RAPD mapping of three QTLs determining trichome formation in Microseris hybrid H27 (Asteraceae:Lactuceae).

Segregation for 289 random amplified polymorphic DNA markers (RAPDs) has been determined in 106 F2 plants of an interspecific hybrid (H27) between Microseris douglasii (strain B14) and M. bigelovii (C94). Multicelluar trichomes ("type D", specific for Microseris) occur on the leaf teeth of early vegetative rosettes of the B14 parent and on the leaf blades of later rosettes in both parents. Trichomes on the leaf blades appear earlier and eventually more densely in B14. Segregation for trichome appearance is quantitative and strongly transgressive in the F2 hybrid. Cosegregation between RAPDs and trichome phenotypes combined with linkage data have revealed a main gene ("quantitative trait locus A", QTL-A) with a pleiotropic effect on all trichome characters and two unlinked additive modifiers (QTL-B, QTL-C). Alleles of both modifiers reduce the main gene effect in each parent. Their recombination explains the occurrence of plants with transgressive phenotypes in the hybrid offspring. Additional QTLs affecting trichomes are at and below the level of statistical significance.