Benzothiadiazole-Mediated Induced Resistance to Fusarium oxysporum f. sp. radicis-lycopersici in Tomato

Benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), a synthetic chemical, was applied as a foliar spray to tomato (Lycopersicon esculentum) plants and evaluated for its potential to confer increased resistance against the soil-borne pathogen Fusarium oxysporum f. sp. radicis-lycopersici (FORL). In nontreated tomato plants all root tissues were massively colonized by FORL hyphae. Pathogen ingress toward the vascular stele was accompanied by severe host cell alterations, including cell wall breakdown. In BTH-treated plants striking differences in the rate and extent of fungal colonization were observed. Pathogen growth was restricted to the epidermis and the outer cortex, and fungal ingress was apparently halted by the formation of callose-enriched wall appositions at sites of fungal penetration. In addition, aggregated deposits, which frequently established close contact with the invading hyphae, accumulated in densely colonized epidermal cells and filled most intercellular spaces. Upon incubation of sections with gold-complexed laccase for localization of phenolic-like compounds, a slight deposition of gold particles was observed over both the host cell walls and the wall appositions. Labeling was also detected over the walls of fungal cells showing signs of obvious alteration ranging from cytoplasm disorganization to protoplasm retraction. We provide evidence that foliar applications of BTH sensitize susceptible tomato plants to react more rapidly and more efficiently to FORL attack through the formation of protective layers at sites of potential fungal entry.     

Implication of Pectic Components in Cell Surface Interactions between Tomato Root Cells and Fusarium oxysporum f. sp. radicis-lycopersici: A Cytochemical Study by Means of a Lectin with Polygalacturonic Acid-Binding Specificity

Aplysia gonad lectin, a polygalacturonic acid-binding lectin isolated from the sea mollusc Aplysia depilans, was complexed to colloidal gold and used for localizing polygalacturonic-acid-containing molecules in tomato root tissues infected with Fusarium oxysporum f. sp. radicis-lycopersici (FORL). Colonization of host tissues by FORL was associated with striking wall modifications including disruption and even loss of middle lamellae. According to the labeling pattern observed in host wall areas adjacent to fungal penetration channels, it is likely that FORL pectolytic enzymes act through localized wall degradation. The release of polygalacturonic acid-rich wall fragments and the accumulation of polygalacturonic acid-containing molecules in some altered phloem cells were frequently observed and considered to be specific host reactions to fungal attack. The heavy deposition of such molecules at strategic sites such as wall oppositions and intercellular spaces provides support to their implication in the plant defense system. The possible interrelation between polygalacturonic acid-containing molecules and other polymers such as lignin and phenolic compounds remains to be investigated further. The role of these molecules in host-pathogen interactions is discussed in relation to plant defense.     

Production of volatile organic compounds by an antagonistic strain Paenibacillus polymyxa WR-2 in the presence of root exudates and organic fertilizer and their antifungal activity against Fusarium oxysporum f. sp. niveum

The volatile organic compounds (VOCs) produced by antagonistic microbes have great antifungal potential against soil-borne fungal pathogens. The VOCs produced by Paenibacillus polymyxa strain WR-2 in the presence of root exudates and organic fertilizer were identified and their effects on the growth and spore germination of Fusarium oxysporum f. sp. niveum were evaluated. The VOCs produced by WR-2 inhibited the growth of F. oxysporum by 38%, 36% and 40% in agar medium, sterilized soil and natural soil, respectively. This inhibitory effect was increased to 60%, 58% and 64% with the addition of organic fertilizer in agar medium, sterilized soil and natural soil, respectively. The addition of root exudates did not affect the production of antifungal VOCs by WR-2. The VOCs produced by WR-2 completely inhibited the germination of F. oxysporum spores. Out of 42 identified VOCs, seven VOCs; benzothiazole, benzaldehyde, undecanal, dodecanal, hexadecanal, 2-tridecanone and phenol were found to inhibit the growth of F. oxysporum. The results of these experiments suggest another significance of using organic fertilizer as a carrier material with the biocontrol agents to control soil-borne fungal pathogens.     

