We performed a QTL analysis on an F2 population of an interspecific cross between P. axillaris and P. exserta and introgressed individual QTL into reciprocal backgrounds. Only two loci on chromosomes II and V are sufficient to explain the interspecific difference in reproductive organ morphology. The locus on chromosome II was narrowed down to a chromosomal region of less than 1 centiMorgan. Interestingly, this locus also controls pistil elongation in a second P. axillaris subspecies, adapted to pollination by long-tongued nocturnal moths. Thus, we propose that the same locus was used to elongate reproductive organs in adaptation to different pollination syndromes during the evolution of Petunia. We studied the cellular basis of pistil elongation and currently use transcriptome data from both parental lines and two introgression lines to identify candidate genes underlying the QTL.
