Genomics Applied to the Analysis of Flowering Time, Abiotic Stress Tolerance and Disease Resistance: A Review of What We Have Learned in Lolium spp.

Abstract

Flowering time, abiotic stress tolerance and disease resistance are important agronomic traits of forage species like Lolium spp. Understanding the genetic control of these traits is enabled by the combination of genomic tools with conventional breeding techniques. Flowering time in this genus represents a complex trait due to the differences in the primary induction requirements among the species. In total, 36 QTLs (Quantitative Trait Locus) were identified across all seven linkage groups of Italian and perennial ryegrass involved in the flowering pathways, with several putative orthologous/homologous genes that have been characterized in other major crops. From the perspective of climate change, abiotic stress tolerance has become an essential feature; many QTLs that are involved in the control of plant responses have been identified, and transcriptional studies focusing on drought tolerance reported several DEGs (Differentially Expressed Genes) involved in carbon and lipid metabolism and signal transduction. Due to the incidence of microbial diseases, QTLs useful to developing cultivars resistant to bacterial wilt (Xanthomonas translucens pv. graminis), ryegrass crown rust (Puccinia coronata f. sp. Lolii) and gray leaf spot (Magnaporthe grisea/oryzae) have been mapped in both L. perenne and L. multiflorum populations. Due to the great importance of Lolium species, especially as forage crops, additional information about the three aforementioned agronomic traits is needed.

Genome-Wide Association Mapping of Crown and Brown Rust Resistance in Perennial Ryegrass

“…However, this resistance mechanism has its limitations, mainly because R genes recognize only a limited number of pathogen races. A second mechanism involves quantitative trait loci (QTLs), where more genes with minor effects confer partial resistance with a certain degree of additivity [ 11 ], hence the name quantitative resistance. Studies support the idea that some quantitative resistance genes share structural and functional similarities with R genes belonging to the nucleotide-binding site and leucine-rich repeat ( NBS-LRR ) class [ 12 , 13 ].…”