Characterizing Crop Timing and Quality Traits of a Petunia integrifolia × P. axillaris Recombinant Inbred Line Population under Different Temperatures

Petunia (Petunia ×hybrida) is often produced in greenhouses in Northern climates in the United States during the late winter and early spring. However, providing optimal temperatures in the early of the year for petunia can cause greenhouse heating costs to be very high. Minimizing energy costs could be achieved by manipulating crop timing traits to reduce production time, such as increasing the leaf unfolding rate (i.e. development rate), or decreasing the number of leaves below the first flower. Petunia integrifolia and P. axillaris, the progenitor species of the cultivated petunia, exhibited a faster development rate than the modern cultivated petunia and may be useful genetic sources to breed faster-developing cultivars. A population of F₇ recombinant inbred lines (RIL) derived from a P. integrifolia × P. axillaris F₂ population was phenotyped in two experiments representing a range of temperatures during Summer 2012 (24 °C) and Winter 2013 (14, 17, 20 °C). The population exhibited considerable variation for several crop timing traits, including leaf unfolding rate and the number of leaves below the first flower, and quality parameters.  The population distribution for development rate increased as temperature decreased.  At 24 °C, the average leaf unfolding rates of the ten fastest and ten slowest lines were 0.820 and 0.458 leaves per day, respectively. In contrast, at 14 °C, the average leaf unfolding rates of the fastest and slowest lines were 0.422 and 0.130 leaves per day. Therefore, as the temperature dropped from 24 °C to 14 °C, the fold change in development rate of the fastest lines compared to the slowest lines increased from 1.8-fold higher to 3.2-fold higher. These results indicate that the leaf unfolding rates of slower-developing lines are more subject to cool temperatures than the fast-developing lines. Thus, introducing the faster-developing trait into the modern cultivated petunia could increase the feasibility of producing petunia at lower temperatures to reduce heating fuel usage. Also, the observed range of variability for a wide range of phenotypic traits observed in the population indicates that these RILs will be very useful for mapping traits of interest.