Abstract:

Qingke barley （Hordeum vulgare var. nudum） is a food and forage crop specifically adapted to the Qinghai-Tibet Plateau in China. Qingke barley has strong cold resistance and short-growth period traits， unique to this variety and making it suitable for use in a cold area at an altitude of more than 4200 meters. However， in recent years Qingke barley crops have been seriously affected by root rot. From June to August 2016， an investigation was carried out on Qingke barley in Gannan Prefecture of Gansu Province， and Haidong and Haibei Prefectures of Qinghai Province， to understand the factors influencing root rot incidence at the seedling and adult-plant growth stages and to collect samples of infected roots. It was found that common root rot was rife in China’s North-West Qinghai-Tibetan Plateau in the Prefectures surveyed. Disease incidence was approximately 5% to 15% within each entire field. Qingke barley， after becoming infected by this disease， will show yellow green leaves； the heads turn white and the seeds are empty. Infected seedlings look weak or die， their roots becoming black， rotted or cracked. Root sections were cut out from the junction of diseased and healthy roots of infected plants. In the laboratory， the root samples were dipped in 70% alcohol for 2-3 s， disinfected in 0.1% mercury bichloride solution for 10 s， rinsed 4 times with sterile water， and dried on sterilized filter paper. Then， the root section ends were sliced with a sterile scalpel and the middle root section so obtained was placed on potato dextrose agar （PDA） and incubated at 25 ℃. About 3-4 days later， two hyphae ends emanating from the root section were transferred to another PDA plate. The fungus was purified by single spore separation and subcultured on a new potato sucrose agar （PSA） plate. The classification status of pathogens was determined by combining morphological characteristics with molecular biological identification. The pathogens were Bipolaris sorokiniana and Alternaria alternata. The pathogenicity was measured and the symptoms similar to those reported from diseased crops of Qingke barely were observed in the inoculated plants. The morphology of the reisolated fungus was consistent with the inoculated one. No symptoms were observed on the control plants. As far as we know， this is the first report in the world of B. sorokiniana and A. alternata causing root rot of Qingke barley. This identification of the causative agents provides a theoretical foundation for development of prevention and control measures for Qingke barley root rot.

Key words: qinke barley, root rot, Bipolaris sorokiniana, Alternaria alternate