PDF(Pubmed)
Abstract：
Perennial ryegrass (Lolium perenne L.) possesses a high level of nutritional quality and is widely used as a forage species to establish permanent pastures in southern Chile. However, the productivity of most such pastures is limited by various environmental agents, such as insect pests and drought. In this context, our work stresses the need for elucidating the ability of fungal endophytes to establish interactions with plants, and to understand how these processes contribute to plant performance and fitness. Therefore, we evaluated the colonization and impact of two native strains of the endophytic insect-pathogenic fungus (EIPF) group isolated from permanent ryegrass pastures in southern Chile. Roots and seeds of ryegrass and scarabaeid larvae were collected from nine different ryegrass pastures in the Los Ríos region of southern Chile to specifically isolate EIPFs belonging to the genera Beauveria and Metarhizium. Fungal isolations were made on 2% water agar with antibiotics, and strains were identified by analyzing the entire internal transcribed spacer (ITS) 1-5.8S-ITS2 ribosomal DNA region. Four strains of Beauveria and 33 strains of Metarhizium were isolated only in scarabaeid larvae from ryegrass pastures across four sites. Experimental mini-pastures that were either not inoculated (control) or co-inoculated with conidia of the strains Beauveria vermiconia NRRL B-67993 (P55_1) and Metarhizium aff. lepidiotae NRRL B-67994 (M25_2) under two soil humidity levels were used. Ryegrass plants were randomly collected from the mini-pastures to characterize EIPF colonization in the roots by real-time PCR and fluorescence microscopy. Aboveground biomass was measured to analyze the putative impact of colonization on the mini-pastures\' aboveground phenotypic traits with R software using a linear mixed-effects model and the ANOVA statistical test. Seasonal variation in the relative abundance of EIPFs was observed, which was similar between both strains from autumn to spring, but different in summer. In summer, the relative abundance of both EIPFs decreased under normal moisture conditions, but it did not differ significantly under water stress. The aboveground biomass of ryegrass also increased from autumn to spring and decreased in summer in both the inoculated and control mini-pastures. Although differences were observed between moisture levels, they were not significant between the control and inoculated mini-pastures, except in July (fresh weight and leaf area) and October (dry weight). Our findings indicate that native strains of B. vermiconia NRRL B-67993 (P55_1) and M. aff. lepidiotae NRRL B-67994 (M25_2) colonize and co-exist in the roots of ryegrass, and these had little or no effect on the mini-pastures\' aboveground biomass; however, they could have other functions, such as protection against root herbivory by insect pests.
摘要：
多年生黑麦草（LoliumperenneL.）具有很高的营养质量，被广泛用作在智利南部建立永久性牧场的牧草。然而,大多数这样的牧场的生产力受到各种环境因素的限制，如虫害和干旱。在这种情况下，我们的工作强调需要阐明真菌内生菌与植物建立相互作用的能力，并了解这些过程如何有助于植物的性能和健康。因此,我们评估了从智利南部永久性黑麦草牧场中分离出的两种内生昆虫病原真菌（EIPF）天然菌株的定殖和影响。从智利南部LosRíos地区的9个不同的黑麦草牧场中收集了黑麦草和圣黑麦草幼虫的根和种子，以专门分离出属于白僵菌属和绿僵菌属的EIPF。用抗生素在2%的水琼脂上进行真菌分离，通过分析整个内部转录间隔区（ITS）1-5.8S-ITS2核糖体DNA区域来鉴定菌株。仅在四个地点的黑麦草牧场中的圣甲虫幼虫中分离出4株白僵菌和33株绿僵菌。未接种（对照）或与白僵菌NRRLB-67993（P55_1）和绿僵菌的分生孢子共同接种的实验性小型牧场。在两种土壤湿度水平下使用lepidiotaeNRRLB-67994（M25_2）。从小型牧场随机收集黑麦草植物，以通过实时PCR和荧光显微镜表征根中的EIPF定殖。使用线性混合效应模型和ANOVA统计检验，使用R软件测量了地上生物量，以分析定植对小型牧场地上表型性状的假定影响。观察到EIPF相对丰度的季节性变化，从秋天到春天，这两种菌株之间是相似的，但在夏天不同。在夏天,在正常水分条件下，两种EIPF的相对丰度均下降，但在水分胁迫下没有显着差异。在接种和对照小型牧场中，黑麦草的地上生物量从秋季到春季也增加，而夏季则减少。尽管在水分水平之间观察到差异，它们在对照和接种的小牧场之间并不显著，7月(鲜重和叶面积)和10月(干重)除外。我们的发现表明，维氏芽孢杆菌NRRLB-67993（P55_1）和M.aff的天然菌株。黑麦草NRRLB-67994（M25_2）在黑麦草的根部定植并共存，这些对小型牧场的地上生物量影响很小或没有影响；然而，它们可以有其他功能，如害虫对根草的保护。
