Evaluating natural variation, heritability, and genetic advance of photosynthetic traits in rice (Oryza sativa)

Abstract

Despite significant advances to harvest index and interception efficiency, photosynthesis has remained largely unimproved through conventional breeding approaches. However, increasing photosynthetic efficiency is a key method for enhancing crop productivity, yield, and sustainability. In this study, photosynthetic and morphological traits were characterized in indica rice to examine natural variation and the potential for hybridization in the future. Additionally, broad‐sense heritability (H2) was calculated for photosynthetic traits, including, for the first time, biochemical limitations to photosynthesis. Heritability was high for CO2 assimilation in saturating light and [CO2] (Amax; H2 = .65), the maximum rate of carboxylation (Vc,max; H2 = .63), the maximum rate of electron transport (Jmax; H2 = .68), and triosephosphate utilization (TPU; H2 = .73). Genetic advances of up to 17.7% were estimated, suggesting that it would be possible to not only select for the improvement of biochemical components of photosynthesis but also achieve significant gains in one generation. Heritability was low for CO2 assimilation at ambient [CO2] in saturating light (Asat; H2 = .22), suggesting that rising [CO2] may increase heritability for photosynthesis in rice.

A model-guided holistic review of exploiting natural variation of photosynthesis traits in crop improvement

“…These findings suggest that TPU limitation to leaf photosynthesis may be regulated by sink feedback at the whole-plant scale. Acevedo-Siaca et al (2021) showed that like V cmax and J max , T p estimated for 30 rice accessions had high heritability. Data of Acevedo-Siaca et al (2021) further showed that rice A max at CO 2 saturation was highly heritable but A max at ambient [CO 2 ] was not, suggesting that genotypic variation in A max might be caused by genotypic sink limitation ( Fabre and Dingkuhn, 2022 ).…”

“…Where CO 2 or light response curves are measured that allow the estimation of V cmax and J max , the variation of A max is often associated with V cmax or J max , or both ( Driever et al , 2014 ; Jahan et al , 2014 ; Carmo-Silva et al , 2017 ; Silva-Perez et al, 2020 ; Acevedo-Siaca et al , 2021 ). In general, V cmax and J max estimated across genotypes/accessions are highly correlated ( Driever et al , 2014 ; McAusland et al , 2020 ; Mathan et al , 2021 ).…”

“…In general, V cmax and J max estimated across genotypes/accessions are highly correlated ( Driever et al , 2014 ; McAusland et al , 2020 ; Mathan et al , 2021 ). Carmo-Silva et al (2017) and Acevedo-Siaca et al (2021) showed that both parameters had high heritabilities.…”

Why is rice Amax (at saturating CO2) more heritable than Asat (at ambient CO2)? A commentary on Acevedo‐Siaca et al. (2021)

“…Based on the above, it is possible that the greater heritability of A max compared with A sat (Acevedo‐Siaca et al, 2021) in part reflects genotypic variation in source–sink relations. This effect is amplified when high or saturating CO 2 levels are applied.…”

“…As an alternative hypothesis explaining the superior heritability of A max compared with A sat (Acevedo‐Siaca et al, 2021), genotypic variation in A sat (ambient [CO 2 ]) may have been simply overwhelmed by noise in stomatal conductance, possibly amplified by plant exposure to the (assumedly) low radiation levels caused by the wet season conditions and additional shading by the screenhouse structure. The CO 2 ‐saturation implemented to measure A max would have eliminated this noise, resulting in greater H 2 for A max .…”