Fusarium xyrophilum, sp. nov., a member of the Fusarium fujikuroi species complex recovered from pseudoflowers on yellow-eyed grass (Xyris spp.) from Guyana

We report on the discovery and characterization of a novel Fusarium species that produced yellow-orange pseudoflowers on Xyris spp. (yellow-eyed grass; Xyridaceae) growing in the savannas of the Pakaraima Mountains of western Guyana. The petaloid fungal structures produced on infected plants mimic host flowers in gross morphology. Molecular phylogenetic analyses of full-length RPB1 (RNA polymerase largest subunit), RPB2 (RNA polymerase second largest subunit), and TEF1 (elongation factor 1-α) DNA sequences mined from genome sequences resolved the fungus, described herein as F. xyrophilum, sp. nov., as sister to F. pseudocircinatum within the African clade of the F. fujikuroi species complex. Results of a polymerase chain reaction (PCR) assay for mating type idiomorph revealed that single-conidial isolates of F. xyrophilum had only one of the MAT idiomorphs (MAT1-1 or MAT1-2), which suggests that the fungus may have a heterothallic sexual reproductive mode. BLASTn searches of whole-genome sequence of three strains of F. xyrophilum indicated that it has the genetic potential to produce secondary metabolites, including phytohormones, pigments, and mycotoxins. However, a polyketide-derived pigment, 8-O-methylbostrycoidin, was the only metabolite detected in cracked maize kernel cultures. When grown on carnation leaf agar, F. xyrophilum is phenotypically distinct from other described Fusarium species in that it produces aseptate microconidia on erect indeterminate synnemata that are up to 2 mm tall and it does not produce multiseptate macroconidia.

本研究报道了在圭亚那西部帕卡赖马山脉稀树草原中生长的黄眼草属（Xyris）植物（黄眼草，黄眼草科Xyridaceae）上产生橙黄色假花的新型镰孢菌属（Fusarium）物种的发现与特征描述。受侵染植株上形成的花瓣状真菌结构在整体形态上与宿主花朵高度相似。通过对从基因组序列中挖掘的全长RPB1（RNA聚合酶最大亚基）、RPB2（RNA聚合酶第二大亚基）及TEF1（延伸因子1-α）DNA序列进行分子系统发育分析，明确该真菌（本文命名为新种镰孢菌Fusarium xyrophilum，sp. nov.）属于藤仓镰孢菌物种复合体的非洲支系，与假旋镰孢菌（Fusarium pseudocircinatum）互为姊妹群。交配型同源异型框（mating type idiomorph）的聚合酶链式反应（PCR）检测结果显示，该新种的单分生孢子分离株仅携带一种MAT idiomorph（MAT1-1或MAT1-2），表明该真菌可能采用异宗配合的有性生殖模式。对3株新种镰孢菌的全基因组序列进行BLASTn检索发现，其具备合成包括植物激素、色素及真菌毒素在内的次生代谢产物的遗传潜力。但在破碎玉米籽粒培养基中仅检测到一种聚酮类色素——8-O-甲基波斯特霉素（8-O-methylbostrycoidin）。在康乃馨叶琼脂培养基上培养时，该新种镰孢菌的表型与其他已描述的镰孢菌属物种存在显著差异：其在高达2毫米的直立不定型分生孢子座上产生无隔小型分生孢子，且不产生多隔大型分生孢子。