scholarly journals Genetic Diversity of Fusarium oxysporum f. sp. cubense, the Fusarium Wilt Pathogen of Banana, in Ecuador

Plants ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 1133
Author(s):  
Freddy Magdama ◽  
Lorena Monserrate-Maggi ◽  
Lizette Serrano ◽  
José García Onofre ◽  
María del Mar Jiménez-Gasco
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Population Biology ◽  
Plant Protection ◽  
Control Strategies ◽  
Compatibility Group ◽  
Race 1 ◽  
Race 4 ◽  
Latin America Countries

The continued dispersal of Fusarium oxysporum f. sp. cubense Tropical race 4 (FocTR4), a quarantine soil-borne pathogen that kills banana, has placed this worldwide industry on alert and triggered enormous pressure on National Plant Protection (NPOs) agencies to limit new incursions. Accordingly, biosecurity plays an important role while long-term control strategies are developed. Aiming to strengthen the contingency response plan of Ecuador against FocTR4, a population biology study—including phylogenetics, mating type, vegetative compatibility group (VCG), and pathogenicity testing—was performed on isolates affecting local bananas, presumably associated with race 1 of F. oxysporum f. sp. cubense (Foc). Our results revealed that Foc populations in Ecuador comprise a single clonal lineage, associated with VCG0120. The lack of diversity observed in Foc populations is consistent with a single introduction event from which secondary outbreaks originated. The predominance of VCG0120, together with previous reports of its presence in Latin America countries, suggests this group as the main cause of the devastating Fusarium wilt epidemics that occurred in the 1950s associated to the demise of ‘Gros Michel’ bananas in the region. The isolates sampled from Ecuador caused disease in cultivars that are susceptible to races 1 and 2 under greenhouse experiments, although Fusarium wilt symptoms in the field were only found in ‘Gros Michel’. Isolates belonging to the same VCG0120 have historically caused disease on Cavendish cultivars in the subtropics. Overall, this study shows how Foc can be easily dispersed to other areas if restriction of contaminated materials is not well enforced. We highlight the need of major efforts on awareness and monitoring campaigns to analyze suspected cases and to contain potential first introduction events of FocTR4 in Ecuador.

Characterisation of Strains of Fusarium oxysporum f.sp. cubense by Production of Volatiles

1991 ◽  
Vol 39 (2) ◽  
pp. 161 ◽  
Author(s):  
NY Moore ◽  
PA Hargreaves ◽  
KG Pegg ◽  
JAG Irwin
Keyword(s):  
Fusarium Oxysporum ◽  
Vegetative Compatibility ◽  
Vegetative Compatibility Group ◽  
Compatibility Group ◽  
Race 1 ◽  
Race 2 ◽  
Race 4

The production of volatiles on steamed rice by Australian isolates of Fusarium oxysporum f. sp. cubense correlated well with race and vegetative compatibility group (VCG). All race 4 isolates (VCGs 0120, 0129) produced distinctive volatile odours which gave characteristic gas chromatograms where the num- ber of peaks equated to VCG. Race 1 (VCGs 0124, 0125) and race 2 (VCG 0128) isolates, as well as non-pathogenic isolates of F. oxysporum from the banana rhizosphere, did not produce detectable volatiles and gave chromatograms without significant peaks.

scholarly journals First Report of Fusarium oxysporum f. sp. cubense Tropical Race 4 Associated with Panama Disease of Banana outside Southeast Asia

Plant Disease ◽  
2014 ◽  
Vol 98 (5) ◽  
pp. 694-694 ◽  
Author(s):  
F. García-Bastidas ◽  
N. Ordóñez ◽  
J. Konkol ◽  
M. Al-Qasim ◽  
Z. Naser ◽  
...  
Keyword(s):  
Southeast Asia ◽  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Plant Diseases ◽  
Jordan Valley ◽  
Panama Disease ◽  
First Report ◽  
Race 1 ◽  
Half Strength ◽  
Race 4

