Causal Agent Of Fusarium Wilt Research Articles

Sensitivity of Fusarium oxysporum f. sp. melongenae, the causal agent of Fusarium wilt of eggplant to some ammonium, potassium, and sodium compounds in vitro and in vivo bioassays

This study evaluated the efficacy of various salts against Fusarium oxysporum f. sp. melongenae (Fomg) in vitro and in vivo bioassays. Ammonium bicarbonate/carbonate, potassium benzoate/sorbate, sodium benzoate/carbonate/metabisulphite at 2.0% entirely halted mycelial growth and spore germination of the fungus. Considering the EC50, minimum inhibitory concentration, and minimum fungicidal concentration values of the salts, sodium metabisulphite was more toxic to the fungus. In soil bioassays, at 0.4% and 0.6%, sodium metabisulphite and potassium sorbate reduced the mycelial growth of the fungus by 98.89%. However, in the soil/seed germination bioassays, potassium sorbate and sodium carbonate at 0.05–0.1% concentrations had a much lower inhibitory effect on root elongation compared to the others. The two salts may be possible to reduce the number of traditional fungicides required by integrating them with disease management strategies. However, the possibility of including inorganic salts in programs to treat fungal diseases requires further research in the greenhouse conditions.

NOVEL SPECIFIC PRIMERS FOR THE SPECIFIC DETECTION OF FUSARIUM OXYSPORUM F. SP. CUBENSE BASED ON SYBR GREEN REAL-TIME PCR

Fusarium oxysporum f. sp. cubense (Foc) is the causal agent of Fusarium wilt of banana worldwide. Foc is transmitted to another banana plantation via an infected banana sucker. A specific and sensitive detection assay could be used for disease-free propagule screening to prevent disease dispersal effectively. In this study, SYBR green-based real-time PCR assay was developed based on novel specific primers targeting the large subunit of RNA polymerase II (RPB1) gene. The partial RPB1 gene was amplified and sequenced from Foc isolate FOC1708 and SK3-2. Regions specific for Foc were identified and used for designing real-time PCR primers. The specificity of the designed primers was evaluated on genomic DNA from Foc isolates and non-target microorganisms. The results showed that the designed primers were specific to only Foc isolates from race 1 and tropical race 4 (TR4). The detection efficiency of the designed primers was compared to other published primers through optimized SYBR green-based real-time PCR assay and nested PCR. The new primers could detect the Foc genomic DNA at a minimum of 5 pg and target pathogen in a symptomless banana sucker. The specificity and sensitivity of the new primers were comparable to the published real-time PCR primers and the nested PCR assay. This developed assay with these novel primers can aid the disease quarantine for effective prevention and control of the Fusarium wilt of banana.

Development of PCR-Based Race-Specific Markers for Differentiation of Indian Fusarium oxysporum f. sp. cubense, the Causal Agent of Fusarium Wilt in Banana.

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc), is the most lethal soil-borne fungal pathogen infecting bananas. Foc race 1 (R1) and 4 (R4) are the two most predominant races affecting the economically important Cavendish group of bananas in India. A total of seven vegetative compatibility groups (VCGs) from three pathogenic races were isolated during our field survey and were found to be highly virulent towards cv. Grande Naine. According to comparative genome analyses, these Indian Foc VCGs were diverse in genomic organization and effector gene profiles. As a result, false-positive results were obtained with currently available molecular markers. In this context, the study has been initiated to develop PCR-based molecular markers for the unambiguous identification of Indian Foc R1 and R4 isolates. Whole-genome sequences of Foc R1 (GCA_011316005.3), Foc TR4 (GCA_014282265.3), and Foc STR4 (GCA_016802205.1), as well as the reference genomes of Foc (ASM799451v1) and F. oxysporum f. sp. lycopersici (Fol; ASM14995v2), were aligned to identify unique variable regions among the Foc races. Using putative chromosome and predicted gene comparison, race-specific unique Foc virulence genes were identified. The putative lineage-specific identified genes encoding products secreted in xylem (SIX) that may be necessary for disease development in the banana. An in silico analysis was performed and primers were designed from a region where sequences were dissimilar with other races to develop a specific marker for Foc R1, R4, TR4, and STR4. These race-specific markers allowed target amplification in the characterized highly virulent Foc isolates, and did not show any cross-amplification to any other Foc races, VCGs or banana pathogens, Fusarium species, and non-pathogenic Fusarium oxysporum isolates. The study demonstrated that the molecular markers developed for all the three Foc races of India could detect the pathogen in planta and up to 0.025 pg µL−1 DNA levels. Thus, the markers developed in this study are novel and could potentially be useful for the accurate diagnosis and detection of the Indian Foc races which are important for the effective management of the disease.

