Causal Agent Of Fusarium Wilt Research Articles

Development of DArT markers and assessment of diversity in Fusarium oxysporum f. sp. ciceris, wilt pathogen of chickpea (Cicer arietinum L.).

BackgroundFusarium oxysporum f. sp. ciceris (Foc), the causal agent of Fusarium wilt of chickpea is highly variable and frequent recurrence of virulent forms have affected chickpea production and exhausted valuable genetic resources. The severity and yield losses of Fusarium wilt differ from place to place owing to existence of physiological races among isolates. Diversity study of fungal population associated with a disease plays a major role in understanding and devising better disease control strategies. The advantages of using molecular markers to understand the distribution of genetic diversity in Foc populations is well understood. The recent development of Diversity Arrays Technology (DArT) offers new possibilities to study the diversity in pathogen population. In this study, we developed DArT markers for Foc population, analysed the genetic diversity existing within and among Foc isolates, compared the genotypic and phenotypic diversity and infer the race scenario of Foc in India.ResultsWe report the successful development of DArT markers for Foc and their utility in genotyping of Foc collections representing five chickpea growing agro-ecological zones of India. The DArT arrays revealed a total 1,813 polymorphic markers with an average genotyping call rate of 91.16% and a scoring reproducibility of 100%. Cluster analysis, principal coordinate analysis and population structure indicated that the different isolates of Foc were partially classified based on geographical source. Diversity in Foc population was compared with the phenotypic variability and it was found that DArT markers were able to group the isolates consistent with its virulence group. A number of race-specific unique and rare alleles were also detected.ConclusionThe present study generated significant information in terms of pathogenic and genetic diversity of Foc which could be used further for development and deployment of region-specific resistant cultivars of chickpea. The DArT markers were proved to be a powerful diagnostic tool to study the genotypic diversity in Foc. The high number of DArT markers allowed a greater resolution of genetic differences among isolates and enabled us to examine the extent of diversity in the Foc population present in India, as well as provided support to know the changing race scenario in Foc population.Electronic supplementary materialThe online version of this article (doi: 10.1186/1471-2164-15-454) contains supplementary material, which is available to authorized users.

Development of a real-time fluorescence loop-mediated isothermal amplification assay for rapid and quantitative detection of Fusarium oxysporum f. sp. cubense tropical race 4 in soil.

Fusarium oxysporum f. sp. cubense (Foc), the causal agent of Fusarium wilt (Panama disease), is one of the most devastating diseases of banana (Musa spp.). The Foc tropical race 4 (TR4) is currently known as a major concern in global banana production. No effective resistance is known in Musa to Foc, and no effective measures for controlling Foc once banana plants have been infected in place. Early and accurate detection of Foc TR4 is essential to protect banana industry and guide banana planting. A real-time fluorescence loop-mediated isothermal amplification assay (RealAmp) was developed for the rapid and quantitative detection of Foc TR4 in soil. The detection limit of the RealAmp assay was approximately 0.4 pg/µl plasmid DNA when mixed with extracted soil DNA or 103 spores/g of artificial infested soil, and no cross-reaction with other relative pathogens were observed. The RealAmp assay for quantifying genomic DNA of TR4 was confirmed by testing both artificially and naturally infested samples. Quantification of the soil-borne pathogen DNA of Foc TR4 in naturally infested samples was no significant difference compared to classic real-time PCR (P>0.05). Additionally, RealAmp assay was visual with an improved closed-tube visual detection system by adding SYBR Green I fluorescent dye to the inside of the lid prior to amplification, which avoided the inhibitory effects of the stain on DNA amplification and makes the assay more convenient in the field and could thus become a simple, rapid and effective technique that has potential as an alternative tool for the detection and monitoring of Foc TR4 in field, which would be a routine DNA-based testing service for the soil-borne pathogen in South China.

