Al-Mahmooli I H, Al-Fahdi A R, Al-Sadi A M, Deadman M L
Department of Crop Sciences, Sultan Qaboos University, Al Khod 123, Sultanate of Oman.
Plant Dis. 2015 Mar;99(3):419. doi: 10.1094/PDIS-08-14-0795-PDN.
In March 2013, 90% of mature bean plants (Phaseolus vulgaris L. cv. Kendo) grown on a commercial farm in the north of Oman (Barka) developed symptoms of root rot and necrotic streaks on the crown area of the stem and wilted. A Pythium spp. was isolated consistently from roots and basal stems on 2.5% potato dextrose agar (PDA) and V8 (100% vegetable juice) plus 1.5% agar technical. Colonies of Pythium spp. on PDA and V8 plus agar developed abundant aerial mycelia, with the main hyphae being up to 10 μm wide. Zoosporangia were made up of terminal complexes of swollen hyphal branches of different lengths and up to 22 μm wide. Oogonia were terminal, globose, and smooth with a 26-μm diameter (average of 20). Antheridia were mostly intercalary, sometimes terminal, and broadly sac-shaped, 15 μm long and 11 μm wide (average of 20). Oospores were aplerotic, 23 μm in diameter (average of 24), with walls 1 to 2 μm thick at 25°C (ambient temperature). The internal transcribed spacer of the ribosomal DNA (ITS1 and ITS4) sequence of the isolates matched the sequence of Pythium aphanidermatum (Edson) Fitzp. in GenBank. The sequence of isolate Py1 was deposited in GenBank as Accession No. KM102739. This isolate was identified as P. aphanidermatum on the basis of morphological and cultural characteristics (1) and the ITS rDNA sequence. The ITS was found to share 100% nucleotide similarity to previously published sequences of the ITS (KJ755088). To fulfill Koch's postulate, a 5-mm plug of 5-day-old mycelium of isolate Py1 grown on 2.5% PDA was used to inoculate healthy seedlings of beans cv. Kendo. The plug was placed adjacent to the bean stem; PDA served as a control. Five replicate plants were used for the treatment and the control. The plants were maintained in a glasshouse at a temperature of 23 to 25°C. The plants were watered every day. The irrigation water had an electrical conductivity value of 0.2 dSm. Eleven days after inoculation, 90% of the plants developed root rot, crown necrosis, and wilt symptoms similar to those observed in the field. On the other hand, control plants did not show any symptoms. The pathogen was re-isolated from roots and basal stems of symptomatic plants. To our knowledge, this is the first report of P. aphanidermatum as the causal agent of root and crown necrosis of mature bean plants in Oman. Future studies should focus on evaluating management options for this disease to avoid possible losses in a crop that has a high export value in Oman. Reference: (1) Y. Serrano et al. Plant Dis. 92:174, 2008.
2013年3月，阿曼北部（巴尔卡）一个商业农场种植的90%成熟菜豆植株（菜豆属普通菜豆品种“剑道”）出现根腐症状，茎基部冠部区域有坏死条纹，并枯萎。从根部和茎基部在2.5%马铃薯葡萄糖琼脂（PDA）和V8（100%蔬菜汁）加1.5%技术琼脂上持续分离出腐霉属真菌。腐霉属真菌在PDA和V8加琼脂上的菌落产生大量气生菌丝，主要菌丝宽达10μm。游动孢子囊由不同长度且宽达22μm的肿胀菌丝分支的末端复合体组成。藏卵器为末端型，球形，表面光滑，直径26μm（20个的平均值）。雄器大多为间生，有时为末端型，宽囊状，长15μm，宽11μm（20个的平均值）。卵孢子无满器，直径23μm（24个的平均值），在25°C（环境温度）下壁厚1至2μm。分离物核糖体DNA的内部转录间隔区（ITS1和ITS4）序列与GenBank中瓜果腐霉（埃德森）菲茨帕特里克的序列匹配。分离物Py1的序列作为登录号KM102739存入GenBank。根据形态和培养特征(1)以及ITS rDNA序列，该分离物被鉴定为瓜果腐霉。发现ITS与先前发表的ITS序列（KJ755088）具有100%的核苷酸相似性。为了满足柯赫氏法则，用在2.5% PDA上生长5天的分离物Py1的5mm菌丝块接种“剑道”菜豆健康幼苗。菌丝块放置在菜豆茎旁边；PDA作为对照。处理组和对照组各用5株重复植株。植株在温室中保持在23至25°C的温度下。每天浇水。灌溉水的电导率值为0.2 dSm。接种11天后，90%的植株出现根腐、冠部坏死和枯萎症状，与田间观察到的症状相似。另一方面，对照植株未出现任何症状。从有症状植株的根部和茎基部重新分离出病原菌。据我们所知，这是瓜果腐霉作为阿曼成熟菜豆植株根和冠坏死病原菌的首次报道。未来的研究应侧重于评估该病的管理措施，以避免阿曼一种具有高出口价值的作物可能遭受的损失。参考文献：(1) Y. Serrano等人，《植物病害》92:174，2008年。
