Abstract

The self-incompatibility mechanism which promotes cross-pollination is well known in the genus Petunia. Of the different species of the genus, P. hybrida is largely grown as an ornamental annual for its wealth of variation in nature of flowers and plant form. This species is known to be of hybrid origin, the parental species being P. integrifoliu and P. axillaris (Darlington and Wylie, 1955; Takehisa, 1963). Structural differentiation of the chromo- somes of the genomes of the two species is considered to be still existent in the garden forms of P. hybrida and the heterozygosity is probably enforced through self incompatibility. Rick (1942) observed that chromosomal deficiencies and duplications can exist in this species without detriment to viability or normal development. A study of the effects of enforced self- pollination in this species would throw light on the advantages conferred by cross pollination in preventing the breakdown of the hybrid from disharmo- nious genetic recombinations or eliminating in breeding depression. The present study confined to a few garden forms of P. hybrida is aimed at a comparison of the cytological behaviour and morphological variation in the open pollinated and selfed progenies.

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