Colonization of lettuce cultivars and rotation crops by Fusarium oxysporum f. sp. lactucae, the cause of fusarium wilt of lettuce

The severity of fusarium wilt is affected by inoculum density in soil, which is expected to decline during intervals when a non‐susceptible crop is grown. However, the anticipated benefits of crop rotation may not be realized if the pathogen can colonize and produce inoculum on a resistant cultivar or rotation crop. The present study documented colonization of roots of broccoli, cauliflower and spinach by Fusarium oxysporum f. sp. lactucae, the cause of fusarium wilt of lettuce. The frequency of infection was significantly lower on all three rotation crops than on a susceptible lettuce cultivar, and the pathogen was restricted to the cortex of roots of broccoli. However, F. oxysporum f. sp. lactucae was isolated from the root vascular stele of 7·4% of cauliflower plants and 50% of spinach plants that were sampled, indicating a greater potential for colonization and production of inoculum on these crops. The pathogen was also recovered from the root vascular stele of five fusarium wilt‐resistant lettuce cultivars. Thus, disease‐resistant plants may support growth of the pathogen and thereby contribute to an increase in soil inoculum density. Cultivars that were indistinguishable based on above‐ground symptoms, differed significantly in the extent to which they were colonized by F. oxysporum f. sp. lactucae. Less extensively colonized cultivars may prove to be superior sources of resistance to fusarium wilt for use in breeding programmes.

First report of Fusarium wilt of eggplant caused by Fusarium oxysporum f. sp. melongenae in Iran

In 2012, eggplant (Solanum melongena) production in several greenhouses and fields was surveyed in Iran. In Hormozgan and Semnan provinces, 15 and 12% of fields surveyed, respectively, were infected with an unknown disease. Those affected plants exhibited leaf chlorosis and slight vein clearing on the outer leaflets, slight yellowing of foliage and wilting of upper leaves and eventual death of the plant. Necrotic tissue fragments from discoloured vascular stem tissue were surface sterilised by soaking in 10% bleach solution for five minutes and plated on potato dextrose agar (PDA). Single-spore isolates were obtained and transferred to PDA and carnation leaf agar (CLA) to investigate culture characteristics and morphology (Nelson et al., 4). Twenty-six isolates were identified as Fusarium., including 12 isolates that were initially identified as Fusarium oxysporum due to production of characteristic three to five septate, sickle-shaped macroconidia with a foot-shaped basal cell, on branched conidiophores or on the surface of sporodochia. Three septate spores were more common. Microconidia were borne on simple phialides arising laterally and were abundant, oval-ellipsoid, straight to curved and non-septate in culture. A typical cream to pink colony developed, often with purple tinge, on PDA (Nelson et al., 4). After PCR amplification of genomic DNA using the specific primer PF02-3 (Baysal et al., 1), morphological identity was confirmed as Fusarium oxysporum f. sp. melongenae by the presence of a specific, characteristic band visible at around 70 bp. The other isolates were identified as F. solani. Pathogenicity tests were performed twice for each of 12 isolates using a root-dip inoculation method (Baysal et al., 1). Wounded roots ofnine S. melongena (cv. ‘Pala‘) seedlings at the six-leaf stage were submerged for 15 min in a conidial suspension (1 times 106 conidia/ml in sterile water), while control plants were dipped in sterile tap water. Seedlings were transplanted into pots and maintained in a growth chamber. After 3-4 weeks, severity of wilt symptoms was assessed using a wilt index ranging from 0 (no symptoms) to 4 (plant death) (Morid et al., 3). All 12 isolates tested were pathogenic to eggplant with a wilt index ranging from 1.2 to 3.4 (average = 2.8). Symptoms observed on inoculated plants were similar to those in commercial greenhouses, including leaf chlorosis and necrosis and eventual death. Control plants showed no symptoms, and two other members of the Solanaceae (tomato and pepper) tested with the same method displayed no symptoms. Fusarium oxysporum f. sp. melongenae was successfully re-isolated from the stems of disease-affected inoculated plants, thereby completing Koch's postulates. Fusarium oxysporum f. sp. melongenae is a major soil-borne pathogen and one of the causal agents of vascular wilt disease in eggplant. Occurrence of F. oxysporum on S. melongena has been reported in Japan, Korea, China, Italy, Greece, Spain, Turkey, the USSR, USA-Florida and Fiji (Yildiz et al., 5). This is the first report of F. oxysporum f. sp. melongenae in Iran. Previously, the causal agent of Fusarium wilt of eggplant in Iran was attributed solely to F. solani (Gerlach & Ershad, 2).