Impact of biosolarization with almond hull and shell amendments for the control of Fusarium oxysporum f. sp. lactucae in a lettuce/tomato cropping system

Biosolarization is an alternative to chemical fumigation that couples solarization and organic amendments to control diseases by increasing temperature and microbial activity. A field study was conducted to evaluate the efficacy of biosolarization, using almond processing residues from two varieties, to control propagules of Fusarium oxysporum f. sp. lactucae, the causal agent of Fusarium wilt of lettuce. Peak soil temperatures of solarized and biosolarized soils were 6–15 °C higher than control soils, and biosolarized soils experienced 1 to 3 °C higher temperatures on average and 10 to 27°C-day higher cumulative temperatures than soil solarized without amendment. Residues were high in endogenous organic acids, between 144 and 298 mM combined acetic, lactic, succinic, and butyric acids. After eight days of treatment, solarized soils only reduced the population of Fusarium oxysporum f. sp. lactucae by 9% compared to the average non-treated non-amended control plots; whereas soils solarized and amended with residues from pollinator varieties of almonds showed a greater pathogen reduction of 63%. In this instance, Fusarium wilt had no effect on plant health due to low pressure and moderate innate plant resistance. Soils amended with nonpareil residues had similar lettuce biomass and health scores to untreated plots, but lower health scores than the solarized treatments. This may be due to residual organic acids detected in biosolarized plots 3–4 weeks after treatments (1–57 mM), which significantly correlated to poor lettuce health score. Roughly, one year after soil treatment, solarized plots continued to out-perform pollinator-residue amended plots. Germination assays indicate biosolarization outcomes may be improved with increased aerobic remediation time.

Grass pea natural variation reveals oligogenic resistance to Fusarium oxysporum f. sp. pisi.

Grass pea (Lathyrus sativus L.) is an annual legume species, phylogenetically close to pea (Pisum sativum L.), that may be infected by Fusarium oxysporum f. sp. pisi (Fop), the causal agent of fusarium wilt in peas with vast worldwide yield losses. A range of responses varying from high resistance to susceptibility to this pathogen has been reported in grass pea germplasm. Nevertheless, the genetic basis of that diversity of responses is still unknown, hampering its breeding exploitation. To identify genomic regions controlling grass pea resistance to fusarium wilt, a genome-wide association study approach was applied on a grass pea worldwide collection of accessions inoculated with Fop race 2. Disease responses were scored in this collection that was also subjected to high-throughput based single nucleotide polymorphisms (SNP) screening through genotyping-by-sequencing. A total of 5,651 high-quality SNPs were considered for association mapping analysis, performed using mixed linear models accounting for population structure. Because of the absence of a fully assembled grass pea reference genome, SNP markers' genomic positions were retrieved from the pea's reference genome v1a. In total, 17 genomic regions were associated with three fusarium wilt response traits in grass pea, anticipating an oligogenic control. Seven of these regions were located on pea chromosomes 1, 6, and 7. The candidate genes underlying these regions were putatively involved in secondary and amino acid metabolism, RNA (regulation of transcription), transport, and development. This study revealed important fusarium wilt resistance favorable grass pea SNP alleles, allowing the development of molecular tools for precision disease resistance breeding.

