Effect of X-radiation on pollen tube growth and seed setting in crosses between Nicotiana tabacum and N. rustica

Abstract

In vitro andin vivo studies of the effect of irradiating pollen with different doses of X-rays were carried out in Nicotiana rustica and N. tabacum. Dosages upto 9600 r were found to enhance the rate of growth of pollen tubers per unit time. Advantage was taken of this observation to overcome the incompatibility normally found in the cross N. tabacum × N. rustica as a result of the inadequate growth of rustica pollen tubes in tabacum style. Thus, when rustica pollen exposed to 4800 r and 9600 r of X-rays were used to pollinate tabacum, fertilization resulting in the formation of viable hybrid seeds occurred. In the cross N. rustica×N. tabacum there is partial seed failure as a result of the hyperplastic development of the nucellar and endothelial cells. However, when X-rayedtabacum pollen were used in the cross, seed development registered a marked improvement. Since there is now evidence for suggesting that the contents of even those pollen tubes which do not participate in fertilization have some role to play in the development of the seed, it seems likely that radiation-induced biochemical changes in pollen may prove advantageous when conditions for seed development are abnormal as in instances of somatoplastic sterility. Besides such indirect biochemical effects, irradiation of pollen may also lead to genetic changes resulting in the inactivation of zygotic lethals. Thus, there is much scope for investigating the use of radiation to overcome inter-specific and inter-generic cross-incompatibility barriers.