E. Mine Soylu

Induction of disease resistance by the plant activator, acibenzolar-S-methyl (ASM), against bacterial canker (Clavibacter michiganensis subsp. michiganensis) in tomato seedlings

The plant defence activator acibenzolar-S-methyl (benzo [1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester, ASM; Bion 50 WG) was assayed on tomato seedlings for its ability to induce resistance against Clavibacter michiganensis subsp. michiganensis (Cmm), the causal agent of bacterial canker of tomato. Pre-treatment of plants with ASM reduced the severity of the disease as well as the growth of the bacteria in planta. In ASM-treated plants, reduction in disease severity (up to 75%) was correlated with suppression of bacterial growth (up to 68.2%) during the time course of infection. In plants treated with ASM, activities of peroxidase (POX) and glutathione peroxidase (GPX) were determined as markers of resistance. Applications of ASM induced a progressive and significant increase of both enzymes in locally treated tissues. Such responses were expressed earlier and with a much higher magnitude when ASM-treated seedlings were challenged with the pathogen, thus providing support to the concept that a signal produced by the pathogen is essential for triggering enhanced synthesis and accumulation of these enzymes. No such activities were observed in water-treated control plants. Therefore, the slower symptom development and reduction in bacterial growth in ASM-treated plants might be due to the increase in activity of both oxidative and antioxidative protection systems in planta.

Inactivation of Penicillum expansum in sour cherry juice, peach and apricot nectars by pulsed electric fields

Inhibitory effects of pulsed electric fields (PEF) on Penicillum expansum inoculated into sour cherry juice, apricot and peach nectars were determined based on germination tube elongation, spore germination rate, and light and scanning electron microscopy (SEM) observations in this study. After inoculation of juice/nectar samples with P. expansum spores at the level of 10(5)-10(6)cfu/mL, the samples were processed by bench scale PEF pulse generator as a function of differing electric field strengths (0, 13, 17, 20, 23, 27, 30 and 34kV/cm) and processing times (0, 62, 94, 123, 163, 198 and 218mus). Results revealed that with an increase in electric field strength and processing time, germination tube elongation and spore germination rate were completely inhibited. Light and SEM observations revealed considerable morphological alterations in fungal conidia such as cytoplasmic coagulation, vacuolations, shrinkage and protoplast leakage. PEF processing of juice/nectars was demonstrated to be effective in inactivating P. expansum. To our knowledge, this is the first study confirming the inhibitory effects of PEF on germination tube elongation and spore germination rate of P. expansum in fruit juice/nectars.

Vegetative compatibility groups in Verticillium dahliae isolates from olive in western Turkey

Verticillium wilt, caused by Verticillium dahliae, is the most serious disease in olive cultivation areas in western Turkey. Two hundred and eight isolates of V. dahliae from olive (Olea europea var. sativa) trees were taken for vegetative compatibility analysis using nitrate non-utilizing (nit) mutants. One isolate did not produce a nit mutant. Nit mutants of 207 isolates were tested against tester strains of internationally known vegetative compatibility groups (VCGs) 1A, 2A, 2B, 3, 4A and 4B, and also paired in many combinations among themselves. One hundred and eighty nine of the isolates (90.9%) were strongly compatible with T9, the tester strain of VCG1A, and thus were assigned to VCG1A. Eight isolates were assigned to VCG2A and four isolates to VCG4B. One isolate was heterokaryon self-incompatible (HSI) and five isolates could not be grouped to any of the VCGs tested. Pathogenicity assays were conducted on a susceptible olive cultivar (O. europea cv. Manzanilla) and a susceptible local cotton cultivar (Gossypium hirsutum cv. Çukurova 1518). Both cotton and olive inoculated with all VCG1A isolates showed defoliating symptoms in greenhouse tests. This is the first report on VCGs in V. dahliae from olive trees in Turkey which demonstrates that VCG1A of the cotton-defoliating type is the most commonly detected form from olive plants in the western part of Turkey.

Vegetative compatibility groups ofVerticillium dahliae from cotton in the southeastern anatolia region of Turkey

Eighty isolates ofVerticillium dahliae from the southeastern Anatolia region and 20 isolates from the east Mediterranean region from wilted cotton plants were used for vegetative compatibility analysis employing nitrate non-utilizing mutants and reference tester strains of vegetative compatibility groups (VCGs) 1A, 2A, 2B, 3, 4A and 4B. Of the 100V. dahliae isolates, 49 were assigned to VCG1A, 39 to VCG2B, nine to VCG2A and three to VCG4B. Pathogenicity assays were conducted on susceptible cotton cv. Çukurova 1518 in the greenhouse. All VCG1A isolates induced defoliation and all VCG2B isolates caused partial defoliation symptoms. Isolates of VCG2A and VCG4B caused typical symptoms of leaf chlorosis without defoliation. This is the first report on VCGs ofV. dahliae in the southeastern Anatolia region of Turkey, which demonstrates that VCG1A of the cotton-defoliating type and VCG2B of the partially defoliating type are prevalent in this region.