Fusarium wilt or Panama disease of banana, caused by Fusarium oxysporum f. sp. cubense (Foc), is among the most destructive plant diseases (3). Race 1 ravaged ‘Gros Michel’-based export trades until the cultivar was replaced by resistant Cavendish cultivars. However, a new variant of Foc, tropical race 4 (TR4), was identified in Southeast Asia in 1992 and has spread throughout the region (3). Cavendish clones, which are most important in subsistence and export production, are among the wide range of cultivars that are affected, and there is a huge concern that TR4 will further disseminate in Africa since its presence was announced in November 2013 and move into Latin America, thereby threatening other vital banana-growing regions. In Jordan, Cavendish bananas are produced on 1,000 to 1,500 ha in the Jordan Valley (32°N, 35.5°E). In 2006, symptoms of Fusarium wilt were observed and sampled for the isolation of Foc. On half-strength PDA amended with 100-ppm streptomycin sulfate, pale salmon-colored colonies with floccose mycelia developed consistently from surface-disinfested xylem. Single microconidia from these colonies were transferred to half-strength PDA, and conidia and mycelia from these monospore colonies were stored at –80°C in 15% glycerol. On banana leaf agar (Co60-irradiated leaf tissue on water agar), isolates resembled F. oxysporum phenotypically by producing infrequent three- to five-celled macroconidia, copious, usually aseptate microconida on monophialides, and terminal and intercalary chlamydospores after 2 weeks (2). With nitrate-nonutilizing (nit) mutants and testers for different vegetative compatibility groups (VCGs), each of seven examined monospore isolates were placed in VCG 01213, which contains only strains of TR4 (3). Total DNA was extracted from six isolates and PCR analyses, which confirmed their identity as TR4 (1). Subsequently, one of the isolates (JV11) was analyzed for pathogenicity. Inoculum production and inoculation were according to (1) by dipping (30 min) root-wounded 10-week-old plants of the Cavendish cv. Grand Naine in 2 liters of spore suspension (1.0 × 106 spores/ml). Inoculated plants were then placed in sand in 3-liter pots under 28°C, 70% relative humidity, and a 16/8-h light/darkness photoperiod. Sets of three plants were each treated with either JV11 or two TR4 controls (isolate II-5 and a strain isolated from an affected Cavendish plant in Mindanao, Philippines, both of which were diagnosed as TR4 by PCR and pathogenicity analyses). Control sets were either treated with race 1 originating from Cruz das Almas, Bahia, Brazil (1), or water. After 2 weeks, plants inoculated with JV11 and TR4 controls produced typical symptoms of Fusarium wilt. After 4 weeks, tissue was collected from all plants and plated on Komada's medium. TR4 was directly confirmed by PCR (1), either directly from symptomatic plants (JV11 and TR4 controls), or from isolates that were recovered from these plants. Nothing was re-isolated from race 1 inoculated plants and water controls, which remained asymptomatic. This is the first report of TR4 affecting Cavendish outside Southeast Asia, is its northernmost outbreak, and represents a dangerous expansion of this destructive race. Currently, 80% of the Jordan Valley production area is affected by Fusarium wilt, and 20 to 80% of the plants are affected in different farms. References: (1) M. A. Dita et al. Plant Pathol. 59:348, 2010. (2) J. F. Leslie and B. A. Summerell. The Fusarium Lab Manual. Blackwell, Ames, 2006. (3) R. C. Ploetz. Phytopathology 96:653, 2006.

scholarly journals Comparative Whole-Genome Sequence Analyses of Fusarium Wilt Pathogen (Foc R1, STR4 and TR4) Infecting Cavendish (AAA) Bananas in India, with a Special Emphasis on Pathogenicity Mechanisms

2021 ◽  
Vol 7 (9) ◽  
pp. 717
Author(s):  
Thangavelu Raman ◽  
Esack Edwin Raj ◽  
Gopi Muthukathan ◽  
Murugan Loganathan ◽  
Pushpakanth Periyasamy ◽  
...  
Keyword(s):  
Fusarium Wilt ◽  
Genome Assembly ◽  
Molecular Mechanisms ◽  
Whole Genome Sequence ◽  
Rate Of Spread ◽  
Compatibility Group ◽  
Race 1 ◽  
Race 2 ◽  
Serious Disease ◽  
Race 4

