Graft Transfer and Viral Nature
Initially, mst was considered as a diseased condition caused by unknown agents, probably a virus. Since viruses are graft-transferrable, grafting of mst stocks over scions and of normal stocks over mst stocks was assayed, to transfer the mst across grafts. This was done by Frankel (1956), who grafted fertile maintainer scion on mst Petunia hybrida rootstocks. Scion mft remained unaltered but mst scion progeny was recovered when scion flowers were selfed or crossed to another maintainer line. A similar transmission was obtained by Edwardson and Corbett (1961). Similarly, however, the mst did not appear in the year of grafting. It increased in the succeeding generations. Graft transfer of this type of mst was also demonstrated in Datura (Blakeslee 1921), sugarbeet (Curtis 1967), tobacco (Corbett and Edwardson 1964) and alfalfa (Thompson and Axtell 1978). The mst transfer in alfalfa was similar to Petunia as scion autonomy was maintained in every case, while some sterile scion F1 progeny was produced in the progeny of three graft combinations. In sugarbeet, scion fertility was altered (some flowers were sterile) and sterile scion progeny was also produced. Reciprocal grafts (sterile scion on maintainer stock) did not induce scion flower mst alterations. Transmission of mst across grafts through dodder (Cuscuta subinclusa) plants was achieved by Grill and Garger (1981). However, later investigations reveal that the transferred sterility is not stable. A similar unstable expression of mst occurred in pepper scions (Daskaloff 1968). In Zea mays, Borowsky (1960) transplanted normal maize embryos into endosperm of mst maize and recovered some mst plants in F1 progenies. Using the technique and utilising both T and S cytoplasms, Edwardson (1970), however, could not obtain mst even up to F2. Shumway and Bauman (1966) used mesocotyl graft technique to unite mst T-cytoplasm maize inbreds with mft plants. No mst progeny plants ever appeared.
KeywordsCucumber Mosaic Virus Female Fertility Helianthus Annuus Maintainer Line Pollen Sterility
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