Seasonal population trends and host preference on 8 common host plants of Calocoris trivialis under field conditions
Responsible Scientific Investigator: Dr. A. Kalaitzaki
Calocoris trivialis is a phytophagous species which is widespread in the olive groves but also in citrus orchards in Greece and in the rest of the Mediterranean region. It is a secondary entomological pest of olives and causes local and occasional damage of economic importance. The last 10 years, under specific conditions, it caused sporadic damage of economic importance in certain olive-growing regions of Chania prefecture. Nymphs and adults feed on buds and blossoms which results in the premature dropping of buds and of flowers respectively. Aim of a study was to evaluate the fluctuation of the population of the insect (seasonal appearance) by field experiments. Weekly samplings from olive groves and citrus orchards will take place in order to estimate the fluctuation of the population of C. trivialis from January until May. Host plant preference were studied (density of the population of the insect to the various plant hosts that are existing in the olive groves and in the citrus orchards). Weekly samplings took place from weeds, olive groves and citrus orchards. All samplings will be carried out between January and May. The economic injury estimation will be defined. It will also be studied the development time of immature stages of Calocoris trivialis at three temperatures (15, 20, 25oC) and its oviposition rate at 25oC on the host plant Sinapis alba with laboratory experiments. |  |
Glyphosate resistance of Horseweed (Conyza canadensis) collected from Crete
Responsible Scientific Investigator: Dr C.N. Giannopolitis
Glyphosate (N-phosphonomethyl glycine) is a foliage active herbicide which controls a broad spectrum of annual and perennial weeds. Since its introduction in 1974, glyphosate became world’s dominate herbicide. The widespread use of glyphosate has increased selection pressure on many weed species and several of them, including horseweed (Conyza canadensis) have expressed resistance. Resistance to glyphosate in horseweed was first reported in the United States in 2000, while resistant biotypes have been reported from other states of the United States but also Brazil, China, Australia and Europe.
Glyphosate inhibits the enzyme involved in this pathway: 5-enolpyruvyl shikimate- 3 phosphate synthase (EPSPS). EPSPS is the critical and essential enzyme that catalyzes the conversion of shikimate 3-phosphate (S3P) and phosphoenolpyruvate (PEP) to EPSP. Inhibition of EPSPS reduces the biosynthesis of the aromatic amino acids (phenylalanine, tyrosine and tryptophan) and leads to plant death. Glyphosate initially causes accumulation of shikimate-3-phosphate, the substrate of EPSP synthase, which is then hydrolyzed in the plant to shikimate. Detection of shikimate in plants can be used to determine whether a plant has been exposed to glyphosate and can also be used to determine whether plants are resistant.
he shikimate pathway and mode of action of glyphosate Conyza canadensis plants and seeds were collected from the different locations in Crete to be further evaluated for resistance
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a) Horseweed in a conventional citrus orchard in Crete
b) individual conyza plants in the greenhouse (G0)
c) conyza seed collection
d) production of different horseweed biotypes for testing in cotyledon stage
e) at the seedling stage
f) at the rosette stage.
Replication of whitefly-transmitted criniviruses
Responsible Scientific Investigator: Dr. I. Livieratos
We have chosen whitefly-transmitted criniviruses as model(s) to study virus replication, analyze genomes and develop diagnostic tools. Crinivirus virus particles possess thread-like, flexuous, filamentous virions with a characteristic “rattlesnake” structure morphology due to the presence of a cluster of structural proteins at one tip of the virion. Their bi-partite single stranded 5`-capped positive-sense RNA genomes (15.000-19.000nt) have an organization that is similar to closteroviruses but divided into two molecules (Karasev, 2000). The complete nucleotide sequence of several crinivirus genomic RNAs have been reported over the last decade. Crinivirus infections cause alterations of the phloem parenchyma and companion cells and form of characteristic inclusion bodies.
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b) virus particle morphology; c) Bemisia tabaci whitefly vector of several criniviruses.
Tomato chlorosis virus (ToCV)-induced infections in greenhouse tomato cultivations are prominent in the Mediterranean area and the United States showing identical yellowing symptoms that cannot be easily distinguished from Tomato infectious chlorosis virus (TICV) infections. In a recent study, both genomic RNA components of a Greek isolate (Gr-535) of ToCV were sequenced and compared with Spanish and American isolates. The prediction of putative structures of the 3’-terminus of ToCV RNA 1 showed the presence of four stem loops and a pseudo-knot. These structures get possibly recognized by the viral RNA dependent RNA polymerase during the initiation of ToCV RNA 1 negative strand synthesis. Diagnostic dot-blot hybridization and reverse transcription–polymerase chain reaction (RT-PCR) assays routinely and specifically detect the virus in 20ng of total RNA extracts from ToCV-infected plants. Dot-blot hybridization can also be performed for virus diagnosis using infected crude plant extracts.
Post-transcriptional gene silencing (PTGS) degrades RNA in a sequence specific manner and is utilised by plants as a natural defence mechanism against virus invaders. Using an Agrobacterium-mediated transient assay on Nicotiana benthamiana wildtype and 16c plants, we screened four Cucurbit yellow stunting disorder virus (CYSDV) RNA 1-encoded proteins (papain-like protease, p25, p5.2 and p22) to determine which one possess PTGS suppressor activity. Amongst these proteins, only CYSDV p25 was able to suppress (double- and single stranded) RNA-induced silencing of the green fluorescent protein (GFP) mRNA (Fig. XX). Restoration of GFP expression by CYSDV p25 in both of these experiments had no apparent effect on the accumulation of the small interfering RNAs.
Last update: 03 of February, 2012