Elevated Temperature Affects Grain Set and Reproductive Growth of Tropical Maize Hybrids.

Global change is predicted to cause variability in temperature, including increased temperatures in many regions where maize (Zea mays L.) is widely grown. These increased temperatures are predicted to result in decreased yields of many current maize genotypes. However, the effects of increased temperature on maize grown to maturity are not well understood, due in part to difficulties growing maize under controlled conditions. Additionally, the potential variability of maize genotypes to mitigate negative effects of high temperature are not well known. We conducted an experiment in a relatively large climate-controlled greenhouse facility that examined the effects of temperature (29/21, 33/25, 37/29, and 41/33^oC) on leaf number, anthesis-silking interval (ASI), pollen viability, kernel weight and kernel number in four maize hybrids (CML 333xW22, CML 322xW22, CML 103xW22, and B73xMo17).  All silks were pollinated with a single outdoor grown pollen donor. All plants were established at 29/21 and temperature treatments were initiated at the V5/V6 stage. At 29/21, leaf number was similar across all hybrids at approx. 18 leaves per plant. Increasing temperature increased leaf number. For example, leaf number averaged about 21 leaves for all hybrids at 37/29, except CML 322xW22, which averaged over 25 leaves per plant. Increasing temperature also increased days to anthesis and silking. Increased temperature decreased pollen viability similarly among all genotypes, and no viable pollen was produced at 41/33 by any of the hybrids. No hybrids produced any silks at the two higher temperature treatments, except for CML 103xW22, which produced silks at all temperatures. From 29/21 to 33/25, ASI was most affected for CML 322xW22, as ASI increased from about 2 to 18 d.  Kernels were only produced in the 29/21 and 33/25 temperatures with a 30% (CML333xW22) to 85% (B73xMo17) decrease in yield compared to 29/21.  Overall, our results indicated that high temperature stress decreased performance across all hybrids evaluated, but some hybrids did better than others due to differences in ASI, leaf number, and yield.