Genetic coefficients of sugarcane phenology traits for crop model refinement

English: Crop models provide a simulation of crop growth and development through the use of mathematical equations and have substantial potential as research tools. They can assist breeding by predicting complex traits (e.g. sucrose yield) through simulating interactions between simple genetic traits (e.g. leaf elongation rate per unit thermal time) and environmental factors (e.g. temperature). The Canegro sugarcane model uses cultivar coefficients to simulate the effects of genotype, environment, and management on crop performance. The current coefficients in the Canegro model are limited to data from the cultivar NCo376 and estimates for a wider range of cultivars are not available for key growth parameters. The primary objective of this study was to quantify the cultivar coefficient values for some tillering and stalk elongation, leaf phenology, and biomass production traits for a diverse range of sugarcane cultivars. An additional objective was to determine the stability and heritability of these traits across environments and crop stages to determine their potential contribution to future model-assisted breeding. Cultivar trials were established at three separate sites on South African Sugarcane Research Institute (SASRI) research farms; Amatikulu (AK), Pongola (PG), and Bruynshill (BH). The same set of 12 cultivars was tested at the three sites. The trials were planted in randomized complete block designs with four replications. The following cultivar traits were determined from within-season growth measurements: peak tiller population (PTP); thermal time to peak tiller population (TTPP); final population (FPOP); tiller survival percentage (TSP); stalk elongation rate (SER); leaf appearance rate (LAR); maximum leaf area (LAmax); thermal time to maximum leaf area (TTLAmax); maximum leaf number (LFmax); and leaf area index (LAI). Cane yield, estimated recoverable crystal percent (ERC%), ERC yield, total biomass, and brown (dead), and green leaf material were determined at each harvest. Plant and first ratoon crops were harvested at AK and PG, while only the plant crop was harvested at BH. The data were analysed using GENSTAT to estimate the variance components associated with cultivar, site, crop, and their interactions. Broad-sense heritability was calculated for each trait. Cultivar rank correlations across sites and across crops within sites were evaluated as a measure of trait stability. The highly significant (P<0.01) effect of cultivar (C) was larger than the cultivar x ratoon (C x R) and cultivar x site (C x S) effects for most traits. Mean trait values for most traits differed significantly between sites and ratoons within sites. Cultivars generally showed consistent rankings for PTP, TSP, SER, LAR, LAmax, LAI, and ERC% across sites for individual crops. Cultivars also showed consistent rankings across ratoons within a site for PTP, FPOP, SER, LAmax, LAR, LFmax, LAI, ERC%, cane yield, and ERC yield. This suggests that some traits are stable and can therefore be used for model-wise exploration of genotype by environment (G x E) interactions in sugarcane. Also, it may be feasible to characterise cultivars for some traits from single-site and single-ratoon experiments in the future. Some cultivars were identified as ideal indicator cultivars for future characterisation studies. Broad sense heritability estimates ranged from 0 to 0.99 for all traits studied. The FPOP, PTP, SER, LAR, LFmax, LAmax, LAI, cane yield, ERC%, and total biomass had high broad sense heritability estimates. These traits are therefore largely genetically controlled and can be selected for in a breeding programme. The cultivar coefficient values determined here will be incorporated into the Canegro crop model and help refine the model’s ability to simulate cultivar growth differences across environments. The range of values determined for these traits will also contribute to model-wise exploration of G x E interactions and future model-assisted breeding efforts for sugarcane.