Browsing by Author "Tok, Fatih Mehmet"

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First report of Verticillium dahliae causing Verticillium wilt on avocado (Persea americana) in Turkey
(SpringerLink, 2022) Tok, Fatih Mehmet; Derviş, Sibel
Avocado (Persea americana Mill.) is an expanding crop in Turkey grown on 949 ha, yielding 4,209 tons of fruit annually (FAO 2021). In June 2021, 5% of 220 5-year-old trees of cv. Hass grafted onto the rootstock Fuerte (36°06′25.6"N 35°59′16.7"E) in Samandağ district of Hatay showed symptoms of twig and branch dieback with brownish black leaf and bark discoloration. Vascular tissues of branches bearing blackened dead twigs were sampled from five trees. Tissues were surface disinfected in 1% NaOCl for 2 min, rinsed with sterile distilled water (SDW), dried, placed on potato dextrose agar, and incubated at 25 °C. After 7 days, a slow-growing fungus was consistently recovered. Colonies were identified as Verticillium dahliae Kleb. on the basis of the presence of black microsclerotia (35.2 to 160.8 × 20.3 to 68.5 μm), verticillate conidiophores, and hyaline, elliptical, single celled conidia (2.9 to 7.3 × 2.2 to 3.8 μm) (Pegg and Brady 2002). Identification was confirmed by sequencing the internal transcribed spacer region (ITS) of rDNA amplified from one single-conidial isolate (AvVd01 deposited in the plant pathogenic fungal collection of the first author’s institution) using universal ITS1/ITS4 primers. BLAST analysis of the amplicon sequenced (GenBank accession No. MZ664289) showed 100% identity with a sequence of V. dahliae from kiwifruit in Turkey (MK287620.1). To fulfill Koch's postulates, 15 healthy 1-year-old P. americana ‘Hass’ seedlings were inoculated by submerging trimmed roots in a conidial suspension of 107 conidia/ml for 5 min using AvVd01. Ten control plants were dipped in SDW in the same manner. Inoculated plants showed symptoms identical to those of naturally infected plants within a month. V. dahliae was reisolated from inoculated plants but not from controls. To our knowledge, this is the first report of V. dahliae causing wilt on avocado in Turkey (Farr and Rossman 2022). It is expected to cause more problems in avocado plantings previously dedicated to vegetable crops.
HOST SELECTIVE VIRULENCE, TEMPERATURE RESPONSE AND GENETIC DIVERSITY IN MACROPHOMINA PHASEOLINA ISOLATES FROM SESAME AND PEANUT IN SOUTHERN TURKEY
(PARLAR SCIENTIFIC PUBLICATIONS (P S P), 2018) Tok, Fatih Mehmet; Dervis, Sibel; Arslan, Mehmet
In this work, host specificity (comparing virulence levels on diverse hosts), temperature response as a physico-morphological characteristic, and genetic diversity of 40 M. phaseolina isolates from sesame and peanut plants with different geographic origins were evaluated. Sesame and peanut isolates of M. phaseolina performed different levels of virulence on maize, watermelon, melon, peanut, and soybean. The temperatures between 25 and 30 degrees C were the optimum temperatures for colony size of isolates from sesame and peanut. A temperature of 25 degrees C was optimal for only 26 isolates (65%), but 30 degrees C was optimal for 39 isolates (97.5%). UPGMA clustering of data indicated that the Sesame and peanut isolates displayed various levels of genetic similarity within a range of 0.79 to 1.0 similarity coefficient index in three major cluster groups. With a few exceptions, isolates from the same or close locations tended to group together.
Vegetative Compatibility and Virulence Diversity of Verticillium dahliae from Okra (Abelmoschus esculentus) Plantations in Turkey and Evaluation of Okra Landraces for Resistance to V. dahliae
(2020) Tok, Fatih Mehmet; Derviş, Sibel; Yetişir, Halit
Forty-four V. dahliae isolates were collected from symptomatic vascular tissues of okra plants each from a different field in eight provinces located in the eastern Mediterranean and western Anatolia regions of Turkey during 2006- 2009. Nitrate-nonutilizing (nit) mutants of V. dahliae from okra were used to determine heterokaryosis and genetic relatedness among isolates. All isolates from okra plants were grouped into two vegetative compatibility groups (VCGs) (1 and 2) and three subgroups as 1A (13.6%, 6/44), 2A (20.5%, 9/44) and 2B (65.9%, 29/44) according to international criteria. Pathogenicity tests were performed on a susceptible local okra (A. esculentus) landrace in greenhouse conditions. All isolates from VCG1A and VCG2B induced defoliation (D) and partial defoliation (PD) symptoms, respectively. Other isolates from VCG2A gave rise to typical leaf chlorosis symptoms without defoliation. The obtained data showed that the virulence level of V. dahliae isolates from okra was related to their VCG belongings. Eighteen okra landraces from diverse geographical origins were screened for resistance to VCG2B and VCG1A of V. dahliae. The results indicated that all landraces were more susceptible to highly virulent VCG1A-D pathotype displaying D or PD symptoms depending on their susceptibility levels with a mean disease severity index of 3.52 than to less virulent VCG2B-PD pathotype of V. dahliae displaying PD and ND symptoms with a mean disease severity index of 2.52. Significant differences were observed among the landraces; however, none of them exhibited a level of resistance. Okra landraces; Çorum, Hatay Has and Şanlıurfa displayed the lowest level of susceptibility or little tolerance to both D and PD pathotypes. VCG2B of PD was prevailing in the surveyed areas and VCG1A of D was the most virulent of the VCGs identified. Introduction of resistant genotypes to Turkish okra germplasm from different sources and breeding new resistant okra cultivars are critical for the sustainability of okra production.