Leaf color, canopy architecture, photosynthetic efficiency, and pigment composition are fundamental traits that collectively govern plant growth, productivity, and adaptive responses to environmental cues. This comprehensive study delves into the intricate interrelationships among these critical attributes within a genetically diverse guava (Psidium guajava L.) mapping population. Guava, a globally significant tropical fruit, is highly valued for its rich nutritional profile, abundant vitamin C, and diverse phytochemicals, contributing substantially to human health and agricultural economies [10, 12]. Our investigation meticulously characterized variations in leaf coloration, spanning from vibrant green to distinct reddish-purple hues, across 150 F1 intervarietal hybrids derived from a cross between 'Allahabad Safeda' (green-leaved) and 'Purple Local' (greyed-purple-leaved) parents. We quantified key photosynthetic parameters using advanced gas exchange and chlorophyll fluorescence techniques, precisely measured the concentrations of primary photosynthetic pigments (chlorophyll a, chlorophyll b, and total chlorophyll), accessory pigments (carotenoids), and photoprotective pigments (anthocyanins), and comprehensively assessed various canopy structural characteristics including plant height, stem girth, and canopy spread.
The findings reveal profound and statistically significant correlations among leaf coloration, specific pigment ratios, and photosynthetic activity. Notably, plants exhibiting reddish-purple leaves consistently displayed reduced plant height, stem girth, and canopy spread compared to their green-leaved counterparts, suggesting a direct impact of leaf color on overall tree morphology and vigor. Furthermore, leaves with higher anthocyanin and carotenoid content, characteristic of the purple phenotype, exhibited significantly lower net CO2 assimilation rates, stomatal conductance, and transpiration rates. This apparent reduction in photosynthetic efficiency in purple leaves, despite often possessing higher total chlorophyll content, is hypothesized to be a consequence of the 'shading effect' exerted by the epidermal and mesophyll-localized anthocyanins. These pigments, acting as internal light attenuators, reduce the amount of photosynthetically active radiation (PAR) reaching the underlying chloroplasts, thereby modulating the photosynthetic machinery and potentially enhancing photoprotection under high light conditions.
Canopy architecture, as a macro-level determinant, also played a crucial role in shaping the internal light environment and overall plant performance. Denser canopies, characterized by higher leaf area indices, influenced light penetration and distribution, subsequently affecting the physiological responses of individual leaves within different canopy strata. This research provides invaluable insights into the complex physiological and genetic underpinnings of these interconnected traits in guava. The observed segregation for leaf color and associated physiological parameters within the mapping population represents a vital genetic resource for quantitative trait loci (QTL) mapping. Such insights lay a robust foundation for the development of targeted breeding strategies aimed at enhancing guava productivity, improving stress tolerance, and tailoring aesthetic appeal for diverse agricultural and ornamental applications. Understanding these relationships is pivotal for optimizing cultivation practices and developing resilient guava cultivars in the face of changing environmental conditions.
