Cultivar Adaptation across Italian Locations in Four Turfgrass Species

Abstract

Crossover genotype × location (GL) interaction may be exploited by site‐specific breeding and cultivar recommendations for distinct subregions. Turf quality and density of 110 elite cultivars belonging to four species [perennial ryegrass (Lolium perenne L.), Kentucky bluegrass (Poa pratensis L.), tall fescue (Festuca arundinacea Schreb.), and red fescue (Festuca rubra L. subsp. rubra, litoralis, and commutata)] were assessed at five locations scattered across the Italian peninsula and its main islands. The 110 cultivars were evaluated for (i) assessing the extent of GL interaction and its implications on cultivar selection and recommendation; (ii) comparing additive main effects and multiplicative interaction (AMMI) vs. joint regression modeling of GL effects; (iii) verifying the consistency between species of site similarity for GL effects; and (iv) defining test locations for the Italian national evaluation program and for local breeding programs. The trials were arranged in a Group Block Design with three replicates, grouping cultivars within species. Genotype × location interaction occurred for all traits (P < 0.05) except turf density in tall fescue and Kentucky bluegrass. The selected, one‐dimensional AMMI model always outperformed the joint regression model for predictive accuracy as estimated by the mean square value of the relevant GL interaction parameter. Wide crossover GL interaction was observed for turf quality among top‐ranking cultivars of red fescue and Kentucky bluegrass, justifying site‐specific recommendations. Variation of top‐ranking cultivars across sites also occurred for turf density in red fescue and perennial ryegrass. Site similarity for GL effects was largely inconsistent across species. However, specific adaptation either to cooler, wetter sites or warmer, drier sites emerged for cultivars of red fescue, perennial ryegrass, and tall fescue. Site‐specific breeding may be valuable especially for red fescue, exploiting the trend toward specific adaptation of its subspecies.