Stay-green (SG) is a term used to describe genotypes that have delayed leaf senescence as compared to reference genotypes. SG could be favorable for grain yield, silage yield and quality, double exploitation (grain for feed and stover for bioenergy), stress resistance, etc. However, some studies show contradictory results regarding the influence of senescence or SG in the uptake and remobilization of nutrients and the yield and moisture of stover and grain. This experiment is aimed to study the impact of senescence in grain and stover yield and moisture in inbred lines of maize and assess the potential of SG genotypes for double exploitation. We also study the influence of senescence in the uptake of N and remobilization of dry matter and N from stover to grain. We evaluated 16 maize inbred lines with contrasting expression of senescence in the field at two locations in Galicia in 2017. We confirmed that SG is functional, meaning that the SG genotypes maintained photosynthesis activity for a lengthy period. Coordinated with a delayed senescence, the grain filling of the SG genotypes was 9 days longer than NSG genotypes. SG genotypes took up more N after flowering, although the remobilization of N and, in general, of dry matter from stover to kernels was less efficient. However, the higher uptake compensated the poor remobilization, and the final effect of SG on the N content of the kernels was favorable. SG was also favorable for kernel weight and the kernels of SG genotypes were 20% heavier than for NSG. The stover yield was also higher in the SG genotypes, indicating a potential of SG for breeding for double purpose (grain for feed and stover for bioenergy).

In this review, we present a comprehensive revisit of past research and advances developed on the stay-green (SG) paradigm. The study aims to provide an application-focused review of the SG phenotypes as crop residuals for bioenergy. Little is known about the SG trait as a germplasm enhancer resource for energy storage as a system for alternative energy. Initially described as a single locus recessive trait, SG was shortly after reported as a quantitative trait governed by complex physiological and metabolic networks including chlorophyll efficiency, nitrogen contents, nutrient remobilization and source-sink balance. Together with the fact that phenotyping efforts have improved rapidly in the last decade, new approaches based on sensing technologies have had an impact in SG identification. Since SG is linked to delayed senescence, we present a review of the term senescence applied to crop residuals and bioenergy. Firstly, we discuss the idiosyncrasy of senescence. Secondly, we present biological processes that determine the fate of senescence. Thirdly, we present the genetics underlying SG for crop-trait improvement in different crops. Further, this review explores the potential uses of senescence for bioenergy crops. Finally, we discuss how high-throughput phenotyping methods assist new technologies such as genomic selection in a cost-efficient manner.