Air temperature effect on leaf development in vegetative propagation of sweetpotato single node cutting under artificial lighting

The number of days to the first harvestable propagule development (t ₀), the harvestable propagule development rate (r) and the number of harvestable propagules per plant (N) of sweetpotato (Ipomoea batatas (L.) Lam., cv. Beniazuma) plants regenerated from single node cuttings were investigated at five levels of air temperature (23, 26, 29, 32 and 35°C). The single node cuttings consisted of one unfolded leaf. The t₀, r and N values were estimated for three different leaf blade length (L) classes. Photosynthetic photon flux, water vapor pressure deficit, photoperiod, CO ₂ concentration and air current speed were maintained at 200μmolm^-2s^-1, 1.1kPa, 16h per day, 1000μmolmol ^-1 and 0.6ms^-1 during experiment period (10 days). At all air temperatures, N increased linearly with time after the first propagule developed. N on day 10 increased with increasing air temperature up to 32°C, and then leveled off around 32-35°C for L≥50mm. N on day 10 decreased at 23 and 26°C but increased at 32 and 35°C with increasing L. t ₀ decreased with increasing air temperature regardless of L. r decreased for L of 10-30mm but increased for L≥50mm with increasing air temperature. Both t₀ and r increased with increasing L at all air temperatures. The increase in r with increasing L became pronounced with increasing air temperature. Results in the present study are important for predicting the number of sweetpotato propagules and perhaps for reducing electric energy and other resources for propagule and transplant production under artificial lighting.