2 accumulated by French bean cells treated with C. lindemuthianum elicitor. Rose cells produced reductant capable of stimulating horseradish (Armoracia lapathifolia) peroxidase to form H2O2 but did not have a peroxidase capable of forming H2O2 in the presence of reductant. Rose and French bean cells thus appear to be responding by different mechanisms to generate the oxidative burst.

Isolation of a superfamily of candidate disease-resistance genes in soybean based on a conserved nucleotide-binding site.

The tobacco N and Arabidopsis RPS2 genes, among several recently cloned disease-resistance genes, share highly conserved structure, a nucleotide-binding site (NBS). Using degenerate oligonucleotide primers for the NBS region of N and RPS2, we have amplified and cloned the NBS sequences from soybean. Each of these PCR-derived NBS clones detected low-or moderate-copy soybean DNA sequences and belongs to 1 of 11 different classes. Sequence analysis showed that all PCR clones encode three motifs (P-loop, kinase-2, and kinase-3a) of NBS nearly identical to those in N and RPS2. The intervening region between P-loop and kinase-3a of the 11 classes has high (26% average) amino acid sequence similarity to the N gene although not as high (19% average) to RPS2. These 11 classes represent a superfamily of NBS-containing soybean genes that are homologous to N and RPS2. Each class or subfamily was assessed for its positional association with known soybean disease-resistance genes through near-isogenic line assays, followed by linkage analysis in F2 populations using restriction fragment length polymorphisms. Five of the 11 subfamilies have thus far been mapped to the vicinity of known soybean genes for resistance to potyviruses (Rsv1 and Rpv), Phytophthora root rot (Rps1, Rps2, and Rps3), and powdery mildew (rmd). The conserved N- or RPS2-homologous NBS sequences and their positional associations with mapped soybean-resistance genes suggest that a number of the soybean disease-resistance genes may belong to this superfamily. The candidate subfamilies of NBS-containing genes identified by genetic mapping should greatly facilitate the molecular cloning of disease-resistance genes.

Mexican papita viroid: putative ancestor of crop viroids.

The potato spindle tuber disease was first observed early in the 20th century in the northeastern United States and shown, in 1971, to be incited by a viroid, potato spindle tuber viroid (PSTVd). No wild-plant PSTVd reservoirs have been identified; thus, the initial source of PSTVd infecting potatoes has remained a mystery. Several variants of a novel viroid, designated Mexican papita viroid (MPVd), have now been isolated from Solanum cardiophyllum Lindl. (papita güera, cimantli) plants growing wild in the Mexican state of Aguascalientes. MPVd's nucleotide sequence is most closely related to those of the tomato planta macho viroid (TPMVd) and PSTVd. From TPMVd, MPVd may be distinguished on the basis of biological properties, such as replication and symptom formation in certain differential hosts. Phylogenetic and ecological data indicate that MPVd and certain viroids now affecting crop plants, such as TPMVd, PSTVd, and possibly others, have a common ancestor. We hypothesize that commercial potatoes grown in the United States have become viroid-infected by chance transfer of MPVd or a similar viroid from endemically infected wild solanaceous plants imported from Mexico as germplasm, conceivably from plants known to have been introduced from Mexico to the United States late in the 19th century in efforts to identify genetic resistance to the potato late blight fungus, Phytophthora infestans.

Oligopeptide elicitor-mediated defense gene activation in cultured parsley cells.

We have used suspension-cultured parsley cells (Petroselinum crispum) and an oligopeptide elicitor derived from a surface glycoprotein of the phytopathogenic fungus Phytophthora megasperma f.sp. glycinea to study the signaling pathway from elicitor recognition to defense gene activation. Immediately after specific binding of the elicitor by a receptor in the plasma membrane, large and transient increases in several inorganic ion fluxes (Ca2+, H+, K+, Cl-) and H2O2 formation are the first detectable plant cell responses. These are rapidly followed by transient changes in the phosphorylation status of various proteins and by the activation of numerous defense-related genes, concomitant with the inactivation of several other, non-defense-related genes. A great diversity of cis-acting elements and trans-acting factors appears to be involved in elicitor-mediated gene regulation, similar to the apparently complex nature of the signal transduced intracellularly. With few exceptions, all individual defense responses analyzed in fungus-infected parsley leaves have been found to be closely mimicked in elicitor-treated, cultured parsley cells, thus validating the use of the elicitor/cell culture system as a valuable model system for these types of study.

