Effects of Planting Date and Genotype on Potato Growth and Yield Determination in a Sub-Tropical Continental Growing Environment

Potato tuber yield-determining seasonal changes, especially in subtropical growing settings, are poorly investigated. This study examined eleven potato genotypes ‘G’ under four planting dates ‘P’ (very early (02 Oct), early (14 Oct), late (26 Oct), and very late (07 Nov)) and their interactive response (P × G) on potato growth and tuber yield in southern Khyber Pakhtunkhwa, Pakistan over two years (2017–2018 and 2018–2019). Early planting improved most yield-determining traits over late planting, extending the growing period (PM_D) and maximizing green canopy cover (C_G, 72.3%), mother stems plant⁻¹ (M_SN, 4.1), leaf number plant⁻¹ (L_N, 50.8), leaf area plant⁻¹ (LA_P, 5343 cm²), cumulative photosynthetic active radiation (PAR_INTC, 900.9 MJ m⁻²) and thermal days (TD_C, 52.9 td), tubers plant⁻¹ (T_N, 11.8), marketable tuber weight (T_WM, 103.0 g), marketable (T_YM, 30.7 t ha⁻¹), and total (T_YT, 32.9 t ha⁻¹) tuber yield. Late plantings reduced PM_D and thus these traits. Considerable genotypic variation was found in plant phenology, growth, and tuber yield traits, however, genotype ranking also varied by planting date, indicating strong P × G interactions. The genotype ‘Arizona’ outperformed others with maximum T_YM (29.2 t ha⁻¹) and T_YT (30.4 t ha⁻¹) across planting dates. We identified key traits including days to emergence (E_D), C_G, PAR_INTC, and TD_C, which are vital indicators of yield potential and important for breeding and selection. Our findings highlight the complexity of yield formation in potatoes and suggest tailored genotype selection and planting strategies to enhance yield stability and resilience, which are crucial for adapting to climate change and meeting food demand.