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

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.

Efficacy of Neem (Azadirachta indica) Leaf Extract Against Fungi Pathogen Associated with Watermelon (Citrullus lanatus) Spoilage

“…This was in conformity with Bashir et al 12 who worked on the effect of sodium carbonate and sodium chloride for the control of black rot disease of Mangifera indica caused by Aspergillus niger, much resistance was also observed by the pathogen even though conidia germination is hindered. Fulton, et al 13 also worked on the fungi diseases of watermelon and found Alternaria leaf blight (Alternaria cucumerina), Anthracnose (Colletotrichum orbiculare), Cercospora leafspot (Cercospora citrullina), downy mildew (Pseudoperonospora cubensis), Fusarium wilt (Fusarium oxysporum), Gummy stem blight (Didymella bryoniae) and powdery mildew (Podosphaera xanthii) affecting the growth of watermelon. He also opined that disease severity is high in areas where there is frequent rainfall and temperatures are high, a characteristic nature of Anyigba where this research was carried out.…”

Fusarium oxysporum f. sp. niveum Molecular Diagnostics Past, Present and Future

“…While DNA extraction and PCR assays require specialized tools, they have become more routine for diagnosis in plant pathology and more widely distributed [39][40][41]. In comparison, the bioassay requires more resources and time to grow multiple different crop hosts before completing the diagnosis (Tables 2 and 3) [23,24,42]. Even then, nonpathogenic strains may not be isolated.…”

“…2021, 22, x FOR PEER REVIEW 4 of 15 aggressiveness than race 1 isolates. This has been argued due to multiple isolates of the same race being tested and showing variation within their aggressiveness [23,24]. Fon is found in most, if not all, watermelon growing regions in the world [25].…”

“…The aggressiveness of Fon has been thought to positively correlate with increased cultivar range, meaning race 3 isolates both have a larger range of pathogenicity (virulence) and aggressiveness than race 1 isolates. This has been argued due to multiple isolates of the same race being tested and showing variation within their aggressiveness [ 23 , 24 ].…”

Genetic Diversity and Population Structure of Head Blight Disease Causing Fungus Fusarium graminearum in Northern Wheat Belt of India

“…Similarly, TEF-1α, β-tubulin and histone 3 regions have been explored by Webb et al [ 48 ] and Taha et al [ 49 ] for dissecting the genetic variability among F. oxysporum isolates. Recently, Fulton et al [ 50 ] employed two different housekeeping genes (BT and TEF) for analyzing the phylogenetic kinship of F. oxysporum f. sp. niveum isolates from the major watermelon-producing regions in north, central, and south Florida.…”