ムギ萎縮病の研究

IV. オオムギ縞萎縮病ウイルスについて(その2)

抄録

It is believed that barley yellow-mosaic virus (BYMV) is a distinct virus found only in Japan and that it differs from other soil-borne viruses of cereal crops. BYMV does not attack wheat and rye, it is not transmitted by insects and is not seed-borne. The writer has investigated continuously the mode of the disease and properties of BYMV. The experimental results obtained are summarized as follows:
(1) In the variety tests of barley sown in BYMV-infested soil, most foreign varieties tested were infected with the virus as well as domestic varieties, with different infection rates or with varied grades of severity of symptoms. In these tests, it was shown that hulled varieties were more susceptible to the virus than hull-less varieties, particularly two-row barley varieties developed severe symptoms. It was observed in the tests, moreover, that the environmental conditions exerted effects upon the infection and expression of symptoms.
(2) Among the tested plants of wild species of Hordeum, H. spontaneum (C.I. 4142) and H. agriocrithon plants were found susceptible, and intracellular inclusions (X-bodies) were recognized in the cells of the diseased plants but all the symptoms shown were rather mild.
(3) In the linkage testers of barley plants, no plant belonging to the linkage groups I or VI was infected with BYMV. But the other plants belonging to the groups II-V and VII were susceptible to the virus with rather severe symptoms.
(4) When pre-germinated seeds, which had already developed 2 or 3 roots, were planted in virus-infested soil out of doors, the infection rate became greater than in the cases of the planting of seeds, which were presoaked but had not yet developed roots. However, the infection rate of the former was not much higher than the latter as shown in the previously reported results, i.e., 2-3 times as high in glass-house tests. It was found, eventually, that the differences between the infection rates of the former and of the latter became greater when the tested plants were kept under unfavorable conditions for the occurrence of infection with the virus.
(5) In the test of stability of BYMV, leaves of barley affected with the virus were clipped into 2-3cm pieces; they were put into a tight bottle containing calcium chloride crystals in the bottom. Then the bottle was placed and stored in an electric household refrigerator which was regulated at 0-2°C for the first one month and at 5-10°C for about two years. After that length of time, inoculation test was made by wiping water extracts of the dried tissues on leaves of seedlings. The infection rate of the dried tissues showed one-third value of the rate in the case when fresh diseased leaves were used as inoculum.