Fusarium wilt is caused by the fungus Fusarium oxysporum f. sp. cubense (Foc) and is the most serious disease affecting bananas (Musa spp.). The fungus is classified into Foc race 1 (R1), Foc race 2, and Foc race 4 based on host specificity. As the rate of spread and the ranges of the devastation of the Foc races exceed the centre of the banana’s origin, even in non-targeted cultivars, there is a possibility of variation in virulence-associated genes. Therefore, the present study investigates the genome assembly of Foc races that infect the Cavendish (AAA) banana group in India, specifically those of the vegetative compatibility group (VCG) 0124 (race 1), 0120 (subtropical race 4), and 01213/16 (tropical race 4). While comparing the general features of the genome sequences (e.g., RNAs, GO, SNPs, and InDels), the study also looked at transposable elements, phylogenetic relationships, and virulence-associated effector genes, and sought insights into race-specific molecular mechanisms of infection based on the presence of unique genes. The results of the analyses revealed variations in the organisation of genome assembly and virulence-associated genes, specifically secreted in xylem (SIX) genes, when compared to their respective reference genomes. The findings contributed to a better understanding of Indian Foc genomes, which will aid in the development of effective Fusarium wilt management techniques for various Foc VCGs in India and beyond.

scholarly journals Evaluating the potential of soil management to reduce the effect of Fusarium oxysporum f. sp. cubense in banana (Musa AAA)

2021 ◽  
Author(s):  
R. A. Segura-Mena ◽  
J. J. Stoorvogel ◽  
F. García-Bastidas ◽  
M. Salacinas-Niez ◽  
G. H. J. Kema ◽  
...  
Keyword(s):  
Soil Properties ◽  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Soil Ph ◽  
Soil Management ◽  
Control Measures ◽  
Crop Development ◽  
Race 1 ◽  
The 1950S ◽  
Race 4

AbstractFusarium oxysporum f. sp. cubense (Foc) causes Fusarium wilt in banana (Musa AAA). Foc Race 1 devastated the subgroup Gros Michel during the first half of the twentieth century. The Gros Michel was largely replaced by the resistant subgroup Cavendish in the 1950s. However, in the 1980s, Foc Tropical Race 4 started to spread affecting Cavendish bananas. No proper control measures have been found to deal with the disease. This paper re-takes an important research line from the 1950s to evaluate the potential of soil management for Fusarium wilt management. The role of soil properties on Fusarium wilt in bananas was studied in two greenhouse experiments. It was evaluated whether the influence of two main soil properties (pH and N) on Fusarium wilt is similar for Race 1 and Tropical Race 4. Two soil pH levels (lower than 5.2 and higher than 6.0) respectively ensured through acidification and liming; and three levels of N (ammonium nitrate, 33.5% N) weekly doses (low:0 N g, medium: 0.08 N g and high: 0.25 N g per plant) were achieved. The first experiment in Costa Rica confirmed the earlier results about the influence of soil pH and nitrogen on Fusarium wilt (Race 1) on Gros Michel bananas. The second experiment in The Netherlands evaluated the influence of pH and N on interactions between Foc (both Race 1 and Tropical Race 4) and Cavendish bananas. Results in both experiments showed that soil pH affected crop development and the disease. Besides, the interaction of the lower pH x the higher N accelerated the infection and reduced plant development. As such, the results showed that soil management has the potential to reduce the impacts of Fusarium wilt while dealing with Race 1 and Tropical Race 4 although it requires confirmation and further evaluation under field conditions.

scholarly journals First report of Fusarium oxysporum f. sp. cubense Tropical Race 4, causing Fusarium wilt in Cavendish bananas in Peru

Plant Disease ◽  
2021 ◽  
Author(s):  
Rosalyn Acuña ◽  
Mathieu Rouard ◽  
Ana Maria Leiva ◽  
Claudio Marques ◽  
Arturo Olortegui ◽  
...  
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Latin American ◽  
Plant Protection ◽  
Water Control ◽  
Illumina Platform ◽  
Single Spore ◽  
Fungal Isolates ◽  
Official Control ◽  
Race 4

Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), the causal agent of Fusarium wilt of banana (FWB), is currently the major threat to the banana industry worldwide (Dita et al. 2018). Restricted to South Asia for more than 20 years, Foc TR4 has spread in the last years to the Middle East, Mozambique, and Colombia (García-Bastidas et al. 2019; https://pestdisplace.org/embed/news/map/disease/11). The incursion of Foc TR4 in Colombia increased awareness and prevention efforts across Latin American and the Caribbean (LAC). However, new Foc TR4 outbreaks in LAC countries were considered a matter of time. In April 2021, banana (Musa spp., Cavendish, AAA) plants (30% of incidence) showing typical symptoms of FWB, such as leave yellowing, wilting and vascular discoloration were observed in one farm (about 1 ha) located in Querecotillo, Peru (4°43’54.84”S 80°33’45.00”W). Mycological analyses of samples (pseudostem strands) collected from 10 symptomatic plants were performed as described by Dita et al. (2010). These analyses revealed a continuous presence of fungal colonies identified as Fusarium oxysporum species complex. Molecular diagnostics targeting two different genome regions (Dita et al 2010; Li et al. 2013) identified nine of these isolates as Foc TR4. These results were further confirmed by qPCR analyses using the commercial Clear Detections TR4 kit. The genome of four single-spore isolates (PerS1, PerS2, PerS3 and PerS4) was sequenced using the Illumina platform (MiSeq Kit, 2x151 bp Paired-End). The strain PerS4 was also sequenced using Oxford Nanopore (FLOW-MIN111; R10.3 chemistry) as described by Lopez-Alvarez et al., (2020). The generated draft assembly yielded 533 contigs for a size of 47 Mbp (BioProject: PRJNA755905), which is comparable with sizes of previously reported Foc TR4 strains (Asai et al. 2019; García-Bastidas et al. 2019; Maymon et al. 2020; Warmington et al. 2019; Zheng et al. 2018). The sequence assembly showed high contiguity (94.9%) and high similarity (95.48%) with the high-quality genome sequence of the Foc TR4 isolate ‘UK0001’ (Warmington et al. 2019). Further analyses to identify the presence/absence of full sequences for the putative effector genes (Secreted In Xylem - SIX) and their allelic copies, also revealed that the SIX genes profile of the strains isolated from Querecotillo matched with previously reported Foc TR4 isolates (Czislowski et al. 2017). Pathogenicity tests with three isolates and water controls were performed as described by Dita et al. (2010), using five Cavendish plantlets per treatment. Four weeks after the inoculation typical external and internal symptoms of FWB were observed only in the inoculated plants. Fungal isolates recovered from inoculated plants tested positive for Foc TR4 when analyzed with PCR diagnostics as mentioned above. No fungal isolates were recovered from water-control plants which did not show any symptoms. Altogether, our results confirm the first incursion of Foc TR4 in Peru. Currently, Foc TR4 has the phytosanitary status of a present pest with restricted distribution in Peru and it is under official control of the National Plant Protection Organization – SENASA. Reinforced prevention and quarantine measures, disease monitoring and capacity building to detect, contain and manage eventual new outbreaks of Foc TR4 are strongly encouraged across LAC banana producing countries, especially for those bordering Peru with larger banana plantations, such as Ecuador and Brazil.

scholarly journals First report of Fusarium oxysporum f.sp. cubense VCG 0125 and VCG 01220 of Race 1 infecting Cavendish bananas(Musa sp. AAA) in India

Plant Disease ◽  
2020 ◽  
Author(s):  
Raman Thangavelu ◽  
Gopi Muthukathan ◽  
Periaswamy Pushpakanth ◽  
Loganathan Murugan ◽  
Esack Edwin Raj ◽  
...  
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Tamil Nadu ◽  
Block Design ◽  
Uttar Pradesh ◽  
Single Spore ◽  
First Report ◽  
Race 1 ◽  
Pcr Method ◽  
Race 4

