First Report of Ophiosphaerella korrae Causing Root Rot of Hordeum vulgare in Korea

Barley (Hordeum vulgare L.) is one of the most important food crops grown all over the world. It is well-known as a nutritious food and used as material for manufacturing of malt and barley tea in Korea. In May 2016, root rot symptoms developed in patches on both top and bottom portions of barley grown in a paddy field in Gimjae, Korea (35.82′N 126.80′E). Diseased plants were less than 1% of the total plant population grown in the field. The heads of the diseased plants turned whitish-brown, and the lower leaves were chlorotic. In addition, the diseased plants were easily pulled up from the soil to reveal severely rotten roots with lesions extending upward into the crown tissue. Samples of the diseased roots were surface sterilized with 1% NaOCl for 60 s and then rinsed in sterile water. The root pieces were then placed on water agar (WA) and incubated at 25°C for 7 days. Three fungal isolates were cultured on potato dextrose agar at 25°C in darkness for 2 weeks. Colonies were 70 mm in diameter, white at first, and became darker with age, with dark gray to black at the center. Pseudothecia produced in abundance on WA with sterilized barley leaves after 1 month were characterized to be erumpent, dark, subglobose, 445 to 580 μm high, and 300 to 500 μm wide. Asci were cylindrical to clavate, bitunicate, eight-spored, narrowed toward the base, 112 to 170 × 11 to 15 μm. Ascospores were filiform, slightly twisted in a bundle, and parallel to one another, pale brown, usually seven septate, 119 to 157 × 3 to 5 μm, widest in the middle, and tapering more toward the base than the apex, rounded at the ends. Pseudoparaphyses were hyaline, septate, numerous, and 1 to 2 μm wide. Based on morphological and cultural characteristics, the three isolates were identified as Ophiosphaerella korrae (Walker and Smith 1972). To clarify taxonomic placement of the three isolates of O. korrae (BJG1601 to BJG1603), rDNA internal transcribed spacer regions (ITS) from the isolates were amplified by polymerase chain reaction (PCR) as previously described (Flores et al. 2017). The PCR products were sequenced and deposited in GenBank with accession numbers MH201147 to MH201149. The ITS sequences of the three isolates were 99% homologous with other O. korrae isolates in GenBank (e.g., KC848509 and KP690980). O. korrae isolates formed a single clade, distinct from other Ophiosphaerella species with significant bootstrap support. Based on molecular characteristics, the isolates were confirmed as O. korrae. Pathogenicity of the three isolates was made on barley plants of cultivar Yeongyangbori grown in 2-liter pots in the greenhouse. The pots containing 30-day-old plants were inoculated by incorporating 5 g of inoculum, previously cultured for a month on autoclaved barley seeds, at a depth of 1 cm. The plants were watered twice a week, and to keep the humidity, the pots were covered with aluminum foil. The same quantity of sterilized barley seeds without inoculum was used as a control. Both the inoculated pots and the control pots were placed in the greenhouse for 45 days at 20 ± 1°C. At 30 days after inoculation, symptoms started to develop yellowing on leaves, which at 45 days ultimately resulted in death of infected plants. No symptoms developed on the noninoculated control plants. The fungus was consistently reisolated from roots of inoculated plants, thus fulfilling Koch’s postulates. To our knowledge, this is the first report that O. korrae causes root rot of barley. Further studies are required to better define the host range of O. korrae in Korea.