GROWTH-RESPONSES OF HYDROPONICALLY GROWN SWEET-POTATO TOLERANT AND INTOLERANT OF A CONTINUOUS DAILY LIGHT PERIOD

Two sweetpotato [Ipomoea batatas (L.) Lam] genotypes ('Georgia Jet' an d the breeding clone TI-155) were grown at 12-, 15-, 18-, and 21-h lig ht/12-, 9-, 6-,3-h dark cycles, respectively, to evaluate their growth and elemental concentration responses to duration and amount of daily lighting, Vine cuttings (15 cm long) of both genotypes were grown in rectangular nutrient film technique channels for 120 days, Conditions were as follows: photosynthetic photon flux (PPF) mean 427 mu mol . m( -2). s(-1), 28C day/22C night air cycle, and 70% +/- 5% relative humid ity, The nutrient solution used was a modified half-strength Hoagland' s solution, Storage root count per plant and per unit area, yield (in grams per square meters per day), and harvest index increased, while p roduction efficiency (in grams per mole) decreased with increased dail y PPF, Stomatal conductance for both genotypes declined with increased daily PPF, Leaves were smallest for both genotypes at the 21-h light period, while storage root yield declined as leaf area index increased , Except for a linear decrease in leaf N and K with increased light pe riod, elemental concentration was not significantly influenced.