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