NOVEL SPECIFIC PRIMERS FOR THE SPECIFIC DETECTION OF FUSARIUM OXYSPORUM F. SP. CUBENSE BASED ON SYBR GREEN REAL-TIME PCR

Fusarium oxysporum f. sp. cubense (Foc) is the causal agent of Fusarium wilt of banana worldwide. Foc is transmitted to another banana plantation via an infected banana sucker. A specific and sensitive detection assay could be used for disease-free propagule screening to prevent disease dispersal effectively. In this study, SYBR green-based real-time PCR assay was developed based on novel specific primers targeting the large subunit of RNA polymerase II (RPB1) gene. The partial RPB1 gene was amplified and sequenced from Foc isolate FOC1708 and SK3-2. Regions specific for Foc were identified and used for designing real-time PCR primers. The specificity of the designed primers was evaluated on genomic DNA from Foc isolates and non-target microorganisms. The results showed that the designed primers were specific to only Foc isolates from race 1 and tropical race 4 (TR4). The detection efficiency of the designed primers was compared to other published primers through optimized SYBR green-based real-time PCR assay and nested PCR. The new primers could detect the Foc genomic DNA at a minimum of 5 pg and target pathogen in a symptomless banana sucker. The specificity and sensitivity of the new primers were comparable to the published real-time PCR primers and the nested PCR assay. This developed assay with these novel primers can aid the disease quarantine for effective prevention and control of the Fusarium wilt of banana.

The Survival and Treatment of Fusarium oxysporum f. sp. cubense in Water.

Fusarium oxysporum f. sp cubense (Foc), the causal agent of Fusarium wilt, is one of the most devastating constraints to banana production worldwide. The spread of Foc in water is particularly concerning, as infested water can rapidly contaminate disease-free areas. The objectives of this study were to investigate the survival of Foc in water and to test the effectiveness of water treatment with chlorine, ozone, UV, and peracetic acid. The study indicated that Foc spores can survive in water for more than 120 days, but that viability was reduced in stagnant water, probably due to anaerobic conditions when spores settled at the bottom. It is therefore recommended that surface water be extracted and treated before it is used for irrigation. The efficacy of all water treatments was reduced in the presence of soil, implying that water needs to be soil-free before treatment. The use of peracetic acid is recommended to treat Foc-contaminated water, as it is safe for use and does not require installation costs although it is effective at treating Foc-contaminated water, ozone would require significant input costs and chlorine can produce harmful disinfection by-products. UV would be impractical for field application because of the high doses required to eliminate Foc.

Molecular Characterization of Laboratory Mutants of Fusarium oxysporum f. sp. niveum Resistant to Prothioconazole, a Demethylation Inhibitor (DMI) Fungicide.

Fusarium oxysporum f. sp. niveum (FON) is the causal agent of Fusarium wilt in watermelon, an international growth-limiting pathogen of watermelon cultivation. A single demethylation inhibitor (DMI) fungicide, prothioconazole, is registered to control this pathogen, so the risk of resistance arising in the field is high. To determine and predict the mechanism by which FON could develop resistance to prothioconazole, FON isolates were mutagenized using UV irradiation and subsequent fungicide exposure to create artificially resistant mutants. Isolates were then put into three groups based on the EC50 values: sensitive, intermediately resistant, and highly resistant. The mean EC50 values were 4.98 µg/mL for the sensitive, 31.77 µg/mL for the intermediately resistant, and 108.33 µg/mL for the highly resistant isolates. Isolates were then sequenced and analyzed for differences in both the coding and promoter regions. Two mutations were found that conferred amino acid changes in the target gene, CYP51A, in both intermediately and highly resistant mutants. An expression analysis for the gene CYP51A also showed a significant increase in the expression of the highly resistant mutants compared to the sensitive controls. In this study, we were able to identify two potential mechanisms of resistance to the DMI fungicide prothioconazole in FON isolates: gene overexpression and multiple point mutations. This research should expedite growers’ and researchers’ ability to detect and manage fungicide-resistant phytopathogens.

Suppressive effect of secondary metabolites from Streptomyces plumbeus isolate F31D against Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt of tomato

Suppressive effect of secondary metabolites from Streptomyces plumbeus isolate F31D against Fusarium oxysporum f. sp. lycopersici, the causal agent of Fusarium wilt of tomato

Characterization of Current Fusarium oxysporum f. sp. vasinfectum Isolates from Cotton in the San Joaquin Valley of California and Lower Valley El Paso, Texas.

