Emine Mine Soylu

In vitro and in vivo antifungal activities of the essential oils of various plants against tomato grey mould disease agent Botrytis cinerea

The aim of this study was to find an alternative to synthetic fungicides currently used in the control of devastating fungal pathogen Botrytis cinerea, the causal agent of grey mould disease of tomato. Antifungal activities of essential oils obtained from aerial parts of aromatic plants, which belong to the Lamiacea family such as origanum (Origanum syriacum L. var. bevanii), lavender (Lavandula stoechas L. var. stoechas) and rosemary (Rosmarinus officinalis L.), were investigated against B. cinerea. Contact and volatile phase effects of different concentrations of the essential oils were found to inhibit the growth of B. cinerea in a dose-dependent manner. Volatile phase effects of essential oils were consistently found to be more effective on fungal growth than contact phase effect. A volatile vapour of origanum oil at 0.2 μg/ml air was found to completely inhibit the growth of B. cinerea. Complete growth inhibition of pathogen by essential oil of lavender and rosemary was, however, observed at 1.6 μg/ml air concentrations. For the determination of the contact phase effects of the tested essential oils, origanum oil at 12.8 μg/ml was found to inhibit the growth of B. cinerea completely. Essential oils of rosemary and lavender were inhibitory at relatively higher concentrations (25.6 μg/ml). Spore germination and germ tube elongation were also inhibited by the essential oils tested. Light and scanning electron microscopic (SEM) observations revealed that the essential oils cause considerable morphological degenerations of the fungal hyphae such as cytoplasmic coagulation, vacuolations, hyphal shrivelling and protoplast leakage and loss of conidiation. In vivo assays with the origanum essential oil, being the most efficient essential oil, under greenhouse conditions using susceptible tomato plants resulted in good protection against grey mould severity especially as a curative treatment. This study has demonstrated that the essential oils are potential and promising antifungal agents which could be used as biofungicide in the protection of tomato against B. cinerea.

Antifungal effects of essential oils from oregano and fennel on Sclerotinia sclerotiorum

Aims:  The antifungal effects of essential oils of oregano (Origanum syriacum var. bevanii) and fennel (Foeniculum vulgare) were evaluated against Sclerotinia sclerotiorum. Effects of the essential oils on morphological structures of hyphae and sclerotia were studied under light and scanning electron microscopes (SEM).

In vitro and in vivo antifungal activity of synthetic pure isothiocyanates against Sclerotinia sclerotiorum

BACKGROUND Isothiocyanates (ITCs) released by the enzymatic hydrolysis of glucosinolates in the Brassicaceae are potentially useful for controlling fungal pathogens. In vitro activity of pure ITCs against Sclerotinia sclerotiorum (Lib.) de Bary was studied by adding them to glass filters in petri dishes and dissolving them in the growing media. RESULTS Methyl, allyl and benzyl ITCs were the most fungitoxic of the compounds in bioassays with S. sclerotiorum isolate Ss31. In the volatile phase, mycelial growth was completely inhibited by these three compounds. Aromatic ITCs were less toxic in the petri dishes but were more toxic than aliphatic ITCs when dissolved in the agar. Benzyl ITC exhibited the highest inhibitory effect on sclerotial germination, with an EC(50) value of 75.1 µmol L(-1) . Butyl and benzyl ITCs reduced apothecial production of S. sclerotiorum by 92.5% at the highest concentration. In in vivo assay, only allyl and 2-phenylethyl ITCs reduced disease incidence (by 76.7 and 70% respectively) at low concentrations. CONCLUSION Sclerotinia sclerotiorum in the soil might be suppressed by the higher concentrations of allyl and benzyl ITCs released from decomposition of Brassica juncea, B. carinata, B. nigra and Sinapis spp.

First Report of Black Spot Disease Caused by Alternaria alternata in Persimmon Fruits in Turkey

In recent years, postharvest rot symptoms have been observed in persimmon fruit (Diospyros kaki L.) during long storage in Hatay Province, one of the main production areas of Turkey. Infection appeared to begin through small cracks around and beneath the calyx. Symptoms developed as small, slightly depressed, dark brown spots. Slices of infected peel were surface sterilized in 1% sodium hypochlorite for 2 min, plated on potato dextrose agar (PDA), and then incubated at 24°C in darkness for 7 days. Hyphal tips from the margin of each developing colony were subcultured on PDA. Fungal colonies were initially white, becoming olivaceous, and turning brown with age. Conidiophores were brown, short, simple, or sometimes branched. Conidia were obclavate, obpyriform or ellipsoidal with a short conical beak, and 18 to 32 μm long and 5 to 14 μm wide at the broadest point. The pathogen was identified as Alternaria alternata (Fr.:Fr.) Keissler based on morphological characteristics (2). Pathogenicity tests were conducted on previously wounded persimmon fruit (cv. Fuyu) by spraying 12 fruits with a conidial suspension (106 conidia per ml). Six control fruits were treated with sterilized water only. All fruit were kept in a moist chamber (100% relative humidity) at 25°C for 3 days, and then moved to a growth chamber at 26°C with a 16-h photoperiod. Many, small, and black sporulating spots were observed on inoculated fruit 5 days after treatment. After 21 days, these spots developed into lesions similar to those produced on naturally infected fruit. No lesions developed on the control fruit. A. alternata was reisolated from inoculated fruit. The disease was previously reported in Israel (1). To our knowledge, this is the first report of A. alternata infecting persimmons in Turkey. References: (1) D. Prusky et al. Phytopathology 71:1124, 1981. (2) E. G. Simmons. Alternaria: An Identification Manual. The American Phytopathological Society, St. Paul, MN, 2007.

