Flowering dynamics, pollen, and pistil contribution to grain yield in response to high temperature during maize flowering

Abstract High temperature (HT) stress during flowering severely threatens crop grain yield, however, little is known about the underlying mechanisms in maize. A HT sensitive maize hybrid was subjected to 32/22 ℃ (maximum/minimum temperature, control), 36/26 ℃, and 40/30 ℃ for 14 consecutive days bracketing flowering (trial 1) and for seven days prior to flowering (trial 2). Maize grain yield did not decrease in the 36/26 ℃ treatment during trial 1 compared to the control treatment, but reduced by 73.6% in the 40/30 ℃ treatment as a result of reduced kernel number rather than kernel weight. High temperature stress advanced tasseling and pollen shedding, extended the anthesis-silking interval, and reduced the number and viability of pollen shed, but had no effects on silking. The shortened duration of pollen shedding was a result of the accelerated flowering speed of the tassel inflorescence. Leaf assimilate can be transferred to the tassel, but cannot be converted into starch in the HT stressed pollen. The damaged pollen morphology and the interrupted sugar to starch physiological process explained the reduced pollen viability. Starch granule number and size in the pollen decreased with the increased temperature. Thus, male organ growth is more sensitive to HT than female organs. Understanding the underlying mechanisms has implications for selecting or breeding HT tolerant maize.