A QTL analysis of host plant effects on fungal endophyte biomass and alkaloid expression in perennial ryegrass
Phenotypic and genetic evaluation of morphological traits associated with herbage biomass production was undertaken in a perennial ryegrass (Lolium perenne L.) biparental F1 mapping population (n = 200) with parent plants from cultivars ‘Grasslands Impact’ and ‘Grasslands Samson’. Morphological traits measured on three clonal replicates of the parental genotypes and 200 F1 progeny in a glasshouse in two separate trials (autumn and spring) included: dry weight (DW), leaf elongation rate (LER), initial tiller number (TNs), final tiller number (TNe), site filling (Fs), tiller weight (TW), leaf lamina length, leaf tip and ligule appearance rates (ALf, ALg) and leaf elongation duration (LED). Principal component analysis of patterns of trait association identified negative correlation between TNs or TNe, and TW as the primary basis for morphological difference and indicated that either high LER or long LED could reduce TN. Plants with higher LER tended to have increased DW. Quantitative trait loci (QTL) were detected on all seven linkage groups (LG) of a perennial ryegrass linkage map for all but three traits. A total of 61 QTL were identified, many of which clustered at 15 shared genome locations. Significant genotype by environment effects were encountered, evidenced both by variation between experiments in genotype rankings and by a general lack of commonality for QTL for the same traits in the different experiments. Only five QTL, for ALf, ALg and TN, were conserved between autumn and spring trials. A QTL for TN and DW on LG6 is a strong candidate for application of MAS in future plant improvement work and was found to be co-linear with QTL for equivalent traits reported on chromosome 2 in rice.