Contribution à l’étude de l’activité Toxique de Fusarium Oxysporum f. sp. Albedinis , Agent Causal du Bayoud

Fusarium oxysporum f. sp. albedinis, causal agent of Fusarium wilt of date palm, synthesizes toxic compounds in culture liquid medium Czapeck-Dox. These compounds cause inhibition of germination, necrosis and accumulation of tannins in the host tissues. Analysis of extracts by TLC has detected several compounds with fusaric acid. The injection of the latter at the collar of seedlings cultivar Deglet Nour causes, three weeks later, wilting of leaves followed by death of the seedling, and a stimulation of the synthesis of anthocyanins in the limb and roots. The results lead us to hypothesize the following: the accumulation of flavonoids, substances involved in resistance in the leaves and roots did not stop the damage caused by this toxin and other toxins probably involved, or in synergy with the ac. Fusaric or other compounds, either alone.

BIOCONTROL POTENTIAL OF TRICHODERMA SPECIES AGAINST WILT DISEASE OF CARNATION (DIANTHUS CARYOPHYLLUS L.) CAUSED BY FUSARIUM OXYSPORUM F.SP. DIANTHI

ABSTRACT A study was carried out to test the antagonistic potential of four isolates of Trichoderma viride and eight isolates of T. harzianum and five isolates of T. reesei against F. oxysporum f. sp. dianthi, the cause of Fusarium wilt in carnation. T. harzianum (Th2) showed the maximum inhibition of mycelial growth of F. oxysporum f. sp. dianthi. (45.33%) over control followed by T. harzianum (Th6) and T. viride (Tv3) with 42.11 and 38.66 per cent inhibition respectively. The Competitive Saprophytic Ability (CSA) and colonization by each isolates of Trichoderma spp. was assessed. Among the 17 isolates, Th2 registered 61.84 per cent colonization followed by Th6 with 59.12 percent colonization. All other isolates of Trichoderma spp. were inferior to Th2 in its saprophytic ability. The antagonistic isolates of Trichoderma spp. were also tested for production of antifungal volatiles and their effect on the growth of F. oxysporum f. sp. dianthi. All the isolates were found to produce volatile metabolites, which inhibited the mycelial growth of test pathogen at varing levels from 16.33 to 50.11 percent.

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.

IN VITRO CONTROL OF FUSARIUM WILT USING AGROINDUSTRIAL SUBPRODUCT-BASED COMPOSTS

Some kinds of compost suppress soil-borne plant pathogens and although their exact mode of action is not yet clear, several mechanisms seem to be involved in the supressive effect. The abiotic component of compost is an important factor for its suppressive effect in soils, however it must be kept in mind that compost is considered a source of biocontrol agents against several serious plant pathogens. The main aim of this work was to discriminate the biotic and abiotic components in agroindustrial subproduct-based composts that could be potentially used as suppressive soil amendments. Results have shown that the compost’s suppressive effect on mycelial development of Fusarium oxysporum f. sp. melonis (FOM), the causal agent of Fusarium wilt of melon, was due to a combination of biotic and abiotic factors. Similar results were observed when compost extracts were used against the pathogenic fungus. In this case, compost extracts with a concentration between 0.1 and 50% inhibited FOM growth. However, sterilized compost extracts inhibited fungal development when applied at a dose lower than 10%, while higher concentrations (>10%) were not effective, probably due to the toxic substances and nutrient content ratio in the culture media. This can be indicative of a masking of the inhibitory effect at high nutritional levels. Based on these results, we conclude that the suppressive effect of compost is due to a combination of biotic and abiotic factors, though the former are mainly responsible for the biocontrol activity against FOM.

Evaluation of pathogenic potential and genetic characterization of Fusarium solani: A cause of Fusarium wilt in potato

Fusarium wilt, caused by Fusarium solani, is economically important disease of potato in Pakistan. Presently, pathogenic potential of F. solani was studied by inoculating potato plants with three F. solani, strains to screen the most virulent isolate among F. solaniFCBP-016, F. solani FCBP-434 and F. solani FCBP-470. Pathogenicity test depicted thatF. solani FCBP-434 was the most pathogenic isolate with variation in genetic level that was determined by RAPD-PCR. F. solani FCBP-434 was 55.66% different with both isolates. This disparity in genetic constitution might be cause of high pathogenicity. Key words: Fusarium wilt, potato, pathogenesity test, RAPD-PCR