Iron-Chelating Compounds Produced by Soil Pseudomonads: Correlation with Fungal Growth Inhibition

Strains of Pseudomonas putida, Pseudomonas sp., and Pseudomonas aeruginosa were examined for their ability to grow in the presence of the iron chelator, ethylenediamine-di-(o-hydroxyphenylacetic acid). In vitro fungal inhibition assays showed that the isolates varied in their ability to inhibit the growth of representative fungal plant pathogens. Fungal inhibition in vitro was superior to that of previously reported Pseudomonas sp. Studies with Fusarium oxysporum forma sp. lycopersici and a susceptible tomato cultivar demonstrated that Pseudomonas putida PPU3.1 was able to significantly reduce wilt disease.     

Chitosan Treatment: An Emerging Strategy for Enhancing Resistance of Greenhouse Tomato Plants to Infection by Fusarium oxysporum f.sp. radicis-lycopersici

The potential of chitosan, a non-toxic and biodegradable polymer of beta -1,4-glucosamine, for controlling fusarium crown and root rot of greenhouse-grown tomato caused by Fusarium oxysporum f.sp. radicis-lycopersici (FORL) was investigated. The amendment of plant growth substratum with chitosan at concentrations of 12.5 or 37.5 mg l-1 significantly reduced plant mortality, root rot symptoms and yield loss attributed to FORL. Maximum disease control was achieved with chitosan at 37.5 mg l-1, when plant mortality was reduced by more than 90% and fruit yield was comparable with that of non-infected plants. In the absence of FORL, chitosan did not adversely affect plant growth and fruit yield. Cytological observations on root samples from FORL-inoculated plants revealed that the beneficial effect of chitosan in reducing disease was associated with increased plant resistance to fungal colonization. In chitosan-treated plants, fungal growth was restricted to the epidermis and the cortex. Invading hyphae showed marked cellular disorganization, characterized by increased vacuolation and even complete loss of the protoplast. The main host reactions included the formation of structural barriers at sites of attempted fungal penetration, the deposition of an opaque material (probably enriched with phenolics according to its electron density) in intercellular spaces and the occlusion of xylem vessels with tyloses, polymorphic bubbles and osmiophilic substances. Although chitosan may also have antifungal properties, the ultrastructural observations provide evidence that chitosan sensitizes tomato plants to respond more rapidly and efficiently to FORL attack. Chitosan has the potential to become a useful agent for controlling greenhouse diseases caused by soil-borne pathogens.     

Evaluation of the strains of Acinetobacter and Enterobacter as potential biocontrol agents against Ralstonia wilt of tomato

Bacterial wilt (Ralstonia solanacearum) of tomato, Lycopersicon esculentum, causes a considerable amount of damage to tomato in Southern China. Biological control is one of the more promising approaches to reduce the disease incidence and yield losses caused by this disease. Based on antagonistic activity against R. solanacearum and three soil-borne fungal pathogens as well as biocontrol efficacy in the greenhouse, two bacterial strains Xa6 (Acinetobacter sp.) and Xy3 (Enterobacter sp.) were selected out of fourteen candidates as potential biocontrol agents. In order to find a suitable antagonist inoculation method, we compared the methods of root-dipping with soil-drenching in the aspects including rhizocompetence, biocontrol efficacy, and effect of promoting plant growth under greenhouse conditions. The drenching treatment resulted in a higher biocontrol efficacy and plant-yield increase, and this method was also easier to operate in the field on a large scale. Field trials were conducted for further evaluation of these two antagonistic strains. In both greenhouse and field experiments, the strain Xy3 had a better control effect against bacterial wilt than Xa6 did, while Xa6 caused higher biomass or yield increases. As recorded on the 75th day after treatment in two field experiments, biocontrol efficacy of Xy3 was about 65% in both field trials, and the yield increases caused by Xa6 were 32.4 and 40.7%, respectively, in the two trials. This is the first report of an Acinetobacter sp. strain used as a BCA against Ralstonia wilt of tomato.     

Screening siderophore producing bacteria as potential biological control agent for fungal rice pathogens in Thailand

