臺灣大豆固氮根瘤菌之鑑定及其寄主範圍探討

Identification of nitrogen-fixing rhizobia from soybean in Taiwan and exploration of their host range

固氮根瘤菌是土壤中常見的革蘭氏陰性細菌，能與豆科植物的根部共生形成根瘤，具有生物性固氮作用，提供植物所需氮素以促進植物生長，可以有效減少氮肥用量。本研究自彰化及嘉義分離得到5株固氮根瘤菌，培養特性皆屬於慢生型，且菌株存在兩種形態差異。經大豆植株接種及再分離測試，完成柯霍氏準則。利用16S rDNA、nodC及nifH等基因序列進行菌種鑑定及親緣分析，顯示4株菌株為Bradyrhizobium yuanmingense，1株菌株為B. elkanii，其中B. yuanmingense是臺灣固氮根瘤菌的新紀錄種，增加臺灣本土固氮根瘤菌之多樣性。經寄主植物範圍試驗結果，B. yuanmingense與B. elkanii兩菌種分別可以感染7種與5種供試豆科植物，並產生有效根瘤。新紀錄種B. yuanmingense菌株在供試的豇豆、翼豆及花生等植株根系，皆具有良好的結瘤能力，而B. elkanii菌株僅能在豇豆根系形成48%有效根瘤。本研究結果顯示B. yuanmingense與B. elkanii兩菌種固氮根瘤菌皆具有微生物肥料之應用潛力，其中B. yuanmingense菌株的寄主範圍及結瘤能力皆優於B. elkanii菌株，將進一步探討其固氮能力及田間環境適應性。

Nitrogen-fixing rhizobia belong to Gram-negative bacteria found universally in soil. Rhizobia can form the symbiotic nodules with the roots of legumes, perform the biological nitrogen fixation to provide nitrogen for plant growth, and effectively reduce the use of nitrogen fertilizers. In this study, five strains of nitrogen-fixing rhizobia were collected from Changhua and Chiayi, and all of them were slow-growing with two kinds of morphological differences. Through inoculation and re-isolation of soybean plants fulfilled the Koch’s postulates. Strains of identification and phylogenetic analysis were performed using the sequences of 16S rDNA, nodC, and nifH genes. Results revealed that four strains belonged to Bradyrhizobium yuanmingense and one strain to B. elkanii. Among these, B. yuanmingense is a new record species of nitrogen-fixing rhizobium in Taiwan, thereby increasing the diversity of indigenous nitrogen-fixing rhizobia. Based on host range experiments, both strains of B. yuanmingense and B. elkanii can infect 7 and 5 tested legume plants respectively, producing effective nodules. The newly recorded species of B. yuanmingense demonstrated good nodulation ability on the root systems of tested plants including cowpea, winged bean, and peanut, whereas the B. elkanii strain infected only cowpea and formed 48% effective nodules. The results of this study indicate that B. yuanmingense and B. elkanii strains possess potential for application as microbial fertilizers. And the B. yuanmingense exhibits superior host range and nodulation capacity compared to B. elkanii. Further explore will focus on its nitrogen-fixing capacity and field adaptability.