Fusarium wilt caused by Fusarium oxysporum f.sp. cubense (Foc) is the most devastating disease affecting commercial and subsistence cultivation of banana (Musa spp.) worldwide. Generally, the Cavendish bananas are resistant to Foc race 1 that destroyed cv. ‘Gros Michel’ (AAA) and susceptible to tropical race 4 (TR4), which is causing severe epidemics in different banana-growing countries including India (Thangavelu et al. 2019). In 2019, a roving survey was conducted in major banana growing states of India such as Bihar, Uttar Pradesh, Gujarat and Tamil Nadu to assess the incidence of Fusarium wilt disease in Cavendish bananas and also to characterize the pathogens by different methods including Vegetative Compatibility Grouping (VCG) and molecular methods. The Fusarium wilt incidence in cv. Grand Naine (Cavendish group-AAA) was 6-65% in Bihar, 30-45% in Uttar Pradesh, 5-15% in Gujarat and 15- 21% in Tamil Nadu. For characterization, a total of 61 samples from the Fusarium wilt infected Cavendish bananas were collected and single spore culture of Foc was obtained. The morphological characterization revealed the presence of one to two oval- to kidney-shaped cells in false heads and sickle-shaped macroconidia and a foot-shaped basal cell. The pathogenicity was demonstrated by adopting randomized block design with five replications on cv. Grand Naine. The Koch’s postulate was successfully completed by re-isolation of the inoculated Foc pathogen and characterization by PCR method. The VCG analysis carried out using nit–M testers of all known VCGs indicated the presence of VCG 0125 from the Foc samples collected from cv. Grand Naine grown in Uttar Pradesh (Siswabazar of Maharakanj district) and Tamil Nadu (Cumbum of Theni district), VCG 01220 from the Foc samples collected from cv. Grand Naine grown in Uttar Pradesh (Siswabazar of Maharakanj district) and Gujarat (Kamrej of Surat district,) and VCG 01213/16 from Foc samples collected from Uttar Pradesh (Siswabazar of Maharakanj district) and Bihar (Falka village of Katihar district) . The molecular confirmation of these VCGs 0125, and 01220 (Foc R1) isolates was carried out by PCR method using the primer set SIX6b_210_F and SIX6b_210_R (Carvalhais et al. 2019) for Foc R1, primer sets Foc TR4-F & Foc TR4 –R (Dita et al. 2010) for Foc TR4 and primer set Foc-1/Foc -2 (Lin et al. 2009) for Race 4. The results showed that only the primer set for Foc R1 has generated the expected amplicon size of 210 bp in the Foc isolates of VCG 0125 and 01220. Besides, the sequencing of Translation Elongation Factor (TEF) 1-α gene and BLAST searches in Genbank for the representative Foc isolates of VCG 0125 (Genbank no. MW 286800) showed 99.84% similarity to Foc R1 (KX365393.1) and Foc isolates of VCG 01220 (Genbank no. MW 286803) showed 99.69% similarity to Foc R1 (KX365413.1). Further, a phylogenetic analysis performed using the TEF1-α gene sequences showed that the Foc race 1 isolates (VCGs 0125 and 01220) from India were grouped with known Foc race 1 isolates from Tanzania and Australia. Based on the experimental results the study has confirmed the presence of VCGs 0125 and 01220 of Foc Race 1 in cv. Grand Naine in India. As these VCGs are most widely distributed and do not found to infect Cavendish bananas so far (Mostert et al. 2017), this report is very important from the quarantine and management perspectives. To the best of our knowledge, this is the first report of the occurrence of VCGs 0125 and 01220 of Foc Race 1 in cv. Grand Naine in India.

scholarly journals The Population of Fusarium oxysporum f. sp. lactucae in California and Arizona

Plant Disease ◽  
2020 ◽  
Vol 104 (6) ◽  
pp. 1811-1816
Author(s):  
Kelley R. Paugh ◽  
Thomas R. Gordon
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Elongation Factor ◽  
Intergenic Spacer ◽  
Intermediate Step ◽  
Translation Elongation ◽  
Intergenic Spacer Region ◽  
Nit Mutants ◽  
Compatibility Group ◽  
Race 1

Fusarium wilt of lettuce, caused by Fusarium oxysporum f. sp. lactucae, is now found in all major lettuce producing regions in California and Arizona. The population structure of F. oxysporum f. sp. lactucae in California and Arizona was characterized based on somatic compatibility and sequences of the translation elongation factor 1-α gene (EF-1α) and rDNA intergenic spacer region (IGS). In this study, 170 isolates were tested for somatic compatibility based on heterokaryon formation, using complementary nitrate nonutilizing (nit) mutants. Five subgroups (A to E) of somatic compatibility group 0300 were identified. Isolates associated with the same subgroup had a strong complementation reaction, whereas reactions between isolates of different subgroups were weak or delayed. An isolate from the first known infestation of Fusarium wilt of lettuce in California was associated with subgroup A, which predominated among isolates in our collection. Isolates representative of each subgroup were confirmed to be associated with race 1, based on the reaction of differential lettuce cultivars. It is possible that somatic compatibility subgroups B to E of F. oxysporum f. sp. lactucae were derived from subgroup A, as a consequence of somatic mutations affecting compatibility. If so, subgroups of F. oxysporum f. sp. lactucae may represent an intermediate step in divergence that will lead to clearly separable compatibility groups. Sequences of EF-1α and IGS were both identical for 58 isolates of F. oxysporum f. sp. lactucae that represented all somatic compatibility subgroups and locations from which isolates were obtained, indicating that subgroups were derived from the same clonal lineage (VCG 0300).

