Kyo-Sun Park

Effects of Temperature on Systemic Infection and Symptom Expression of Turnip mosaic virus in Chinese cabbage (Brassica campestris)

Using the Chinese cabbage (Brassica campestris) cultivar ‘Chun-goang’ as a host and turnip mosaic virus (TuMV) as a pathogen, we studied the effects of ambient temperature (13°C, 18°C, 23°C, 28°C and 33°C) on disease intensity and the speed of systemic infection. The optimal temperature for symptom expression of TuMV was 18–28°C. However, symptoms of viral infection were initiated at 23–28°C and 6 days post infection (dpi). Plants maintained at 33°C were systemically infected as early as 6 dpi and remained symptomless until 12 or 22 dpi, depending on growth stage at the time of inoculation. It took 45 days for infection of plants grown at 13°C. Quantitative real-time polymerase chain reaction (q-PCR) results showed that the accumulation of virus coat protein was greater in plants grown at 23–28°C. The speed of systemic infection increased linearly with rising ambient temperature, up to 23°C. The zero-infection temperature was 10.1°C. To study the effects of abruptly elevated temperatures on systemic infection, plants inoculated with TuMV were maintained at 10°C for 20 d; transferred to a growth chamber at temperatures of 13°C, 18°C, 23°C, 28°C, or 33°C for 1, 2, or 3 d; and then moved back to 10°C. The numbers of plants infected increased as duration of exposure to higher temperatures and dpi increased.

In vivo Evaluation of Resistance of Grape Varieties to Crown Gall Disease

The resistance to crown gall in grape rootstocks was evaluated by inoculating cuttings from 27 grape rootstock varieties with Agrobacterium vitis strain Cheonan 493. Thmors were formed in all varieties of grape rootstocks tested in this study. The symptoms were observed in the stems of all plants tested including `196-17` and `41B`. Based on the measurement of tumor weight on the stems of grape rootstocks, `779P` was found to be higbly susceptible to crown gall. While some varieties such as `Gloire`, `140R`, `101-14M`, `3309C`, and `333EM` were found to be relatively resistance to crown gall. Varieties such as `99R`, `1447P`, `Rupestris du lot`, `ll0R`, `Freedom`, and `41B` were also found to be susceptibl~ to crown gall. Other~ varieties including `l103P`, `Teleki. 5C`, `420A`, `Golia`, and `5BB` were found to be moderately susceptible.