Banana DMR6 induction tracks Fusarium wilt progression in Prata-Ana

Infection with Fusarium oxysporum f. sp. cubense in the commercially important Brazilian banana cultivar ‘Prata-Ana’ was associated with a sharp rise in expression of the susceptibility gene MusaDMR6 as the fungus advanced from root invasion toward severe vascular disease. In a controlled inoculation experiment, researchers measured DMR6 transcripts by reverse-transcription quantitative PCR at zero, 24, 48 and 72 hours after inoculation. Expression initially fell below the corresponding non-inoculated baseline, with log2 relative-expression values of −2.3 at 24 hours and −2.7 at 48 hours. It then reversed direction, reaching a log2 value of 2.7 at 72 hours, equivalent to an approximately 6.5-fold increase. Analysis of variance identified a statistically significant difference between inoculated and control plants at 72 hours, with p = 0.00185. The findings associate late DMR6 induction with active Fusarium wilt colonization, but they do not establish that editing the gene will produce resistant banana plants.

Fusarium wilt is described in the study as the most devastating disease affecting global banana production, with a particularly serious effect on ‘Prata-Ana’, an AAB-group cultivar cultivated in Brazil. The soil-borne fungus behaves initially as a hemibiotroph, colonizing living tissues before shifting toward an aggressive necrotrophic phase. This progression can culminate in vascular blockage, leaf chlorosis, necrosis, wilting and plant death. Foc can persist in infested soil for decades through chlamydospores, making land contaminated by highly virulent strains unsuitable for cultivation over long periods. Conventional breeding based on resistance genes has been hindered by banana’s polyploidy, sterility and long generation cycles, while maintaining fruit quality remains important. The emergence of virulent races capable of overcoming particular resistance genes adds to the incentive to investigate alternatives, including precise modification of host susceptibility factors.

MusaDMR6, also known as Downy Mildew Resistance 6, encodes a 2-oxoglutarate Fe(II)-dependent oxygenase associated with negative regulation of salicylic-acid-mediated plant immunity. Editing a susceptibility gene differs from adding a new resistance gene because the objective is to disrupt a host component that supports pathogen compatibility. DMR6 was selected because previous genetic, transcriptional and functional evidence in bananas and other plant species had identified it as a conserved immune regulator and plausible target for genome editing. The experiment was conducted at the Embrapa experimental station in Cruz das Almas, Bahia, using 35 ‘Prata-Ana’ plantlets that had been acclimatized and cultivated for 30 days in plastic pots. The substrate combined pine bark and coconut fiber at a ratio of 5:1 by volume. The completely randomized design used three biological replicates per treatment for molecular and histological sampling.

The pathogen was Foc isolate CNPMF 218, belonging to Subtropical Race 4 and selected because of its high virulence toward banana. The fungus was reactivated on potato dextrose agar and then allowed to colonize sterilized rice, producing an inoculum whose concentration was adjusted by colony-forming-unit counts to 1 × 10^6 CFU per gram of colonized rice. Approximately 40 grams of this inoculum was mixed with the substrate in each pot before the plantlets were transplanted. Root and leaf material was collected from three inoculated and three non-inoculated plants at each molecular sampling time. At 90 days after inoculation, additional plants were assessed by longitudinally sectioning their rhizomes and scoring internal vascular discoloration on a five-point scale. Samples for microscopy were fixed and embedded, while root tissue for RNA analysis was frozen in liquid nitrogen. This design allowed the timing of gene induction to be considered alongside fungal penetration, host structural responses and eventual disease severity.

Microscopic analysis showed that Foc successfully colonized ‘Prata-Ana’ roots. Hyphae and spores were detected in inoculated tissue, providing direct evidence that the molecular changes occurred in an infected host. The plant nevertheless mounted several visible defense responses. Fluorescence microscopy after aniline-blue staining identified callose deposition in cortical parenchyma and xylem vessels at 24, 48 and 72 hours after inoculation. Ferric chloride staining revealed phenolic compounds in cortical cells, appearing as dark deposits in infected roots. These observations indicate that defense-associated responses occurred during infection, but their presence did not establish resistance. The study notes that the timing and magnitude of such responses can matter as much as whether they occur, allowing virulent isolates to overcome barriers in a susceptible cultivar. Infected plants later developed leaf chlorosis, necrosis and wilting, while dark-brown to black discoloration extended through the vascular cylinder and toward the cortex.

