Abstract
Hybrid lethality is one of the expressions of cross-incompatibility, limiting the scope of wide hybridization. The immature embryos of the cross Nicotiana suaveolens × N.sylvestris did not grow and could not be rescued by conventional ovule culture. We observed that culture of the ovules at high temperatures(30, 32, 34°C) enabled to suppress this obstacle temporarily. Although many plantlets were obtained through ovule culture at high temperatures, the plants did not grow to maturity. On the other hand, ovule culture with a high concentration of cytokinin was effective in overcoming the obstacle. In ovule culture on 1/2 MS + BAP(10mg/l), many hybrid plantlets of the cross N.suaveolens × N.sylvestris developed and formed vigorous multiple shoots. The hybrid plants obtained from multiple shoots grew vigorously and matured in a greenhouse. Because the characteristics of the obstacle were similar to those of hybrid lethality exhibited by the seedlings of the cross between N.suaveolens and N.tabacum, we suggested that the obstacle was due to hybrid lethality that developed just after fertilization. Furthermore, we were able to obtain many mature hybrid plantlets in the cross N.suaveolens × N.sylvestris by ovule culture on a medium containing cytokinin. This is the first report on the production of mature interspecific hybrids that did not develop any lethal symptoms in this cross combination.
