A review of perennial ryegrass variety evaluation in Ireland

Abstract

Official National List (NL) testing of perennial ryegrasses commenced in Ireland at the start of the 1970s with Northern Ireland (NI) having one site as part of the UK NL testing network, and the Republic of Ireland (ROI) using 5 sites. The different testing strategies adopted to achieve sufficient precision for regional Recommended Listing in ROI from a multi-site system and from a single-site system in NI were considered, including the test protocols, use of sequential sowings, timeframes and ‘merit scores’. The precision with which varieties can be discriminated for yield potential was shown to decline at lower trial plot yields. Furthermore, reducing the number of data sets used for decision making was shown to increase the ‘breeder’s risk’ of having an improved variety incorrectly rejected but not the ‘tester’s risk’ of erroneously recommending a variety that was not a clear improvement, because statistical analysis expanded confidence limits. These variety lists initially assessed only yield and persistency, giving a progressive improvement in recommended varieties and despite high genotype-x-environment interaction effects was most clearly evident in spring productivity improvements. The lists have been highly influential in both jurisdictions as almost all agricultural grass seed sales were recommended in ROI or NI, but the overuse of late maturing varieties in the ROI market and declining reseeding levels across Ireland indicated the current limits of this influence. This, and increasing requirements from Irish farmers for improvement in the nutritive value of varieties to support greater dependence on grass for animal production, has led to increased testing for digestibility and other quality parameters. While there is valid scientific evidence that shows that improvements in perennial ryegrass varieties has increased milk and meat production, more detailed information is required to satisfy the specific needs of local farmers. Consequently, a research initiative has been instigated to develop an index that will incorporate all the yield, persistence and quality performances of each recommended variety into a ranking score for a specific herd management system. This guidance should simplify recommendations and better quantify variety improvements in financial terms. It is envisaged that this will encourage an increase in the renewal of Irish pastures, promote selection of varieties based on enterprise-specific value and will continue to enhance the profitability and sustainability of grass-dependent Irish farming as has been achieved since recommended lists were first introduced in Ireland.