Effect of rhizobia primed with flavonoid on growth, root development and nodulation in leguminous cover crops grown under low temperature condition

在日本西部温带地区的大田豌豆（Pisum sativum）中，晚播条件下的低温是早熟的限制因素。在抑制机制中，减少豆科植物根部释放的黄酮类化合物对nod基因激活的影响可能是重要的。研究了黄酮诱导和对照接种后的根瘤形成情况。黄酮类化合物处理的单株根瘤数高于对照。接种了根瘤菌的植株根系结构发生改变，二级侧根数量减少，沿根轴连续形成根瘤。这些结果表明，黄酮类化合物引发根瘤菌可能通过抑制侧根分化而促进根瘤的早期形成，表明在不适宜的环境条件下，豌豆根系的发育是在结瘤和侧根分枝之间进行权衡的。

In field pea(Pisum sativum) grown in temperate region of western Japan, low temperature under late seeding condition should be considered as a limiting factor for early growth. Of inhibition mechanisms, decreasing flavonoid compounds released from legume roots for nod gene activation might be of importance. Root nodule formation was investigated after inoculation in both flavonoid priming and the control. Root nodule numbers per plant were higher in flavonoid priming than the control. Plants inoculated with primed rhizobia showed alterative root structure such as reduction of the number of the second order lateral roots and the continuous nodule formation along the root axis. These results suggest that priming treatment of rhizobia with flavonoid might induce earlier formation of root nodules due to inhibiting lateral root differentiation, indicating that root system development of pea plants occurs with a trade-off between the nodulation and lateral branching under unsuitable environmental conditions.