Phenotypic plasticity and genetic trends in the past 30 years of sugarcane genetic improvement in Louisiana

Sugar yield, which results from the combination of stalk biomass (SB) and sugar content (SC), stands as the critical trait for sugarcane breeding programs in Louisiana. Nevertheless, it remains uncertain how SB and SC have individually contributed to the recent increase in sugar yield and how the environment governs their relationship. We applied linear mixed models and the Finlay-Wilkinson model to analyze historical data from the Louisiana outfield variety trials, from plant cane to the third ratoon in multiple environments. The primary objectives were to determine (i) SC and SB genetic gain, (ii) the nature of the relationship between SB and SC, and (iii) whether genotypes are widely or specifically adapted to the environment. Our results showed that the breeding increased sugar yield by relying mostly on SB (0.600-0.652 Mg ha-1 year-1 and 0.893%-0.950% per year) and less on SC (0.371-0.384 kg year-1 and 0.282%-0.292% per year). This was achieved by increasing genotypes SB sensitivity to environmental conditions (0.310% per year) on the plant cane rather than ratoon (nonsignificant). Additionally, the environment strongly controlled the relationship between SB and SC without a significant positive or negative trend on the population mean. From an environmental perspective, high-yielding environments also provided conditions for high SC on plant cane. Our study highlights that environment characterization is fundamental to sugarcane breeding and emphasizes the opportunity to direct efforts on selecting genotypes that are responsive to the environmental quality by producing superior SB in the ratoon crop cycles. Stalk biomass increase ranged from 0.893% to 0.950% per year, while sugar content ranged from 0.282% to 0.292% per year.Breeding relied primarily on plant cane stalk biomass sensitivity to increase sugar yield over the years.Contrasting environmental conditions in the multi-environment trials is essential to select high-yield genotypes.Stalk biomass and sugar concentration relationship is uncertain with strong environmental control.High-yielding environments also provided conditions for high sugar content only in plant cane.