Table 1 Percentage abnormalities in the embryo sac samples of N22 and IR64 at six days after exposure to control (30 °C) and heat stresses (38 °C -HT38; 40 °C -HT40) during gametogenesis and heading stage (at recovery)

Developing embryo sac (spikelets) at six days after exposure to temperature treatments

Number of observed samples

275

311

298

333

329

348

Embryo sac. with normal developing structure (%)

92.36

89.39

90.60

92.19

88.45

82.47

With degenerated megaspore mother cell (%)

0.73

1.93

0.34

1.20

2.74

1.72

With degenerated all four megaspores (%)

5.45

5.47

6.38

5.41

5.17

10.06

Abnormal two-nucleate embryo sac (%)

1.09

2.57

1.68

0.90

1.22

2.87

Abnormal eight-nucleate embryo sac (%)

0.00

0.64

0.34

0.00

2.13

1.44

Shrunken embryo sac (%)

0.36

0.00

0.67

0.30

0.30

1.44

Mature embryo sac (Spikelets) at heading stage

Number of observed samples

113

116

108

107

183

152

Mature embryo sac. with normal structure (%)

95.58

93.37

94.44

96.26

85.25

83.55

Degenerated embryo sac (%)

0.00

0.86

0.93

0.00

0.55

1.32

With degenerated both egg cell and polar nuclei (%)

1.77

1.72

0.93

1.87

6.01

6.58

With degenerated egg cell (%)

1.77

1.72

2.78

1.87

7.10

7.24

With improperly positioned egg cell and/or polar nuclei (%)

0.88

1.72

0.93

0.00

1.09

1.32