|摘要: ||台稉9號(TK9)為台灣最受歡迎的良質米品種之一，具有良好株型，產量穩定、米質優良等特性，但對白葉枯病(bacterial blight disease, BBD)抗性差，急需進行改良。本論文運用分子標誌輔助回交育種(marker-assisted backcrossing, MAB)策略，將多個白葉枯病抗性基因座 Xa導入台稉九號，改良 TK9之抗性。選用包含三個與五個白葉枯病抗性基因座 Xa的秈稻品種 IR24近同源系：IRBB62 (Xa4/Xa7/Xa21)與 IRBB66(Xa4/xa5/Xa7/xa13/Xa21)作為抗性基因之提供親(donor parent)，分別與輪迴親(recurrent parent)TK9品種雜交產生 F1，兩組分別稱為962 F1與966 F1。F1再與 TK9回交，產生 BC1F1，將多個白葉枯病抗性基因座導入 TK9中，改良其白葉枯病之抗性，並維持 TK9的優良特性。回交子代配合標誌輔助選拔技術，由兩個層級進行篩選：一為前景選拔(foreground selection, FS)，即以分子標誌篩選出具抗性基因座的子代。其次，進行背景選拔(background selection, BS)，即以標誌篩選含 TK9背景的重組體。選拔的植株再以白葉枯病原菌接種，確認抗感表現，並篩選外表型與 TK9相似的植株，選出的植株再與 TK9回交。每個 BC世代皆進行前景、背景與外表型三種選拔。目前進行至 BC3F1世代，基因型篩選結果與病原菌接種外表型相符，即堆疊三個以上基因座的植株，其白葉枯病抗病性較佳；而標誌輔助背景篩選結果也和外表型相符，其中已有背景相似度達90％以上之植株，且隨著輪迴親基因組(recurrent parent genome, RPG)比率越高，植株外表型也與 TK9越相似。未來自交產生 BC3F2後，使基因組同質化，即可育成具 TK9背景，且含多個白葉枯病抗性基因之改良的 TK9品種。本研究結果證明分子標誌輔助回交育種可快速、有效的改良水稻品種白葉枯病抗性。|
TK9 is one of the most popular japonica type rice varieties in Taiwan because of its good plant type, stable yield and excellent grain quality. However, TK9 is very susceptible to bacterial blight disease (BBD) causing by Xanthomonas oryzae pv. Oryzae (Xoo). In this study, markers assisted backcross (MAB) strategy was conducted to introgress Xa genes into TK9 to improve its BBD resistance. Two indica varieties, IRBB62 (Xa4, Xa7 and Xa21) and IRBB66 (Xa4, xa5, Xa7, xa13 and Xa21) containing various BBD resistance genes (Xa) were used as the resistance donor for this purpose. Two crosses designated as 962 (TK9/IBB62) and 966 (TK9/IRBB66) were obtained by crossing the recurrent parent TK9 with IRBB62 and IRBB66, respectively. F1 hybrids were backcrossed with TK9 to proceed the generation, PCR based markers were applied to perform foreground and background selection in each generation, and accompany with phenotypic selection by pathogen challenge and agronomical trait investigation. Genotype of each BC plant was consistent with the lesion length of pathogen inoculation suggested that the more Xa genes pyramided the higher BBD resistance. Plants from backcrossing contain higher recurrent parent genome (RPG) show more similarity to TK9 phenotype. So far, we obtained BC3F1 progenies with RPG higher than 90％ and show good plant type as of TK9. With one self-crossing to reach BC3F2 and homozygous Xa genes, we can breed a new TK9 variety with BBD resistance and good grain quality. This study demonstrates that MAB is an efficient method for improving disease resistance without trait penalty within four years.