SOMACLONAL VARIATION AS A SOURCE OF TOMATO SPOTTED WILT VIRUS-RESISTANCE IN PLANTS

摘要

Our investigations show that somaclonal variation may be used in tobacco breeding for resistance to TSWV and to provide sources of TSWV-resistant somaclones, protoclones and androclones (Shcherbatenko and Oleshchenko, 1995). Additionally, somaclonal variation provides opportunities to increase the fertility of TSWV-resistant tobacco hybrids and to overcome the cross-ability barriers between tobacco cultivars and TSWV-resistant Nicotiana species. Fertile virus-resistant hybrids were produced by regeneration of somaclones from leaf-derived callus of sterile hybrids; by hybridization of selected virus-resistant somaclones of susceptible tobacco varieties with resistant wild species; by intercrossing between semifertile somaclones of interspecific hybrids and for the in vitro production of plants from nongermitable seed.rnUnfortunately, the approach is both time-consuming and somewhat uncertain in terms of durability. Somaclones from tobacco cultivars and hybrids showed a negative correlation between TSWV-resistance and plant self-fertility as well as significant variability in response to TSWV, from delay in symptom development to complete resistance. The yield of resistant variants varied widely and was strongly influenced by tobacco variety whereas the inheritance of resistance seemed more to depend on the dynamics of plant damage in parental clones. The dynamics of pathogenicity is the more suitable criterion for selection of virus-resistant variants than the yield of resistant specimens in populations of somaclones.rnThe resistant variants segregated in selfed progenies and tended to loose resistance in subsequent generations. However, some clones showed heritable resistance, which leads to an increase in the proportion of resistant plants in successive generations. These somaclones seemed likely to be potentially useful breeding material and have indeed been used in breeding of tobacco for TSWV resistance. The American 63 tobacco selected (Rud et al., 2000) combines a high productivity, high production quality and moderate TSWV resistance in the field.rnSomaclonal variation has been used successfully for the selection of Fijivirus-resistant sugarcane (Krishnamurthi and Thaskal, 1974), PVX- and TMV-resistant tobacco (Shepard, 1975; Murakishi and Carlson, 1976, 1982; Saha and Gupta, 1989; Toyoda et al., 1989), TMV-resistant tomato (Barden et al., 1986), PVX-, PVY-, and PLRV-resistant potato (Jellis et al., 1984; Wenzel and Uhrig, 1981), BaYMV-resistant barley and wheat (Foroughi-Wehr and Friedt, 1984; Comeau and Plourde, 1987), virus-resistant melon (Lotfi et al., 2003) or in the breeding of plants for resistance to other pathogens (e.g. Liu and Zheng, 2002; Van den Bulk, 1991).