Changes in the Panicle-Related Traits of Different Rice Cultivars under High Temperature Condition Young-Jun Mo 1 *, Ki-Young Kim 1, Hyun-su Park, Jong-Cheol Ko 1, Woon-Chul Shin 1, Jeong-Kwon Nam 1, Bo-Kyeong Kim 1, Jae-Kwon Ko 1 1 Department of Rice and Winter Cereal Crop, National Institute of Crop Science, Rural Development Administration, Iksan , Korea Temperature rise by global warming causes deterioration in rice yield and grain quality. This study was conducted to investigate the changes in rice panicle-related traits under the high temperature condition. Objective z Values with a different letter are significantly different at P < A total of 40 Korean rice cultivars including 27 japonica and 13 Tongil-type (japonica-indica cross) were cultivated in two plots in the field. Eight weeks after transplanting, a greenhouse was set over one plot for high temperature treatment. Plants were harvested upon maturity and 13 panicle-related traits were investigated. Materials and Methods Group (n) Date Accumulated temp. during the treatment (°C) (average temp.) Seeding (transplanting) Treat ment Harvest Ambient (a) Treatment (b) b - a Ⅰ (5) Apr 30 (May 29) Jul 24 Sep (24.4) (25.5) 59.4 (1.1) Ⅱ (9)Sep (23.1) (24.4) 88.1 (1.3) Ⅲ (12)Oct (22.6) (24.0) (1.4) Ⅳ (14)Oct (21.9) (23.4) (1.5) Table 1. Accumulated and average temperatures in the field and the greenhouse conditions during the high temperature treatment. VariablesTraits x1Number of spikelets per panicle x2Number of rachis-branches per panicle x3Number of primariy rachis-branches (PRBs) per panicle x4Number of spikelets on PRBs per panicle x5Mean number of spikelets on a PRB x6Number of secondary rachis-branches (SRBs) per panicle x7Number of spikelets on SRBs per panicle x8Mean number of spikelets on a SRB x9Ratio of SRBs to PRBs x10Percent ripened grain of PRBs x11Percent ripened grain of SRBs x12Percent ripened grain per panicle x13Head rice percentage Table 2. Panicle-related traits investigated in this study. Results Ecotype (n) x1x2x3x4x5x6x7 japonica (27) 145.4a z (102~183) 37.8a (26~50) 11.3a (9~14) 65a (53~77) 5.8a (5.5~6.0) 26.6a (17~36) 80.4a (49~111) Tongil (13) 188.8b (149~217) 48.4b (36~59) 11.5a (10~15) 62.1b (49~78) 5.4b (4.7~5.9) 36.9b (25.3~48) 126.7b (87~158) Total (40) (102~217) 41.3 (26~59) 11.3 (9~15) 64.1 (49~78) 5.7 (4.7~6.0) 29.9 (17~48) 95.5 (49~158) Ecotypex8x9x10x11x12x13 japonica 3.0a (2.7~3.3) 2.3a (1.6~3.0) 96.5a (93.8~98.8) 94.0a (87.9~97.4) 95.1a (90.6~97.9) 90.5a (67.3~96.5) Tongil 3.4b (3.0~3.8) 3.2b (2.3~4.2) 91.7b (86.4~96.1) 90.6b (84.6~96.1) 90.9b (86.2~95.9) 77.9b (62.1~90.9) Total 3.2 (2.7~3.8) 2.6 (1.6~4.2) 95.0 (86.4~98.8) 92.9 (84.6~97.4) 93.8 (86.2~97.9) 86.4 (62.1~96.5) Table 3. Average and range of the panicle-related traits of 40 rice varieties in ambient condition. Trait Eigenvector Prin1*Prin2 x x x x x x x x x x x x x Eigenvalue Contributaion (%) Cumulative contribution (%) Fig. 1. Cluster analysis of 40 rice varieties based on the panicle- related traits in ambient condition. Fig. 2. Principal component analysis of the 13 panicle-related traits from 40 rice varieties in ambient condition. Three groups show clusters designated in Fig. 1. Prin1 and Prin2 indicate the first and second principal components, respectively. x2x3x4x5x6x7x8x9x10x11x12x13 x1 0.97**0.61**0.42**-0.36**0.96**0.97**0.58**0.80**-0.30** -0.38**-0.21 x2 0.59**0.37**-0.46**0.99**0.95**0.42**0.85**-0.27**-0.32**-0.38**-0.20 x3 0.90**-0.13*0.47**0.42** x4 0.31**0.25**0.20** * * x ** -0.25**-0.51**0.21**0.17**0.26**0.34** x6 