STUDIES ON SOIL-BORNE CEREAL MOSAICS
V. THE NATURE OF SOIL-TRANSMISSION IN SOIL-BORNE CEREAL MOSAIC VIRUSES
1959 Volume 9 Issue 2 Pages 109-118
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1959 Volume 9 Issue 2 Pages 109-118
Literature concerning the mechanism of soil-transmission in soil-borne cereal mosaic viruses and in other soil-borne plant viruses has accumulated during recent years. It is believed by most workers, that perhaps soil-borne viruses preserve their activities in some soil-inhabiting microorganism which carries the viruses and introduces them into the underground parts of the plants. However, the exact mechanism of the soil-transmission is not yet understood, because no microorganism is experimentally found as a vector.
The present work was undertaken in order to ascertain the exact relation of these soil-borne viruses to the soil and to understand the nature of soil-transmission, making use of two kind of soil materials which were certainly infested with wheat yellow-mosaic virus (WYMV, Marmor tritici var. fulvum McK.) and barley yellow-mosaic virus (BYMV).
A small number of plants were infected when grown in clean soil in which ground tissues of plants affected with WYMV or BYMV had been buried about two years previously (Table 1).
Soil particles were separated mechanically by water from WYMV- or BYMV-infested soil, moreover, very small particles were separated according to Stokes' Law in soil science. Some kind of tests of the infectivity of separated soil particle fractions were made by planting seeds in them or by rubbing seedlings with them (Tables 2-4). It was found, eventually, that the infectivity of the clay fraction (‘<2μ’ particle fraction, including inorganic and organic colloidal substances) was very much stronger than the other particle fraction (‘>2μ’ particle fraction, including a small quantity of ‘<2μ’ particles) in both WYMV- and BYMV-infested soils, when the separated suspension including these particles was concentrated by centrifugation at 4000 r.p.m. (2000g) for 15-20 minutes (Tables 4 and 5). In the pile of clay particles, no special soil-inhabiting microorganism regarded as a vector was recognized under microscope. It was shown, moreover, that a small number of plants could be infected by rubbing method of inoculation with mud composed of above-mentioned clay fraction (Table 5).
These findings may support the writer's view that these viruses exist adsorbed in soil particles of clay fraction which have colloidal characteristics and ability to adsorb proteins, and that no soil-inhabiting microorganism is necessarily needed to explain the mechanism of soil-transmission in soil-borne cereal mosaic viruses.
