Effects of Root-Zone Temperature Regulation on Early Growth and Heat Stress Response in Papaya (Carica papaya L.) Seedlings: A Preliminary Assessment

Papaya (Carica papaya L.) is a highly valued tropical fruit. However, its sensitivity to environmental stress, particularly temperature fluctuations, poses a significant challenge to its successful cultivation. This preliminary study assesses the responses to regulated root-zone temperature in papaya seedlings planted under controlled conditions during initial growth and survival. This research study was conducted at the Institute of Sustainable Agrotechnology (INSAT), Universiti Malaysia Perlis (UniMAP), Malaysia, using papaya seedlings grown under three different temperature treatments: ambient conditions (T0), moderate heat (±30°C, T1), and high heat (±45°C, T2). The experiment employed a Completely Randomized Design (CRD), with growth parameters, including survival rate, shoot and root dry weights, and root-to-shoot ratio, assessed over a 16-day period. The results revealed that papaya seedlings exhibited the highest survival rates under ambient conditions (T0), whereas exposure to ±30°C (T1) resulted in a gradual decline in survival, suggesting an adaptive response to moderate heat stress. However, seedlings exposed to ±45°C (T2) experienced complete mortality within five days, highlighting their extreme sensitivity to high-temperature stress. Biomass allocation analysis showed that seedlings under moderate heat (T1) exhibited a significantly higher root-to-shoot ratio compared to the control (P = 0.05), indicating a potential stress-induced adaptation mechanism that favors root growth under elevated temperatures. Despite this, overall shoot and root dry weights did not differ significantly between T0 and T1. This study highlights the susceptibility of papaya seedlings to heat stress during early growth conditions. While moderate heat (±30°C) may enhance root development, excessive temperatures (±45°C) are detrimental to seedling survival, suggesting a narrow thermal threshold for early-stage papaya growth. The findings provide valuable insights into temperature management strategies for papaya cultivation, contributing to improved propagation techniques under changing climatic conditions. Further studies are warranted to explore the physiological and molecular responses of papaya seedlings to temperature stress, which could aid in developing more resilient cultivation practices in the face of climate change.