Chromosomal variation in hybrids between Nicotiana repanda Willd. and N. tabacum L. through pollen and egg-cell irradiation techniques

Abstract

Viable interspecific hybrids between Nicotiana repanda Willd. and N. tabacum L. are not possible by conventional hybridization but can be obtained by irradiation treatments of pollen or egg cells combined with in vitro culture of fertilized ovules. In this study cytological analyses were conducted to define chromosomal variation among viable interspecific hybrids obtained by irradiation-mediated techniques. Pollen of N. tabacum was subjected to gamma-ray irradiation dosages of 5–40 kR and used to fertilize N. repanda. Similarly, egg cells of N. repanda were treated with 1–4 kR irradiation and pollinated with N. tabacum. Chromosome number decreases in resulting interspecific hybrids were not as great as had been reported in previous studies, but exposure to higher doses of radiation induced a considerable degree of chromosomal rearrangement. Among resulting hybrids, a number reached the flowering stage. The longevity of the hybrids seemed to be correlated with their ability to generate roots (i.e., rooting vigor). Although the dosage ranges used in the egg-cell irradiation (1–4 kR) were lower than those used in the pollen irradiation (5–20 kR), the degree and quality of the chromosomal variation did not differ.Key words: wide hybridization, hybrid inviability, chromosome variation, tobacco.