Inheritance of Crop Timing and Quality Attributes In Petunia Interspecific Hybrid Populations

The rate of node appearance (i.e. leaf unfolding rate) is one factor determining crop timing.  Many greenhouse crop growers in northern climates have reduced greenhouse temperature in an attempt to reduce heating costs.  Leaf unfolding rate is a temperature dependent process; therefore lowering greenhouse temperature decreases the rate of development, increasing production time.   Developing cultivars with higher rates of development at lower temperatures is one long-term strategy for improving energy efficiency of greenhouse crop production.  Initial experiments indicated that wild relative species of the modern cultivated petunia (Petunia hybrida Vilm.) have higher leaf unfolding rates than modern cultivars and may therefore be useful genetic sources to develop cultivars with decreased production time, particularly at cool (<20 ºC) temperatures.  Three interspecific F₂ populations, P. axillaris (Lam.) Britton et al. × P. hybrida ‘Mitchell’, P. axillaris × P. exserta Stehmann and P. integrifolia (Hook.) Schinz & Thell. × P. axillaris were phenotyped for 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.  All three populations exhibited transgressive segregation for leaf unfolding rate.  Leaf unfolding rate was not correlated with time to flower in any of the populations, suggesting these traits could be selecting for independently to develop genotypes with high leaf unfolding rate and reduced time to flower.  Leaf number below the first flower was positively correlated with leaf unfolding rate in all populations except P. integrifolia × P. axillaris.  Time to flower was strongly positively correlated with flower bud number in the P. axillaris × P. hybrida ‘Mitchell’ population (P<0.001), weakly correlated in the P. integrifolia × P. axillaris population (P=0.042), but not significantly correlated in P. axillaris × P. exserta individuals.  Together, these results indicate that wild germplasm could be useful for developing petunia cultivars with accelerated time to flower, but reductions in crop quality parameters may need to be overcome.