Antifungal Activities of Essential Oils Against Citrus Black Rot Disease Agent Alternaria alternata

Abstract: Antifungal effects of plant essential oils (Origanum onites L., Thymbra spicata L., Lavandula stoechas L. subsp. stoechas L., Foeniculum vulgare Mill. and Laurus nobilis L.) were investigated in vitro conditions against post-harvest fungal pathogen of Citrus, Alternaria alternata. O. onites and T. spicata essential oils exhibited the strongest antifungal activity against A. alternata by inhibiting completely mycelial growth of A.alternata at 20.0 and 80.0 µg ml-1 concentrations, respectively. Conidial germination and germ tube elongation of the pathogen was also completely inhibited by O. onites, T. spicata and F. vulgare essential oils used at the minimum concentrations of 10.0 µg ml-1. Light and scanning electron microscopic observations on fungal structures, exposed to volatile phase of themost efficient essential oils, revealed considerable structural deformations such as cytoplasmic coagulation, vacuolations and protoplast leakage. The plant essential oils showing potent fungitoxic efficacies may be recommended as a plant-based preservative in the management of fungal infestation of fruits and vegetables during storage.

Pathogenic races and inoculum density ofFusarium oxysporum f.sp.niveum in commercial watermelon fields in southern Turkey

Systematic surveys forFusarium oxysporum f.sp.niveum (Fon) were conducted in a total of 141 fields in the watermelon-growing areas of the Mediterranean and southeastern Anatolia regions of Turkey in 2004 and 2005. The mean incidence and prevalence of the disease were higher in the southeastern Anatolia region than in the Mediterranean region. Maximum disease incidence during the 2-year survey was 46.3%. However, mean disease prevalence ranged from 27.3% to 63.6% in southern Turkey. Of the 33 isolates ofFon recovered, 19 were recovered from Adana, two from Mersin, one from Gaziantep, four from Sanlıurfa, five from Adıyaman, one from Batman, one from Diyarbakır. The physiological race of each isolate was determined by the disease reaction in five differential watermelon cultivars (Citrullus lanatus (Thunb.) Matsum. & Nakai). Of the isolates recovered from the Mediterranean region, 47.6% were identified as race 0, 38.1% as race 1, and 14.3% as race 2. Among the 12 isolates recovered from the southeastern Anatolia region, four isolates were identified as race 0, and eight isolates as race 1. Race 2 was not detected in this region. This is the first report ofFon races 0 and 1 in southeastern Anatolia. The population density ofFon in both the Mediterranean and southeastern Anatolia regions ranged from 116.1 to 4444.7 CFU g−1 of soil. The mean inoculum density was much higher in watermelon-growing areas in the southeastern Anatolia region in comparison with the Mediterranean region, with a mean inoculum density of 1547.2 CFU g−1. Race 0 and race 1 were the most prevalent races in the fields with the mean highest and lowest inoculum density, respectively.

Antifungal Efficacies of Plant Essential Oils and Main Constituents Against Soil-Borne Fungal Disease Agents of Bean

Abstract In this study, in vitro antifungal efficacies of essential oils (EOs) obtained from taxonomically different medicinal plants such as oregano (Origanum syriacum L), fennel (Foeniculum vulgare Mill.) and laurel (Laurus nobilis L.), naturally growing in the different regions of Hatay province, and their major constituents (carvacrol, trans-anethole and 1,8-cineole) were investigated against soil-borne fungal disease agents of bean plants such as Sclerotium rolfsii, Rhizoctonia solani and Macrophomina phaseolina. Inhibitory effects of volatile and contact phases of different concentrations of the essential oils used were determined on fungal hyphae. While contact phases of O. syriacum and F. vulgare EOs completely inhibited mycelial growth of fungal pathogens at 160 to 320 µg/ml concentrations, L. nobilis EO, however, completely inhibited mycelial growth at relatively higher concentrations (1440 to 2880 µg/ml). In comparison, volatile phases of all EO have completely inhibited mycelial growth at relatively lower concentrations (20 to 200 µg/ml). Major components of O. syriacum, and F. vulgare EOs, carvacrol and trans-anethole respectively, also completely inhibited mycelial growth at 130 to 440 µg/ml concentrations. Major component of L. nobilis EO, 1,8-cineole, was, however, able to show antifungal activity against only M. phaseolina at the highest concentration (3000 µg/ ml). Antimicrobial activities shown by EOs and their major constituents against fungal disease agents revealed their potential to be used as a new alternative control measures against fungal diseases of economically important plant.