Inheritance Study and Molecular Marker Development for Powdery Mildew Resistance in Gerbera

Gerbera (Gerbera hybrida) is an important floricultural crop in the United States and worldwide. Powdery mildew (PM) is the most common and destructive disease in gerbera production and landscape use. The primary causal agent of this disease in the southern United States is Podosphaera fusca. Previously two sources of PM resistance were identified out of 2,000+ gerbera lines screened in central Florida. The PM resistance has been transferred into a number of advanced gerbera breeding lines and new cultivars. One of the resistant lines (UFGE 4033) was crossed reciprocally with a susceptible cultivar (‘Sunburst Snow White’) and two segregating populations were created. Progeny of these populations (110 in total) were evaluated in 2011 and again in 2012 for resistance to PM.  The distribution of PM resistance based on PM-infected leaf area and the area under disease pressure curve (AUDPC) among the progeny in both years was continuous but with two peaks.  Thus the phenotyping data suggest that the PM resistance is quantitative in nature but with major genes contributing to the resistance.  Bulked segregant analysis was performed using the target region amplification polymorphism (TRAP) marker system to develop molecular markers for the major genes. Screening 415 primer combinations and more than 14,000 DNA bands resulted in the identification of nine DNA bands that were polymorphic between UFGE 4033 and ‘Sunburst Snow White’ and between the PM-resistant and the PM-susceptible segregant bulks. The nine DNA markers were mapped to one genetic linkage group, and one region of the linkage group defined by three markers accounted for 51.5% to 70.7% of the variance in PM resistance in the two segregating populations. These results indicate the identification of a major gene responsible for PM resistance in gerbera.