Enhancing seed germination in hybrid tea roses

Rose breeders need reliable and efficient germination protocols to exploit all viable embryos in their breeding programme. A combined physical restriction of the seed coat and a physiological dormancy are present in the achenes of hybrid tea roses resulting in variable and not uniform seed germination. In this study, different treatment combinations were assessed to overcome the mechanical resistence of the pericarp and enhance germination. Both chemical and microbial seed scarification were carried out. A mild scarification with sodium hypochlorite (NaOCl) before stratification promoted a more uniform germination and enhanced the percentage of germination from 49.2% to 65.9%. Epiphytic bacteria, EmercalTM (a product composed by bacteria and co-metabolites produced by bacterial fermentation), or Remedier® (a commercial formulation of Trichoderma harzianum and Trichoderma viridae), added to the stratification sand, enhanced percentage of germinated seeds but had no effect on the uniformity of germination. Addition of a compost activator to the stratification sand did not improve seed germination. After stratification, pre-sowing treatments with GA3 were carried out. Immersion of stratified seeds in 1 g l-1 GA3 highly enhanced percentage of seed germination (77.6%), mean germination time (26.0 days) and uniformity of germination (2.5%) compared to immersion in water (respectively 64.8%, 32.8 days and 7.9%). Therefore, this study proposes a combination of treatments as a reliable optimisation of seed germination protocols for hybrid tea roses.