Presence of putative pathogenicity genes in isolates of Fusarium oxysporum f. sp. cubense from Australia

Fusarium oxysporum f. sp. cubense (Foc), causal agent of Fusarium wilt of banana, is among the most destructive pathogens of banana and plantain. Understanding pathogenicity in Foc is of key importance to disease management, yet its genetic basis is poorly understood. Recent research with F. oxysporum f. sp. lycopersici (Fol), causal agent of Fusarium wilt of tomato, has elucidated the role of SIX-genes (secreted in xylem) in pathogenicity in the Fol-tomato pathosystem. Using hybridisation analysis and PCR, we detected homologues of three SIX-genes, SIX1, SIX7 and SIX8, in isolates of Foc from Australia and sequenced these putative Foc pathogenicity genes.

Control of Fusarium Wilt of Tomato Caused byFusarium oxysporumF. Sp. Radicis-Lycopersici Using Mixture of Vegetable andPosidonia oceanicaCompost

A compost of vegetable waste andPosidonia oceanicamixture (70 : 30% vol : vol) was testedin vitroandin vivofor its efficacy againstFusarium oxysporumf.spradicis-lycopersici(Forl), the causal agent of Fusarium wilt of Tomato (Lycopersicon esculentumcv. chourouk).The incorporation of non-sterilized VPC in the culture medium showed potent antifungal activity against Forl and complete inhibition of mycelium growth was observed for all the tested compost rates (0.5, 1, 2, 4, 6, 8, 10, 15 and 20%). However, only the highest rates (15 and 20%) of a sterilized suspension of VPC were effective in preventing mycelial growth. Nine indigenous bacterial strains isolated from VPC exhibited antagonism against Forl. Based on 16S rDNA sequence analysis, the isolates were assigned toBacillus sphaericus(B12 and BS2),Pseudomonas putidaPPS7 andBurkholderia gladioliBuC16. Under green house condition, seed inoculation by B12, BS2, PP7 and BuC16 strains protected significantly tomato againstFusarium oxysporumf.spradicis-lycopersici(Forl) attacks.

Fusarium oxysporum as causal agent of tomato wilt and fruit rot

Tomatoes are parasitized by a number of pathogens, including Fusarium oxysporum f. sp. lycopersici, causal agent of fusarium wilt. Fresh vegetable fruits can be contaminated with various fungi that produce mycotoxins, which is an important issue for human health. The objective of this paper was to isolate, determine, and identify causal organisms of tomato wilt and fruit rot, based on the pathogens morphological and molecular characteristics. Samples of diseased plants showing symptoms of tomato wilt were collected from different localities in the production region of Vojvodina. Fruits with symptoms of fusarium rot were collected from storage and warehouses. The isolation and morphological determination of the fungus were performed on PDA and Czapek?s nutrient media. Isolates from diseased plants growing in field, designated as TFW1-TFW12 and seven isolates from diseased tomato fruits (TFM1-TFM7) were chosen for further investigation. For identification of the fungal isolates, the polymerase chain reaction (PCR) was also used. The EF1/EF2 primer pair was used for molecular identification of Fusarium sp. Nine analyzed samples were found to contain DNA fragments 700 bp in size.

Horticultural Characteristics Of Licorice Waste Compost

Licorice (Glycyrrhiza glabra L.) is a leguminous herbaceous perennial. Its root extracts are commonly used for medicinal uses and as a flavoring agent in the food and tobacco industries. After extraction, about 10,000 tones of licorice root residues are accumulated in Israel annually with no recycling outlet. The objectives of the current research were to develop a reliable protocol for licorice root wastes composting, to test the use of licorice compost as a peat substitute in growing media and to study its suppressiveness against Fusarium oxysporum f. sp. melonis (FOM) – the causal agent of Fusarium wilt of melon (Cucumis melo L.). Licorice root wastes were cocomposted using temperature controlled forced aeration with the coarse fraction of separated cow manure, in order to enrich both its nutrients content and microbial population. Thermophilic conditions prevailed in the pile for 90 days and the compost stabilized and reached ambient temperature 110 days from start. The physical characteristics of the resulted compost were comparable to that of peat. Nutrient content was high and salinity was relatively low. No phytotoxicity was found in the compost extract, based on the cress germination test. Tomato plants grown in compost showed enhanced development as compared to peat. The number of surviving FOM spores incubated in the compost declined faster then in peat. Fusarium infested melon plants survived much better if planted in the licorice compost, as compared to peat. It is concluded that licorice compost can serve as a peat substitute with preferable qualities.

