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Papers by Michalis Omirou

Applied Soil Ecology, 2013

ABSTRACT Horticultural crops in the Mediterranean basin have to cope with severe drought conditio... more ABSTRACT Horticultural crops in the Mediterranean basin have to cope with severe drought conditions. The effect of inoculating watermelon plants grown under limited water availability conditions with AM fungi on the fruit yield, water use efficiency (WUE), root-N and -P content was examined. We focused on the impact of watering level and inoculation with allochthonous AM fungi on the diversity and presence of AM fungi in the watermelon roots using molecular techniques. An open field experiment was conducted and plants were grown with (M) and without AM fungal inoculum (NM), subjected to water stress (NW) and no stress conditions (W). Suboptimal water application (NW) resulted in significant reduction of fruit yield, root-N and -P content. Inoculation of plants grown under water stress resulted in a significant increase of WUE (19%), fruit yield (19%), root-N (27%) and -P (40%). However, only root-P responded to AM inoculation under non water stress conditions demonstrating 23% increase in M plants. DNA extracted from root samples was subjected to PCR–DGGE analysis. The native mycorrhizal population colonized watermelon roots, as indicated by DGGE bands in NM treatments. Some members of this colonizer community appear sensitive to the introduction of allochthonous inocula and to water stress conditions. Cloning and sequencing of AM fungi revealed that watermelon roots were colonized by Glomus and Paraglomus species. A TaqMan real-time PCR assay was also carried out targeting the 18S rRNA gene for the quantification of AM nucleic acids. The 18S rRNA copy numbers of AM fungi were significantly increased in M plants compared to NM plants under water stress. On the contrary, under non stress conditions M and NM plants did not show significant differences, indicating that inoculation with AM fungi was related to the response of plants to water stress conditions. Principle coordinate analysis of the DGGE banding patterns showed that the diversity of AM fungal colonizers was strongly affected (i) by inoculation and (ii) by water stress in the inoculated plants. Inoculation affected fungal presence under water limitation conditions only. The latter was in line with the significant beneficial effect of inoculation on both WUE and yield only under water limitation.

Pest Management Science, 2014

The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is the most important pest ... more The olive fruit fly, Bactrocera oleae (Rossi) (Diptera: Tephritidae), is the most important pest of olives. Its control is based mostly on organophosphate (OP) insecticides, a practice that has led to resistance development. OP resistance in B. oleae has been associated with three mutations in the acetylcholinesterase (AChE), the product of ace gene. The current study presents new diagnostic tests for the detection of the ace mutations and aims at monitoring the frequency of the Δ3Q mutation, which appears associated with resistance at higher OP doses in natural olive fly populations. An allele-specific polymerase chain reaction (PCR), a PCR-RFLP (restriction fragment length polymorphism) and a Taq-Man test were developed for the Δ3Q mutation detection and a new duplex quantitative PCR assay was designed for the G488S and I214V mutations. Moreover, the frequency of Δ3Q mutation was examined in ten populations of eight countries around the Mediterranean basin. The highest frequencies (10%) were found in Greece and Italy, whereas a gradual decrease of Δ3Q frequency towards the western Mediterranean was noted. Robust tests for insecticide resistance mutations at their incipient levels are essential tools to monitor the increase and geographical spread of such mutations. Three different tests were developed for AChE-Δ3Q that indicated its association with OP applications across the Mediterranean.

Food Chemistry, 2009

The behaviour of the insecticide thiacloprid and the fungicide iprodione was investigated in gree... more The behaviour of the insecticide thiacloprid and the fungicide iprodione was investigated in greenhouse tomato fruits, when both pesticides were applied in two different rates (normal dose-ND, and double dose-DD). Thiacloprid residues were below the already established EU MRLs (0.5 mg/kg) 2 and 7 days after ND and DD application, respectively. Iprodione residues were always below EU MRLs (5 mg/kg) in both application rates. The impact of storage on pesticide residues in tomatoes was also assessed. Significantly higher iprodione residue levels were observed during post harvest storage compared with those determined in fresh harvested tomatoes. Mean residue levels determined in fresh harvested tomatoes 12 days after iprodione application were 0.69 mg/kg whereas, in post harvest tomatoes stored for the same period was 0.86 mg/kg. On the contrary, no differences were noticed in thiacloprid residues between post harvest stored and fresh harvested tomatoes. Model equations that best describe the dissipation curves obtained from the experimental data of iprodione and thiacloprid in tomatoes showing different behaviour of the two pesticides. Half-life period of iprodione in ND treatment, calculated by the best fitted experimental data, (2nd order model) was 6.8 days, whilst for thiacloprid the best fitted to experimental data, model equation (R.F. 1st order model) gave a half-life of 1.9 days.

European Journal of Soil …, Jan 1, 2011

Fusarium solani strain FsK (FsK), isolated from a plant pathogen-suppressive compost, grows endop... more Fusarium solani strain FsK (FsK), isolated from a plant pathogen-suppressive compost, grows endophytically in tomato roots and controls infestations by Fusarium oxysporum f.sp. radicis-lycopersici (FORL). The effect of root colonization by the two fungi on the diversity of rhizosphere microbial community was studied. Tomato plants were inoculated with FsK and/or FORL and rhizosphere soil was collected 8, 15 and 30 days post inoculation (dpi) and analyzed by denaturating gradient gel electrophoresis (DGGE) of PCR-amplified internal transcribed spacer (ITS) sequences of fungi and 16S rRNA gene sequences of common rhizosphere bacterial guilds like alpha-proteobacteria and pseudomonads. Cluster analysis of DGGE fingerprints showed that FsK had a transient impact on the fungal and alpha-proteobacterial community only during its endophytic stage (15 dpi), while FORL had a readily distinguished and persistent effect on the fungal community. The changes observed in the rhizosphere fungal and bacterial communities may depict the interactions of the two fungal inocula with the plant. Cloning of selected DGGE bands stimulated by FsK showed that the responsive bacteria were closely related to species known to include biological control agents (BCA). Overall, the inoculation of FsK in tomato rhizosphere did not appear to have a significant impact on the diversity of non-target microbial groups inhabiting plant rhizosphere.

