The Brazilian population of Fusarium oxysporum f. sp. cubense is not structured by VCG or by geographic origin

Abstract

Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc), is considered one of the most destructive diseases of bananas. Paradoxically, knowledge of the genetics of the pathogen population in the Americas is very limited. In this study, a collection of 178 monosporic isolates from several banana producing regions, located in different climatic zones along a South to North transect in Brazil, was formed to assess the genetic structure of the population of Foc. The isolates underwent pathogenicity tests, PCR diagnosis for the detection of Tropical race 4 and screening to SIX homologs. The VCG of 119 isolates was determined by pairing against 17 testers. A group of 158 isolates was selected for microsatellite genotyping. There was moderate diversity of Foc in Brazil. Eight VCGs were identified: 0120, 0122, 0124, 0125, 0128, 01215, 01220, and 01222, of which 78% of isolates belong to a single VCG, while 22% of isolates belong to complexes of VCGs. The distribution of VCGs is uneven and independent of the banana genotype. VCGs were correlated with homologs of the SIX genes and varied according to geographic regions. Four SSR loci were polymorphic and on average 7.5 alleles were detected per locus. Thirty-five multilocus genotypes (MLGs) were identified. There was no association between VCG and MLGs and no genetic structure of the population of Foc in Brazil was detected.

Evidence of Correlation between Pathogenicity, Avirulence Genes, and Aggressiveness of Fusarium oxysporum f. sp. cubense in Banana “Cavendish” and “Prata” Subgroups

“…In the present study, it is also shown that the majority of the more aggressive/virulent isolates (68%) were also collected in Cavendish cultivars, especially in the state of São Paulo (Table S1). The presented data reinforce the existence of variations in the virulence profile of some isolates and may be associated with the occurrence and widespread distribution of ST4 among Foc isolates in Brazil under favorable environmental conditions in different regions of the country [27].…”

“…cubense (Foc), adverse environmental conditions also contribute to the incidence of Foc in banana-producing areas in Brazil. In the latest study on the population structure of Foc in Brazil, the presence of TR4 was investigated in a collection of isolates and the genetic structure was determined based on an expanded set of markers [27]. In this study, the Foc population appears to have low to moderate genetic variability given the high clonal fraction.…”

“…The overcoming of genetic resistance is a constant threat to field management of Fusarium wilt and this problem can be closely related to the high variability of the fungus [26,27,[53][54][55]. According to Buddenhagen [11], tropical race 4 (TR4) evolution was associated with the emergence of the ability to cause disease in banana cultivars of the Cavendish subgroup from spontaneous mutations that generated variants with potential to colonize and cause damage to this subgroup.…”

“…In our work, the 214 isolates analyzed by SSR markers were separated into 52 distinct haplotypes and distributed in different banana-producing regions of Brazil, but no Foc population structure, based on host or geographic regions, was found. Recently, Batista et al [27] quantified the genetic variability present in Foc isolates from the Brazilian population to investigate the presence of TR4 and to determine the genetic structure based on the SIX gene profile, VCG tests, IGS PCR-RFLP, and SSR markers. In their study, the authors showed that Brazil is, in fact, free of Foc TR4 isolates.…”

Selection of Improved Banana Diploid Resistant to<em> Fusarium oxysporum f. sp. </em>cubense Races 1 and Subtropical 4

“…R4 has further subdivisions into tropical race 4 (TR4) and subtropical race 4 (ST4). TR4 affects Cavendish in both tropical and subtropical conditions, while Foc ST4 isolates cause disease in Cavendish cultivars in subtropical regions under specific conditions, such as temperature extremes or water deficit [8,9]. The ST4 and TR4 variants can be differentiated by their Vegetative compatibility group (VCGs).…”