Assessment of the Genetic Distinctiveness and Uniformity of Pre-Basic Seed Stocks of Italian Ryegrass Varieties

Lolium multiflorum Lam., commonly known as Italian ryegrass, is a forage grass mostly valued for its high palatability and digestibility, along with its high productivity. However, Italian ryegrass has an outbreeding nature and therefore has high genetic heterogeneity within each variety. Consequently, the exclusive use of morphological descriptors in the existing varietal identification and registration process based on the Distinctness, Uniformity, and Stability (DUS) test results in an inadequately precise assessment. The primary objective of this work was to effectively test whether the uniformity observed at the phenological level within each population of Italian ryegrass was confirmed at the genetic level through an SSR marker analysis. In this research, using 12 polymorphic SSR loci, we analyzed 672 samples belonging to 14 different Italian ryegrass commercial varieties to determine the pairwise genetic similarity (GS), verified the distribution of genetic diversity within and among varieties, and investigated the population structure. Although the fourteen commercial varieties did not show elevated genetic differentiation, with only 13% of the total variation attributable to among-cultivar genetic variation, when analyzed as a core, each variety constitutes a genetic cluster on its own, resulting in distinct characteristics from the others, except for two varieties. In this way, by combining a genetic tool with the traditional morphological approach, we were able to limit biases linked to the environmental effect of field trials, assessing the real source of diversity among varieties and concretely answering the key requisites of the Plant Variety Protection (PVP) system.