台灣水稻品種不同生育期耐熱性評估與施用水楊酸對緩解高溫逆境下稻米品質劣化影響之研究

Abstract

台灣栽培之水稻品種以日本型稉稻(Japonica rice)為主，是日本型稻栽培最南、緯度最低與溫度最高之區域，未來將受到全球暖化嚴重影響。本研究評估台灣重要水稻品種不同時期耐熱能力，包括秧苗期之生長和成熟期之稔實率與稻米品質，期望篩選出具有良好耐熱特性之品種，以作為未來育種之基礎，同時也探討水楊酸在高溫下緩解稻米品質劣化之應用，期能建立高溫環境下水稻栽培可使用之因應資材。 在秧苗期耐熱性評估部分，以漸進溫度誘導(Temperature-induced response, TIR)後再進行高溫處理或直接高溫處理等多樣高溫處理方式，評估台灣水稻種原耐熱性，進一步對耐性品種及敏感品種之細胞膜穩定性 (cell membrane stability, CMS)、細胞活性(2,3,5-triphenyl-tetrazolium chloride, TTC)、丙二醛 (Malondialdehyde, MDA) 及親緣距離、育種年代等進行分析。在幼苗萌芽初期，品種間對熱逆境反應具有顯著差異，若先經TIR處理後，可顯著提高水稻幼苗於高溫逆境下之存活率及地上部相對生長量，但TIR處理對耐熱性提升會因品種有所差異。將篩選出之耐熱品種在盆栽試驗及CMS、TTC測定結果上確實有較佳之耐熱表現，但幼苗生長率與種子發芽耐熱性兩者間相關性不高。在親源分析圖譜上，耐性基因並非集中在親緣接近之特定品種群，而育種年代與耐熱性間並無相關性。未來幼苗期耐熱育種策略可能需要以不同親緣分群之高耐性品種為親本以聚集堆疊不同之耐熱基因。不同生育期如發芽期、幼苗期、穀粒成熟期之耐熱性相關不高，不同階段之耐熱品種需於其生育階段進行篩選。本研究初步篩選出TK14、HC56、TT30、TNG70、TK8等幼苗期具有良好耐熱性之品種，供未來進一步耐熱育種應用。 在成熟期高溫對稔實率評估方面，分別進行孕穗期至成熟收穫期之長期高溫(35/30℃)處理，與孕穗期進行14天短期高溫(35/30℃)處理。其中長期高溫處理4個不同年期，高溫下稔實率與常溫對照組平均數比較下降15 - 52％，以CNG242 (67.2％)、TK14 (65.0％)、TCS10 (63.8％)等品種表現較佳。短期高溫處理下， 2批次試驗結果各年期品種稔實率平均數分別為75.2%、73.8%，比對照組下降7.7 - 14.67％，以CNG242 (92.5％)、TK2 (89.2％)、TN5 (89.0％)、TK16 (85.2％) 等品種表現較佳。 在稻米品質耐熱性評估上，分別進行了齊穗期後至收穫之長期高溫(35/30℃)處理，與齊穗期後14天之短期高溫(35/30℃)處理。長期高溫處理結果顯示各參試品種白米完整粒比率皆表現甚差，參試的台灣品種在35/30℃下沒有能維持較佳稻米品質之耐熱品種存在。短期高溫處理結果顯示2批次試驗白米完整粒各品種平均數分別為37.8%和26.9%，以TCS10 (84.4％)、Koshihikari (64.4％)、HL20 (59.6％)、TK8 (59.5％)、TK2 (53.0％)、CNG242 (52.2％)表現較佳。 在應用水楊酸緩解高溫逆境下水稻米質劣化可行性研究方面，於台灣大學人工氣候室進行4批次試驗並調查米質相關數據，初步結果顯示，日夜溫30/25℃下對4品種水稻具有提高完整米粒比率效果，但35/30℃下對米質外觀改善並無顯著結果。另於花蓮縣吉安鄉花蓮區農改場走入式生長箱以32/27℃ 處理並施用水楊酸，結果顯示具有提高完整米粒比率、稔實率及千粒重效果。總體而言在一定溫度範圍內水楊酸處理顯示具有米質促進效果之潛力。植株生理表現方面，在32/27℃處理條件下，兩參試品種劍葉細胞相對離子滲漏率在施用水楊酸後均有下降，而高溫下水楊酸處理較高溫對照組穀粒有較低的α-Amylase相對活性及相對總可溶性糖含量，有助於可減緩穀粒白堊質之發生。 綜合言之，本研究結果顯示台灣水稻品種在秧苗期生長、成熟期稔實率與稻米品質等不同時期耐熱能力具有顯著的品種間差異，也已初步篩選出幼苗期及成熟期稔實率或米質表現較佳品種，未來可以利用這些具有高溫耐性品種進一步育種。在水稻田間栽培緩解高溫傷害之因應技術方面，試驗結果顯示施用水楊酸在一定範圍內具有減緩高溫下稻米品質劣化、提高完整米率及減少白堊質發生率之效果，具有未來進一步利用之潛力。

