4 | DISCUSSION
We found the negative effects of DS, HS and DHS around flowering on maize grain filling. The early stress around flowering reduced kernel weight by shortened grain filling duration, accelerated leaf senescence, and decreased net photosynthesis in field condition. When the source supply was sufficient by vitro cultured in laboratory incubation, the early stress still significantly decreased kernel weight. These results clearly showed that the independent and combined drought and heat stress around flowering stage had significant impact on the subsequent grain filling even with sufficient source supply (Figure 10).