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.

Design and validation of a robust multiplex polymerase chain reaction assay for MAT idiomorph within the Fusarium fujikuroi species complex.

We discovered that published polymerase chain reaction (PCR) assays for determining mating type (MAT) idiomorph failed to genotype some of the Fusarium fujikuroi species complex (FFSC) isolates recovered from Mangifera indica (mango), Swietenia macrophylla (big-leaf mahogany), Annona muricata (soursop), Bursera sp., and Tabebuia sp. in Mexico. Thus, the primary objective of this study was to design and validate a robust multiplex PCR-based diagnostic for typing MAT within the FFSC. To accomplish this objective, we mined the MAT1-1 or MAT1-2 locus from the genomes of 60 FFSC isolates, representing 56 phylospecies, and from four species in its sister group, the F. nisikadoi species complex (FNSC). Bioinformatic searches were facilitated by targeting DNA lyase (SLA2) and apurinic endonuclease (APN1), the genes that flank the MAT locus in Fusarium. As expected, three genes were identified within MAT1-1 (MAT1-1-1, MAT1-1-2, and MAT1-1-3) and two in MAT1-2 (MAT1-2-1 and MAT1-2-9), using the ab initio prediction tool AUGUSTUS. Of the three multiplex PCR assays we designed and tested, the one targeting MAT1-1-2 and MAT1-2-1 successfully genotyped the entire 71-isolate validation panel, which included 56 FFSC and 4 FNSC phylospecies. By contrast, the published PCR assays we tested produced positive genotypes for only 46.5-59% of the 71-isolate validation panel, but only when they were run as a uniplex assay. Although only one-fifth of the FFSC/FNSC are known to reproduce sexually, our results suggest that if they possess a sexual cycle, it is heterothallic (self-sterile).