Molecular systematics of two sister clades, the Fusarium concolor and F. babinda species complexes, and the discovery of a novel microcycle macroconidium–producing species from South Africa

Multilocus DNA sequence data were used to investigate species identity and diversity in two sister clades, the Fusarium concolor (FCOSC) and F. babinda species complexes. Of the 109 isolates analyzed, only 4 were received correctly identified to species and these included 1/46 F. concolor, 1/31 F. babinda, and 2/3 F. anguioides. The majority of the F. concolor and F. babinda isolates were received as F. polyphialidicum, which is a heterotypic synonym of the former species. Previously documented from South America, Africa, Europe, and Australia, our data show that F. concolor is also present in North America. The present study expands the known distribution of F. babinda in Australia to Asia, Europe, and North America. The molecular phylogenetic results support the recognition of a novel Fusarium species within the FCOSC, which is described and illustrated here as F. austroafricanum, sp. nov. It was isolated as an endophyte of kikuyu grass associated with a putative mycotoxicosis of cattle and from plant debris in soil in South Africa. Fusarium austroafricanum is most similar morphologically to F. concolor and F. babinda but differs from the latter two species in producing (i) much longer macroconidia in which the apical cell is blunt to slightly papillate and the basal cell is only slightly notched and (ii) macroconidia via microcycle conidiation on water agar. BLASTn searches of the whole genome sequence of F. austroafricanum NRRL 53441 were conducted to predict mycotoxin potential, using genes known to be essential for the synthesis of several mycotoxins and biologically active metabolites. Based on the presence of intact gene clusters that confer the ability to synthesize mycotoxins and pigments, we analyzed cracked corn kernel cultures of F. austroafricanum via liquid chromatography–mass spectrometry (LC-MS) but failed to detect these metabolites in vitro.

本研究采用多位点DNA序列数据，探究了姊妹支系同色镰刀菌物种复合体（Fusarium concolor species complex, FCOSC）与芭宾达镰刀菌物种复合体的物种鉴定与多样性情况。在所分析的109株分离菌株中，仅4株经准确鉴定至种水平，分别为46株色变镰刀菌（F. concolor）中的1株、31株芭宾达镰刀菌（F. babinda）中的1株，以及3株细长镰刀菌（F. anguioides）中的2株。大部分色变镰刀菌与芭宾达镰刀菌的分离菌株最初被鉴定为多瓶梗镰刀菌（F. polyphialidicum），该物种实为前者的异型同物异名。此前已有研究在南美洲、非洲、欧洲及澳大利亚报道过色变镰刀菌，本研究数据证实其在北美亦有分布；同时本研究将芭宾达镰刀菌在澳大利亚的已知分布范围扩展至亚洲、欧洲与北美。分子系统发育分析结果支持在FCOSC支系中存在一个新的镰刀菌物种，本文将其描述并命名为南非镰刀菌（F. austroafricanum）sp. nov.。该菌株分离自南非与牛疑似真菌毒素中毒症相关的基库尤草内生真菌，以及土壤中的植物残体。南非镰刀菌在形态上与色变镰刀菌、芭宾达镰刀菌最为相近，但可通过以下两点与后两者区分：（1）产生更长的大型分生孢子，其顶细胞钝圆至略具乳突，基细胞仅具浅凹刻；（2）通过水琼脂培养基上的微循环产孢方式形成大型分生孢子。本研究针对南非镰刀菌NRRL 53441的全基因组序列开展BLASTn搜索，结合已知的多种真菌毒素及生物活性代谢物合成必需基因，预测其产毒潜力。基于完整的真菌毒素与色素合成基因簇的存在情况，我们通过液相色谱-质谱联用法（liquid chromatography–mass spectrometry, LC-MS）对南非镰刀菌的破碎玉米籽粒培养物进行了分析，但未在体外培养条件下检测到上述代谢产物。