Modeling flower induction in Lilium longiflorum

The effectiveness of long photoperiods and cold temperature in inducing flowering of Lilium longiflorum Thunb. 'Nellie White' was determined by comparing flower induction index (FII) values. FII was calculated by multiplying the relative effectiveness of a treatment in reducing total leaf number by the fraction of flowering plants resulting from the treatment. FII increased as the storage duration increased from 0 to 8 weeks and as the storage temperature decreased from 17.5 to 5C. Nonlinear regression analysis was used to model FII as a function of storage duration and temperature. The resulting model yielded an estimated optimum vernalization temperature of 4.0C. The surface generated by the model resembled an asymmetric hill. LDs during vernalization were not effective above 20C or below 10C and were not as effective as cold temperatures in inducing flowering. LDs induced flowering best at 17.5C. Substituting LDs for cold temperatures resulted in lower FII values. Plants were more responsive when LDs were preceded by cold temperatures. LDs alone were least effective in inducing flowering.