Fusarium oxysporum f. sp. vasinfectum race 4 is a causal agent of Fusarium wilt of cotton (Gossypium spp.). This study aimed to characterize the existing distribution and frequency of current field populations of F. oxysporum f. sp. vasinfectum race 4 genotypes in the San Joaquin Valley (SJV) of California and Lower Valley El Paso, TX and examine representative isolates for aggressiveness during different stages of seedling development. A survey was conducted from 2017 to 2019 across 13 locations in the SJV and one location in El Paso, TX during 2018. From the SJV, isolates identified as the F. oxysporum f. sp. vasinfectum race 4 T genotype were dispersed across the SJV, whereas isolates identified as the F. oxysporum f. sp. vasinfectum race 4 N genotype were most frequently isolated from cotton fields in the northern county of Merced. The F. oxysporum f. sp. vasinfectum race 4 isolates from the Texas location were identified as the MT genotype. A selection of representative isolates was evaluated using three inoculation assays (rolled-towel, F. oxysporum f. sp. vasinfectum-infested oat seed, and root-dip inoculation) to test the isolates' abilities to produce symptoms during seedling stages of cotton development. All isolates tested were capable of producing symptoms on cotton; however, isolate aggressiveness varied within and across inoculation assays. In all assays, higher levels of disease development were observed in the moderately susceptible Pima (Gossypium barbadense L.) cultivars (DP-340 or PHY-830) when compared with the moderately tolerant Upland (G. hirsutum L.) cultivar (FM-2334). However, no correlation was found among the different response variables for the rolled-towel assay when compared with the root-dip and infested oat seed assays. These results suggest that different genes are involved in the resistance response during the early seedling development stage measured in the rolled-towel assay compared with the later seedling development stages measured during the root-dip inoculation and infested oat seed assays, revealing the complexity of the Fusarium wilt disease and host-plant resistance mechanisms.

Phytotoxic Metabolites Produce by Fusarium oxysporum f. sp. cubense Race 2.

Banana is a major tropical fruit crop but banana production worldwide is seriously threatened due to Fusarium wilt. Fusarium oxysporum f. sp. cubense (Foc), the causal agent of Fusarium wilt of banana (also referred as Panama disease) is an asexual, soil inhabiting facultative parasite. Foc isolates can be classified into three races that are not defined genetically, but for their pathogenicity to different banana cultivars. Despite mycotoxins being some of the best studied virulence factors of phytopathogenic fungi and these have been useful for the prediction of Foc virulence on banana plants, toxins produced by Foc race 2 strains have not been previously identified. The aim of this contribution was to identify the phytotoxic metabolites closely related to banana wilt caused by a Foc race 2 strain. We used an in vitro bioassay on detached banana leaves to evaluate the specificity of the microbial culture filtrates before a partial purification and further identification of Foc race 2 phytotoxins. A 29-day-old host-specific culture filtrate was obtained but specificity of culture filtrate was unrecovered after partial purification. The non-specific phytotoxins were characterized as fusaric acid, beauvericin, and enniatin A. Whereas some, if not all, of these phytotoxins are important virulence factors, a proteinaceous fraction from the specific 29-day-old culture filtrate protected the leaves of the resistant banana cultivar from damage caused by such phytotoxic metabolites.

Survival of Fusarium oxysporum f. sp. lactucae on Crop Residue in Soil.

Fusarium oxysporum f. sp. lactucae, the cause of Fusarium wilt of lettuce, can survive on crop residue in soil. Persistence of the pathogen over time will be influenced by the rate at which residue decomposes. We evaluated the effect of drying and fragmenting crop residue on the rate of decomposition and survival of F. oxysporum f. sp. lactucae. In a controlled experiment that represented optimal drying conditions, fragmenting and oven drying infested lettuce taproots at 30°C significantly reduced the frequency of recovery of the pathogen, compared with untreated tissue. However, in a field experiment, drying infested crop residue on the soil surface prior to incorporation did not significantly reduce survival of F. oxysporum f. sp. lactucae after 1 year. Regardless of treatment, there was not a significant decrease in soil inoculum density between 1 and 12 months after residue was incorporated. In a greenhouse experiment, fragmenting crop residue prior to incorporation in pathogen-free soil resulted in significantly higher inoculum densities of F. oxysporum f. sp. lactucae after 1 year. The increase in inoculum levels was associated with a faster rate of residue decomposition, which may be beneficial in the long run but not where lettuce will be replanted within the next year.

