The 2012 ASHS Annual Conference

Petunia (Petunia × hybrida) ranks first in wholesale value among bedding plant crops grown in the United States.  Profitability of bedding plant production faces several economic challenges, including greenhouse heating and labor costs.  Reducing crop production time is one strategy for addressing these challenges.  Understanding the genetics of plant development rate offers the opportunity to breed faster developing cultivars, particularly under suboptimal conditions such as cool temperatures, short photoperiods and low irradiance levels.  We previously determined that the progenitor species of cultivated petunia (P. integrifolia and P. axillaris) exhibited faster development (leaf unfolding) rates than any of a panel of modern cultivars. Two interspecific F₂ populations, P. axillaris × P. exserta and P. integrifolia × P. axillaris, exhibited transgressive segregation for many crop timing and quality parameters, including leaf number below first flower, time to flower, leaf unfolding rate, branch number, flower bud number, and flower size, indicating their potential utility as sources of novel alleles for commercial petunia breeding.  To develop molecular markers, approximately 20,000 P. axillaris expressed sequence tags (ESTs) were mined for simple sequence repeats (SSRs), with 694 SSRs meeting the search criteria.  Of these, 162 sequences were polymorphic between P. axillaris and P. integrifolia, and 113 sequences were polymorphic between P. axillaris and P. exserta.  Seventy-four markers were polymorphic across both parental species combinations.  The P. integrifolia × P. axillaris F₂ population was genotyped with 114 SSRs and 11 cleaved amplified polymorphic sequence (CAPS) markers.  From this, a genetic linkage map comprising 101 markers assigned to seven linkage groups was generated.   Utilizing this genetic linkage map and our preliminary phenotypic data for leaf unfolding rate, we identified three quantitative trait loci (QTL) for leaf unfolding rate, two on linkage group 1, and one on linkage group 5.  Together, these three QTL explained 49% of the variability for leaf unfolding rate observed in this mapping population.  We are currently developing recombinant inbred lines for these interspecific hybrid populations to evaluate the robustness of the identified QTL.