Rice (Oryza sativa) is a staple food in Thailand and, in addition, feeds around one half of the world’s population. Therefore, diseases of rice are of special concern. Rice is destroyed by 2 main pathogens, Fusarium oxysporum and Pyricularia oryzae the causative agents of root rot and blast in rice respectively. These pathogens result in low grain yield in Thailand and other Southeast Asian countries. Soil samples were taken from paddy fields in Northern Thailand and bacteria were isolated using the soil dilution plate method on Nutrient agar. Isolation yielded 216 bacterial isolates which were subsequently tested for their siderophore production and effectiveness in inhibiting mycelial growth in vitro of the rice pathogenic fungi; Alternaria sp., Fusarium oxysporum, Pyricularia oryzae and Sclerotium sp., the causal agent of leaf spot, root rot, blast and stem rot in rice. It was found that 23% of the bacteria isolated produced siderophore on solid plating medium and liquid medium, In dual culture technique, the siderophore producing rhizobacteria showed a strong antagonistic effect against the Alternaria (35.4%), Fusarium oxysporum (37.5%), Pyricularia oryzae (31.2%) and Sclerotium sp. (10.4%) strains tested. Streptomyces sp. strain A 130 and Pseudomonas sp. strain MW 2.6 in particular showed a significant higher antagonistic effect against Alternaria sp. while Ochrobactrum anthropi D 5.2 exhibited a good antagonistic effect against F. oxysporum. Bacillus firmus D 4.1 inhibited P. oryzae and Kocuria rhizophila 4(2.1.1) strongly inhibited Sclerotium sp. P. aureofaciens AR 1 was the best siderophore producer overall and secreted hydroxamate type siderophore. This strain exhibits an in vitro antagonistic effect against Alternaria sp., F. oxysporum and P. oryzae. Siderophore production in this isolate was maximal after 15 days and at an optimal temperature of 30°C, yielding 99.96 ± 0.46 μg ml^?1 of siderophore. The most effective isolates were identified by biochemical tests and molecular techniques as members of the Genus Bacillus, Pseudomonas and Kocuria including B. firmus D 4.1, P. aureofaciens AR1 and Kocuria rhizophila 4(2.1.1). The study demonstrated antagonistic activity towards the target pathogens discussed and are thus potential agents for biocontrol of soil borne diseases of rice in Thailand and other countries.     

Role of ethylene in the protection of tomato plants against soil-borne fungal pathogens conferred by an endophytic Fusarium solani strain

An endophytic fungal isolate (Fs-K), identified as a Fusarium solani strain, was obtained from root tissues of tomato plants grown on a compost which suppressed soil and foliar pathogens. Strain Fs-K was able to colonize root tissues and subsequently protect plants against the root pathogen Fusarium oxysporum f.sp. radicis-lycopersici (FORL), and elicit induced systemic resistance against the tomato foliar pathogen Septoria lycopersici. Interestingly, attenuated expression of certain pathogenesis-related genes, i.e. PR5 and PR7, was detected in tomato roots inoculated with strain Fs-K compared with non-inoculated plants. The expression pattern of PR genes was either not affected or aberrant in leaves. A genetic approach, using mutant tomato plant lines, was used to determine the role of ethylene and jasmonic acid in the plant's response to infection by the soil-borne pathogen F. oxysporum f.sp. radicis-lycopersici (FORL), in the presence or absence of isolate Fs-K. Mutant tomato lines Never ripe (Nr) and epinastic (epi1), both impaired in ethylene-mediated plant responses, inoculated with FORL are not protected by isolate Fs-K, indicating that the ethylene signalling pathway is required for the mode of action used by the endophyte to confer resistance. On the contrary, def1 mutants, affected in jasmonate biosynthesis, show reduced susceptibility to FORL, in the presence Fs-K, which suggests that jasmonic acid is not essential for the mediation of biocontrol activity of isolate Fs-K.     

Increased Growth and Yield of Hydroponically Grown Greenhouse Tomato Plants Inoculated with Arbuscular Mycorrhizal Fungi and Fusarium oxysporum f. sp. radicis-lycopersici

The arbuscular mycorrhizal fungi Glomus monosporum, G. vesiculiferum, G. deserticola, G. intraradices, G. mosseae, and two unidentified species were tested to determine their effect on plant growth and fruit production of tomato (Lycopersicon esculentum Mill.) cv. Trust inoculated with Fusarium oxysporum f. sp. radicis-lycopersici (FORL) under near-commercial greenhouse conditions. Inoculation with G. monosporum and G. mosseae significantly increased fruit yield and fruit number of tomato plants grown hydroponically in sawdust. Plant height and plant dry weight increased significantly when inoculated with G. monosporum and G. mosseae. Further, plants inoculated with G. monosporum and G. mosseae showed significantly lower FORL root infection than the untreated control plants.     