Rates of spread of marine pathogens

Epidemics of marine pathogens can spread at extremely rapid rates. For example, herpes virus spread through pilchard populations in Australia at a rate in excess of 10 000 km year(-1), and morbillivirus infections in seals and dolphins have spread at more than 3000 km year(-1). In terrestrial environments, only the epidemics of myxomatosis and calicivirus in Australian rabbits and West Nile Virus in birds in North America have rates of spread in excess of 1000 km year(-1). The rapid rates of spread of these epidemics has been attributed to flying insect vectors, but flying vectors have not been proposed for any marine pathogen. The most likely explanation for the relatively rapid spread of marine pathogens is the lack of barriers to dispersal in some parts of the ocean, and the potential for long-term survival of pathogens outside the host. These findings caution that pathogens may pose a particularly severe problem in the ocean. There is a need to develop epidemic models capable of generating these high rates of spread and obtain more estimates of disease spread rate.

First report of Tubercularia lateritia as the causal agent of canker on macadamia

Tubercularia lateritia was recorded for the first time as causing canker, characterised by a sunken centre surrounded by galls or callus, on macadamia. The fungus was isolated and inoculated on young macadamia trees in the glasshouse and produced characteristic disease symptoms from which the fungus was successfully reisolated.

Identification of a novel transcriptional activator involved in plastid-nucleus communication during the plant response to stress

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Identification of a novel transcriptional activator involved in plastid-nucleus communication during the plant response to stress

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Caracterización del agente causal de la producción radicular del aguacate y Trichoderma sp., como potencial agente de control biológico en Nicaragua.

En el cultivo de aguacate (Persea americana Mill.) se presentan problemas fitosanitarios importantes dentro de los cuales sobresalen por su relevancia las enfermedades de la raíz. Un fitopatógeno limitante de este cultivo es el oomicete Phytophthora cinnamomi Rands, que puede causar pérdidas hasta del 90%. Por tal razón el principal objetivo del estudio fue generar información acerca de la etiología del agente causal de la pudrición radicular del aguacate utilizando marcadores morfológicos y moleculares, además de proponer alternativas de manejo de carácter biológico que estén enmarcadas dentro de un programa de manejo integrado de la enfermedad. Se realizaron colectas de muestras de suelo en cuatro localidades del departamento de Masaya. La identificación morfológica del patógeno se realizó mediante claves taxonómicas y se confirmó a través de la técnica PCR-RFLP. Se identificó a P. cinnamomi como el principal agente causal de la pudrición radicular del aguacate. Los aislados de P. cinnamomi fueron enfrentados con Trichoderma sp por el método de cultivo dual en cajas Petri con medio PDA. Se determinó el porcentaje de inhibición de crecimiento radial (PICR) a las 72 horas, así como el grado de antagonismo de cada una de las cepas de Trichoderma sp utilizadas en el estudio. Las cepas de Trichoderma al enfrentarlas a aislados del patógeno P. cinnamomi se ubicaron en las Clases 1 y 2 de la escala de evaluación, por lo tanto se consideraron altamente antagonistas. Existe la posibilidad de manejo biológico de las poblaciones de P. cinnamomi con microorganismos antagonistas del género Trichoderma no solamente en agroecosistemas de aguacate, sino también en otros sistemas agrícolas y forestales donde el patógeno esté presente.

Developing a commercial hot water treatment to control post-harvest rots on ‘Fiji Red’ papaya

Fiji exports approximately 800 t year-1 of 'Solo Sunrise' papaya marketed as 'Fiji Red' to international markets which include New Zealand, Australia and Japan. The wet weather conditions from November to April each year result in a significant increase in fungal diseases present in Fiji papaya orchards. The two major pathogens that are causing significant post-harvest losses are: stem end rot (Phytophthora palmivora) and anthracnose (Colletotrichum spp.). The high incidence of post-harvest rots has led to increased rejection rates all along the supply chain, causing a reduction in income to farmers, exporters, importers and retailers of Fiji papaya. It has also undermined the superior quality reputation on the market. In response to this issue, the Fiji Papaya industry led by Nature's Way Cooperative, embarked on series of trials supported by the Australian Centre for International Agricultural Research (ACIAR) to determine the most effective and economical post-harvest control in Fiji papaya. Of all the treatments that were examined, a hot water dip treatment was selected by the industry as the most appropriate technology given the level of control that it provide, the cost effectiveness of the treatment and the fact that it was non-chemical. A commercial hot water unit that fits with the existing quarantine treatment and packing facilities has been designed and a cost benefit analysis for the investment carried out. This paper explores the research findings as well as the industry process that has led to the commercial uptake of this important technology.

