Genetic analysis of a Microseris douglasii (Asteraceae) population polymorphic for an alien chloroplast type

Recent evidence suggests chloroplast introgression from Microseris bigelovii into M. douglasii. We have examined 23 plants from a population of M. douglasii polymorphic for M. douglasii and M. bigelovii chloroplast types. All 23 plants were completely homozygous for morphological and RAPD markers, and inbred lines derived by selfing have been used for DNA analysis. Chloroplast RFLP analysis identified 16 plants with M. bigelovii chloroplasts and seven with M. douglasii chloroplasts. The nuclear genomes of the 16 plants with M. bigelovii chloroplasts were examined with 22 primers for RAPD amplification products shared exclusively with M. bigelovii. Five of 268 markers appeared to be shared between M. bigelovii and one or more of these 16 plants on the basis of their position in gels. Detailed examination of these five amplification products showed that none of them are nuclear DNA from M. bigelovii. Very little, if any, nuclear DNA from M. bigelovii can be present in M. douglasii plants with chloroplasts typical of M. bigelovii. The study demonstrates the usefulness of the RAPD technique for screening large numbers of markers to select a few potentially informative ones for rigorous examination.