Abstract:
The distribution and performance of mango (Mangifera indica L.) varieties across Kenya’s rainfall and temperature gradients remain largely undocumented. This study examined varietal plasticity to soil water stress and modeled mango suitability under climate change to inform future adaptation strategies. The objectives were: (1) to determine distribution patterns and factors influencing adoption of Improved Mango Varieties (IMVs) in lower eastern Kenya; (2) to assess morphological and physiological variability of mango under induced water stress; and (3) to model future bioclimatic suitability under climate scenarios SSP1.9–2.6, SSP2–4.5 and SSP3–7.0. Field surveys were conducted on 268 farms across five Agroecological Zones (AEZs)—IL, LM, UM, LH, UH—using systematic random sampling. Greenhouse trials involved eight grafted mango varieties subjected to water stress treatments (90%, 65%, 35% of field capacity) in a split-plot design. Data on shoot height (SH), shoot diameter (SD), leaf water potential (LWP), chlorophyll content (LCHL), leaf temperature (LTEMP), and leaf area index (LAI) were collected and analyzed using ANOVA and correlation methods. Climate suitability modeling used downscaled data (1984–2023) from HadCM3, WorldClim, and NASA Power, run through MaxEnt and visualized in ArcGIS. Twenty-eight mango varieties were identified, grouped into Floridan (F), Kenyan Large (KL), and Kenyan Small (KS) types. Floridan and KL types are IMVs, which constituted 88.4% of inventoried trees. Most IMVs (99%) occurred in LM and UM AEZs, aligning with optimal temperature (20–26°C) and rainfall (500–1000 mm yr⁻¹). Key factors influencing IMV adoption (p < 0.001) included market access, reliable planting material, use as a cash crop, and farmers’ perception of changing climate. Under severe water stress (35% FC), significant declines in SH and SD and increases in LTEMP were observed, with Kent and Sabine showing best drought resilience. LTEMP and LWP were strongly negatively correlated (r = -0.94). These findings suggest varietal suitability differences that can inform climate-smart mango selection. Model projections indicate a marked shift in mango suitability from the semi-arid IL and LM zones toward sub-humid UM areas by 2050–2080. Under SSP3–7.0, up to 60% of current areas may become marginal or unsuitable, with only one-third retaining optimal conditions. This will negatively affect mango productivity, particularly in Kitui and Makueni. Recommended adaptation measures include promoting drought-tolerant varieties (Kent, Sabine, Van Dyke), soil moisture conservation, and improved market access. Without such measures, farmers may need to abandon mango for other crops.
