Does Canopy Angle Influence Radiation Use Efficiency of Sugar Beet?

Sugar beet varieties differ greatly in their canopy architecture and can be classified into canopy types according to their petiole angle. Leaf angle is one of the key factors which determines the efficiency with which plant canopies utilise incident and absorbed light for photosynthesis. Sugar beet yield is strongly correlated with accumulated intercepted light but the impact of canopy angle on light interception, biomass accumulation and sugar yield has not been explored. This study aims to analyse these relationships and also to determine if varieties can be selected according to their canopy types for high radiation use efficiency (RUE) and yields. Field trials were conducted with four varieties in 2019 (one upright, one prostrate and two intermediate canopy types) and six varieties in 2021 (two each of upright, intermediate, and prostrate) as well as one alternate sowing treatment (upright and prostrate in alternate rows). Varietal differences in petiole angle were stable across the season in 2019 and consistent between canopy closure and final harvest in 2021. The upright canopy type had a lower maximum canopy cover modelled from canopy expansion curves in both years. The upright canopy type was also slower to achieve canopy closure in 2019 and had a lower LAI at canopy closure in both years. There was a linear relationship between accumulated intercepted radiation and total plant biomass across all canopy types. The intermediate canopy types had the highest RUE in 2019 and highest sugar yield in both years. The upright canopy types had the highest RUE when harvested later in 2021, possibly due to the upright canopy type being better suited to intercept and utilise sunlight during the winter months when the sun angle is lower in the sky. The root to shoot ratio was greater in the high yielding intermediate variety suggesting that, in addition to RUE, biomass partitioning is an important determinant of sugar yield. The results from this study will aid in the selection of varieties to improve sugar beet yields. Whilst canopy angle is an important contributing factor to RUE and yield in sugar beet, other factors, such as leaf level photosynthesis and biomass partitioning are also important.