Kemal Benlioglu

First Report of Strawberry Dieback Caused by Lasiodiplodia theobromae

With a typical Mediterranean climate, Aydin is the third largest strawberry-producing province, responsible for 13% of the overall strawberry production in Turkey. Strawberries (Fragaria × ananassa Duchesne) are mainly grown in raised, plastic-mulched beds under tunnels and soil solarization is the most effectively used management practice to control soil-borne pathogens. During October 2011 and 2012, 2 months after planting, wilting and collapse of plants were observed on commercial strawberry (cv. strawberry Festival) fields in Sultanhisar town of Aydin Province. Eleven percent of the plants were wilted and died. Symptomatic plants exhibited blackened necrotic discoloration of roots and in the cross section of crowns. A fungus was consistently isolated from pieces of infected tissue cut aseptically from the crowns and placed on potato dextrose agar. Fungus produced white colonies and later turned olivaecious black with dense aerial mycelium after 4 to 5 days incubation at 27°C. Dark brown to black pycnidia that formed on 20- to 30-day-old pure cultures under daylight conditions produced abundant conidia that were two-celled, thick-walled, and oval shaped with longitudinal striations. Single spore isolates from 12 samples were obtained and stored for further identification. The average size of 300 conidia was 25.42 ± 2.12 × 12.87 ± 1.08 μm. The morphology of the fungus was similar to Lasiodiplodia theobromae (Pat.) Griff. & Maubl. (syn. Botryodiplodia theobromae Pat.). To confirm the identity of the isolates, the internal transcribed spacer (ITS) region of ribosomal DNA and the elongation factor 1-alpha gene were amplified with the universal ITS1/ITS4 and EF1-688F/EF1-1251R (1) primers, respectively. The amplicons from 12 isolates were commercially sequenced at Macrogen (Korea) and were deposited in GenBank under consecutive accession numbers KF910369 to KF910380 and KJ641536 to KJ641547. Sequence comparison and phylogenetic analysis revealed that all 12 isolates were closely related and belonged to L. theobromae. Pathogenicity tests were performed by the toothpick technique (2) under greenhouse conditions (28°C, 14/10-h day/night, 70% RH) on potted strawberry plants (cv. strawberry Festival). Toothpicks carrying fungal growth taken from 1-week-old corn meal agar cultures of the tested isolates was placed into the basal crown tissue of the plants by piercing about 5 mm depth. Six plants were inoculated for each isolate and six were treated with sterile toothpick for control. All inoculated plants developed wilting and dieback symptoms resembling those of naturally infected plants within 2 to 3 weeks of incubation. All plants inoculated with the tested isolates collapsed after 4 weeks and showed discoloration of internal crown tissue. Control plants did not exhibit any disease symptoms, and crown tissue was symptomless. L. theobromae was successfully re-isolated from lesions of all inoculated plants. L. theobromae has been reported to cause cankers and dieback in a wide range of hosts in tropical and subtropical regions of the world (3). To the best of our knowledge, this is the first report of L. theobromae causing dieback on strawberry plants. References: (1) A. Alves et al. Fungal Divers. 28:1, 2008. (2) M. E. A. El-Morsi and I. A. Ibrahim. Wudpecker J. Agric. Res. 1:215, 2012. (3) E. Punithalingam. Plant diseases attributed to Botryodiplodia theobromae Pat. J. Cramer, Vaduz, 1980.

Enhanced Biological Control of Phytophthora Blight of Pepper by Biosurfactant-Producing Pseudomonas

Pseudomonas isolates from different crop plants were screened for in vitro growth inhibition of Phytophthora capsici and production of biosurfactant. Two in vivo experiments were performed to determine the efficacy of selected Pseudomonas strains against Phytophthora blight of pepper by comparing two fungicide treatments [acibenzolar-S-methyl (ASM) and ASM + mefenoxam]. Bacterial isolates were applied by soil drenching (1 × 109 cells/ml), ASM (0.1 μg a.i./ml) and ASM + mefenoxam (0.2 mg product/ml) were applied by foliar spraying, and P. capsici inoculum was incorporated into the pot soil three days after treatments. In the first experiment, four Pseudomonas strains resulted in significant reduction from 48.4 to 61.3% in Phytophthora blight severity. In the second experiment, bacterial treatments combining with olive oil (5 mL per plant) significantly enhanced biological control activity, resulting in a reduction of disease level ranging from 56.8 to 81.1%. ASM + mefenoxam was the most effective treatment while ASM alone was less effective in both bioassays. These results indicate that our Pseudomonas fluorescens strains (6L10, 6ba6 and 3ss9) that have biosurfactant-producing abilities are effective against P. capsici on pepper, and enhanced disease suppression could be achieved when they were used in combination with olive oil.

