Precision Mapping of a Maize MAGIC Population Identified a Candidate Gene for the Senescence-Associated Physiological Traits.

Senescence is an important trait in maize (Zea mais L.), 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.

Redefining Agricultural Residues as Bioenergy Feedstocks.

The use of plant biomass is a sustainable alternative to the reduction of CO2 emissions. Agricultural residues are interesting bioenergy feedstocks because they do not compete with food and add extra value to the crop, which might help to manage these residues in many regions. Breeding crops for dual production of food and bioenergy has been reported previously, but the ideal plant features are different when lignocellulosic residues are burnt for heat or electricity, or fermented for biofuel production. Stover moisture is one of the most important traits in the management of agricultural waste for bioenergy production which can be modified by genetic improvement. A delayed leaf senescence or the stay-green characteristic contributes to higher grain and biomass yield in standard, low nutrient, and drought-prone environments. In addition, the stay-green trait could be favorable for the development of dual purpose varieties because this trait could be associated with a reduction in biomass losses and lodging. On the other hand, the stay-green trait could be detrimental for the management of agricultural waste if it is associated with higher stover moisture at harvest, although this hypothesis has been insufficiently tested. In this paper, a review of traits relevant to the development of dual purpose varieties is presented with particular emphasis on stover moisture and stay-green, because less attention has been paid to these important traits in the literature. The possibility of developing new varieties for combined production is discussed from a breeding perspective.