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.

Increased consumption of vegetables has been recommended worldwide as a part of a healthy diet; therefore, determining gene function among breeding materials is crucial for vegetable improvement to meet the sustainable development of new vegetable varieties. However, genetic transformation is time-consuming and laborious, which limits the exploration of gene function for various vegetable crops. Virus-Induced Gene Silencing (VIGS) can perform large-scale and rapid gene silencing in plants due to a reduction in the experimental period and its independence from the stable genetic transformation, providing an excellent opportunity for functional research. VIGS can accelerate model plant research and make it easier to analyze gene function and validation in vegetable crops. Moreover, with the advent of technologies such as virus-mediated heterologous protein expression and the development of CRISPR/Cas9 technology, virus-mediated genetic tools have ushered in a new era in genetics and crop improvement. This study summarizes recent achievements in VIGS and Virus-Induced Gene Editing (VIGE) in vegetables. We also identify several challenges in the current state of VIGS technology in vegetables, serving as a guide for future research.

Onion thrips ( Thrips tabaci ) is the main insect pest of onion ( Allium cepa ), and feeding damage routinely causes serious yield losses. Lower amounts of epicuticular waxes on onion leaves have been associated with fewer onion thrips and less feeding damage, and research is needed to assess the relationships between amounts and composition of epicuticular waxes and feeding damage by onion thrips. This study used gas chromatography mass spectroscopy to determine amounts and types of epicuticular waxes on the foliage of onion accessions that had been field-selected for lower damage from onion thrips. Hentriacontanone-16 (H16), octaconasol-1, and triacontanol-1 were the most prevalent waxes on the foliage of these selections. Amounts of H16 were significantly lower on selections visually classified as having glossy or semiglossy foliage. Semiglossy selections were identified with similar amounts of total epicuticular wax as waxy phenotypes, due primarily to lower amounts of H16 and higher amounts of other waxes. These semiglossy selections suffered significantly less feeding damage from onion thrips in a field evaluation, supporting the identification of unique wax profiles toward the development of thrips-resistant onion.

Senescence is an important trait in maize (Zea maisL.), a key crop that provides nutrition values and a renewable source of bioenergy worldwide. Genome-wide association studies (GWAS) can be used to identify causative genetic variants that influence the major physiological measures of senescence, which is used by plants as a defense mechanism against abiotic and biotic stresses affecting its performance. We measured four physiological and two agronomic traits that affect senescence. Six hundred seventy-two recombinant inbred lines (RILs) were evaluated in two consecutive years. Thirty-six candidate genes were identified by genome-wide association study (GWAS), and 11 of them were supported by additional evidence for involvement in senescence-related processes including proteolysis, sugar transport, and sink activity. We identified a candidate gene, Zm00001d043586, significantly associated with chlorophyll, and independently studied its transcription expression in an independent panel. Our results showed that Zm00001d043586 affects chlorophyl rate degradation, a key determinant of senescence, at late plant development stages. These results contribute to better understand the genetic relationship of the important trait senescence with physiology related parameters in maize and provide new putative molecular markers that can be used in marker assisted selection for line development.

Epicuticular waxes on the surface of plant leaves are important for the tolerance to abiotic stresses and plant–parasite interactions. In the onion (Allium cepa L.), the variation for the amounts and types of epicuticular waxes is significantly associated with less feeding damage by the insect Thrips tabaci (thrips). Epicuticular wax profiles are measured using used gas chromatography mass spectrometry (GCMS), which is a labor intensive and relatively expensive approach. Biochemical spectroscopy is a non-destructive tool for measurement and analysis of physiological and chemical features of plants. This study used GCMS and full-range biochemical spectroscopy to characterize epicuticular waxes on seven onion accessions with visually glossy (low wax), semi-glossy (intermediate wax), or waxy (copious wax) foliage, as well as a segregating family from the cross of glossy and waxy onions. In agreement with previous studies, GCMS revealed that the three main waxes on the leaves of a wild type waxy onion were the ketone hentriacontanone-16 (H16) and fatty alcohols octacosanol-1 (Oct) and triacontanol-1 (Tri). The glossy cultivar “Odourless Greenleaf” had a unique phenotype with essentially no H16 and Tri and higher amounts of Oct and the fatty alcohol hexacosanol-1 (Hex). Hyperspectral reflectance profiles were measured on leaves of the onion accessions and segregating family, and partial least-squares regression (PLSR) was utilized to generate a spectral coefficient for every wavelength and prediction models for the amounts of the three major wax components. PLSR predictions were robust with independent validation coefficients of determination at 0.72, 0.70, and 0.42 for H16, Oct, and Tri, respectively. The predicted amounts of H16, Oct, and Tri are the result of an additive effect of multiple spectral features of different intensities. The variation of reflectance for H16, Oct, and Tri revealed unique spectral features at 2259 nm, 645 nm, and 730 nm, respectively. Reflectance spectroscopy successfully revealed a major quantitative trait locus (QTL) for amounts of H16, Oct, and Tri in the segregating family, agreeing with previous genetic studies. This study demonstrates that hyperspectral signatures can be used for non-destructive measurement of major waxes on onion leaves as a basis for rapid plant assessment in support of developing thrips-resistant onions.

Maize biomass from agricultural residues can be a substrate for biofuel production. However, commercial breeding programs have focused on grain yield for food and feed, and whole plant yield and nutritive value for silage, with little attention paid directly to stover yield or composition. Enhancing the energy content of crop residues with higher quality cellulosic biomass for ethanol conversion should provide a complementary use to grain use. We also question whether there is maize germplasm predisposed to dual use as second-generation biofuel. Twenty genotypes, including landraces from Spain, Atlantic, and Mediterranean Europe and genotypes derived from Iowa stiff stalk synthetic, Lancaster, and commercial hybrids were studied in a randomized complete block design across environments in Galicia (Spain) in 2010 and 2011. Germplasm was evaluated for agronomic characteristics and fiber parameters. Results show high heritability for all characteristics and parameters, ranging from 0.81 to 0.98. Principal components analysis revealed clear differences among origin of the varieties studied. Hybrids had the highest grain yield values and B73xMo17 and PR34G13 had the highest grain yield overall, at 10133 and 9349 kg/ha, respectively. European landrace varieties had lower harvest indexes (HI) than the hybrid origin, with Faro and BSL having HI of 0.43–0.47, compared to hybrid PR34613 at 0.56. Fiber concentrations were significantly correlated with yield performance, with values ranging from 0.38 to 0.61 for cob fibers and between −0.14 to −0.57 for stover fibers. Fiber concentrations were significantly different, based on the origins, in cobs but not in stover, with the Atlantic European group showing a favorable trend for cob exploitation with low acid detergent lignin and high acid detergent fiber and neutral detergent fiber values. In summary, population origin showed a reservoir of genetic diversity for breeding to improve residue quality, suggesting that adaptation played a role for stover yield and quality. European landraces could be used in prebreeding programs with stover yield and fiber quality as target traits for dual-purpose maize.