由Phytophthora nagaii及Phytophthora bisheria引起之玫瑰疫病

First report of rose blight caused by Phytophthora nagaii and Phytophthora bisheria in Taiwan

"2015年9月在台灣南投埔里的玫瑰花發生一種新病害，罹病葉片呈現黃化及萎凋，受感染的植株根腐及莖基部褐化，且褐化現象從莖基部向上擴展，最後導致植株死亡。將玫瑰根部及莖基部之罹病組織進行分離，分別在不同花圃的罹病株上分離得2種疫病菌，將分離到的疫病菌游走子懸浮液接種於玫瑰苗齡40–50天之扦插苗，於溫度32°C及光照12小時的環境條件下，14–28天後即可造成植株葉片黃化、莖基部褐化及植株死亡，與田間所發生之病徵相符合，並能再分離得原先接種之病原菌以完成柯霍氏法則（Koch's postulates）。觀察此2種疫病菌之形態特徵，第1種疫病菌的孢囊形態為橢圓形或卵圓形，孢囊單頂生，不具乳突且孢囊不脫落，大小為51.4-91.0×35.5-70.0（平均63.0×45.1）μm，孢囊內再生，具有不規則狀之菌絲膨脹體和球狀之厚膜孢子。有性世代為同絲型，藏卵器大小為29.6–45.5（平均38.0）μm，大部分卵孢子為未充滿型，大小為23.1–40.9（平均31.5）μm；其藏精器主要以側著為主，少部分為底著，大小為11.0–22.7×9.1–19.0（平均16.7×14.6）μm。第2種疫病菌的孢囊為卵圓形、卵梨形，單頂生，大小為32.3–50.0×25.6–36.9（平均40.8×30.8）μm，具明顯乳突，其有性世代亦屬於同絲型，藏卵器大小為23.5–34.5（平均28.7）μm，卵孢子為未充滿型，大小為19.7–32.6（平均26.2）μm，藏精器為側著，大小為7.1–14.8×7.0–11.0（平均9.8×8.5）μm。由形態特徵及鄰近連接（Neighbor-Joining, NJ）核酸序列ITS分析的結果，鑑定第1種疫病菌為屬於Clade 7的Phytophthora nagaii；而第2種疫病菌為屬於Clade 2的Phytophthora bisheria。以盆栽接種結果顯示此2種疫病菌僅感染某些品種的玫瑰花與草莓。本研究玫瑰疫病為台灣首次報導，並鑑定2種病原菌為台灣疫病菌之新紀錄種。"

"In September 2015, a severe root rot disease of rose was observed in Puli Township, Nantou County, Taiwan. Disease symptoms included yellowing and wilting of leaves and finally plant death. All the infected plants showed root necrosis, sometimes extending to the basal stem. Two Phytophthora species were consistently isolated from the infected plants. The pathogenicity of these two Phytophthora species was confirmed to fulfil the Koch's postulates by zoospore suspension inoculation on basal stem of rose seeding plants, and the diseased plants showed leaf-yellowing 14 days and died 28 days after inoculation at 32 °C, similar to those observed in naturally infected plants. On 10% V8 agar, the first Phytophthora species could grow at 8–33 °C with a growth rate of 7 mm/day at the optimum temperature of 28 °C, showing radiate colony pattern. Sporangia are ovoid shaped, produced on the top of unbranched sporangiophores, nonpapillate and nondeciduous, 51.491.0 × 35.5-70.0 (avg. 63.0 × 45.1) μm, proliferated internally. Occasionally spherical hyphal swellings and chlamydospores are observed on 10% V8 agar and agar discs in water. The pathogen is homothallic, and produced oogonia 29.6–45.5 (avg. 38.0) μm in diameter with smooth walls. Oospores are mostly aplerotic, and 23.1–40.9 (31.5) μm in diameter. Antheridia are mostly paragynous, sometimes amphigynous, 11.0-22.7 × 9.1-19.0 (avg. 16.7 × 14.6) μm. The second Phytophthora species could grow at 16–32 °C at a rate of 12 mm/day on 10% V8 agar at the optimum temperature of 28 °C showing rosette colony pattern. Sporangia were pear shaped, produced on the top of unbranched or occasionally simple sympodial sporangiophores, semipapillate and nondeciduous, 32.3–50.0 × 25.6–36.9 (avg. 40.8 × 30.8) μm. Hyphal swellings and chlamydospores are both absent on 10% V8 agar and in water. The pathogen is homothallic, and produced oogonia 23.5–34.5 (avg. 28.7) μm in diameter with smooth walls. Oospores are mostly aplerotic, and 19.7–32.6 (avg. 26.2) μm in diameter. Antheridia are paragynous, 7.1–14.8 × 7.0–11.0 (avg. 9.8 × 8.5) μm. Based on morphological characteristics and neighbor-joining analysis of DNA sequences of internal transcribed spacer (ITS), the two pathogens were respectively identified as P. nagaii (clade 7) and P. bisheria (clade 2). The host range test showed that these two Phytophthora species only infected some rose cultivars and strawberry. This is the first report of Phytophthora nagaii and causing rose disease in Taiwan."