At 90 days, inoculated plants received an average internal disease rating of 4.0 on the five-point scale, corresponding to an Internal Damage Index of 80%, which the researchers characterized as a highly severe compatible interaction. Non-inoculated controls remained asymptomatic, had healthy rhizomes and received a rating of 1.0, for an index of 0%. The severe outcome was therefore closely associated with exposure to the virulent isolate under the experimental conditions, while the controls showed no background disease. The experiment concerned one cultivar in a controlled substrate system; it did not compare resistance among cultivars or quantify field-level yield losses. The 80% index describes internal vascular damage among the inoculated plants under the stated conditions, rather than the percentage of an entire agricultural crop affected in production.

The biphasic DMR6 response adds temporal detail to the infection process. Its early repression at 24 and 48 hours may reflect an attempt to preserve salicylic-acid accumulation and limit initial fungal establishment, whereas the strong induction at 72 hours is consistent with the fungus having altered host gene expression in a way that favors continued colonization. That interpretation remains mechanistic rather than directly demonstrated. The study measured transcript abundance, defense-associated deposits and disease progression, but it did not directly quantify salicylic acid, measure DMR6 protein activity or disrupt the gene to test causality. The expression peak nevertheless coincided with observations of spore formation and advanced vascular colonization. The authors therefore considered the pattern consistent with DMR6 contributing to suppression of immunity during Fusarium wilt, while distinguishing transcriptional evidence from functional validation.

The proposed target also has precedents in other plant–pathogen systems. Earlier work cited in the study showed that CRISPR/Cas9-mediated knockout of DMR6 enhanced resistance to bacterial and other pathogens in potato and tomato without major reported growth or developmental penalties. Banana knockouts had previously produced enhanced resistance to Xanthomonas campestris pv. musacearum and Ralstonia syzygii. Those results support the biological rationale for investigating MusaDMR6 against a fungal pathogen, but they do not demonstrate resistance to Foc in ‘Prata-Ana’. Complete loss of an immune-regulating function could also produce defense–growth trade-offs, making it necessary to monitor edited plants throughout development. Resistance to one pathogen therefore cannot be treated as proof of equivalent performance against another or as evidence that edited plants will retain desirable agricultural characteristics.

Targeted editing is attractive for banana because CRISPR/Cas9 can modify an elite polyploid cultivar without the extensive crossing required by conventional breeding, potentially helping preserve existing fruit characteristics. The authors identify MusaDMR6 as a candidate for precise knockout, but present it as a target for future validation rather than a completed intervention. The immediate next step would be to generate edited lines and evaluate their response to Foc in controlled conditions, followed by testing under field conditions. Such work would need to assess whether editing changes disease severity, plant development, yield, fruit quality and other possible phenotypic effects. The study itself did not create edited plants or test these outcomes. Other candidate targets, including members of the MLO, PMR4, SWEET and WRKY gene families, may eventually provide options for combined editing strategies, but none was functionally evaluated here.

Overall, the study supplies a molecular and cellular context for pursuing susceptibility-gene editing in banana. It documents Foc colonization, early suppression followed by strong late induction of MusaDMR6, activation of callose and phenolic defenses, and severe internal vascular damage in ‘Prata-Ana’. The evidence supports DMR6 as a transcriptionally responsive candidate that may contribute to susceptibility and merits functional testing. It stops short of showing that a DMR6 knockout will limit Fusarium wilt in the field or in commercial fruit. A decisive follow-up would evaluate edited ‘Prata-Ana’ lines against Foc and then assess resistance durability, developmental effects and preservation of fruit quality in realistic cultivation settings.

Subject of Research: Transcriptional and histological analysis of MusaDMR6 during Fusarium oxysporum infection of Prata-Ana banana.

Article Title: A banana susceptibility gene underlying fusarium wilt: validation as a target for disease resistance

Article References: da Silveira Fonseca, M. L., de Souza Júnior, L. C., dos SantosNascimento, F., de Souza Ramos, A. P., Santana, W. S., Mascarenhas, M. S., Amorim, E. P., & Ferreira, C. F. (2026). A banana susceptibility gene underlying fusarium wilt: validation as a target for disease resistance. Molecular Biology Reports, 53(1), Article 1491. https://doi.org/10.1007/s11033-026-12689-8

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12689-8

Keywords: banana, Fusarium wilt, MusaDMR6, susceptibility gene, Prata-Ana, Fusarium oxysporum, plant immunity, gene expression, pathogen colonization, genome editing, susceptibility, gene