Exploring the biocontrol potential of fungal endophytes from an Andean Colombian Paramo ecosystem

We studied the diversity and biocontrol potential of 100 fungal endophytes isolated from Espeletia spp., endemic plant species from the Paramo in the Andean mountain range. Our sample was genotypically highly diverse at all ITS similarity levels. The antagonistic properties of these isolates were tested against common crop pathogens in Colombia, including Pectobacterium carotovorum, Ralstonia solanacearum, Pseudomonas syringae, Xanthomonas campestris, Rhizoctonia solani, Botrytis cinerea, Fusarium oxysporum, and Phytophthora infestans. All endophytic isolates were able to significantly inhibit the growth of at least one of the plant pathogens tested (P?<?0.05). Three main types of endophyte/pathogen interactions were observed. However, only those endophytes that produced an evident inhibition halo were further studied using their crude extracts to confirm that the inhibitory effect was due to the production of endophytic bioactive metabolites. From these experiments, nine promising isolates were selected for co-inoculation tests with R. solani in tomato plants. The isolates identified as Aureobasidium pullulans and Paraconiothyrium sporulosum not only protected the plants against this pathogen but also allowed them to exhibit similar growth and development as the uninoculated control. This work explores new alternatives for disease management without the application of chemical pesticides.     

Genetic and Functional Diversity Among the Antagonistic Potential Fluorescent Pseudomonads Isolated from Tea Rhizosphere

Twenty-five fluorescent pseudomonads from rhizospheric soil of six tea gardens in four district of Upper Assam, India were isolated and screened for antagonistic activity against fungal pathogens such as Fusarium oxysporum f. sp. raphani (For), Fusarium oxysporum f. sp. ciceri (Foc), Fusarium semitectum (Fs), and Rhizoctonia solani (Rs); and bacterial pathogens—Staphylococcus aureus (Sa), Escherichia coli (Ec), and Klebsiella pneumoniae (Kp). Most of the isolates exhibited strong antagonistic activity against the fungal pathogens and gram-positive bacterium i.e. Staphylococcus aureus. Productions of siderophore, salicylic acid (SA), hydrogen cyanide (HCN), and cell wall-degrading enzyme (chitinase) were studied to observe the possible mechanisms of antagonistic activity of the isolates. Correlation between the antagonistic potentiality of some isolates and their levels of production of siderophore, salicylic acid, and hydrogen cyanide was observed. Out of the 25 isolates, antibiotic-coding genes, 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT) were detected in the isolates, Pf12 and Pf373, respectively. Genetic diversity of these fluorescent pseudomonads were analyzed with reference to four strains of Pseudomonas fluorescens NICM 2099^T, P. aeruginosa MTCC 2582^T, P. aureofaciens NICM 2026^T, and P. syringae MTCC 673^T. 16S rDNA-RFLP analysis of these isolates using three tetra cutter restriction enzymes (HaeIII, AluI and MspI) revealed two distinct clusters. Cluster A comprised only two isolates Pf141 and 24-PfM3, and cluster B comprised 23 isolates along with four reference strains.     

Rapid Tomato Seedling Assay for Virulent Isolates of Fusarium oxysporum F. sp. Radicis-lycopersici (FORL), the Tomato Crown and Root Rot Pathogen

A rapid tomato seedling assay was developed for determining the relative wilt capacity of isolates of Fusarium oxysporum f. sp. radicis-lyco-persici (FORL), a virulent strain of the tomato pathogen. The procedures for the assay require that 5-day-old cv. Bonny Best tomato seedlings be dipped in 30-day cell-free concentrated culture filtrates of FORL isolates, which were grown in Czapek-Dox medium with 2% Bacto-casamino acids (CDA). The seedlings in the culture filtrates were then incubated at 30 C under artificial light (1200 ftcandles) at 28% relative humidity in a wind stream of 100–150 m min. The relative pathogenicity of the isolates was determined by inoculating the roots of 18-day-old seedlings with cultures of FORL isolates. The pattern of cell-free filtrate wilt among the isolates was the same as that for the disease caused by cultures of the isolates. The seedlings treated with the filtrate from the most virulent isolate (Harrow HRS-182) wilted in 20 min. The filtrates from less virulent isolates took progressively longer. up to 90 min. to cause comparable wilt. Isolate HRS-082 was the first isolate also to induce disease in 10-day-old seedling assay. Both assays indicate three levels of wilt and disease capacities amongthe isolates examined. The utility of the assay in research and breeding for resistance is discussed.     

