Balancing gain and diversity: Optimal contribution selection for sustainable genetic improvement in sugarcane.

Sugarcane (Saccharum spp. hybrids), the source of ∼80% of the worlds sugar, has experienced a plateau in genetic improvement over recent decades. This stagnation is largely due to the crop's complex polyploid genome and long breeding cycles, which limit the efficiency of traditional selection methods. Genomic selection (GS) has been proposed to accelerate breeding progress in sugarcane by enabling faster improvement of key commercial traits such as cane yield, sugar content, and disease resistance. However, especially in clonally propagated outbred crops like sugarcane, intensive GS can reduce genetic diversity. Prioritizing short-term genetic gain without managing diversity risks inbreeding depression, resulting in reduced vigor and decreased productivity and compromising long-term gains and potential for adaptability to changing environments. Optimal contribution selection (OCS) offers a strategic solution by optimizing parental contributions to maximize genetic gain while controlling the rate of inbreeding. This review outlines the challenges in sugarcane breeding, including high ploidy, complex genetic architecture, and low trait heritabilities. We propose the first conceptual framework for applying OCS in sugarcane, highlighting its potential to achieve sustainable genetic improvement. Furthermore, we explore extensions to the OCS framework that incorporate non-additive genetic effects (e.g., dominance and epistasis), allele dosages, and the multi-species germplasm that underpins modern cultivars. By balancing genetic gain with diversity retention, OCS provides a pathway for long-term progress in sugarcane breeding. In the context of rising global sugar demand and climate change, this balanced approach supports improved yield, quality, and resilience while maintaining the genetic diversity essential for future gains.