A DETECTION METHOD FOR TROPICAL RACE 4 OF THE BANANA PATHOGEN FUSARIUM OXYSPORUM F. SP. CUBENSE

Fusarium oxysporum f. sp. cubense (Foc) is the causal agent of Fusarium wilt, the devastating disease that ruined the ‘Gros Michel’ (AAA)-based banana production in the first half of the 20th century. The occurrence of a new variant in Southeast Asia that overcomes the resistance in Cavendish clones such as ‘Grand Naine’ (AAA) is a major concern to current banana production worldwide. The threat posed by this new variant, called tropical race 4 (TR4), may be overcome by the introduction of resistant cultivars. However, the identification of new resistant sources or breeding for resistance is a long-term effort. Currently, the only option to control the disease is to avoid or reduce the spread of the pathogen by eradication of infected plants and isolation of infested plantations. This requires sensitive and highly specific diagnostics that enable early detection of the pathogen. A two-locus database of DNA sequences, from over 800 different isolates from multiple formae speciales of F. oxysporum, was used to develop a molecular diagnostic tool that specifically detects isolates from the vegetative compatibility group (VCG) 01213, which encompasses the Foc TR4 genotype. This diagnostic tool was able to detect all Foc TR4 isolates tested, while none of the Foc isolates from 19 VCGs other than 01213 showed any reaction. In addition, the developed diagnostic tool was able to detect Foc TR4 when using DNA samples from different tissues of ‘Grand Naine’ plants inoculated with TR4 isolates

COMPARISON OF HOST REACTION TO FUSARIUM OXYSPORUM F. SP. CUBENSE TROPICAL RACE 4 AND AGRONOMIC PERFORMANCE OF SOMACLONAL VARIANT 'GCTCV-119' (AAA, CAVENDISH) AND 'GRAND NAINE' (AAA, CAVENDISH) IN COMMERCIAL FARMS IN THE PHILIPPINES

The original publication is available at www.actahort.org. Recent reports of the occurrence of Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), causal agent of Fusarium wilt, in some commercial Cavendish banana plantations in the Philippines is of great concern to the Philippine banana industry. In an effort to mitigate the disease, 'GCTCV-119', a Foc TR4-resistant somaclonal variant of 'Giant Cavendish' selected by the Taiwan Banana Research Institute, was evaluated and compared with the commercial cultivar 'Grand Naine' in Foc-infested farms in Davao, Philippines. Isolates obtained from infected samples from these farms were previously typed as VCG1213/16, the vegetative compatibility group associated with TR4. Tissue culture-derived planting materials of 'GCTCV-119' and 'Grand Naine' were planted in randomised blocks in two farms where severe Fusarium wilt incidence was previously observed. After 12 months of disease incidence monitoring, 'GCTCV-119' showed no Fusarium infection, while 36 and 51% incidence was recorded for 'Grand Naine' in Calinan and Quibilan farms, respectively. Two years after establishment, 'GCTCV-119' plots in the Quibilan farm are still free from infection of Fusarium wilt while the 'Grand Naine' plots have been totally eradicated because of severe disease incidence. Agronomic and fruit quality traits were also recorded. Although 'GCTCV-119' proved to be highly resistant to TR4, it matured later and had a lower bunch weight and greater hand curvature resulting in more rejects when packed. 'GCTCV-119' is however sweeter as it has more total sugars and total soluble solids than 'Grand Naine'.

