In Florida, lettuce is cultivated in the southern region in wintertime, a period marked by environmental fluctuations. The dominant Histosols in this area are prone to subsidence and exhibit an increased pH due to the incorporation of calcium carbonate, leading to a reduction in phosphorus (P) availability. In the northern part of Florida, lettuce has the potential to be cultivated in sandy soil to supply the high demand of lettuce, however this type of soils naturally exhibits low P availability. To sustainably produce lettuce in these soils, P efficient cultivars should be bred. Prior, lettuce genotypes were identified as P-efficient and P-inefficient across types. The objective of this study was to determine the influence of Genotype × Environment (G×E) interaction on lettuce cultivated under low P inputs. A multi-environment trial was conducted using 22 P-efficient or P-inefficient genotypes in eight experiments distributed across the lettuce season (Fall, Winter, and Spring) at two locations and distributed in a randomized complete block design with four replicates. Five experiments were conducted in histosol soils, and three in sandy soils. Each experiment was cultivated under a standard and a reduced P fertilizer rate . Data collected included head weight, and marketability. The analysis of the G×E for these traits under low P conditions utilized three methodologies: the Finlay-Wilkinson approach, that determines the stability of each genotype across environments independently; the Genotype Genotype × Environment biplots, that discerns the 'which-won-where' patterns for mega-environments and identifies the most stable genotype(s) across environments; and the Bayesian AMMI, that aims to understand genotype stability across environmental factors. The results demonstrated that both crossover and non-crossover G×E interactions are statistically significant, accounting for 16% of the variance for season and for soil types in head weight. These interactions explained 27% of the variance for marketability for P fertilizer treatments, accounting 15% and 9% for season and soil types, respectively. The romaine breeding line 60183 and cultivar Tall Guzmaine were identified as P-efficient, exhibiting non-crossover interaction and stability across P rates, seasons, and soil types. Iceberg cultivars Honcho II, and Cibola, and the loose-leaf RSX743 were P-efficient and exhibited crossover interactions. The analysis revealed that winter planting in both soil types is the most stable and productive environment, with histosol soils achieving higher yields under low P input. Results of this study highlight the importance of G×E interactions to be considered when breeding lettuce cultivars for low P inputs.
