Light Interception and Radiation Use Efficiency of Three Cassava Genotypes with Different Plant Types and Seasonal Variations

The yield potential of cassava might be increased by enhancing light interception and the ability to convert energy into biomass and yield, which is described as radiation use efficiency (RUE). The objective of this study was to determine light interception, extinction coefficient (k), and RUE of three cassava genotypes (Kasetsart 50 (KU50), Rayong 11 (RY11), and CMR38-125-77) under seasonal variations. The field experiments were conducted in a randomized complete block design with four replications, using two planting dates for 2 years at Khon Kaen, Thailand. Data were recorded for weather conditions, light interception, leaf area index (LAI), and biomass. Solar radiation interception, RUE, and k were calculated. Light interception of the crop planted in May sharply increased in the early growth stage, whereas the crop planted in November slowly increased and could maintain higher light interception from the mid-late growth stages. Light interception and LAI had a moderate to high coefficient of determination (R-2 = 0.61-0.89) for three cassava genotypes and all planting dates. The k values ranged from 0.59 to 0.94, varying by genotypes and planting dates, indicating that the leaf orientation of the three cassava genotypes was horizontally oriented. The relationship between biomass accumulation and cumulative solar radiation produced a high value of R-2 (0.86-0.99). The RUE for biomass (RUEbi) varied by genotype and planting date, ranging from 0.66 g MJ(-1) to 0.97 g MJ(-1). However, the RUE for storage root dry weight (RUEsr) ranged from 0.29 g MJ(-1) to 0.66 g MJ(-1). The RUEbi and RUEsr in each genotype on each planting date were significantly different. The highest RUEbi and RUEsr were found at 4-6 and 7-9 MAP for almost all genotypes and planting dates, except for the crop planted in November 2015, when both RY11 and CMR38-125-77 had the highest RUEbi at 10-12 MAP. RY11 had a lower LAI compared to other genotypes, which contributed to lower light disruption and lower RUEbi and RUEsr. KU50 and CMR38-125-77 could maintain canopy light interception during canopy development and storage root accumulation stages and had high RUEbi and RUEsr, resulting in high biomass and crop yield.