Citricultura desenvolvida na agricultura de base familiar do município de Russas, Ceará.

Brasil é o maior produtor mundial de laranjas doces [Citrus sinensis (L.) Osbeck]. A citricultura distribui-se nacionalmente, enquanto o Nordeste constitui-se segundo maior produtor (IBGE, 2015). Russas sobresaiu-se historicamente pelo extrativismo da carnaúba (Copernícia prunífera) ecultivo da laranja doce, recebendo o título "Terra da Laranja Doce", devido ao dominio histórico de uma variedade nativa,chamada ?Laranja de Russas?. Porém, entre as cheias que ocorreram nos anos de 1974 e 1985, a ?gomose? (Phytophthora spp.) proliferou-se e atingiu 90% dos pomares citricos do município, constituídos da ?laranja de Russas? propagada seminalmente (pé franco), levando ao declínio da cadeia produtiva, que desenvolvia-se basicamente através da agricultura familiar. Recentemente, uma parceria entre Embrapa Mandioca e Fruticultura Tropical e Secretaria de Agricultura (SEAGRI-RUSSAS), inicou pesquisas voltadas a revitalização da citricultura no município, através da seleção de exemplares da laranja de ?Russas?, identificando-se oito clones de ?Russas? de elevada produtividade e fitossanidade (PASSOS et. al, 2013); introdução de porta-enxertos híbridos com tendências ao nanismo e resistentes as principais doenças, principalmente ?Gomose?; além da implantação de pomares na agricultura familiar e assistência técnica. Portanto, o presente trabalho objetivou-se alevantar e caracterizar os principais aspectos e técnicas empregadas pelos agricultores familiares de Russas na implantação e desenvolvimento inicial dos pomares cítricos.

The exploration of potato-associated bacteria in the Central Andean Highlands and their application in integrated crop management systems

Potato is the most important food crop after wheat and rice. A changing climate, coupled with a heightened consumer awareness of how food is produced and legislative changes governing the usage of agrochemicals, means that alternative more integrated and sustainable approaches are needed for crop management practices. Bioprospecting in the Central Andean Highlands resulted in the isolation and in vitro screening of 600 bacterial isolates. The best performing isolates, under in vitro conditions, were field trialled in their home countries. Six of the isolates, Pseudomonas sp. R41805 (Bolivia), Pseudomonas palleroniana R43631 (Peru), Bacillus sp. R47065, R47131, Paenibacillus sp. B3a R49541, and Bacillus simplex M3-4 R49538 (Ecuador), showed significant increase in the yield of potato. Using – omic technologies (i.e. volatilomic, transcriptomic, proteomic and metabolomic), the influence of microbial isolates on plant defence responses was determined. Volatile organic compounds of bacterial isolates were identified using GC/MS. RT-qPCR analysis revealed the significant expression of Ethylene Response Factor 3 (ERF3) and the results of this study suggest that the dual inoculation of potato with Pseudomonas sp. R41805 and Rhizophagus irregularis MUCL 41833 may play a part in the activation of plant defence system via ERF3. The proteomic analysis by 2-DE study has shown that priming by Pseudomonas sp. R41805 can induce the expression of proteins related to photosynthesis and protein folding in in vitro potato plantlets. The metabolomics study has shown that the total glycoalkaloid (TGA) content of greenhouse-grown potato tubers following inoculation with Pseudomonas sp. R41805 did not exceed the acceptable safety limit (200 mg kg-1 FW). As a result of this study, a number of bacteria have been identified with commercial potential that may offer sustainable alternatives in both Andean and European agricultural settings.

Fitopatógenos habitantes do solo na Amazônia.

Neste trabalho são descritos alguns patógenos habitantes do solo, dentre dezenas, que se destacam com os mais importantes na agricultura amazônica: Ralstonia solanacearum, raça 2. Thanatephorus cucumeris. Sclerotium coffeicola. Phytophthora drechsleri. Phytophthora palmivora. Aspergillus flavus e A. parasiticus. Lasiodiplodia theobromae. Ganoderma philippii, Rigidoporus lignosus e Phellinus noxius. Meloidogyne exigua, M. incognita e M. javanica. Radopholus similis.