Heat Stress Response in the Male Gametophyte of Early Maturing Varieties of Soybean ( <scp> <i>Glycine max</i> </scp> )

ABSTRACT The cultivation of soybean ( Glycine max (L.) Merr.) is becoming more widespread for its desirable high protein content and versatile use as a feed crop and key ingredient for transformed food products. However, high temperatures attributed to climate change continue to present challenges for crop productivity and yield, thus impacting global food security. Seed set in soybean requires fertilisation, and the performance of the male gametophyte (pollen) is thus a fundamental element determining yield. Pollen is highly susceptible to heat stress and in particular the progamic phase—the growth of the pollen tube through the female flower tissues—is highly sensitive even to short and moderate temperature shocks. To determine the impact of high temperature stress on soybean reproduction in early maturing varieties, pollen from three different soybean lines in MG00 was exposed to high temperature treatments. Mean cardinal temperatures ( T min , T opt , T max ) were established to be 10.3°C, 30.2°C, and 50.1°C, respectively, for coupled pollen tube length and 12.0°C, 33.7°C and 55.4°C, respectively, for uncoupled pollen tube length. T opt and T max for pollen germination were at 21.6°C and 54.6°C, respectively. This suggests that high temperature stress affects all stages of the progamic phase in early maturing soybean varieties with pollen germination being more susceptible than pollen tube growth. A decrease in both pollen germination rate and pollen tube length was observed in vitro at temperatures above optimum ( T opt ). Pointing at cellular processes particularly affected by temperature stress were observations of aberrant callose accumulation at the growing tip of heat‐stressed pollen tubes while cellulose distribution was unaltered.