Genetic variation in perennial ryegrass for root profile characteristics

Fifteen plants, replicated twice, of each of 20 half-sib families of perennial ryegrass were grown in deep sand tubes irrigated with a low ionic strength nutrient solution in a glasshouse. Top growth was measured. Roots were turned out, cut into 10 cm profile increments, washed free of sand, dried and weighed. For top growth, total root growth and root-shoot ratio, there were significant differences among families translating to narrow sense heritability coefficients between 0.3 and 0.4. However, the ratio between root in the top 10 cm and total root, and a parameter for a well-fitting exponential model describing root profile showed variation between individuals but very little or no variation between families. This translated to narrow sense heritability coefficients of less than 0.1.