Chapter 1 12 1.2.1. Shade avoidance and neighbour detection for farming Light serves as a fundamental driver of plant growth and development, fuelling photosynthesis, through which plants convert light energy into chemical energy. Plants engage in a struggle for light and adapt their growth patterns to secure optimal light capture in the future. The quality and quantity of light received by plants exert a profound influence on various physiological and developmental processes, including seed germination, stem elongation, leaf development, flowering, and tuber formation. SAS enables plants to elongate stems and adjust leaf angles in an attempt to maximize light capture and mitigate the negative effects of shading (Pantazopoulou et al., 2017). Of particular importance is the ratio of red to far-red (R:FR) light (Osborne, 1991; Franklin, 2008; Ballaré and Pierik, 2017), which acts as a crucial signaling mechanism, conveying information about neighbouring plants and redirecting resource availability into growth, for example, at the cost of seed production (Smith and Whitelam, 1997; Hewitt, 1998; Yang and Li, 2017). Smallholder farmers worldwide often confront common challenges, including constraints on resources, food insecurity, and heightened vulnerability to the impacts of climate change. These issues have been reported in various regions, such as Sub-Saharan Africa (Ariom et al., 2022), South Asia (Cerling et al., 1997), Southeast Asia (Nor Diana et al., 2022), and East Africa (Ndoli, 2018). In these areas, the reduction of fallow periods or continuous cropping practices, driven by population pressure, has led to soil erosion, diminished soil organic matter, and nutrient depletion without adequate replenishment. Consequently, agricultural productivity has been negatively affected, exacerbating the problem of food shortages. Addressing these challenges necessitates the adoption of sustainable agricultural practices and innovative solutions that consider the shade avoidance responses of crops to ensure the resilience and well-being of smallholder farmers globally. 1.2.2 Shade signal detection Canopies formed by plants typically have decreased photosynthetically active radiation (PAR) compared to direct sunlight. Therefore, many plants will adjust their photosynthetic activity and growth (Lichtenthaler et al., 1981; Casal, 2013). Plants absorb photosynthetically active wavelengths (380 nm – 750 nm), including red (R) light (750 nm) and blue (B) light (450 nm). They hardly absorb far-red light (FR, >750 nm) light, and hence the reflected and transmitted light is enriched in FR wavelengths (Figure 1.3). In a situation where there are multiple plants in dense vegetation, FR light
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