Adaptability and Phenotypic Stability of Early-Maturing Cowpea (Vigna unguiculata (L.) Walp.) Lines in the Peruvian Amazon

This study evaluated the suitability of three floodplain environments near Iquitos for cowpea cultivar recommendations and estimated the adaptability and phenotypic stability of 12 cowpea lines evaluated in 2004. Climatic conditions between 2004 and 2020–2024 were also compared. Three field trials used a randomized complete block design with 12 lines and two replications, assessing grain yield, number of pods per plant, days to flowering, days to 50% maturity, and days to harvest. Combined Analysis of Variance (ANOVA), Duncan’s means test, Genotype + Genotype Environment Interaction (GGE) biplot, and Additive Main Effects and Multiplicative Interactions Interaction (AMMI) analyses revealed that the three sites are contrasting. The Annicchiarico index, GGE biplot, and AMMI analyses identified line CAR 3010 as having superior adaptability and stability. Paired t-tests and Mann–Kendall analyses showed that climatic conditions in 2020–2024 differed significantly from 2004. Therefore, Muyuy, Rafael Belaunde, and San Miguel are suitable locations for testing advanced cowpea lines prior to cultivar recommendation. Line CAR 3010 is recommended for breeding programs in the Peruvian Amazon in response to ongoing climate change. This research addresses a critical knowledge gap as the first study evaluating cowpea adaptability and stability across multiple floodplain locations in the Peruvian Amazon.