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. 2021 Mar 25;16(3):e0248364.
doi: 10.1371/journal.pone.0248364. eCollection 2021.

Phylogenetic and phenotypic characterization of Fusarium oxysporum f. sp. niveum isolates from Florida-grown watermelon

James C Fulton  1 , B Sajeewa Amaradasa  2 , Tülin S Ertek  3   4 , Fanny B Iriarte  4 , Tatiana Sanchez  5 , Pingsheng Ji  6 , Mathews L Paret  1   4 , Owen Hudson  6 , Md Emran Ali  6 , Nicholas S Dufault  1
Affiliations

Phylogenetic and phenotypic characterization of Fusarium oxysporum f. sp. niveum isolates from Florida-grown watermelon

James C Fulton et al. PLoS One. .

Abstract

Fusarium wilt of watermelon (Citrullus lanatus) caused by Fusarium oxysporum f. sp. niveum (Fon), has become an increasing concern of farmers in the southeastern USA, especially in Florida. Management of this disease, most often through the use of resistant cultivars and crop rotation, requires an accurate understanding of an area's pathogen population structure and phenotypic characteristics. This study improved the understanding of the state's pathogen population by completing multilocus sequence analysis (MLSA) of two housekeeping genes (BT and TEF) and two loci (ITS and IGS), aggressiveness and race-determining bioassays on 72 isolates collected between 2011 and 2015 from major watermelon production areas in North, Central, and South Florida. Multilocus sequence analysis (MLSA) failed to group race 3 isolates into a single large clade; moreover, clade membership was not apparently correlated with aggressiveness (which varied both within and between clades), and only slightly with sampling location. The failure of multilocus sequence analysis using four highly conserved housekeeping genes and loci to clearly group and delineate known Fon races provides justification for future whole genome sequencing efforts whose more robust genomic comparisons will provide higher resolution of intra-species genetic distinctions. Consequently, these results suggest that identification of Fon isolates by race determination alone may fail to detect economically important phenotypic characteristics such as aggressiveness leading to inaccurate risk assessment.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Molecular phylogenetic analysis from concatenated gene sequences.
The evolutionary history was inferred by using a (A) Neighbor-joining (NJ) tree with Kimura-2-parameter and a (B) Maximum Likelihood method based on the nearest-neighbor interchange algorithm and general time-reversible (GTR) substitution model. The bootstrap values >65% from 500 replications are shown above the branches. Trees are drawn to scale, with branch lengths measured in the number of substitutions per site. 74 nucleotide sequences were included in the analysis. All positions containing gaps and missing data were eliminated.
Fig 2
Fig 2. Haplotype network derived from concatenated sequencing data of BT, IGS, ITS, and TEF genes and loci and color-coded for Fusarium oxysporum f. sp. niveum subpopulations: North (Pop1, 44 isolates), central (Pop2, 16 isolates), and south (Pop3, 11 isolates).
The connecting lines are proportional to number of mutations between isolates.
Fig 3
Fig 3. Haplotype network derived from concatenated sequencing data of BT, IGS, ITS, and TEF genes and loci and color-coded for level of aggressiveness (non-aggressive, weak, moderate, severe) of Fusarium oxysporum f. sp. niveum isolates.
The connecting lines are proportional to number of mutations between isolates.
See this image and copyright information in PMC

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