A study on the susceptibility of the model legume plant Medicago truncatula to the soil-borne pathogen Fusarium oxysporum

Fusarium wilt is a soil-borne disease caused by formae specialis of Fusarium oxysporum on a large number of cultivated and wild plants. The susceptibility of the model legume plant Medicago truncatula to Fusarium oxysporum was studied by root-inoculating young plants in a miniaturised hydroponic culture. Among eight tested M. truncatula lines, all were susceptible to F. oxysporum f.sp. medicaginis, the causal agent of Fusarium wilt in alfalfa. However, a tolerant line, F83005.5, and a susceptible line, A17, could be distinguished by scoring the disease index. The fungus was transformed with the GFP marker gene and colonisation of the plant roots was analysed by epifluorescence and confocal microscopy. A slightly atypical pattern of root colonisation was observed, with massive fungal growth in the cortex. Although colonisation was not significantly different between susceptible and tolerant plants, the expression of some defence-related genes showed discrimination between both lines. A study with 10 strains from various host-plants indicated that M. truncatula was a permissive host to F. oxysporum.

Evolutionary Relationships among theFusarium oxysporumf. sp.cubenseVegetative Compatibility Groups

Fusarium oxysporum f. sp. cubense, the causal agent of fusarium wilt of banana (Musa spp.), is one of the most destructive strains of the vascular wilt fungus F. oxysporum. Genetic relatedness among and within vegetative compatibility groups (VCGs) of F. oxysporum f. sp. cubense was studied by sequencing two nuclear and two mitochondrial DNA regions in a collection of 70 F. oxysporum isolates that include representatives of 20 VCGs of F. oxysporum f. sp. cubense, other formae speciales, and nonpathogens. To determine the ability of F. oxysporum f. sp. cubense to sexually recombine, crosses were made between isolates of opposite mating types. Phylogenetic analysis separated the F. oxysporum isolates into two clades and eight lineages. Phylogenetic relationships between F. oxysporum f. sp. cubense and other formae speciales of F. oxysporum and the relationships among VCGs and races of F. oxysporum f. sp. cubense clearly showed that F. oxysporum f. sp. cubense's ability to cause disease on banana has emerged multiple times, independently, and that the ability to cause disease to a specific banana cultivar is also a polyphyletic trait. These analyses further suggest that both coevolution with the host and horizontal gene transfer may have played important roles in the evolutionary history of the pathogen. All examined isolates harbored one of the two mating-type idiomorphs, but never both, which suggests a heterothallic mating system should sexual reproduction occur. Although, no sexual structures were observed, some lineages of F. oxysporum f. sp. cubense harbored MAT-1 and MAT-2 isolates, suggesting a potential that these lineages have a sexual origin that might be more recent than initially anticipated.

MOLECULAR CHARACTERIZATION OF FUSARIUM OXYSPORUM CAUSING WILT OF PROTEACEAE

Fusarium wilt of Proteaceae was first reported in 1998 on the genus Protea in the North West province of South Africa and in Zimbabwe. Subsequently it has been reported from the Canary Islands (Tenerife), Chile and Portugal and might also be a potential risk in Australia. Fusarium oxysporum, the causal agent of Fusarium wilt, blocks the vascular tissue of the host plant, thereby causing wilt, chlorosis and plant death. In this study, molecular techniques have been employed to characterise the pathogen, which has only been morphologically identified thus far. Fusarium oxysporum isolates were obtained from Agathosma, Leucadendron, Leucospermum, Protea and Lavandula originating from South Africa, Zimbabwe and Portugal. Partial sequences of the translation elongation factor 1 alpha (EF-1α) gene and the mitochondrial small subunit (mtSSU) region were generated. Phylogenetic analysis of the sequence data confirmed all the isolates to be Fusarium oxysporum. Fusarium oxysporum isolates from a specific host did not cluster together, indicating that isolates from the same host are not clonal. The DNA phylogenies did not follow the formae speciales classification system.

First Report of Vascular Wilt Caused by Fusarium redolens on Lentil in Italy.

