The contribution of perennial ryegrass (Lolium perenne L.) breeding to whole pasture productivity under dairy cattle grazing in New Zealand. 1. Variation in yield, nutritive value and persistence‐related traits

Abstract

Perennial ryegrass (PRG, Lolium perenne L.) breeding effort in New Zealand (NZ) has increased since c. 1990, resulting in greater functional trait diversity (e.g. heading date, ploidy, and associated Epichloë endophyte strain) in commercial products. This study quantified the variation, associations and interactions in dry matter (DM) yield, nutritive value and persistence‐related traits among commercial cultivar‐endophyte combinations released between 1973 and 2012, as a basis for assessing gains in value being delivered to the pasture‐based livestock industries. Twenty‐four or 28 combinations were compared over 3 years in two trials in each of two regions: Waikato in northern NZ (dryland), and Canterbury in central eastern South Island (irrigated). Cultivar‐endophyte combinations were sown in mixtures with white clover, and pastures were intensively grazed 8–11 times per year by dairy cows. Principal Component Analysis identified 4 distinct clusters for the DM yield variables and for metabolisable energy (ME) content in each of the four trials. A broadly‐adapted group of three late‐season flowering, AR37‐infected diploids with NZ and Spanish breeding backgrounds dominated the highest‐yielding clusters. Tetraploids dominated the high ME content clusters. Interactions with region were observed throughout the data set: the strongest of these was driven by endophyte strain effects in Waikato. High‐yielding cultivar‐endophyte combinations in these trials were also generally high‐yielding in the standard cultivar merit testing system operated in New Zealand, as interpreted via the DairyNZ Forage Value Index. However, alignment was poorer for medium‐ and lower‐yielding cultivar‐endophyte combinations. Several implications for forage evaluation methods and end‐user industries are identified.

The contribution of perennial ryegrass (Lolium perenne L.) breeding to whole pasture productivity under dairy cattle grazing in New Zealand. 2. Rates of gain in production traits and economic value

“…Briefly, two trials were conducted in each of two regions: Waikato in warm‐temperate northern New Zealand (non‐irrigated) and Canterbury in cool temperate southern New Zealand (irrigated). Trial 1 was established in autumn 2013 and ended in early winter 2016; Trial 2 was established in autumn 2016 and the measurements reported in Chapman et al (n.d.) ceased in early winter 2019. In each region by trial combination, replicated ( n = 4) plots of 24 (Trial 1) or 28 (Trial 2) cultivar‐endophyte combinations were established in a row‐column design and grazed by dairy cows between 8 and 12 times per year, to a residual sward height of ~45 mm above ground level.…”

“…A full description of the field trial designs, management and measurement programmes is presented in the first paper in this series (Chapman et al, n.d.).…”

“…Ryegrasses included in the trials represented the range of material traded commercially in New Zealand over four decades, starting with ‘Grasslands Nui’ released in 1973 (Armstrong, 1977). Ryegrasses released in the 1980s and 1990s were dominantly mid‐season heading diploids (see Table 1 in Chapman et al, n.d.). Late‐season diploids started emerging from breeding programmes in the mid‐1990s, and became the dominant product in the diploid category thereafter.…”

“…Simple linear regression (Proc GLM) was used to quantify genetic gain. Separate analyses were performed for each trial, region, and season, and the model included the year in which an application was submitted for Plant Variety Rights (PVR) in New Zealand for each ryegrass cultivar (Table 1, Chapman et al, n.d.) as fixed effect. Four of the entries included in the study had not been submitted for PVR: in these cases, the year of commercial release (obtained via personal communication with the breeding company owner) was used instead.…”

“…The objectives of the analysis reported here were to quantify rates of genetic gain in perennial ryegrass, and identify where gains are coming from, in mixed ryegrass‐clover pastures managed under industry standard grazing practices and typical N fertilizer inputs in different environments. The analysis was based on the data set described in the first paper of this series (Chapman et al, n.d.). It considered trends from 1973 to 2012 in physical production traits and the estimated economic value of trends in those traits.…”