Plant and Soil, Jan 1, 2011

Background and Aims Rocket salad (Eruca sativa Mills) is one of the major leafy vegetables produc... more Background and Aims Rocket salad (Eruca sativa Mills) is one of the major leafy vegetables produced worldwide and has been characterized as a rich source of chemoprotective glucosinolates (GSL). The relationship between N fertilization and the resulting plant biomass and N status with GSL quantity and quality in rocket leaves was examined. Methods A pot experiment was conducted, applying ten different N-rates and destructive sampling was carried out 15, 30 and 45 days after transplanting (DAT). The Mitscherlich equation was used to establish NO 3 -N critical levels at each growth stage and as an indicator of N demand for relative maximum dry matter accumulation and glucosinolate content and composition was determined. Results Glucosinolate content was significantly influenced by N rate, growth stage and their interaction. Different GSL types showed dissimilar responses to N fertilization: aliphatic GSLs were significantly reduced under increased N rates whereas indole GSL showed the reverse. Under excess N fertilization (>1.

Microbial ecology, Jan 1, 2011

Biofumigation (BIOF) is carried out mainly by the incorporation of brassica plant parts into the ... more Biofumigation (BIOF) is carried out mainly by the incorporation of brassica plant parts into the soil, and this fumigation activity has been linked to their high glucosinolate (GSL) content. GSLs are hydrolyzed by the endogenous enzyme myrosinase to release isothiocyanates (ITCs). A microcosm study was conducted to investigate the effects induced on the soil microbial community by the incorporation of broccoli residues into soil either with (BM) or without (B) added myrosinase and of chemical fumigation, either as soil application of 2-phenylethyl ITC (PITC) or metham sodium (MS). Soil microbial activity was evaluated by measuring fluorescein diacetate hydrolysis and soil respiration. Effects on Electronic supplementary material The online version of this article (

Phytochemical …, Jan 1, 2009

Glucosinolates (GSLs) are secondary plant metabolites that are abundant in brassicas and their hy... more Glucosinolates (GSLs) are secondary plant metabolites that are abundant in brassicas and their hydrolysis products, isothiocyanates, are toxic to soil pathogens. Efficiency and extraction time are critical for routine analysis of GSLs in plant tissues. Robust analytical procedures are required for the extraction of GSL from soil. Development and optimisation of a microwave-assisted extraction (MAE) method for the recovery of GSL from plant tissues and soil and comparison of its efficiency with other established extraction methods. Solvents, temperature, microwave power and extraction time were examined as parameters controlling MAE efficiency. In rocket seeds the efficiency of MAE was determined through recovery of GSLs from seeds and of sinigrin (1) that was used as internal standard. MAE was then compared with the certified ISO-9167 method and an ultrasonic-assisted extraction (UAE). MAE was also applied for the extraction of GSLs from soils fortified with 1 at three fortification levels. The efficiency of MAE was compared with a recently proposed agitation-filtration (AGIT) extraction method. The optimum conditions identified for extraction of GSLs from seeds were: methanol extraction at 250 W and 80 degrees C for 10 min. MAE and ISO methods showed comparable efficiencies and higher than UAE. In soil, both methods resulted in nearly 100% recovery of 1 at all fortification levels, although MAE achieved this recovery after a single extraction step compared with AGIT, which required two. The MAE developed is a simple and rapid method for the extraction of GSLs from plant tissues and soil that can be applied to a large number of samples, thus reducing the time of analysis.

… of agricultural and …, Jan 1, 2009

Broccoli (Brassica oleracea var. italica) is one of the most important winter season vegetables a... more Broccoli (Brassica oleracea var. italica) is one of the most important winter season vegetables and a rich source of chemoprotective molecules, including glucosinolates (GSL). The aim of this study was to investigate the impact of nitrogen (N) and sulfur (S) fertilization on GSL concentration and composition in different parts of broccoli plants. A greenhouse experiment was performed, with four different treatments of sulfur (10, 30, 70, and 150 kg/ha) and three treatments of nitrogen (50, 250, and 600 kg/ha). GSL concentrations and plant growth responded to the N supply, but this was not observed above the 250 kg N/ha dose. On the contrary, plant growth did not respond to the S supply, whereas GSL concentrations showed a sharp response to the whole range of S applications (from 10 to 150 kg/ha). Glucosinolate composition was altered differentially in the examined plant parts. Aliphatic GSL were more abundant in the florets and leaves, whereas indolyl GSLs were dominant in roots, in which aromatic GSL were also observed. High nitrogen fertilization had a higher impact on indolyl compared to aliphatic GSLs concentration. More importantly, a high concentration of aliphatic GSL, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;2.4 micromol/g dry weight (dw), and high S assimilation into aliphatic GSL were consistently observed in the florets compared to other broccoli parts, indicating adaptable processes for nitrogen and sulfur regarding synthesis and transport of aliphatic GSL for these organs.