Characterization of 11 Hybrid Rose Populations for Petal Number under Cool- and Warm-season Conditions

Rose (Rosa spp.) is an important ornamental crop which is commercially utilized for garden plants, cut flower, and food/medicinal/aroma industry. Heat stress is a major abiotic stress which reduces the flower size and value of the rose. The average petal number was estimated by counting the petals per flower for three flowers per plant in August 2013 (warm season, mean temperature 30.7 °C) and in November 2013 (cool season, mean temperature 13.6 °C). As these populations are segregating for single (5–8 petals) versus double (> 8 petals) flowers as conditioned by a major dominant gene for double flowers, it was decided to concentrate on the petal numbers of the double flowers in the analysis. Although the petal numbers were well correlated between seasons (R² = 0.60), the double flowers generally had more petals per flower during the cool (average petal number 53) versus the warm (average petal number 38) season. Among the populations only a few showed a significant decrease in petal numbers in the warm versus cool season. Genetic variance was calculated using restricted maximum likelihood (REML) method with all factors considered as random effects. This analysis indicated a small GxE effect. Most of the variance was due to additive effects as indicated by the high narrow sense heritability (h²= 0.80).