Ayhan Yildiz

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.

Weed hosts of Verticillium dahliae in cotton fields in Turkey and characterization of V. dahliae isolates from weeds

A weed survey conducted in 2004 and 2005 in Aydin province of Turkey showed that Solanum nigrum, Xanthium strumarium, Amaranthus retroflexus, Portulaca oleracea, Sonchus oleraceus and Datura stramonium were the most prevalent weeds in the cotton fields exhibiting Verticillium wilt. Verticillium dahliae Kleb. was recovered from A. retroflexus and X. strumarium in those cotton fields. This is the first report of V. dahliae occurring naturally in A. retroflexus in Turkey. Pathogenicity tests on cotton and weeds showed that the virulence of V. dahliae isolates from weeds was higher on cotton plants than on weeds, with the disease severity ranging from 31.7% to 98.0%. Disease severity of V. dahliae isolates was 54.7–93.9% on eggplant, 23.7–51.6% on cucumber and 11.0–16.4% on tomato, whereas it did not cause any disease symptoms, or only low levels, on pepper and bell pepper. Two vegetative compatibility groups (VCGs) were identified among seven tested weed isolates: VCG2A (two isolates) and VCG2B (three isolates) using international reference strains.

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.

A laboratory bioassay for evaluating pathogenicity of Macrophomina phaseolina and Rhizoctonia solani isolates to strawberry stolons

Macrophomina phaseolina and Rhizoctonia spp. are the most important soilborne pathogens of the strawberry crop that cause seriously reduced yields. Various methods are being used to determine pathogenicity of these fungi isolated from strawberry; however, they take a long time to grow strawberry plants. They also encounter some problems to provide a large number of healthy plants for the pathogenicity tests. Therefore, the aim of this study was to develop a faster and more reliable pathogenicity test for soilborne fungal pathogens of strawberry by using the stolons of healthy strawberry plants. The stolon inoculation method was demonstrated to be easy and rapid for properly distinguishing soilborne fungal species of strawberry, whether pathogenic or non-pathogenic, and also for assessing the isolates for virulence.