Seed yield in perennial ryegrass (Lolium perenne L.): comparative importance of component traits and detection of seed-yield-related QTL

The aims of our study were to evaluate relationships amongst morphological traits associated with seed production in a perennial ryegrass biparental population and to identify genomic regions associated with phenotypic variation in those traits using QTL analysis. This was achieved using data from two field experiments at Palmerston North and Lincoln, New Zealand, in 2003, and days to heading (DTH), reassessed in 2004. Trait association was determined for the Palmerston North experiment where measured traits included seed yield per plant (SYPlant), seed yield per spike (SYSp), reproductive tiller number (RTiller), spikelets per spike (SpktSp), florets per spikelet (FSpkt), 1000 seed weight (TSW), spike length (SpLen), florets per spike (FSp), floret site utilization (FSUtil), spread of heading (SOH) and plant growth habit (PGHabit). Traits contributing to SYPlant in order of descending value were FSpkt, FSUtil, and RTiller. High TSW was only weakly linked to SYPlant. FSUtil, SOH and RTiller were identified as valuable breeding targets for improving seed yield potential in perennial ryegrass. QTL were identified for all traits except for RTiller. QTL for SYPlant occurred on linkage groups (LG) 2 and 6. Both were co-located with QTL for SYSp and sets of SYPlant components or related traits (FSpkt, FSp; FSUtil and TSW). Major QTL for DTH were identified on LG2 and LG4 and minor QTL on LG7 in consecutive years. There was a strong genotype-by-environment interaction for SYPlant that was reflected in a lack of consistent QTL across environments, while QTL for SYSp and DTH were stable across environments. Identification of component traits and QTL important for seed yield may accelerate genetic improvement in perennial ryegrass through conventional and marker-assisted breeding, respectively.