Research Information System
Plant Disease, vol.100, no.1, pp.210, 2016 (SCI-Expanded)
Kiwifruit (Actinidia deliciosa(A. Chev.) C. F. Liang & A. R. Ferguson) was introduced into Turkey in 1988. Since its entrance, kiwifruit cultivation has expanded to 29,000 ha, mainly in the Marmara, Black Sea, Mediterranean, and Aegean regions. In June 2013, crown and root rot symptoms were observed on approximately 10% of 3-year-old kiwifruit vines (cv. Hayward) in an experimental 200-vine orchard in Elazığ Province (38°29ʹ01ʺ N; 38°34ʹ44ʺ E). Under the bark, necrotic lesions and decay extended from the fine roots to the crown and basal stem area. Crown and root samples from 12 kiwifruit vines exhibiting symptoms were collected, cut into 1-cm2pieces, soaked in a solution of 0.5% sodium hypochlorite for 2 min, rinsed in several changes of sterile water, and blotted dry using filter paper. The pieces were placed on corn meal agar amended with P5ARP (17 g of cornmeal agar, 5 mg of pimaricin, 250 mg of ampicillin, 10 mg of rifampicin, and 100 mg of pentachloronitrobenzene in 1 liter of water) (Jeffers and Martin, 1986), and incubated in darkness at 27°C for 7 to 12 days. Twelve isolates of aPhytophthoraspp., each from a different vine, were obtained in pure culture by hyphal tip transfer to V8 juice agar medium. Isolates of this putative pathogen had a subtle chrysanthemum pattern on the top side of this medium. The minimum, optimum, and maximum temperatures for mycelium growth on PDA were 11, 27, and 34°C, respectively. Agar discs with mycelium sampled from the margin of the actively growing colonies were submerged in sterilized deionized water for 5 days at 25°C. On submerged discs, all isolates produced conspicuous papillate, caducous, hyaline sporangia of varying shapes, mostly elliptical to ovoid with the widest part close to the base on sympodial sporangiophores. Sporangia with short pedicels (3.3 μm) were 34 to 66 × 26 to 41 μm with a length/width ratio of 1.4 to 1.7. Terminal and intercalary chlamydospores of the isolate were globose and 35 μm in diameter. On the basis of morphology, the pathogen was identified asPhytophthora palmivora(E. J. Butler) E. J. Butler (Stamps 1985). Pathogenicity of three isolates was evaluated on 8-month-old kiwifruit cv. Hayward seedlings under glasshouse conditions (25 to 32°C during the day, above 20°C at night). Inoculations were performed by pipetting 100 ml of a zoospore suspension (105zoospores per ml) into each of four 90-mm-diameter holes located in root tissue within 10 cm of the base of each seedling (7 seedlings per isolate). Ten plants were treated with sterilized water as control. Upper surfaces of holes were covered by sterilized soil. Plants were watered daily as required to keep the soil wet. All inoculated kiwifruit plants showed decline symptoms similar to those observed in the field: necrotic leaves; defoliation; and a 40% reduction of roots after 2 months.P. palmivorawas reisolated from the root lesions on all inoculated plants; control plants remained healthy. The ITS region of rDNA was amplified with primers ITS6/ITS4 (Cooke et al. 2000) and sequenced. BLAST analysis revealed 99 to 100% identity withP. palmivoraisolates deposited at GenBank (Accession Nos. EU194438 and KC415919) and the Phytophthora database (http://www.phytophthoradb.org). The nucleotide sequence (723 bp) was submitted to GenBank as Accession No. KP985656. To our knowledge, this is the first report worldwide ofP. palmivoracausing crown and root on kiwifruit vines, which represents a new host for this oomycete. In 2015, all kiwifruit vines in the experimental orchard were killed by this oomycete.P. palmivorahas the potential to be a major limiting factor in kiwifruit production.