Journal of Taiwan Agricultural Research

Author:Chia-Hsun Ho, Chwen-Ming Yang*, Chiao-Ling Hsiao, and Ming-Hsing Lai

Abstract:

    Climatic conditions during heading to harvest stage are important factors affecting quality of rice (Oryza sativa).  The objective of this study was to determine effects of major climatic variables during the key growth stage from heading to harvest on quality of rice by conducting multiple-year feld experiments at the experimental farm of Taiwan Agricultural Research Institute at Wufeng, Taichung, Taiwan, using a widely cultivated variety TNG 71.  The variety TNG 71 was grown for a total of 41 crops from December 2006 to August 2009 with 22 crops produced in the frst half year and 19 crops produced in the second half year.  For each crop season, accumulated values of daily mean air temperature (ADMAT), daily maximum air temperature (ADMAXAT), daily minimum air temperature (ADMINAT), daily sunshine hours (ADSH), and daily irradiance (ADIR) were collected during heading to harvest stage.  These fve climatic variables were used for analysis of quality traits of rice.  Results of correlation matrix analyses showed that correlation coeffcients among climatic variables were generally higher in the crop of frst half year than those in the crop of second half year, suggesting a more stable climatic environment and hence a closer link between variables in the frst half year during the experimental period of 2006–2009.  From pooled data, crude protein of brown rice was correlated with all the fve climatic variables and free fatty acid content was positively correlated with ADMAXAT and ADSH.  In milled rice, crude protein was positively correlated with ADMAT, ADMAXAT and ADSH, while amylose was negatively correlated with ADMINAT.  The whiteness of milled rice was negatively correlated with ADMAT, ADMAXAT, ADSH and ADIR, and the transparency of grain kernel was negatively correlated with all the climatic variables.  The ratio of head rice was negatively correlated with ADMAT, ADMAXAT, ADMINAT and ADSH, while the ratio of non-head rice was positively correlated with ADMAT and ADMINAT.  The grain length was negatively correlated with ADIR, whereas grain thickness was positively correlated with ADIR.  Except crude protein, the correlations of length and length width ratio of grains with climatic variables were generally higher in the crop of frst half year than in the crop of second half year.  Results of multiple linear regression analyses showed that, ADMINAT, ADSH and ADIR were the three major climatic variables accounted for variations of chemical and physical components of rice.  This study indicates that changes in climatic conditions during the period of heading to harvest are important factors affecting chemical components and physical characteristics of rice grains.  Thus, selection of suitable location for cultivation of rice and planting season are some strategies for minimizing negative impacts of climatic factors on rice quality.

Key words:Rice quality, Climatic variable, Key growth stage, Chemical composition, Physical char-acteristics

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