Horizontal chromosome transfer and independent evolution drive diversification in Fusarium oxysporum f. sp. fragariae.

Summary The genes required for host‐specific pathogenicity in Fusarium oxysporum can be acquired through horizontal chromosome transfer (HCT). However, it is unknown if HCT commonly contributes to the diversification of pathotypes.Using comparative genomics and pathogenicity phenotyping, we explored the role of HCT in the evolution of F. oxysporum f. sp. fragariae, the cause of Fusarium wilt of strawberry, with isolates from four continents.We observed two distinct syndromes: one included chlorosis (‘yellows‐fragariae’) and the other did not (‘wilt‐fragariae’). All yellows‐fragariae isolates carried a predicted pathogenicity chromosome, ‘chrY‐frag’, that was horizontally transferred at least four times. chrY‐frag was associated with virulence on specific cultivars and encoded predicted effectors that were highly upregulated during infection. chrY‐frag was not present in wilt‐fragariae; isolates causing this syndrome evolved pathogenicity independently. All origins of F. oxysporum f. sp. fragariae occurred outside of the host’s native range.Our data support the conclusion that HCT is widespread in F. oxysporum, but pathogenicity can also evolve independently. The absence of chrY‐frag in wilt‐fragariae suggests that multiple, distinct pathogenicity chromosomes can confer the same host specificity. The wild progenitors of cultivated strawberry (Fragaria × ananassa) did not co‐evolve with this pathogen, yet we discovered several sources of genetic resistance.

English

Antifungal metal structures, using silver at nanoscale, were synthesized using leaves extract of two indigenous trees i.e., Morus alba (white mulberry) and Aegle marmelos (bael fruit). The antifungal characteristics of synthesized silver nanoparticles (AgNPs) was verified against Fusarium oxysporum, the causal agent of Fusarium wilt and Macrophomina phaseolina, the pathogen of charcoal rot, taking tomato as a model plant. Synthesized nanoparticles were checked against selected fungi in concentrations of 25, 50, 75 and 100 μg/mL. Negative control received no nanoparticles but sterilized water, whereas positive control plants were treated with chemical fungicide (Nativo). Result of in vitro and greenhouse experiments confirmed the potential of synthesized nanoparticles to reduce fungal growth and disease incidence. However, the NPs synthesized using leaves extract of white mulberry were more effective. In green house trials, the plants treated with NPs in a concentration of 100 μg/mL showed parallel results as were recorded in plants receiving fungicide. Similarly, both selected fungi also depicted slight variation in their responses towards various treatments as percentage of growth inhibition as well as disease incidence was more in F. oxysporum than in M. phaseolina. UV-spectrophotometer ascertained the optimization conditions by adjusting concentrations of silver nitrate between 1, 1.5, 2, 2.5 and 3 mM, incubation period of 24, 48, 72 and 96 h and pH of biosynthesis system adjusted at 4, 6, 8, 10 and 12. FTIR confirmed the presence of different functional groups available both in plant extracts and nanoparticles while, SEM indicated spherical, polydisperse morphology of AgNPs with size ranges from 20–48 nm respectively. In pot experiment nanoparticles synthesized using white mulberry leaves reduced fusarium infection up to 97% and macrophomina rot up to 92%. Nanoparticles synthesized using bael leaves extract were comparatively less effective against selected fungi than those synthesized using white mulberry leaves extract. Hence these results provided basis for the use of green synthesized NPs using white mulberry leaves extract as an alternative to conventional fungicides to help reduce environmental pollution. © 2021 Friends Science Publishers

Colonization of Wild Blackberry Plants in California by Fusarium oxysporum f. sp. mori.

