Papaya is an important tropical fruit crop cultivated in Iran under greenhouse conditions and propagated through seed. Rapid growth and excessive height of seedlings represent major challenges in greenhouse papaya production. Contact of branches with the greenhouse roof and breakage caused by the heavy fruit load often force growers to remove trees and replace them with new seedlings. To evaluate the effects of root pruning and soil application of different concentrations of paclobutrazol (PBZ) on vegetative growth, yield, and fruit quality of papaya cv. ‘Sweet Sense’, an experiment was conducted in a completely randomized design with six treatments and three replications (each replication comprising two trees) during 2023–2024 in Dezful, Khuzestan Province, Iran. The treatments included: control (no root pruning and no paclobutrazol), root pruning (25% balanced removal of root volume), combined root pruning + 250 mg L⁻¹ PBZ, and application of PBZ at 250, 500, and 1000 mg L⁻¹. The results showed that the treatments had significant effects on tree height and trunk cross-sectional area (TCSA). The tallest trees and largest TCSA were recorded in the control, whereas the shortest trees were observed in the combined root pruning + 250 mg L⁻¹ PBZ treatment (43% reduction compared with control). The greatest reduction in TCSA occurred in the root-pruning treatment (30% reduction). Yield components—including flower number, fruit number, and fruit yield—were significantly influenced by the treatments. The highest yields were obtained with 250, 500, and 1000 mg L⁻¹ PBZ (212, 191, and 175 kg per tree, respectively), while the lowest yield occurred in the root-pruning treatment (109 kg per tree). Average fruit weight was also greatest in the 250, 1000, and 500 mg L⁻¹ PBZ treatments (1120, 944, and 988 g, respectively), and lowest in the control (796 g). Except for total soluble solids (TSS) and titratable acidity (TA), other fruit quality traits were not significantly affected. The highest TSS (10.67 °Brix) and TA (0.30 g per 100 g fresh weight) were recorded in the combined root pruning + 250 mg L⁻¹ PBZ treatment. Overall, soil application of 250 and 500 mg L⁻¹ PBZ was identified as the most effective, reducing vegetative growth by 7% and 10% and increasing yield by 32% and 20%, respectively, without negatively affecting fruit quality. These results highlight the potential of root pruning and PBZ for growth control and yield enhancement in greenhouse-grown papaya. |
