大豆疫霉对寄主大豆和非寄主菜豆根及根分泌物的响应与其对寄主选择性的关系

Response of Phytophthora sojae zoospores to the rootlet and root exudates of host soybean and non-host common bean and host selectivity

摘要:

【背景】大豆疫霉根腐病作为大豆生产上的一种毁灭性病害已被美国、加拿大等多国报道，其病原菌大豆疫霉(Phtophthora sojae Kaufmann and Gerdemann)为典型的土传病原菌。近年来，土传病原菌与植物根系的互作成为研究土传病原菌寄主选择机制的主要方向。【目的】探究寄主大豆和非寄主菜豆根及根分泌物对大豆疫霉的不同影响，阐明这种影响与大豆疫霉对寄主选择的关系。【方法】应用原位土培法种植大豆疫霉感病品种Sloan、抗病品种Williams82和非寄主菜豆一点红，测定了单个大豆疫霉游动孢子对寄主大豆和非寄主菜豆幼根的侵染行为，收集了寄主及非寄主根分泌物，测定了根分泌物对大豆疫霉游动孢子的趋化作用，包括吸引游动孢子的能力以及对游动孢子成囊、孢囊萌发和芽管生长的影响。【结果】大豆疫霉单个游动孢子对寄主大豆幼根表现强烈趋向性，沿着根面进行多次试探性接触后在根尖伸长区快速成囊并萌发，产生的芽管顶端贴附在幼根表面，在感病大豆品种根面上的芽管比抗病大豆品种上的短且粗，而对非寄主菜豆幼根则不具有趋向性，接触一次后即远离，最终在距离幼根75 μm的位置成囊萌发，且芽管生长不具有方向性。此外，大豆疫霉游动孢子对抗病、感病大豆和非寄主菜豆幼根的侵染行为差异完全在根分泌物试验中重现，即寄主大豆根分泌物对大豆疫霉游动孢子具有较强的趋向作用，能够有效吸引游动孢子，促进游动孢子快速成囊及萌发，抑制芽管的伸长，而非寄主菜豆根分泌物不具有上述作用。【结论】大豆疫霉对寄主的选择性与根分泌物有关，为进一步了解大豆疫霉的寄主选择机制提供理论依据。

Abstract:

[Background] Phytophthora root rot as a devastating soybean disease has been reported in the United States, Canada and many other countries, its pathogen Phytophthora sojae is a typical soil-borne pathogen. In recent years, the interaction between soil-borne pathogens and plant roots has become the main direction for studying the host selectivity mechanism of soil-borne pathogens. [Objective] To study the effects of Phytophthora sojae zoospores to the rootlet and root exudates of host soybean and non-host common bean, illustrate the relationship between these effects and P. sojae selecting its host. [Methods] The soybean susceptible cultivar Sloan and resistant cultivar Williams82 as well as non-host common bean Yidianhong of P. sojae were cultivated by the method of situ soil culture. The pre-infection behavior of the single zoospore of P. sojae to the rootlet of host soybean and non-host common bean was determined. The root exudates of host soybean and non-host common bean were collected and the chemotaxis of P. sojae zoospores to the root exudates was measured, including taxis of the zoospores to the root exudates, the promotion of the root exudates on the zoospores encystment, and on the germination and the growth of the germ tubes. [Results] The single zoospore had strong chemotaxis to the host rootlet. It encysted and germinated rapidly on the elongation zone of the root tip after several exploratory contacts along the root surface. The tip of the germ tube attached to the rootlet surface. The difference between the susceptible and resistant cultivar was that the germ tube on the rootlet of susceptible cultivar is shorter and thicker. However, the single zoospore had no chemotaxis to the rootlet of non-host common bean rootlet. It ran away from the rootlet after first visit of the rootlet surface, then encysted and germinated in a random growth direction at the location of approximately 75 μm far away from the rootlet. The substantial difference in the behavior which the P. sojae zoospores infected the rootlet of host soybean and non-host common bean had been repeated in the experiments with root exudates, that is P. sojae zoospores had strong chemotaxis to host root exudates. The host root exudates could effectively attract zoospores and promote encystment of the zoospores and germination of cysts, but inhibit the growth of the germ tube, whilst the root exudates of non-host common bean had no effect on the zoospores. [Conclusion] P. sojae selects its host depending on the root exudates, which will provide a theoretical basis for further understanding the host selection mechanism of P. sojae.