"International Journal of Geography, Geology and Environment"

The commercial propagation of red pulp guava (Psidium guajava L.) is largely dependent on the successful establishment of graft unions and early scion survival, which together determine the uniformity and productivity of orchard plantations. Despite the widespread adoption of cleft grafting in guava nurseries, inconsistent graft success rates remain a persistent constraint, often attributed to fluctuations in microclimatic conditions during the critical healing phase. This study investigates the influence of key environmental determinants namely temperature, relative humidity (RH), and shade intensity on callus initiation, vascular bridge formation, and subsequent graft survival in red pulp guava. A factorial experimental design comprising four temperature regimes (20, 25, 30, and 35 °C), three relative humidity levels (60, 75, and 90 %), and three shade treatments (0, 30, and 50 %) was simulated under controlled nursery conditions. Quantitative indices of callus development, graft survival percentage, and union firmness were recorded and analyzed through analysis of variance and interaction modeling. Results revealed significant effects of temperature and RH, with notable interactions among all three factors. Optimum conditions were observed at 28–30 °C and 80–85 % RH under approximately 30–40 % shade, yielding superior callus proliferation (mean index = 8.4±0.7) and graft survival (≈ 94 %). Excessive temperatures or humidity deviations outside these ranges led to desiccation or delayed lignification at the graft interface.

The findings underscore the necessity of maintaining a stable microclimate during the 10–14-day healing period, supported by regulated misting, shading, and gradual hardening protocols. These results align with contemporary trends in tropical fruit propagation that emphasize environmental precision and quality assurance. By defining quantitative microclimatic thresholds for graft success, this study provides a reproducible framework for nursery standardization and enhanced productivity in red pulp guava propagation.