栽培稻臺稉8號帶抗稻熱病基因Pik-KU之探討

Identification of blast resistance gene Pik-KU in a rice cultivar Taikeng 8

栽培稻臺稉8號於1992年由臺南區農業改良場推出，在臺灣部分地區對稻熱病呈現抗病。為探討其抗性來源，本研究以臺稉8號與感病水稻麗江新團黑穀雜交所得之325個F2子代，透過接種本土稻熱病菌菌株13TN-HB1-3分析抗性表現型，並針對主要抗稻熱病基因座Pi2/9、Pik、Pita與Ptr（Pita-2），以四組cleaved amplified polymorphic sequences（CAPS）分子標誌進行基因型鑑定與連鎖分析，發現臺稉8號之抗性與Pik顯著相關。進一步參考上述基因座內已報導之等位基因設計引子對並進行定序，確認臺稉8號於Pik上帶有與水稻Kusabue相同之抗性等位基因（Pik-KU），而在Pi2/9、Pita與Ptr（Pita-2）則帶有感病等位基因。由於IRBLk-Ka（帶有Pik-KA）於全臺各地病圃均呈現感病，而臺稉8號所帶之Pik-KU與Pik-KA僅具有兩個胺基酸之差異，其抗性被病原菌族群克服的風險高，因此Pi2/9、Pik、Pita與Ptr（Pita-2）等基因座均可作為未來臺稉8號抗性改良的目標。

"The rice cultivar Taikeng 8, released by Tainan District Agricultural Research and Extension Station in 1992, has exhibited resistance to rice blast in some areas in Taiwan, respectively. To identify the resistance source, a population of 325 F2 progeny derived from the cross of Taikeng 8 and a susceptible cultivar Lijianxintuanheigu (LTH) was developed and used for linkage analysis. The F2 plants were inoculated with a local Magnaporthe oryzae isolate 13TN-HB1-3, and genotyped with four cleaved amplified polymorphic sequences (CAPS) markers targeting the major blast resistance genes Pi2/9, Pik, Pita, and Ptr (Pita-2). Trait-marker linkage analysis suggested that the resistance was significantly associated with Pik. Sequencing analysis by the primers designed based on known alleles of the resistance genes revealed that Taikeng 8 carries a resistant allele at Pik (identical to the resistant allele Pik-KU in Kusabue) and susceptible alleles at Pi2/9, Pik, and Ptr (Pik-2). Because IRBLk-Ka (carrying Pik-KA) has exhibited susceptibility in different blast nursery fields around Taiwan, and Pik-KU differs from Pik-KA only by two amino acid, so there is a high risk that the Pik-KU resistance of Taikeng 8 can be easily overcome by the pathogen population. To improve the blast resistance of Taikeng 8, Pi2/9, Pik, Pita, and Ptr (Pita-2) can all be considered as target loci in resistance breeding in the future."