First report of white blister rust disease caused by Albugo occidentalis on spinach in Turkey

Spinach (Spinacia oleracea L.) is an increasingly important vegetable crop in Turkey as is the case for many parts of the world. In March 2017, detailed field surveys were conducted to investigate the occurrence of leaf diseases in major spinach fields in Hatay Province of Turkey. White blister rust disease was sporadically present in many production fields. The disease incidence on affected crops ranged from 21 to 45% across all the areas surveyed. Initial symptoms were small chlorotic spots on the upper leaf surface. As the disease developed, white pustules (sori) or blisters were frequently produced as irregularly oval, elongated concentric rings, 3 to 4 mm in diameter, mostly on the lower leaf surface but also often on the upper surface. In the advanced stages of the disease, the white pustules often coalesced, and lesions appeared grainy due to the production of numerous oospores, rendering infected leaves unmarketable. A representative specimen (SAL2) was deposited in the Korea University Herbarium (KUS-F30037). Microscopic examination revealed that sporangia were born in basipetal chains, globose to oval, with a smooth wall surface and measured 12.5 to 15.0 × 17.5 to 20.0 μm (n = 100). The small stalked spherical haustoria, which were produced within mesophyll cells, were connected to the intercellular coenocytic hyphae, and measured 5.0 μm in diameter (n = 50). Dark-colored oospores were produced in subepidermal tissue, finely reticulated, 45 to 60 µm in diameter, with a wall thickness of 5 μm (n = 50). The morphological characteristics closely resembled those reported for Albugo occidentalis by Choi and Priest (1995). To confirm the morphological identification, both the internal transcribed spacer (ITS) rDNA and the cytochrome oxidase II (cox2) mtDNA were amplified with ITS1-O and LR0 for ITS and cox2-F and cox2-RC4 and directly sequenced (Choi et al. 2015). The resulting sequences were deposited in GenBank (accession nos. MF991148 for ITS, MF991149 for cox2). A BLASTn search revealed that the Turkish isolate is identical to the ITS and the cox2 sequences (KC676794, KC676795) of A. occidentalis in GenBank. A pathogenicity test was conducted by spraying a sporangial suspension (10⁵ sporangia/ml) onto 10 healthy leaves of 3-week-old spinach plants (cv. Matador). Inoculated plants were incubated in a dew chamber for 72 h at 18°C and then maintained in a greenhouse at 20°C with a 10-h photoperiod. Ten control plants were sprayed with distilled water and maintained under the same conditions as the inoculated plants. After 10 to 12 days, white rust pustules similar to the original symptoms observed in the field developed on inoculated plants, whereas the control plants remained symptomless. The pathogen present on the inoculated plants was morphologically identical to the original one observed on the diseased plants, fulfilling Koch’s postulates. Based on morphological characteristics, molecular sequencing data, and pathogenicity test, it was concluded that the pathogen on spinach in Turkey is A. occidentalis. The causal agent has been reported as an economically important pathogen of spinach in the United States, Mexico, Greece (Farr and Rossman 2017), and Iran (Ebrahimi and Afzali 2000). To our knowledge, this is the first report of A. occidentalis in Turkey. Although prevalence and host range of the causal disease agent is limited, major spinach production areas may be vulnerable to the introduction of this disease due to an increasing demand for this crop.

Natural infection of potato by Sclerotinia sclerotiorum causing stem rot disease in Turkey

Potato [Solanum tuberosum] is an extensively consumed vegetable in Turkey. In March 2016, typical stem rot (also known as white mould) symptoms were observed on commercially produced potato plants (cv. Rosetta) in several fields inspected in Hatay province of Turkey. White mycelium and large, irregular, black sclerotia were observed on infected stems, crowns and occasionally on leaves. Apothecia development from sclerotia were also observed on moist sand. Based on morphological characteristics of mycelia and sclerotia, all isolates were tentatively identified as Sclerotinia sclerotiorum. The identity of the fungal isolate was confirmed using MALDI-TOF MS and sequencing of the ITS rDNA region, using ITS4/ITS5 primers. To our knowledge, this is the first report of stem rot disease on potato caused by S. sclerotiorum in Turkey.