0.97**0.44**0.91**-0.29**-0.34**-0.41**-0.23* x7 0.64**0.90**-0.34** -0.44**-0.30** x8 0.46**-0.33**-0.19**-0.32**-0.36** x **-0.40**-0.48**-0.29** x **0.74**0.20 x **0.15 x Table 4. Correlation coefficients among the panicle-related traits in ambient condition. * and ** indicate significance at P < 0.05 and P < 0.01, respectively.. Ecotype (n) x1x2x3x4x5x6x7 japonica (27) 151.3a z (111~222) 39.4a (27~57) 11.3a (9~14) 65.5a (50~83) 5.8a (5.5~6.1) 28.1a (17~44) 85.8a (51.8~145.5) Tongil (13) 207.4b (154~258) 52.6b (37~67) 11.9b (10~16) 65.4a (46~88) 5.5b (4.5~6.1) 40.7b (27~55) 142.0b (92~195.7) Total (40) (111~258) 43.7 (27~67) 11.5 (9~16) 65.5 (46~88) 5.7 (4.5~6.1) 32.2 (17~55) (51.8~195.7) Ecotypex8x9x10x11x12x13 japonica 3.0a (2.7~3.3) 2.5a (1.8~3.4) 94.7a (88.4~98.3) 90.6a (82.8~99) 92.4a (85.8~98.6) 76.8a (62.2~87.1) Tongil 3.5b (3~3.7) 3.5b (2.2~4.6) 85.2b (71.4~93.5) 80.0b (69.7~90.9) 81.6b (72.5~91.9) 71.9b (50.2~86.4) Total 3.2 (2.7~3.7) 2.8 (1.8~4.6) 91.6 (71.4~98.3) 87.2 (69.7~99) 88.9 (72.5~98.6) 75.2 (50.2~87.1) Table 5. Average and range of the panicle-related traits of 40 rice varieties in high temperature condition. z Values with a different letter are significantly different at P < Fig. 3. Cluster analysis of 40 rice varieties based on the panicle- related traits in high temperature condition. Trait Eigenvector Prin1Prin2 x x x x x x x x x x x x x Eigenvalue Contributaion (%) Cumulative contribution (%) Fig. 4. Principal component analysis of the 13 panicle-related traits from 40 rice varieties in high temperature condition. Three groups show clusters designated in Fig. 3. Prin1 and Prin2 indicate the first and second principal components, respectively. x2x3x4x5x6x7x8x9x10x11x12x13 x1 0.97**0.57**0.45**-0.28**0.96**0.97**0.69**0.76**-0.29**-0.44** x2 0.54**0.37**-0.42**0.99**0.96**0.55**0.82**-0.28**-0.41**-0.42**-0.18 x3 0.93** **0.37**0.14* x4 0.27**0.24**0.22** ** x **-0.38** **0.16*0.18**0.20**0.30** x6 0.98**0.57**0.89**-0.30**-0.42**-0.44**-0.19 x7 0.72**0.88**-0.33**-0.46**-0.49**-0.17 x8 0.55**-0.35**-0.45**-0.48**-0.10 x **-0.41**-0.46**-0.18 x **0.88**0.13 x **0.14 x Table 6. Correlation coefficients among the panicle-related traits in high temperature condition. Conclusion In both conditions, Tongil-type showed higher sink size-related characters than japonica, while japonica had higher percent ripened grain and percentage of head rice than Tongil-type. The number of SRBs per panicle and the number of spikelets on SRBs per panicle were positively correlated with the numbers of spikelets and rachis-branches per panicle (r > 0.95) while negatively correlated with the percent ripened grain (r < -0.40). On ecotype level, numbers of spikelets and rachis-branches per panicle, the number of SRBs per panicle, and the number of spikelets on SRBs per panicle were significantly increased in Tongil-type under the high temperature condition, while those in japonica did not show any significant change. Decrease in the percent ripened grain was more severe in the spikelets on SRBs than PRBs in both ecotypes and Tongil-type showed significantly higher decrease in the percent ripened grain than japonica. Therefore, it is concluded that the sink size of Tongil-type cultivars were increased under the high temperature more than japonica cultivars by the significant increase in SRBs, which caused more severe reduction in percent ripened grain. * and ** indicate significance at P < 0.05 and P < 0.01, respectively.. * Corresponding author: Tel