First report of bacterial blight caused by Pseudomonas syringae pv. pisi on pea in Turkey.

In April of 2009, leaf blight symptoms were observed on field peas (Pisum sativum L.) grown in Söke, Torbali, and Ödemis counties in the Aegean Region of Turkey. Field inspections revealed disease incidence as high as 45% and the disease was found in 13 commercial fields. Initial symptoms consisted of small, dark green, water-soaked lesions on leaves, stipules, and stems near ground level. Lesions often enlarged and coalesced and turned chocolate brown with a water-soaked margin. Stem infections usually coalesced and girdled the stem spreading upward to stipules and leaflets forming a fan-like lesion on the stipule. A fluorescent, gram-negative bacterium was consistently isolated from diseased tissues onto Kings B medium. Twelve strains (five from cv. Early Sweet, three from cv. Geneva, two from cv. Bolero, and two from cv. Carina) from thirteen pea fields were obtained. All strains metabolized glucose oxidatively, and their reactions in LOPAT tests were +, -, -, -, +, and thus classified as belonging to Pseudomonas syringae LOPAT group Ia (1). The 12 strains utilized homoserine, inositol, sorbitol, sucrose, mannitol, and mannose but did not utilize erythritol, trehalose, and L-tartarate. All showed ice nucleation activity but variable results were obtained for gelatin liquefaction and esculin hydrolysis. Identification of P. syringae pv. pisi was confirmed by sequencing the 16S rDNA with primers Univ-1390R (3) and 27F (2). Sequences of the three local strains (Bz2, Bz4, and Bz8) were 100% identical to a type culture strain. The nucleotide sequence of strain Bz4 was submitted to GenBank (Accession No. GU332546). Pathogenicity tests were performed on greenhouse-grown 2-week-old pea plants cv. Geneva as three replicates in 12-cm pots containing a steamed sand/peat/soil mixture. Plants were stab inoculated by puncturing the main stem at its junction with the stipules at the second node from the apical end with a 26-gauge needle through a 5-μl drop of 108 CFU/ml bacterial suspensions. Control plants were inoculated with sterile water. After 10 days of incubation in a growth chamber at 24 ± 1°C with a 14-h photoperiod, stems inoculated with pea isolates resulted in water-soaked tissue spreading from the site of inoculation along the veins on stipules and leaflets that were identical to symptoms seen in the field. Control plants remained symptomless. Isolates recovered from the symptomatic stems showed the same morphological and biochemical features of the original isolates. All physiological and biochemical tests as well as the pathogenicity assay were performed at least twice and the type strain of P. syringae pv. pisi (NCPPB 2585) was used as reference. On the basis of the physiological, biochemical, genetic, and pathological characteristics, all strains were identified as P. syringae pv. pisi. To our knowledge, this is the first report of P. syringae pv. pisi causing bacterial blight on pea in Turkey. Turkey currently produces approximately 93.000 t of peas annually and three-quarters of that is produced in Western Anatolia. The new disease may represent a limiting factor for future production. References: (1) R. A. Lelliott et al. J. Appl. Bacteriol. 29:470, 1966. (2) W. G. Weisburg et al. J. Bacteriol. 173:697, 1991. (3) D. Zeng et al. Appl. Environ. Microbiol. 62:4504, 1996.

Effects of soil amendments combined with solarization on the soil microbial community in strawberry cultivation using quantitative real-time PCR

Experiments were conducted in commercial fields of strawberry-growing areas of the Aydin Province of Turkey during two cropping seasons: 2010–2011 and 2011–2012. Each year, eight separate treatments were used: (1) untreated control (C), (2) solarization alone (S), (3) solarization + broccoli (SBr), (4) solarization + fava bean (SFB), (5) solarization + dry olive-mill wastewater (SDOMW), (6) solarization + rice hulls (SRH), (7) solarization + sulfur powder (SSu), and (8) solarization + vermicast (SVe). DNA was extracted from bulk soil samples before and after solarization. The populations of the major taxonomic groups of bacteria and soil-borne fungal pathogens of strawberry were quantitatively calculated by quantitative real-time PCR (qPCR) with specific primer pairs using standard curves. The marketable fruit yield was recorded in the experimental plots. After the 6-week solarization period, there were significant reductions for total bacteria and for α-Proteobacteria in all of the experimental plots, except for SDOMW. However, the abundance of β-Proteobacteria significantly increased in all of the experimental plots (except for C and SFB in 2011). Significant increases in Firmicutes and Actinobacteria were also recorded in all of the treated plots. The highest significant increase was noticed with SDOMW treatments for total bacteria, α-Proteobacteria, β-Proteobacteria, Firmicutes and Actinobacteria in both years. The target level of Verticillium spp. Rhizoctonia solani and Fusarium oxysporum decreased significantly in all of the treated plots after solarization in both years. The reductions of M. phaseolina were significant in S, SVe, and SSu and were the highest in SDOMW in 2011; these reductions were significant in S, SSu and SDOMW in 2012. The abundance of Trichoderma spp. decreased insignificantly in all of the experimental plots. The highest significant yields were obtained from the combination of SDOMW, SRH and SSu compared to solarization alone in both seasons.

