|Using GGE Bi-Plot to Evaluate Paddy Genotypic Variation in Cd Concentrations of Brown Rice and Interaction with Environmental Effects
|鎘;水稻;GGE雙軸圖;品種與環境交感;栽培種;cadmium;paddy rice;GGE bi-plot;Interaction between genotype and environment;cultivar
水稻為亞洲國家的主食，水田土壤受鎘污染導致水稻穀粒的鎘累積，使鎘米事件的議題備受關注，水稻穀粒累積鎘的差異性不僅與環境與品種有關，也受品種與環境交感效應所影響。本研究應用GGE雙軸圖解析影響穀粒鎘累積之品種效應 (G) 以及品種與環境的交感效應 (G × E)，以主成份 (principle components) 得分繪圖說明品種間差異受環境影響的程度；本研究分別於台中市后里區 (Houli; HL) 及彰化縣彰化市 (Changhua; CH) 兩處土壤鎘污染之試驗田區，栽種國內常見的21 種水稻栽培種，經試驗調查取得土壤與水稻穀粒樣本，分析測定獲得不同品種水稻根圈土壤及糙米鎘濃度之資料，供GGE雙軸圖分析以篩選出環境穩定的低鎘累積品種。研究結果顯示，秈型稻的鎘累積能力於兩處試驗區皆呈現高於稉型稻的趨勢；因兩處試驗區HL與CH 的環境差異對不同品種的影響程度不同，兩處試驗區糙米鎘濃度較低之品種並不一致。再者，經GGE分析可將品種及品種與環境交感效應的主導變異轉換至2項獨立主成份 (即是PC1 與PC2) 可達84%，經繪製雙軸圖有效呈現出不同品種水稻糙米鎘濃度對應兩處試驗區環境效應的差異性，其結果顯示「高雄139 號」(‘KH139’)、「台稉糯3 號」(‘TKW3’)、「台農糯73 號」(‘TNGW73’) 及「台東33 號」(‘TT33’) 相較其他品種，兼具環境穩定且低鎘累積之特性。因此，試驗區土壤鎘濃度是決定不同水稻品種吸收鎘與糙米鎘累積濃度的主要因子，而不同期作的氣候條件與管理因素則是次要因子；從品種間的比較可確認秈稻鎘累積量遠高於稉稻，而稉稻品種間之鎘累積差異並不顯著，故相對穩定低吸收品種也皆為稉稻。期望能藉由本研究之方法篩選出穩定低鎘累積之國產水稻品種，後續再輔以適當田間農藝管理方法，將可有效降低稻米鎘累積濃度超標(0.4 mg kg-1) 之風險。
Paddy rice (Oryza sativa L.) is the staple food of Asian countries. However, paddy rice cadmium (Cd) pollution continuingly happened due to the increase in soil Cd concentration and the issue has attracted more attention. As well known, the accumulation of Cd in rice grains is affected by paddy variety, environmental effects, and the interaction effects between variety and environment. In this study, the GGE bi-plot was used to analyze the main effect of genotype (G) and the interaction effect between genotype and environment (G × E) on Cd accumulation in rice grains. According to the scores of principle components obtained from GGE analysis for different rice varieties, the bi-plots thus were drawn to illustrate the levels of environmental effect on rice genotypes. There were two Cd-contaminated sites in Houli District (HL), Taichung City, and Changhua City (CH), respectively, for a multiple-environment trail to plant 21 rice cultivars in 2 crop seasons. The Cd concentrations in rhizosphere soil samples and brown rice for the rice varieties were measured, and then the observed data were used to screen out the environmentally stably low Cd-accumulation varieties. The results show that most indica varieties had higher cadmium accumulations than japonica rice did. The profiles of brown rice Cd concentrations for the paddy varieties in sites HL and CH are different. The lower Cd-accumulation varieties in HL were not completely consistent with those in CH. This revealed that the interaction between genotype and environment would be a dominant figure in brown rice Cd concentrations. In addition, according to the GGE analysis, the effect G and the interaction effect G × E on Cd accumulation in rice grains have been transported into the 2 principal components (i.e., PC1 and PC2), which were mutually independent and dominated the variation of G and G × E approaching to 84%. The bi-plot gave PC1 and PC2 as the coordinate axes were used to quantify the variation due to environmental effects in brown rice Cd concentration for each paddy variety. The brown rice Cd concentrations of the varieties, ‘KH139’, ‘TKW3’, ‘TNGW73’, and ‘TT33’, were relatively low and less varied with different sites and cropping seasons. That is, they would be the more environmentally stably low Cd-accumulation varieties. Therefore, Cd concentration and availability in the soil will dominate the Cd absorption by different paddy rice varieties and accumulation in brown rice; the weather condition and management practices in different cropping periods may be a secondary factor. In a comparison of indica and japonica types for accumulation of Cd in brown rice, the indica was superior to the japonica. The relatively stable Cd low-absorption varieties all were japonica rice. One can try to reduce the risk of brown rice Cd being higher than the threshold (i.e., 0.4 mg kg-1) by selecting environmentally stably low Cd-accumulation varieties and adopting the agronomic practices to go into a decline of soil Cd availability.
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