Effect of flavonoids on the development of Fusarium oxysporum f. sp. lycopersici

Abstract

In the present study the effect of flavonoid compounds on the germination and fungal growth of the soil-borne tomato pathogen Fusarium oxysporum f. sp. lycopersici was studied. Out of 12 flavonoid compounds only myricetin and luteolin exhibited a low stimulating activity on microconidia germination of Fusarium oxysporum f. sp. lycopersici, whereas the other flavonoids tested were inactive when applied at five different concentrations. In our study the tested flavonoids affect fungal growth differently to microconidia germination. Individual flavonoid concentrations resulted in a small increase of fungal growth, but the lowest flavonoid concentrations showed an inhibiting effect on fungal growth for all flavonoids tested. There is evidence to suggest, that low flavonoid concentrations exhibit slight antimicrobial properties against Fusarium oxysporum f. sp. lycopersici.     

Biocontrol Activity of Aspergillus terreus ANU-301 against Two Distinct Plant Diseases,Tomato Fusarium Wilt and Potato Soft Rot

To screen antagonistic fungi against plant pathogens, dual culture assay (DCA) and culture filtrate assay (CFA) were performed with unknown soil-born fungi. Among the different fungi isolated and screened from the soil, fungal isolate ANU-301 successfully inhibited growth of different plant pathogenic fungi, Colletotrichum acutatum, Alternaria alternata, and Fusarium oxysporum, in DCA and CFA. Morphological characteristics and rDNA internal transcribed spacer sequence analysis identified ANU-301 as Aspergillus terreus. Inoculation of tomato plants with Fusarium oxysporum f. sp. lycopersici (FOL) induced severe wilting symptom; however, co-inoculation with ANU-301 significantly enhanced resistance of tomato plants against FOL. In addition, culture filtrate (CF) of ANU-301 not only showed bacterial growth inhibition activity against Dickeya chrysanthemi (Dc), but also demonstrated protective effect in potato tuber against soft rot disease. Gas chromatography-tandem mass spectrometry analysis of CF of ANU-301 identified 2,4-bis(1-methyl-1-phenylethyl)-phenol (MPP) as the most abundant compound. MPP inhibited growth of Dc, but not of FOL, in a dose-dependent manner, and protected potato tuber from the soft rot disease induced by Dc. In conclusion, Aspergillus terreus ANU-301 could be used and further tested as a potential biological control agent.     

Characterization of composted olive mill wastes to predict potential plant disease suppressiveness

Despite its proven agronomic value, the plant disease suppressive effect of composts from olive waste has not been adequately investigated. In the present study, the disease suppressive potential of two olive waste (OW) composts against soil-borne plant pathogens was investigated. Both OW composts showed sizeable, active microbial populations, which were able to grow actively on chitin and cellulose. In plate inhibition trials, OW compost water extracts (CWEs) exerted a significant inhibitory effect on the growth of the pathogens Fusarium oxysporum f.sp. lycopersici (Fol), Pythium ultimum, Phytophtora infestans, Sclerotina sclerotiorum and Verticillium dahliae; and in pot experiments, the OW composts significantly reduced P. ultimum damping-off and Fol wilt diseases on tomato seedlings. The disease suppressive effect of OW composts seems to be due to the combined effects of suppression phenomena caused by the presence of microorganisms competing for both nutrients and space as well as by the activity of specific antagonistic microorganisms.     

Characterization of antifungal activity of Paenibacillus ehimensis KWN38 against soilborne phytopathogenic fungi belonging to various taxonomic groups

Soilborne fungal phytopathogens cause significant losses in many economically important crops and vegetables. The only way to control these devastating pathogens is by using higher doses of fungicides which not only increase the cost of production but also cause significant damage to the environment. Therefore alternate control measures are always looked for. In the present study, an antagonistic strain was isolated from the soil of the pepper fields around the seashore of Jellanamdo, South Korea and identified as Paenibacillus ehimensis KWN38 based on 16S rRNA sequencing. The strain showed high antifungal activity against six tested fungal pathogens belonging to various taxonomic groups on dual culture plates. Furthermore, the strain produced volatile antimicrobial compounds which had strong fungal growth inhibitory effect. The strain also showed high chitinase, cellulase, glucanase and protease activities. The hyphal morphologies of Rhizoctonia solani AG-1 (IA), Fusarium oxysporum f.sp. lycopersici and Phytophthora capsici were significantly destroyed by the crude enzymes and butanol extract from the culture supernatant and the affected hyphae showed abnormal bending, tip curling, and irregular branching. Hence, Paenibacillus ehimensis KWN38 is considered as a potential biocontrol agent of the soil-borne fungi causing plant diseases which is an important perspective of the present study.     

