Extent of Crown Rust Infection in a Perennial Ryegrass (Lolium perenne L.) Association Mapping Population

One of the most damaging foliar diseases on perennial ryegrass is crown rust, caused by Puccinia coronata f. sp. lolli. Crown rust causes severe losses to yield and quality of forage and results in decreased palatability and digestibility for ruminants. Crown rust was scored in 1800 individually spaced plants in two replicates on a scale of 1 (no infection) to 9 (severely infected) at three time points (June, August & September 2014) in a block design experiment. These 1800 individuals represent 30 populations with different population structures: ten synthetic varieties, eight full-sib breeding families, eight half-sib breeding families and four Irish ecotypes. The disease progression was observed in all populations, with highest pressure of crown rust seen in September and lowest disease pressure observed in June. Significant differences (p < 0.001) were recorded among populations, among time points and for the population x time point interaction. The Irish ecotypes were more susceptible to crown rust compared to the other populations. Crown rust phenotypic data will be used to conduct association analysis on these populations to identify significant marker trait associations.