Pre-anthesis phosphorus sprays boost reproductive development and seed yield in heat-stressed Phaseolus vulgaris L.

Climate change intensifies heat waves, threatening global food security. Common bean (Phaseolus vulgaris L.) is highly sensitive to heat waves during flowering, which disrupts source-sink relationships, reduces pollen viability, and diminishes seed yield. Phosphorus (P) deficiency further limits carbohydrate transport to reproductive tissues during heat waves. This study evaluated the efficacy of leaf P spraying in mitigating heat wave effects in common bean plants facing P deficiency (PD) and P sufficiency (PS) during flowering, i.e., phenological phases V4 to R6. A complete factorial experiment evaluated two substrate P availability during flowering (PD and PS), two leaf P spraying treatments applied during the pre-anthesis (without P spraying, -P; and with P spraying, +P), and two air temperature regimes during flowering: control (28/18 °C, day/night) and heat wave (38/28 °C, day/night). Preventive leaf P spraying improved photochemical efficiency, reduced oxidative stress, and avoided decreases in photosynthetic pigment content under heat wave. P-sprayed plants exhibited greater starch deposition in pollen grains and higher soluble carbohydrate concentration, showing less cellular damage caused by heat wave. As a result, leaf P spraying also increased seed yield under heat wave by sustaining pollen viability owing to improved supply of soluble carbohydrates to reproductive structures. These findings underscore the critical role of leaf P spraying in alleviating heat wave and impaired P acquisition in common bean during flowering by enhancing reproductive resilience and yield stability. This study highlights the potential of such a strategy of preventive leaf P spraying at critical phenological phases to improve crop performance under heat wave conditions caused by climate change.