The rice varieties grown in Taiwan are mainly Japonica-type rice varieties, which are grown in the southernmost-, lowest-latitude and hottest Japonica-type rice cultivation area in the world. It will also be severely affected by global warming in the future. This study explores the evaluation of heat tolerance of different important rice varieties in Taiwan at different stages, including the growth at the seedling stage, the spikelet fertility and the rice quality at maturity, we hope to select varieties with good heat tolerance as a basis for further breeding. The application of salicylic acid to alleviate the deterioration of rice quality under high temperature was also explored, and it is expected to establish materials that can be used for rice cultivation under high temperature environments. In the evaluation of heat tolerance at the rice seedling stage, several high temperature treatment methods such as temperature-induced response (TIR) followed by high temperature treatment or direct high temperature treatments were used to evaluate the heat tolerance of Taiwan rice varieties. After the temperature induction response technique (TIR) treatment, the seedling survival rate and relative growth rate of the rice varieties under high temperature stress were significantly improved. In addition, the seedlings of the thermotolerant varieties demonstrated greater thermotolerance performance in the pot experiment as well as cell membrane stability (CMS) and cell activity (2, 3, 5-triphenyl-tetrazolium chloride; TTC) test results. However, the correlation between the thermotolerance of the seedlings and seeds was low. A phylogenetic dendrogram was plotted and revealed that thermotolerant genes did not group in specific clusters. Furthermore, there was a non-significant correlation between the thermotolerance of the varieties and the years in which they were released. Additionally, thermotolerance during different growth stages (i.e., the germination, seedling, and grain maturation stages) exhibited low correlations. In this study, the varieties obtained through preliminary screening (i.e., TK14, HC56, TT30, TNG70, and TK8) exhibited outstanding thermotolerance at the seedling stage. Regarding the evaluation of the spikelet fertility under high temperature, the rice plants were moved into the phytotron of 35/30℃ at the booting stage either until harvest (long term), or 14 days under high temperature and moved back to the field (short term). Under the long term treatment, the rate of spikelet fertility at different years decreased by 15 – 52 % compared with the means of the field temperature control. Varieties such as CNG242 (67.2%), TK14 (65.0%) and TCS10 (63.8%) performed better. Under short-term high-temperature treatment, two batches of experiments were carried out. The results showed that the average rate of spikelet fertility rate for each year was 75.2% and 73.8%, which were 7.7 - 14.67% lower than that of the control. TK 2 (89.2%), TN5 (89.0%), TK16 (85.2%) performed better. In the evaluation of rice quality under high temperature, long-term treatment at 35/30°C after the full heading stage to harvest and short-term treatment at 35/30°C after the 14th days from full heading period were performed. The long-term treatment results at rice quality showed that all the tested varieties have poor performance with the percentage of head rice. Among the Taiwan varieties tested in this study, there were no heat-resistant varieties that could maintain better rice quality at 35/30℃. The results of short-term high-temperature treatment of rice quality showed that the average percentage of head rice in the two batches were 37.8% and 26.9%, with TCS10 (84.4%), Koshihikari (64.4%), HL20 (59.6%), TK8 (59.5%), TK 2 (53.0%) and CNG242 (52.2%) performed better. In the evaluation of the salicylic acid application to alleviate the deterioration of rice quality under high temperature stress, the rice quality assessment after spraying salicylic acid at the full heading stage of rice was conducted in the phytotron of Taiwan University. Results showed that the percentage of head rice in 4 different varieties were increased by the application of salicylic acid under 30/25°C (day and night temperatures), but there was no significant effect on the improvement of the percentage of head rice at 35/30 °C. Further, the study of the application of salicylic acid under 32/27 ℃ in the temperature controlled growth chamber of the Hualien District agricultural research and extension station, Ji'an Township, Hualien County was conducted, and the results showed that there was the significant effect of improving the percentage of head rice, the spikelet fertility rate and the weight of thousand kernels. Overall, salicylic acid treatment has the potential to promote rice quality in a certain high temperature range. However, there are different responses on salicylic acid-induced tolerance effects in different varieties, and the best application method should be further study in future. In addition, the changes in physiological characteristics of flag leaves and grains of rice after spraying salicylic acid at 32/27℃ have also been investigated. The results showed that the relative cell membrane leakage rate of the flag leaves of the two tested varieties at 32/27℃ were higher than the control treatment at 25/20℃, but lower after the application of salicylic acid. The relative α-Amylase activity and relative total soluble sugar content were lower under the salicylic acid treatment compared with the higher temperature treatment and can help to slow down the occurrence of chalkiness in the grains. In summary, there were significant difference in thermotolerance among Taiwan rice varieties at different growth stages. And the varieties with better thermotolerance performance in rice seedling stage or maturity stage have been screened out, which can be used for further breeding in the future. In rice field cultivation technology to alleviate high temperature damage, the results showed that the application of salicylic acid could alleviate the deterioration of rice quality under high temperature, improving the average percentage of head rice and reducing the occurrence of chalky rice grains in a certain temperature range. The application of salicylic acid in the field has the potential to be further utilized in the future to combat high temperature stress.