Fusarium oxysporum f. sp. mori, the causal agent of Fusarium wilt of blackberry, was first reported in California and Mexico in 2016. A limited survey of the population revealed this pathogen to be one of the most diverse formae speciales of F. oxysporum. We explored the possibility that strains of F. oxysporum pathogenic to commercial blackberry could also be recovered from wild blackberry (Rubus spp.) in California. For this purpose, wild Rubus species in blackberry nurseries, fruit production fields, and nearby areas were collected between 2017 and 2019. Thirty-four isolates of F. oxysporum were recovered from asymptomatic Rubus armeniacus and Rubus ursinus plants. Based on sequence of the translation elongation factor 1-α, somatic compatibility, and pathogenicity to blackberry, 16 isolates were confirmed as F. oxysporum f. sp. mori. These isolates were associated with three somatic compatibility groups, one of which was first identified in this study. Recovery of the pathogen confirmed that wild blackberry plants can act as a reservoir of inoculum of F. oxysporum f. sp. mori and that it can move from wild blackberry plants to commercial cultivars or vice versa.

Wheat/faba bean intercropping improves physiological and structural resistance of faba bean to fusaric acid stress

AbstractFusarium oxysporum f. sp. fabae is the causal agent of fusarium wilt. Fusaric acid (FA), produced by F. oxysporum, plays an important role in the occurrence of disease, and intercropping is an effective measure for control of disease and for improving host resistance in plants. The objective of this study was to investigate the physiological and biochemical responses, and mechanisms of tissue structure resistance, of intercropped faba beans following exposure to different concentrations of FA. Results demonstrated that intercropping reduced the occurrence of fusarium wilt, and improved faba bean growth and yield. In addition, wheat intercropping significantly reduced red ink absorption of faba bean (33.2%), increased water content (3.1%), and increased activity of the root antioxidant enzymes peroxidase (POD) and catalase (CAT) (26.3% and 2.2.%, respectively). Furthermore, increased lignin content and callose deposition in plant vessels were observed (12.5% and 42.7%, respectively) when subjected to the highest concentration of FA stress (200 mg/L). Intercropping resulted in more intact root cell morphology, increased occurrence of intracellular vacuoles, increased cell wall thickness, and an increase in the number of mitochondria and rough endoplasmic reticulum. Intercropping alleviated the wilting effect of FA on faba bean via enhanced physiological, biochemical, and tissue structure resistance of faba bean root.

Genome Sequence of Fusarium oxysporum f. sp. conglutinans, the Etiological Agent of Cabbage Fusarium Wilt.

Fusarium oxysporum f. sp. conglutinans is the causal agent of Fusarium wilt of cabbage (Brassica oleracea var. capitata L.), which results in severe yield loss. Here, we report a high-quality genome sequence of a race 1 strain (IVC-1) of F. oxysporum f. sp. conglutinans, which was assembled using a combination of PacBio long-read and Illumina short-read sequences. The assembled IVC-1 genome has a total size of 71.18 Mb, with a contig N50 length of 4.59 Mb, and encodes 23,374 predicted protein-coding genes. The high-quality genome of IVC-1 provides a valuable resource for facilitating our understanding of F. oxysporum f. sp. conglutinans-cabbage interaction.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Ex Ante Assessment of Returns on Research Investments to Address the Impact of Fusarium Wilt Tropical Race 4 on Global Banana Production.

