树栖真菌对扩散型松材线虫生活史的影响

 松材线虫病是一种涉及多个生物因子的复杂病害系统,其病原松材线虫的生活史受媒介昆虫、寄主、树栖真菌和伴生细菌等多种因素影响。利用感染松材线虫病的马尾松林内的两种优势内栖真菌的3个菌株,松球壳孢(Sphaeropsis sapinea)E11、MHS7.3和小孢拟盘多毛孢(Pestalotiopsis microspora)M32,接种于松褐天牛模拟蛹室,研究松褐天牛蛹期和羽化过程松材线虫种群动态,以及松褐天牛携带扩散型松材线虫的动态变化。结果表明,天牛发育处于蛹期时,松材线虫主要以扩散型三龄幼虫(J_Ⅲ)附着于天牛体表;发育至羽化期时,松材线虫主要以扩散型四龄幼虫(J_Ⅳ)位于天牛体内。不同优势内栖真菌接种处理下,松褐天牛携带的扩散型幼虫数量的大小顺序为:小孢拟盘多毛孢M32>松球壳孢E11>松球壳孢MHS7.3,这与模拟蛹室中松材线虫种群的大小顺序是一致的,表明松褐天牛携带的线虫数目与蛹室中线虫种群的大小关系密切。在松褐天牛携带的J_Ⅲ、J_Ⅳ和扩散型幼虫(J_Ⅲ＋J_Ⅳ)占线虫种群比例方面,松球壳孢E11和MHS7.3均大于小孢拟盘多毛孢M32,显示不适宜繁殖的真菌能促进群体内更多个体转化为扩散型虫态。J_Ⅳ在蛹期的第二天即从天牛体内分离得到,但数量极少,随着J_Ⅲ在羽化前达到最大值,J_Ⅳ也开始大量出现,预示着较大J_Ⅲ种群数量可能是J_Ⅳ大量发生的基础条件之一。研究结果表明在松材线虫的扩散过程中,松林优势树栖真菌对媒介天牛携带的松材线虫数量产生显著影响。

Effect of tree-inhabitant fungi on the life cycle of the dispersal forms of Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae) carried by Monochamus alternatus (Coleoptera: Cerambycidae) in vitro

Pine wilt disease primarily caused by pine wood nematode, Bursaphelenchus xylophilus is a disease complex involved with a series of biotic factors, including vector beetles, host pines, tree-inhabitant fungi and associated bacteria, which directly impacts the life cycle of the nematode and contributes to the wilt syndrome to some extent. Three strains of two dominant fungi isolated from the infected Pinus massoniana forests in eastern China, Zhejiang Province, were tested as the potential food for propagation of the nematode, B. xylophilus, and the effect of these tree-inhabitant fungi on the formation of dispersal larvae of the nematode were also evaluated during the pupation and eclosion of Monochamus alternatus in mimic pupal chambers. The results showed that the third-stage dispersal juveniles (J_Ⅲ) of the nematode were mainly carried by the pupae stage of the beetles on the body surface; and the fourth-stage dispersal juveniles (J_Ⅳ) of the nematode were carried by the eclosed beetles inside their bodies. Of the three strains, Pestalotiopsis microspora M32 could increase the nematode population to its highest level and the inoculated chambers contained the beetles with the highest amounts of dispersal juveniles. In comparison, two strains of Sphaeropsis sapinea, E11 and MHS7.3 could only maintain the nematode population at lower levels and the dispersal juveniles carried by the treated beetles were also at lower levels. The proportion of the dispersal nematodes (J_Ⅲ＋J_Ⅳ) in total nematodes in M32 treatment was much lower than that in E11 and MHS7.3 treatments, indicating the unsuitable fungi induced the conversion of the nematodes from propagative forms to dispersal forms. J_Ⅳ first appeared two days after the beetle pupation and then dramatically increased at the beginning of eclosion. J_Ⅲ reached to peak before eclosion in P. microspora inoculation predicted the large amount of J_Ⅲ might be necessary for them to molt to J_Ⅳ. We concluded that the tree-inhabitant fungi can significantly impact the spread efficiency of B. xylophilus vectored by M. alternatus, which on the other hand provides a new insight for the disease management.