Grape marc compost: microbial studies and suppression of soil-borne mycosis in vegetable seedlings

Compost suppression of soil-borne diseases in horticultural crops has been attributed to the activities of antagonistic microorganisms. A great diversity of microorganisms, capable of suppressing pathogens naturally colonize compost. A large number of microbes appeared in microbiological analyses of grape marc compost. Most microorganisms were bacteria. Average percentages were 31% mesophilic and 28% thermophylic bacteria, 16% mesophilic actinomycetes and 20% thermophylic actinomycetes. Only a few mould and yeast morphologies were obtained, 4% and 1% respectively. Antagonist in vitro assays were performed with 432 microbial morphologies isolated from grape marc compost. The microbes isolated were extremely effective antagonists in in vitro assays against all the fungal pathogens tested. Seven microorganisms were selected for further bioassay with Rhizoctonia solani in radish, Fusarium oxysporum f. sp. radicis-cucumerinum in melon, and Phytophthora parasitica in tomato and two microorganisms with Pythium aphanidermatum in cucumber. Those experiments indicate that grape marc compost reduces the severity of Pythium damping-off in cucumber, but does not reduce the severity of Phytophthora root rot in tomato, Fusarium oxysporum f. sp. radicis-cucumerinum in melon and Rhizoctonia solani in radish. Better suppressive effects were not demonstrated by either compost or vermiculite amended with microbes selected from grape marc compost.     

Tomato growth and resistance promotion by Enterobacter hormaechei subsp. steigerwaltii EB8D

Fusarium wilt is an economically important disease of tomato crop (Solanum lycopersicum L). Plant growth-promoting rhizobacteria (PGPR) represent an alternative to improve plant growth and yield as well as to act as agent of biocontrol. In this study, antagonistic effects of four selected isolates (EB8D, EB20J, EB24L and EB26M) were evaluated against Fusarium oxysporum f.sp. radicis lycopersici (FORL) as potential biocontrol agents in vitro and in vivo. After 30?days of culture, dry weight, length of stem and root were significantly (p?≤?.05) higher compared with the non-inoculated control. Compared with the control plate (inoculated only with pathogen), EB8D had showed efficient antagonism against FORL (48.88%). The different strains have been screened for siderophore production, solubilisation of mineral phosphates, synthesis of indolic acetic acid (IAA) to show the plant growth-promoting potential. The experimental groups were compared with a control group that did not receive any treatment by FORL, and EB8D was the best isolate in terms of growth promotion with an improvement of 73.85% of the stem length, 110.86% of the root length and 118.85% of the dry weight comparing with the non-treated controls. Compared with a control group treated by FORL, biocontrol activity has shown that EB8D strain improved the stem length with 111.85%, the root length with 118.85% and the dry weight with 452.38%. 16S rRNA analysis has confirmed that this strain belongs to the genus Enterobacter and has high similarity with Enterobacter hormaechei subsp. steigerwaltii (99.71%). EB8D has a significant strong protective potential against FORL and lead to better tomato growth and might have biotechnological potential for controlling fusarium wilt in tomato plants.     

Development of a breeder-friendly functional codominant DNA marker for the I2 locus covering resistance to Fusarium oxysporum f. sp. lycopersici

Fusarium oxysporum f. sp. lycopersici Snyder & Hans. (FOL) is a major soil-borne pathogen and the causal agent of Fusarium wilt of tomato, resulting in significant production yield losses. Resistant cultivars have become the most effective method for controlling this fungal disease, and the most important resistance locus to F. oxysporum f. sp. lycopersici in tomato is I2, conferring resistance to race 2 of the pathogen, and widely used in breeding programs. Although this locus was cloned, a robust codominant DNA marker for the I2 locus is not available to date. The development of such a marker has been hindered by the presence of seven homologous sequences at this locus that tend to amplify, and by the absence of information about the structure of the recessive I2 locus. We performed a comparative analysis of the I2 locus nucleotide sequences of tomato genotypes resistant and susceptible to Fusarium wilt. We developed a breeder-friendly functional codominant cleaved amplified polymorphic sequence marker of I2 based on this analysis that can be used in tomato breeding programs for resistance to FOL race 2.