Freitas Priscila P, Hampton John G, Rolston M Phil, Glare Travis R, Miller Poppy P, Card Stuart D
Bio-Protection Research Centre, Lincoln University, Lincoln, New Zealand.
Forage Science, AgResearch Limited, Lincoln Research Centre, Lincoln, New Zealand.
Front Plant Sci. 2020 May 8;11:530. doi: 10.3389/fpls.2020.00530. eCollection 2020.
Many cool-season grasses form permanent, mutualistic symbioses with asexual endophytes. These fungal symbionts often perform a protective role within the association as many strains produce secondary metabolites that deter certain mammalian and invertebrate herbivores. Although initially a serious issue for agriculture, due to mammalian toxins that manifested in major animal health issues, selected strains that provide abiotic stress protection to plants with minimal ill effects to livestock are now commercialized and routinely used to enhance pasture performance in many farming systems. These fungal endophytes and their grass hosts have coevolved over millions of years, and it is now generally accepted that most taxonomic groupings of are confined to forming compatible associations (i.e., symptomless associations) with related grass genera within a tribe. The most desired compounds associated with var. , an endophyte species associated with perennial ryegrass, are peramine and epoxy-janthitrems. No other major secondary metabolites with invertebrate bioactivity have been identified within this association. However, other agriculturally beneficial compounds, such as lolines, have been discovered in related endophyte species that form associations with fescue grasses. A rationale therefore existed to develop novel grass-endophyte associations between loline-producing endophytes originally isolated from tall fescue with elite cultivars of perennial ryegrass to achieve a wider spectrum of insect bioactivity. A suitable loline-producing endophyte strain of sp. FaTG-3 was selected and inoculated into perennial ryegrass. We hypothesed that endophyte transmission frequency, endophyte mycelial biomass and endophyte-derived alkaloid production would differ between the original tall fescue host and the artificial association. Consistent with our hypothesis, our data strongly suggest that plant species significantly affected the plant-endophyte association. This effect became more apparent for transmission frequency and endophyte biomass as the plants matured. Overall, the viable endophyte infection frequency was greater in the tall fescue host than in perennial ryegrass, at all sampling dates. Additionally, temperature was found to be a significant factor affecting endophyte transmission frequency, endophyte mycelial biomass and alkaloid production. Implications for the development of novel grass-endophyte associations are discussed.
许多冷季型草与无性内生真菌形成永久性的互利共生关系。这些真菌共生体在共生关系中常常发挥保护作用，因为许多菌株会产生次生代谢产物，可抵御某些哺乳动物和无脊椎动物食草动物。尽管这一现象最初对农业来说是个严重问题，因为哺乳动物毒素会引发重大动物健康问题，但现在，那些对植物具有非生物胁迫保护作用且对牲畜影响极小的特定菌株已实现商业化，并在许多养殖系统中常规用于提高牧场性能。这些真菌内生菌与其禾本科宿主已经共同进化了数百万年，现在人们普遍认为，大多数分类群仅限于与一个族内的相关禾本科属形成兼容共生关系（即无症状共生关系）。与多年生黑麦草相关的内生菌物种——Epichloë festucae var. lolii产生的最理想化合物是哌嗪和环氧-詹丝菌素。在这种共生关系中尚未鉴定出其他具有无脊椎动物生物活性的主要次生代谢产物。然而，在与羊茅属草形成共生关系的相关内生菌物种中发现了其他对农业有益的化合物，如洛林生物碱。因此，有理由在最初从高羊茅中分离出的产洛林生物碱的内生菌与多年生黑麦草的优良品种之间建立新型禾本科-内生菌共生关系，以实现更广泛的昆虫生物活性谱。选择了一种合适的产洛林生物碱的内生菌菌株Epichloë sp. FaTG-3，并将其接种到多年生黑麦草中。我们假设，内生菌传播频率、内生菌菌丝体生物量和内生菌衍生生物碱的产生在原来的高羊茅宿主和人工共生关系之间会有所不同。与我们的假设一致，我们的数据有力地表明，植物物种显著影响植物-内生菌共生关系。随着植物成熟，这种影响在传播频率和内生菌生物量方面变得更加明显。总体而言，在所有采样日期，高羊茅宿主中活内生菌的感染频率都高于多年生黑麦草。此外，发现温度是影响内生菌传播频率、内生菌菌丝体生物量和生物碱产生的一个重要因素。本文讨论了新型禾本科-内生菌共生关系发展的相关影响。
