At the root of it all: a QTL analysis of root distribution in perennial ryegrass

Abstract

Perennial ryegrass is the key forage component in pasture systems in New Zealand, Australia and Europe, and is typically characterised by a shallow root system. Breeding for a deeper root profile is desirable, as root depth influences drought tolerance, anchoring of plants against removal by grazing animals, and nutrient capture. Difficulties associated with conventional selection for root traits may be alleviated by developing marker-assisted selection (MAS) tools, the first stage of which is the identification of quantitative trait loci (QTL). The objective here was to detect QTL influencing vertical root distribution in ryegrass. A root distribution ratio, RTD, was measured in a replicated mapping population (n=188) grown in sand-filled tubes. Six QTL for RTD were detected on five linkage groups, individually accounting for 4 - 18% of phenotypic variation in this trait. In silico comparative analysis indicated colinearity between ryegrass RTD QTL and QTL for root traits in the rice genome. To enrich marker density specifically at RTD QTL, comparative information was used to develop sequence-tagged site (STS) markers from rice genome-aligned ryegrass expressed sequence tags, with, thus far, STS markers ppt014 and ppt019 successfully targeted to QTL qRTD-3.2 and qRTD-6, respectively. This investigation represents the first step towards developing a MAS strategy for improved root distribution and, subsequently, perennial ryegrass cultivars with superior persistence and environmental performance.