Adaptation strategy, germplasm type and adaptive traits for field pea improvement in Italy based on variety responses across climatically contrasting environments

A pea breeding strategy is required to cope with the large climatic variation featuring south-European environments. Thirty-seven recent cultivars bred by 21 European or Australian institutions were grown in two climatically contrasting Italian sites (Lodi, subcontinental; Foggia, Mediterranean), two cropping years per site and two sowing times per year, to define various elements of this strategy. The study assessed: (i) the impact of genotypexenvironment (GE) interaction due to spatial and temporal factors on the consistency of top-yielding cultivars; (ii) the similarity between environments for GE effects and its implications on adaptation strategies; (iii) the extent of genotypic and GE interaction effects, and the relationship with adaptive responses, for various morphophysiological traits; (iv) the adaptation pattern and the combination of adaptive traits featuring three germplasm types, i.e. European spring and winter types, and germplasm selected in Mediterranean environments; (v) the predicted efficiency of direct and indirect selection procedures for grain yield. The geoclimatic area had a major impact on crop yield (5.15t/ha in Lodi vs. 2.52t/ha in Foggia) but tended to affect GE interaction less than time or year of autumn sowing, suggesting to breed for wide adaptation. Top-yielding cultivars as modeled by additive main effects and multiplicative interaction were environment-specific. On average, spring and winter materials outyielded the Mediterranean germplasm but the spring type, characterized by wide entry variation, included most widely- and specifically-adapted top-yielding cultivars. Cold-tolerant spring-type germplasm is preferable to breed for wide adaptation as it may combine high yield potential with adaptation to winter cold and terminal drought and heat stress. Lodging susceptibility, harvest index, onset and duration of flowering, and canopy height at maturity assessed in individual environments showed moderate to fairly high broad-sense heritability on a plot basis (h ² >0.20) and tended to correlation with yield over test environments (r >=0.20). An indirect selection index including harvest index and canopy height exhibited about 20% greater predicted efficiency than direct selection for yield when using one selection environment and could be preferred for early selection stages. Direct yield selection in late selection stages should ideally be performed across 2 years in two environments that contrast for geoclimatic area and time of autumn sowing.