Soil disinfestation options in Aydın province, Turkey, strawberry cultivation

Two field experiments were conducted in the two successive seasons of 2005/2006 and 2006/2007 in strawberry-growing areas of Aydin province of Turkey to (a) compare soil solarization and metam sodium (MS) combinations with low-density polyethylene (LDPE) and virtually impermeable film (VIF); and (b) evaluate strawberry fruit yield, soilborne disease and weed control efficacy. Disinfestation treatments were as follows: (i) raised bed solarization for about 6 weeks, (ii) raised bed solarization for 3 weeks, (iii) raised bed solarization for 2 weeks + MS (50 ml m-2), (iv) MS (50 ml m-2) with LPDE (v) MS (100 ml m-2) with LDPE, (vi) MS (50 ml m-2) with VIF, (vii) MS (100 ml m-2) with VIF. Results indicated that Macrophomina phaseolina and Fusarium spp. were the major fungal pathogens isolated from the crown of dead or dying plants in both cropping seasons. MS treatment (100 ml m-2) through the drip irrigation system under LDPE sheet or VIF reduced soilborne diseases significantly while reduced dosage of MS (50 ml m-2) under LDPE or VIF and in combination with 2-week soil solarization controlled the soilborne diseases to a greater extent than soil solarization treatments. All treatments controlled the following weed species: Portulaca oleracea, Amaranthus spp., Poa annua, Alopecurus myosuroides, Matricaria chamomilla, Digitaria sanguinalis, Raphanus raphanistrum, Seteria verticillata, Chenopodium album, Stelleria media, Capsella bursa-pastoris, Echinochloa cruss-galli, Veronica hederifolia, Lamium amplexicaule and Silybum marianum. None of the treatments provided acceptable control of horseweed (Conyza canadensis). Metam sodium application (100 ml m-2) significantly increased yields by 18.5% and 14.5% in the 2005/2006 and 21.6% and 18.5% in the 2006/2007 season under LDPE and VIF, respectively, while marketable fruit yield was not significantly increased by soil solarization treatments in either trial. There was no significant difference between MS applications under LDPE and VIF for the weed and disease control, and marketable fruit yield.

Rhizoctonia fragariae causes black root rot on strawberry seedlings in Turkey

Samples of strawberry transplants were randomly collected from 47 growers in Aydın province of Turkey. A total of 10 Rhizoctonia isolates were identified by morphological characterization, analysis of rDNA-ITS sequences. Pathogenicity tests were carried on strawberry seedlings and detached stolon. Ten pathogenic binucleate Rhizoctonia isolates were defined as AG-A, AG-G and AG-K on the basis of ITS region sequence analysis. To our knowledge, this is the first report of the presence of Rhizoctonia fragariae in strawberry transplants in Turkey.

Bacterial leaf spot of lettuce caused by Xanthomonas hortorum pv. vitians in the Aegean Region of Turkey

Samples of diseased plants were collected from 12 lettuce fields in Aydin province of the Aegean Region of Turkey. A total of 8 bacterial isolates were identified by morphological characterization, sequence analysis of 16S rDNA and gyrB genes, and pathogenicity. The survey included twelve lettuce fields of three different cultivars [Yedikule (romaine type), Robinson and Chianti (iceberg type)]. The incidence of the disease ranged from 48 to 95%. Plants of cv. Chianti were the most severely infected cultivars. To our knowledge, this is the first report of the presence of Xanthomonas hortorum pv. vitians in lettuce plants in Turkey.

Orta Anadolu Bölgesi Patates Ekim Alanlarının Halkalı Çürüklük Hastalığı Yönünden İncelenmesi

Orta Anadolu Bolgesi Patates Ekim Alanlarinin Halkali Curukluk Hastaligi Yonunden Incelenmesi