Reproductive characteristics of amphidiploids derived from an interspecific hybrid between Nicotiana trigonophylla Dun and N-tabacum L

Amphidiploid plants were obtained by colchicine treatment of an interspecific hybrid between N, trigonophylla (2n = 24) and N, tabacum (2n = 48) that had been produced through ovule culture, Eight colchicine-treated plantlets were found to be amphidiploids with a chromosome number of 2n = 72, namely, the sum of the chromosome numbers of the two parents, The plant, flowers and leaves of the amphidiploids were morphologically similar to those of untreated F-1 plants, which had characteristics intermediate between those of the parents, Even though pollen fertility was high (more than 90%), only about 1.5% of the ovules developed into viable seeds, From histological observations of selfed amphidiploids, we found that the fertilized ovule ratio was also low (12-14%) although the embryo sacs appeared normal, The low seed set percentage was mainly due to the fact that most of the pollen tubes terminated in the style and very few pollen tubes were observed in the ovarian cavity, There was obvious pollen-pistil incongruity, In reciprocal crosses between an amphidiploid and its parents, the reproductive barrier in the style was more complicated, When the amphidiploid was used as female parent, no viable seeds were obtained from the cross with N. tabacum and a few viable seeds were obtained from the cross with N, trigonophylla. By contrast, when an amphidiploid was used as the male parent, some viable seeds were obtained, The fertilized ovule ratio and the seed set percentage corresponded closely to the number of pollen tubes that reached the ovarian cavity. The results indicate that unilateral pollen-pistil incongruity existed in the reciprocal crosses between an amphidiploid and its parents, The result that the pollen-pistil incongruity observed in the amphidiploid was very different from that in the F-1 hybrid indicated the complicated nature of genomic interactions and interspecific incongruity. It is likely that the incongruity occurred among three kinds of genome in the style of the amphidiploid because N, tabacum arose as an amphidiploid from N, sylvestris and N, tomentosiformis.