Lentil (Lens culinaris Medik.) is a traditional crop in Sicily, Italy. Near Villalba (Caltanissetta), a local lentil landrace, "Lenticchia di Villalba", is commonly grown. From 2002 to 2004, wilt was observed in five lentil fields (≈1 ha each) at rates from 5 to 20%. Affected plants were yellow and stunted with discoloration in the vascular tissue of stems and crowns. Pieces of brown vascular tissue from stems were disinfested in 2% sodium hypochlorite for 2 min, rinsed with sterile distilled water, placed on potato dextrose agar, and incubated at 23°C. Isolates with morphological characteristics of Fusarium oxysporum Schlecht.:Fr. (2) were consistently recovered from affected plants. For molecular identification of five isolates, the rDNA internal transcribed spacer (ITS) region and a portion of the elongation factor EF-1α were sequenced using ITS5/4 and EF1/2 primers, respectively (1). Two sequences of the ITS region were obtained: a 468-bp sequence from isolates ER1259, ER1260, and ER1275 (submitted as GenBank Accession No. EU159118) and a 483-bp sequence from isolates ER1274 and ER1276 (submitted as GenBank Accession No. EU281661). The two sequences shared 93% similarity. A sequence homology search using the NCBI BLAST program revealed that the first sequence had 100% homology with the ITS sequences of more than 50 F. oxysporum isolates of various formae speciales in GenBank and the second shared 100% homology with the ITS sequences of five isolates of F. redolens Wollenw. (e.g., GenBank Accession No. X94169 of the strain CBS 360.87). Amplification of the EF-1α produced a sequence from isolates ER1274 and ER1276 (submitted as GenBank Accession No. EU281660) with 99 to 100% homology to sequences of F. redolens and a sequence from strains ER1259, ER1275, and ER1260 (submitted as GenBank Accession No. EU281659) with 100% homology to that of more than 50 F. oxysporum strains in GenBank. Although F. redolens and F. oxysporum are morphologically similar, recent molecular studies have shown that they are distinct and phylogenetically distant species (3). On the basis of genetic sequences, isolates ER1274 and ER1276 were identified as F. redolens. These isolates were evaluated for pathogenicity on lentil. For each isolate, 10 2-week-old seedlings of "Lenticchia di Villalba" were inoculated by submerging roots in a suspension of 2.5 × 106 conidia/ml for 10 min. Plants were put into separate tubes containing 70 ml of a nutritional liquid medium (7 ml of HydroPlus Olikani per liter; Yara, Nanterre, France) and incubated in a growth chamber at 20°C with 12 h of light per day. Seedlings dipped in sterile water served as the control treatment. The pathogenicity test was repeated twice. Inoculated seedlings started to wilt 1 week after inoculation and developed root rot and vascular discoloration. After 2 weeks, 70% of the inoculated plants were affected by both isolates and 40 and 10% died when inoculated with ER1274 and ER1276 isolates, respectively. F. redolens was consistently reisolated from the stems of wilted plants. Noninoculated plants remained healthy. Currently, only F. oxysporum f. sp. lentis Vasud. and Sriniv. has been reported as the cause of Fusarium wilt of lentil. To our knowledge, this is the first report of F. redolens as a pathogen on lentil.

Characterization and Inheritance of a New Source of Resistance to Fusarium oxysporum f. sp. melonis Race 1.2 in Cucumis melo.

Four physiological races (0, 1, 2, and 1.2) of Fusarium oxysporum f. sp. melonis, causal agent of Fusarium wilt in melons, have been described. Whereas resistance against each of the races 0, 1, and 2 is encoded by a single dominant R-gene, resistance against the fourth race, FOM 1.2, is polygenically inherited and was recently characterized in the cultivar Isabelle. In the present study, we report on an independently derived source of resistance to race 1.2, the Israeli breeding line BIZ. The disease response of BIZ seedlings was compared with two susceptible genotypes, Line 33 and PI 414723, and the partially resistant genotype, Isabelle, at increasing concentrations of inoculum. BIZ exhibited near-complete resistance to race 1.2, even at inoculum levels of 106 spores per ml and root wounding, indicating that such resistance is stronger than that in Isabelle. Although in previous studies the F1 hybrids between BIZ and the sensitive lines displayed full resistance in the field, in the present study they were susceptible under artificial inoculation conditions that involve high inoculum concentrations of 106 spores per ml and root wounding; under intermediate inoculum levels (105 and 5 × 105 spores per ml) they were partially resistant. Segregation of the resistance response in the F2 and back-cross-1 progeny from a cross between BIZ and PI 414723 supported a model in which two complementary, recessive genes are required to obtain full resistance. While the fungus was shown to colonize root tissue of both resistant and susceptible lines, colonization was markedly lower in the resistant plants, and the fungus was nearly absent from upper stem segments.