Serial passage through resistant and susceptible cucumber cultivars affects the virulence of Fusarium oxysporum f. sp. cucumerinum

Abstract

Fusarium oxysporum f. sp. cucumerinum (Foc) is the causal pathogen of cucumber Fusarium wilt resulting in losses to cucumber production. To investigate the effects of the selective pressures of host plants on the virulence of Foc, a low virulence isolate, foc-3b, was successively inoculated on resistant and susceptible cucumber cultivars for five generations. The virulence of the original isolate diverged; virulence was significantly strengthened after serial passage on the resistant cultivar and weakened on the susceptible plants (p ˂ .05). The expression of four virulence-related genes of F. oxysporum, G-protein α subunit gene fga1, sucrose nonfermenting 1 gene snf1, F-box protein gene frp1, and Class V chitin synthase gene chsV, was quantified using real-time PCR. All genes were significantly upregulated after serial passage on the resistant cultivar, compared to the original strain, and the expression of snf1 was downregulated in strains re-isolated from the susceptible plants (p ˂ .05). A significant positive correlation was found between the expression levels of gene snf1, frp1, and chsV and disease severity of cucumber Fusarium wilt, suggesting these genes may impact virulence differentiation. This study will improve the management of cucumber Fusarium wilt and provide insight into the mechanisms underlying virulence of F. oxysporum.

Successive passaging through an apple host of six low-virulent <i>Neonectria ditissima </i>isolates increased virulence in one of them

“…However, that the re-isolates could have arisen from an introduced contaminant cannot be entirely ruled out. To confirm provenance of re-isolates, selected marker genes (Huang et al 2019) or whole genome sequences (WGS) of the isolates and re-isolates could be compared (Malapi-Wight et al 2016;Chalupowicz et al 2019). Field inoculum was significantly more virulent than all other isolates in every aspect: lesions appeared earlier, were longer, and the AUDPC of both disease incidence and lesion length were greater, confirming that all isolates used in this study, and their re-isolates, were low-virulent isolates.…”

“…The mechanisms underlying these changes in virulence were not investigated explicitly during these studies. However, sequence variations (although without a correlation with virulence alterations; Wang et al 2008), and moderated virulence gene expression (Huang et al 2019) were both observed. Thus, in these pathosystems, alterations in virulence with passaging through the host may have been be due to sequence mutations.…”

“…The same letter indicates means which were not significantly different based on Bonferroni adjusted least significant difference (LSD). (Wang et al 2008;Alkher et al 2009;Gao et al 2012;Huang et al 2019), although results from susceptible hosts are somewhat variable, with decreases also apparent (Huang et al 2019). The mechanisms underlying these changes in virulence were not investigated explicitly during these studies.…”

Transcriptome analysis of virulence-differentiated Fusarium oxysporum f. sp. cucumerinum isolates during cucumber colonisation reveals pathogenicity profiles

“…In a previous study, a mild virulence isolate, foc-3b, was successively inoculated on resistant and susceptible cucumber cultivars for five generations. The virulence of the original isolate diverged rapidly; virulence was significantly increased after serial passage on the resistant cultivar, especially in the fourth generation, but decreased on the susceptible plants ( p < 0.05) [8]. This suggests a specific interaction with the plant that selects for enhanced virulence in the pathogen.…”

“…So far, only a few pathogenicity-related genes of Foc have been identified, mainly including fga1 , fga2 and fgb1 that encodes G-protein α and β subunits [11–13] and FocVel1 that encodes a velvet protein [14]. In addition, several virulence factors of F. oxysporum involved in synthesis or regulation of plant cell wall degradation enzymes (CWDEs) and in breaking plant defense have been found to relate to pathogenicity differentiation of Foc [8]. Pathogenicity related genes are often encoded in accessory genome regions of F. oxysporum and up-regulated during infection [15–18].…”