IMPROVEMENT OF THE METHOD FOR OVERCOMING THE HYBRID LETHALITY BETWEENNICOTIANA SUAVEOLENS AND NICOTIANA-TABACUM BY CULTURE OF F1 SEEDS IN LIQUID-MEDIA CONTAINING CYTOKININS

Hybrid lethality system is one of the most serious barriers in wide hy bridization. Hybrid plants between N. suaueolens and N. tabacum exhibi t lethality and die at the cotyledonary stage, Intact seedling culture on solidified media containing cytokinins is a simple method for over coming the lethality in this cross-combination. In order to improve th e method, we cultured F-1 seeds in liquid media containing cytokinins. Two types of cytokinins, purine-type (kinetin, 6-benzylaminopurine (B AP) and t-zeatin) and urea-type (N-phenyl-N'-(1, 2, 3-thidiazol-5-yl) urea (TDZ), N-(2-chloro-4-pyrizyl)-N'-phenylurea (CPPU)), were used at various concentrations (0-10 mg/l). In the liquid media containing 0. 01-10 mg/l cytokinin, shoot-like structures were formed at the hypocot yl and the primary root of the dying seedlings. The shoot-like structu res did not exhibit lethality and grew up to vigorous shoots without d eveloping any lethal symptoms within a month, Vigorous multiple shoots developed from the shoot-like structures in the liquid media containi ng more than 0.2 mg/l cytokinins. The regenerated shoots were transfer red to the medium containing 2 mg/l indole-3-acetic acid (IAA) to acce lerate rooting. The hybrid seedlings displayed a vigorous growth witho ut developing any lethal symptoms up to maturity in a greenhouse, Fort y chromosomes were counted in root tip cells of the seedlings and morp hological characters of the seedlings were intermediate between those of parental species, In this experiment, we developed a simplified met hod using liquid media with urea-type cytokinins and obtained more hyb rid seedlings in a shorter period of time.