Variability and heritability of photosynthetic traits in Saccharum complex

Evidence of photosynthetic acclimation to self-shading in sugarcane canopies

“…2A). Such photosynthetic variability was already reported and ascribed to differences in leaf anatomy and morphology, stomatal conductance, leaf nitrogen content, and phosphoenolpyruvate carboxylase (PEPC) and Rubisco abundances and activities (Irvine 1967(Irvine , 1975(Irvine , 1983Marchiori et al 2010Marchiori et al , 2014Jackson et al 2016, Li et al 2017, Almeida et al 2021. As a novelty, our data revealed that some sugarcane canopies have similar PN in leaves +1 and +4 (IACCTC06-8126, IACSP95-5000, IAC87-3396, SP70-1143, IACSP94-2094, CTC4, and IAC48-65) while others have leaf +1 with higher P N than that of leaf +4 (S. spontaneum, S. robustum, S. officinarum, SP80-3280, IACSP01-5503, and RB83-5486) under high light (Fig.…”

“…1C,D; 2S). Among the biochemical changes underlying shade acclimation of photosynthetic apparatus in leaves +4, we would suggest increases in activity and abundance of PEPC and Rubisco, pyruvate orthophosphate dikinase, NADP-dependent malate dehydrogenase, and phosphoenolpyruvate carboxykinase (Sales et al 2018, Almeida et al 2021 2021) -a subject to be further explored in future research. Such acclimation to low-light availability leading to the maintenance of the photosynthetic capacity of shaded leaves under high light would improve photosynthesis during sun flecks and then canopy photosynthesis (Waldron et al 1967, Machado et al 1982.…”

“…The commercial cultivars developed by breeding programs are inter-or intraspecific hybrids (crosses of S. officinarum, S. spontaneum, S. robustum, and S. barberi) derived mainly from the crossing of the noble species S. officinarum (~ 70-80%) and the wild species S. spontaneum (~ 10-20%) (Moore et al 2014). As high heritability for photosynthesis and stomatal conductance in sugarcane has been reported by Jackson et al (2016), Li et al (2017), andAlmeida et al (2021) and there is significant variation in photosynthesis of both light-exposed and shaded leaves reported herein, our data indicate that there is room for improving canopy photosynthesis through breeding. Sugarcane plants with erectophile-like leaves at the upper canopy layer that allows light penetration (Marchiori et al 2014), and planophile-like leaves at bottom canopy positions (Slattery et al 2016, Walker et al 2018, with high photosynthetic capacity due to shading acclimation, would have a phenotype favoring higher conversion of sunlight energy into biomass.…”

“…However, the physiological processes underlying the light-conversion efficiency and yield remain poorly understood in fieldgrown sugarcane plants (Zhu et al 2010, Lopes et al 2011, Moore et al 2014. Recently, Almeida et al (2021) reported a significant variation in photosynthesis among sugarcane genotypes and identified valuable and heritable photosynthetic traits. However, Almeida et al (2021) evaluated only one fully expanded and sun-exposed leaf in sugarcane plants, as done by others (Irvine 1967(Irvine , 1975Jackson et al 2016, Li et al 2017.…”

“…Recently, Almeida et al (2021) reported a significant variation in photosynthesis among sugarcane genotypes and identified valuable and heritable photosynthetic traits. However, Almeida et al (2021) evaluated only one fully expanded and sun-exposed leaf in sugarcane plants, as done by others (Irvine 1967(Irvine , 1975Jackson et al 2016, Li et al 2017. Then, an intriguing question arises: would shaded leaves have a photosynthetic capacity similar to the light-exposed leaves in field-grown sugarcane plants?…”