Physiological and morphological drivers of early-spring vigor in warm-climate crops under suboptimal temperatures

Shifting the sowing date of summer crops such as melon (Cucumis melo L.) to early spring presents both agronomic opportunities and challenges. Under suboptimal temperatures, slowed physiological development allows weeds to gain a competitive advantage. Enhancing early seedling vigor under cool conditions is therefore essential for successful crop establishment and effective weed suppression. In this study, ten melon accessions representing a broader collection (~ 180) were evaluated for early vigor and performance under suboptimal temperatures. Pulling resistance, root system scanning, and physiological measurements were used to identify key traits associated with early root establishment. Accessions were compared under optimal (25 °C) and suboptimal (16 °C) temperature regimes. Pulling strength showed a strong correlation with root biomass and volume across accessions. The AY accession exhibited clear tolerance to low temperatures, maintaining high physiological activity, whereas PI414723 displayed reduced carbon assimilation due to diffusional limitations. These findings demonstrate that tolerance to suboptimal temperatures exists even within warm-climate crops such as melon and highlight the potential of AY as a valuable genetic resource for developing early-season, stress-tolerant melon varieties.