Characterisation of genetic diversity for resistance and quality traits using molecular tools

Several decades of molecular studies in forage crops like Lolium revealed to some extent the genetic control of traits such as crown rust resistance, flowering time, vernalisation response, and water soluble carbohydrates. The first studies focussed on only a very limited genetic diversity, up to a dozen of alleles in a series of diverse linkage mapping populations, and identified major genes or QTLs with a major effect. In more complex traits such as dry matter yield and fodder quality where multiple physiological processes contribute to the phenotype, a greater number of genes are involved and the environment often has a masking effect on the genetic component of the trait. Unraveling the genetic control of these complex traits requires the use of populations with more genetic diversity and with shorter LD. It further requires the development of high resolution phenotyping methods and molecular tools to discover and screen a wider range of genetic diversity. The different research strategies used in these highly heterozygous cross-pollinating species shifted from constructing mapping populations with a very restricted number of alleles towards association mapping in a diverse collection of germplasm, or linkage mapping in highly structured and interlinked populations. With recent developments in high-throughput genotyping, phenotyping and advanced statistical approaches for highly heterozygous and genetic diverse species such as Lolium more genetic diversity can be screened and exploited to understand the genetic control of agronomic important complex traits. This shift towards high resolution molecular studies on complex traits using wide genetic diversity, opens new strategies for innovative breeding in forage crops.