scholarly journals A New Race of Fusarium oxysporum f. sp. melonis Causing Fusarium Wilt of Muskmelon in the Central Valley of California

Plant Disease ◽  
1997 ◽  
Vol 81 (9) ◽  
pp. 1095-1095 ◽  
Author(s):  
B. J. Gwynne ◽  
T. R. Gordon ◽  
R. M. Davis
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Central Valley ◽  
Differential Host ◽  
Resistant Varieties ◽  
Compatibility Group ◽  
Race 1 ◽  
New Race ◽  
Race 2 ◽  
Cucumis Melo L

In 1996, cantaloupe (Cucumis melo L. cv. Durango) vines in two fields exhibited wilt, vascular discoloration, and necrotic streaks on the stems. Fusarium oxysporum Schlechtend.:Fr. was isolated from the stems of vines from both fields. One isolate from each field was compared with known isolates of F. oxysporum f. sp. melonis (Leach & Currence) W.C. Snyder & H.N. Hansen races 1 and 2 in a differential host range experiment in the greenhouse. Three-week-old seedlings were root-dip inoculated with monoconidial isolates at a concentration of 5 × 105 spores per ml. Control plants were dipped in water. In two experiments, the test isolates killed the susceptible varieties Top Mark and Magnum .45 and the race 2 resistant varieties Durango, Gold Mine, and Perlita FR. Seedlings of variety Charentais with the Fom2 gene conferring resistance to race 1 were resistant to both test isolates. It was determined that both of these isolates are associated with vegetative compatibility group (VCG) 0134 (1). This is the first report of race 1 and VCG 0134 of F. oxysporum f. sp. melonis causing Fusarium wilt of muskmelon in the Central Valley of California, and the first reported occurrence of race 1 in California since 1973 (2). Cantaloupe varieties currently grown in California are susceptible to race 1 of F. oxysporum f. sp. melonis References: (1) D. J. Jacobson and T. R. Gordon. Phytopathology 78:668, 1988. (2) J. V. Leary and W. D. Wilbur. Phytopathology 66:15, 1976.

scholarly journals Relationships Among Wilt-Inducing Isolates of Fusarium oxysporum from Sweetpotato and Tobacco

Plant Disease ◽  
1998 ◽  
Vol 82 (5) ◽  
pp. 530-536 ◽  
Author(s):  
C. A. Clark ◽  
J-W. Hyun ◽  
M. W. Hoy
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Random Amplified Polymorphic Dna ◽  
Severe Disease ◽  
Vegetative Compatibility ◽  
Vegetative Compatibility Group ◽  
Burley Tobacco ◽  
Compatibility Group ◽  
Race 1 ◽  
New Race

Thirty-five isolates of Fusarium oxysporum obtained from diseased sweetpotato or tobacco were compared for pathogenicity on two cultivars each of sweetpotato and tobacco, by random amplified polymorphic DNA (RAPD) profiles, and by vegetative compatibility group (VCG) analysis. Analysis of RAPD profiles revealed five clusters of isolates that corresponded to patterns of pathogenicity. One cluster of isolates, designated as F. oxysporum f. sp. nicotianae, induced severe wilting on both tobacco cultivars but varied from weakly to highly aggressive on the sweetpotato cultivars. Four of the 16 isolates from this group were originally isolated from sweetpotato, and 1 isolate caused severe disease on both crops. Three clusters included isolates from sweetpotato that were virulent on Porto Rico, caused little or no disease on Beauregard and burley tobacco (cv. Kentucky 5), and did not cause wilt on flue-cured tobacco (cv. Gold Dollar). These isolates were designated as race 0 of F. oxysporum f. sp. batatas. Isolates obtained from sweetpotato from California clustered separately from other sweetpotato isolates and the tobacco isolates. They differed from other sweetpotato isolates in being virulent on Beauregard and are proposed as a new race 1 of F. oxysporum f. sp. batatas. VCG analysis was of limited value with the isolates in this study because many isolates were self-incompatible. In each case, all members of a VCG fell within the same cluster defined by RAPDs. This study demonstrated that F. oxysporum from at least three genetically distinct lineages can cause Fusarium wilt on sweetpotato, and that the host ranges of F. oxysporum f. sp. batatas and F. oxysporum f. sp. nicotianae overlap and include plants from two different families.

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