Main content area

First Report of Fig Decline Caused by Phytophthora niederhauserii in Taiwan

Lin, C. P., Tsai, J. N., Ann, P. J.
Plant disease 2019 v.103 no.5 pp. 1046
Ficus carica, Phytophthora, ampicillin, calcium carbonate, chlamydospores, chlorosis, cotton, cytochrome-c oxidase, decline, discoloration, figs, fruit trees, gardens, greenhouses, holotypes, hyphae, leaves, monitoring, necrosis, nystatin, orchards, ornamental plants, pathogenicity, peat, perlite, quintozene, ribosomal DNA, roots, selective media, soil, sporangia, stems, tissues, underground parts, vegetable juices, vermiculite, wilting, zoospores, Taiwan
In June 2006 and October 2016, we found sporadically diseased figs (Ficus carica) showing necrosis symptoms on the roots and at least half of the basal stems, leading to wilting and leaf chlorosis of the fig in the orchards and garden shops at Changhwa and Yunlin counties in Taiwan. To identify the disease-causing organism, the symptomatic tissues were cut into pieces, surface sterilized with 0.3% NaOCl for 1 to 5 s, and placed on selective medium (200 ppm of ampicillin, 50 ppm of nystatin, 10 ppm of pentachloronitrobenzene, 5% V8 vegetable juice, 0.02% CaCO₃, and 2% Bacto agar) (Ko et al. 1978). Phytophthora niederhauserii Z.G. Abad & J.A. Abad was isolated and identified according to the morphological and molecular characteristics. P. niederhauserii has been known to associate with or cause disease of some ornamentals and fruit trees in other countries (Abad et al. 2014) but has not been reported as a pathogen of fig. A total of five P. niederhauserii isolates were obtained, including TARI216036 and TARI206231, and were all of A1 mating type. Sporangia of isolate TARI216036 were nonpapillate, ellipsoid, with a size range of 85.0 to 106.9 to 140.0 × 40.0 to 47.0 to 54.0 μm (minimum to average to maximum; length × width), ratio of 1.7 to 2.3 to 2.8 (length/width), and proliferated internally in both nested and extended ways. Chlamydospores were absent, whereas toruloid to lobate hyphal swellings were frequently found when grown on V8 agar. The morphologic characteristics of isolate TARI206231 were similar except for the range of sporangia size, which was of 65.0 to 83.2 to 100.0 × 40.0 to 44.1 to 50.0 μm and ratio of 1.6 to 1.9 to 2.1. The sequences of the ribosomal DNA internal transcribed spacers and cytochrome oxidase subunit II and I regions of TARI216036 (GenBank accession nos. MH352420 and MH481286) both showed 100% identity with the same regions of the holotype of P. niederhauserii (AY550915 and GU222091), respectively, and those of TARI206231 (GU111617 and MH481285) showed 99 and 100% identity, respectively. Both morphological and molecular characteristics were consistent with the features of P. niederhauserii belonging to clade 7c. For the pathogenicity test, we pulled out healthy, about 6-month-old, and approximately 50-cm-tall fig plants from pots, gently removed most of the attached soil, and immersed their underground parts for 30 min in zoospore suspensions (10⁴ zoospores/ml) of P. niederhauserii isolate TARI216036, or in distilled water as the control. Afterward, we grew the plants in pots with sterilized perlite, vermiculite, and peat mixture (1:1:3, volume ratio), surrounded the basal stems with cotton, poured another 200 ml of the zoospore suspensions or water, and kept them in a greenhouse at 25 to 29°C. Ten days later, whereas the control plants looked healthy, three out of five plants inoculated with P. niederhauserii were wilted, had lesions at the root and basal stems, and had vascular discoloration at the stems, similar to those symptoms of diseased figs in the fields. P. niederhauserii was reisolated from the diseased tissues. To our knowledge, this is the first report that confirms the existence of P. niederhauserii in Taiwan and P. niederhauserii as a pathogen of fig. So far, in Taiwan, P. niederhauserii was isolated only in fig with moderate frequency since monitoring began in 2006. Both isolates TARI206231 and TARI216036 have been deposited at the Bioresource Collection and Research Center in Taiwan as CH30303 and CH30304, respectively.