Estimation of Shoot Development for a Single-stemmed Rose 'Vital' Based on Thermal Units in a Plant Factory System

This study was conducted to predict number and fresh weight of leaves, and total leaf area of a single-stemmed rose 'Vital' based on the accumulated thermal units, and to develop a model of shoot development for the prediction of the time when the flowering shoot reaches a phenological stage in a plant factory system. The base temperature (T∧b), optimum temperature (T∧opt), and maximum temperature (T∧max) were estimated by regressing the rate of shoot development against the temperature gradient. The rate of shoot development (R, d-¹) for the phase from cutting to bud break (CT-BB) was best described by a linear model R∧b (d-¹) = -0.0089 + 0.0016ㆍtemp. The rate of shoot development for the phase from bud break to harvest (BB-HV) was fitted to the parabolic model R∧h (d-¹) = -0.0001ㆍtemp² + 0.0054ㆍtemp - 0.0484. The T∧b, T∧opt, and T∧max values were 5.56, 27.0, and 42.7℃, respectively. The T∧b value was used in the thermal unit computations for the shoot development. Number of leaves, leaf area (LA), and leaf fresh weight showed sigmoidal curves regardless of the cut time. The shoot development and leaf area model was described as a sigmoidal function using thermal units. Leaf area was described as LA = 578.7 [1 + (thermal units/956.1)∨-8.54]-¹. Estimated and observed shoot length and leaf fresh weight showed a reasonably good fit with 1.060 (R² = 0.976***) and 1.043 (R² = 0.955***), respectively. The average thermal units required from cutting to transplant and from transplant to harvest stages were 426 ± 42℃ㆍd and 783 ± 24℃ㆍd, respectively.