The spread of Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), causal agent of Fusarium wilt of banana (FWB), has been projected to reach 17% of the global banana-growing area by 2040 equaling 36 million tons of production worth over US$10 billion. This potential loss has fueled (inter)national discussions about the best responses to protect production and small-scale growers’ livelihoods. As part of a multi-crop ex ante assessment of returns on research investments conducted by the CGIAR Research Program on Roots, Tubers, and Bananas (RTB) from 2012 to 2016, four FWB research options were assessed: (i) improved exclusion, surveillance, eradication, and containment (ESEC) measures to reduce Foc TR4 spread, (ii) integrated crop and disease management (ICDM) to facilitate production of partially FWB resistant cultivars on Foc-infested soils, (iii) conventional breeding of FWB-resistant cultivars (CBRC), and (iv) genetically modified (GM) FWB-resistant cultivars (GMRC). Building on a risk index (Foc scale) predicting the initial occurrence and internal spread of Foc TR4 in 29 countries, an economic surplus (ES) model, cost-benefit analysis, and poverty impact simulations were used to assess impact under two adoption scenarios. All options yield positive net present values (NPVs) and internal rates of return (IRRs) above the standard 10% rate. For the conservative scenario with 50% reduced adoption, IRRs were still 30% for ICDM, 20% for CBRC, and 28% for GMRC. ESEC has IRRs between 11 and 14%, due to higher costs of capacity strengthening, on-going surveillance, farmer awareness campaigns, and implementation of farm biosecurity practices, which could be effective for other diseases and benefit multiple crops. The research investments would reach between 2.7 million (GMRC) and 14 million (ESEC) small-scale beneficiaries across Asia/Pacific, Sub-Saharan Africa, and Latin America/Caribbean. The options varied in their potential to reduce poverty, with the largest poverty reduction resulting from CBRC with 850,000 and ESEC with 807,000 persons lifted out of poverty (higher adoption scenario). In the discussion, we address the data needs for more fine-grained calculations to better guide research investment decisions. Our results show the potential of public investments in concerted research addressing the spread of Foc TR4 to yield high returns and substantially slow down disease spread.

The potential for Fusarium oxysporum f. sp. fragariae, cause of fusarium wilt of strawberry, to colonize organic matter in soil and persist through anaerobic soil disinfestation

AbstractFusarium wilt of strawberry, caused by Fusarium oxysporum f. sp. fragariae, is a disease of primary concern for strawberry production in many countries. Crop rotation and anaerobic soil disinfestation (ASD) have gained recent interest for their potential to contribute to management of this disease. Both techniques involve incorporation of organic matter into soil, which may be utilized by strains of Fusarium that are competitive saprophytes. We show that F. oxysporum f. sp. fragariae can colonize strawberry, lettuce, raspberry, and broccoli leaf tissues, which are sources of organic matter generated during crop rotation. This pathogen increased in soil population density during ASD treatments that did not become anaerobic, possibly as a result of growth on the organic amendment. However, significant population decreases were observed after ASD treatment when at least 100,000 cumulative reduced mV hours occurred in a 14‐day experiment. Post‐ASD abundance of F. oxysporum f. sp. fragariae in soil was negatively correlated with cumulative reduced mV hours. The only treatment that consistently caused disinfestation was exposed to a maximum temperature of 22 °C, which indicates there is potential for developing effective ASD treatments in the cool climates where strawberries are grown. Awareness that F. oxysporum f. sp. fragariae can act as a competitive soil saprophyte should be further investigated for its potential to alter disease outcomes where organic amendments are applied.

Current state of Fusarium wilt of banana in the subtropics

Subtropically grown bananas have different interactions with Fusarium oxysporum f. sp. cubense (Foc), causal agent of Fusarium wilt of banana (FWB), when compared with those grown in the tropics. The designation ‘subtropical’ race 4 (SR4) was assigned to Foc strains able to infect Cavendish (AAA) cultivars in the subtropics, but not in the tropics. ‘Tropical’ race 4 (TR4) gained prominence with the appearance and spread of a Foc strain that severely affects Cavendish bananas in both the tropics and subtropics. Recent surveys in Asia revealed TR4 as the predominant strain both in the tropics and subtropics, affecting not only Cavendish, but also many other cultivars. In many subtropical banana zones, Foc races 1 and 2, which complete the racial structure of Foc, are also found and cause severe losses in certain market-preferred dessert bananas. Environmental constraints increase the susceptibility of Cavendish bananas to SR4. However, the role of abiotic stresses in cultivar susceptibility to Foc needs to be better understood. It is not clear why some Foc strains only affect Cavendish in the subtropics, and what other factors, including pathogen virulence and microbial functional diversity, might be driving disease epidemics. Field experience suggests that optimum soil and water management strategies can reduce disease intensity, but targeted studies are needed to understand the virulence of different strains, the impact of fluctuating temperatures, soil pH, organic matter breakdown and soil microbial dynamics. Research findings on the epidemiology and management of FWB in Australia, Brazil, China, India and South Africa are discussed to propose priority areas for the development of improved disease management practices. © 2020 International Society for Horticultural Science. All rights reserved.