The value of early root development traits in breeding programs for biomass yield in perennial ryegrass (Lolium perenne L.)

Abstract

Early root traits, particularly total root length, are heritable and show positive genetic correlations with biomass yield in perennial ryegrass; incorporating them into breeding programs can enhance genetic gain. Perennial ryegrass (Lolium perenne L.) is an important forage grass widely used in pastures and lawns, valued for its high nutritive value and environmental benefits. Despite its importance, genetic improvements in biomass yield have been slow, mainly due to its outbreeding nature and the challenges of improving multiple traits simultaneously. This study aims to assess the potential advantages of including early root traits in the perennial ryegrass breeding process. Root traits, including total root length (TRL) and root angle (RA) were phenotyped in a greenhouse using rhizoboxes, and genetic correlations with field yield were estimated across three European locations over two years. Bivariate models estimated significant genetic correlations of 0.40 (SE = 0.14) between TRL and field yield, and a weak but positive correlation to RA of 0.15 (SE = 0.14). Heritability estimates were 0.36 for TRL, 0.39 for RA, and 0.31 for field yield across locations. Incorporating root trait data into selection criteria can improve the efficiency of breeding programs, potentially increasing genetic gain by approximately 10%. This results highlight the potential of early root traits to refine selection criteria in perennial ryegrass breeding programs, contributing to higher yield and efficiency.

Fig. 1

Yield recordings (n = 9190) for each location (Denmark, UK, and Ireland) and cut across two growing seasons of the experiment

Fig. 2

Scatter plot showing the genetic association between predicted breeding values for total root length (TRL) measured in greenhouse rhizobox experiments and field yield across all locations and years. Each point represents one of the 239 families evaluated. The x-axis displays the breeding values for TRL (kilopixels), and the y-axis shows the breeding values for log-transformed field yield (kg per cut). The solid line represents the linear regression fit, indicating a positive association between TRL and yield. The genetic correlation between TRL and field yield was estimated to be 0.40 (standard error = 0.14)

Fig. 3

Scatter plots showing the genetic associations between predicted breeding values for TRL measured in greenhouse rhizobox experiments and field yield at each of the three locations: a Denmark, b United Kingdom, and (c) Ireland. Each point represents one of the 239 families evaluated. The x-axis displays breeding values for TRL (kilopixels), and the y-axis shows breeding values for log-transformed field yield (kg per cut). Solid lines represent linear regression fits for each location. The genetic correlations between TRL and field yield were estimated to be a 0.45 (standard error = 0.15) for Denmark, (b) 0.26 (SE = 0.15) for the UK, and c 0.22 (SE = 0.17) for Ireland

Fig. 4

The expected genetic gain in two breeding scenarios: one without pre-selection from rhizoboxes (field only, empty black circles) and another incorporating pre-selecting data from three rhizoboxes per family (solid black points). The genetic gain is presented relative to the baseline genetic gain obtained from a field experiment with four replicates and no rhizobox information