3.4 Grain yield and yield components in heat-vulnerable regions of central Myanmar
Grain yield and yield components were evaluated in heat-vulnerable regions of central Myanmar for seven crop seasons across four years (Table 5). Average daily maximum temperatures during heading ranged from 35.0 oC to 38.3 oC (Table 5). Grain yield per plant was significantly higher in IR64+qEMF3 than IR64, resulting in yield advantage of IR64+qEMF3 by 22.4% over IR64 on an average. PN was similar between genotypes, while SN and 1000GW was significantly lower in IR64+qEMF3 than in IR64. Such a trend in PN, SN, and 1000GW characters was similar in other locations as well, as shown in Table 4. Significant interaction between the genotype and environment was observed in PFG; difference in PFG between genotypes in each season ranged from 0.8% to 17.4%, and PFG was 9.3% higher in IR64+qEMF3 than in IR64 on an average (Table 5). Multiple regression analysis revealed a significant positive effect of PFG on yield advantage of IR64+qEMF3 , while other parameters such as PN, SN and 1000GW did not have a significant effect (Figure 1). The relationship between PFG and average daily maximum temperatures during heading is plotted in Figure 2. Difference in PFG between genotypes was small when average daily maximum temperatures during heading was below 36.5 oC. PFG steadily decreased in IR64 when average daily maximum temperatures during heading was greater than 36.5oC, and it sharply dropped to 65.6% at 37.9oC (Figure 2). On the contrary, PFG was stable at the high level of around 90% until 37 oC and gradually decreased to 83.0% at 38.3 oC in IR64+qEMF3(Figure 2).
Spikelet sterility was examined in different time periods of flower opening (Figure 3). During flowering pattern observation (recorded with different colored pens), air temperature steadily increased from 25.8oC at 0700H to 30.0 oC at 0930H, and up to 34.0 oC at noon (Figure 3a). Under such air temperature condition, flower opening in IR64+qEMF3 started after 0730H, peaked at 0900H, and almost ended by 0930H (Figure 3a). On the other hand, flower opening in IR64 started after 0830H, peaked at 0930H, and ended by 1030H (Figure 3a). Spikelet sterility in each time period was 3.2% and 8.6% for spikelets that flowered during 0700-0830H (green-lined bar) and during 0830-1000H (purple-lined bar), respectively, in IR64+qEMF3 (Figure 3b). On the other hand, spikelet sterility was 10.2% and 47.2% for spikelets flowered during 0830-1000H (purple bar) and after 1000H (black bar), respectively, in IR64 (Figure 3b). As a consequence, spikelet sterility was 17.0% and 8.9% in IR64 and IR64+qEMF3 , respectively, on that single day (Figure 3b).
DISCUSSION