Characterization of self-incompatibility in Campanula rapunculoides (Campanulaceae) through genetic analyses and microscopy

In this paper, we seek to identify the genetic basis of self-incompatibility (SI) in Campanula rapunculoides L. through diallel analysis of full siblings; to characterize the growth of pollen tubes in vivo after incompatible and compatible pollination; and to determine whether the SI system is based on pistil S-RNases. Pollinations were performed among individuals from five diallel crosses and scored for both fruit set and pollen-tube growth to determine the genetic basis of SI. On a subset of these individuals with known cross-(in)compatibility relationships, additional crosses were performed and pistils collected 1, 3, 6, 12, and 24 h after pollination to assess both the percentage of pollen grains that had germinated on the stigma, and the number of pollen tubes that had grown 20%, 40% 60%, 80%, and 100% of the distance down the pistil over five time intervals. Finally, total pistillate proteins were extracted and subjected to isoelectric focusing and RNase activity staining to find evidence of a highly basic S-RNases associated with SI in the Solanaceae. We found evidence that the SI system was based on the haplotype of the male gametophyte, and was not sporophytic. Protein analyses showed that SI was not based on a pistillate S-RNase. The existence of modifiers of SI and possible polyploidy at the S-locus complicated the expression of SI in this species, and single-gene inheritance could not be determined. This represents the first published characterization of incompatibility in the family Campanulaceae.