A COMPARISON OF HETEROMORPHIC INCOMPATIBILITIES IN PRIMULA

Available from UMI in association with The British Library.; Most of the 500 or so members of the genus Primula are heterostylous. They have a sporophytically controlled, diallelic incompatibility system. The genus was chosen for this project in an attempt to investigate how much an incompatibility system, and in particular incompatibility reactions, can vary within a genus and also to discover any trends which indicate that there has been evolutionary development within the incompatibility system.; The inhibition of pollen and pollen tubes after an incompatible cross was studied in 59 heteromorphic Primula species and hybrids. The incompatibility reaction can occur on the stigma surface or within the stigma and style in different species. It usually differs between pin x pin and thrum x thrum crosses. Each Primula species has a consistent and often characteristic incompatibility reaction.; Closely related Primula species usually have a similar incompatibility reaction. Incompatibility reactions which involve inhibition of pollen tubes in the stigma or style are associated with Primula species that are often considered to be amongst the more primitive members of the genus. Stigma surface incompatibility reactions are associated with the more highly evolved Primula species, indicating that there has been evolutionary development within the incompatibility system.; A study of incompatibility reactions in crosses between different heterostylous Primula species shows that pollen and pollen tube inhibition in interspecific illegitimate crosses is similar to that seen in intraspecific crosses of the species concerned. In legitimate interspecific crosses inhibition of pollen tubes occurs low in the style or in the ovary.; A study of the incompatibility reactions seen in crosses between heterostyles and homostyles in the subgenus Aleuritia shows that in such crosses homostyle stigmas behave as if pin and homostyle pollen as if thrum. This result reinforces the idea that the homostylous species in subgenus Aleuritia evolved from heterostylous self incompatible ancestors.; Observations of incompatibility reactions in Primula by SEM and sectioning of resin embedded material show that illegitimate pollen grains usually lie nearer to the tips of the stigmatic papillae than do legitimate pollen grains. The attachment of illegitimate pollen grains to the stigma is weaker than that of legitimate grains.; Experiments to study the effect of increased relative humidity and temperature on incompatibility in P. polyneura show that a high relative humidity increases illegitimate pollen germination. High temperature inhibits the growth of both legitimate and illegitimate pollen tubes.