First Report of Fusarium Wilt Caused by Fusarium oxysporum f. sp. niveum Race 2 in Georgia Watermelons

Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is the number one specialty crop grown in Georgia, a state that ranks fourth nationally in watermelon production. In the last 5 years, Fusarium wilt caused by Fusarium oxysporum f. sp. niveum (Fon) has been the greatest yield-limiting disease of watermelon in Georgia. In 2004, a seedless-watermelon field of ‘Regency’ and ‘Tri-X 313’ in Berrien County, GA exhibited approximately 40% of wilted plants. Affected plants also exhibited strong discoloration in the crown xylem. Plant samples (cultivars unknown) from a similarly affected field were also tested from Crisp County, GA. Xylem tissue was excised from the main stem of eight diseased plants in the area between the second and third internode, surface sterilized for 1 min in 1% NaOCl, rinsed with 80% ethanol, and plated onto water agar amended with 100 μg/liter of streptomycin sulfate. Fungi with the morphological characteristics of Fusarium oxysporum (4) were consistently recovered from the diseased tissue of all eight plants. The isolates were hyphal tipped and maintained in vials of sterile artificial potting mix until ready for use (1). Isolates were grown on Esposito and Fletcher medium (2) for 10 days, filtered through cheesecloth, and adjusted to 1 × 106 spores/ml. Reference isolates of race 1 and 2 were used as comparisons for race determination of the unknowns. In each of four studies, plants at the two-leaf stage were removed from potting mix, washed gently, and their roots were uniformly trimmed to 2.5 cm. Before repotting, the seedlings were subjected to a 2-min root-dip in the respective spore-containing media. In each study, approximately 40 plants of each watermelon differential were inoculated with the respective isolates. In disease scoring, each plant was considered a rep. ‘Black Diamond’ is susceptible to races 0, 1, and 2; ‘Charleston Gray’ is resistant to race 0; ‘Calhoun Gray’ is resistant to races 0 and 1, and PI-296341-FR (3) is resistant to races 0, 1, and 2 of Fon. Four plants were planted per 15-cm plastic pot, maintained in an air-conditioned headhouse for 24 h, and then placed in the greenhouse in a randomized complete block design. After 30 days, all plants were rated as to healthy, wilted, or dead plants. From eight isolates tested, one isolate from each county was determined to be Fon race 2 on the basis of its ability to wilt/kill a high percentage of the race 1 resistant differential, i.e., ‘Calhoun Gray’. Mean disease percentages for the isolates from each of the two counties on the watermelon differentials were 95 and 100% on ‘Black Diamond’, 68 and 80% on ‘Charleston Gray’, and 70 and 86% on ‘Calhoun Gray.’ Because of apparent genetic drift within our PI-296341-FR population, we determined that these data were not useful for identifying race 2. In fact, we observed a range of 17 to 80% wilt/death in the PI-296341-FR over a total of four studies that included a known race 2 isolate (Calg 13(15); E. Vivoda). To our knowledge, this is the first report of race 2 in Georgia and it increases the number of states to seven in which race 2 has been identified. Five of the top 10 watermelon-producing states have now reported race 2 of Fon for which there is no genetic resistance within commercial cultivars. References: (1) B. D. Bruton et al. Plant Dis. 84:907, 2000. (2) R. Esposito and A. Fletcher. Arch. Biochem. Biophys. 93:369, 1961. (3) R. D. Martyn and D. Netzer. HortScience 26:429, 1991. (4) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983.

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First Report of Fusarium oxysporum f. sp. niveum Race 2 as Causal Agent of Fusarium Wilt of Watermelon in Indiana

Plant Disease ◽

10.1094/pd-89-0108a ◽

2005 ◽

Vol 89 (1) ◽

pp. 108-108 ◽

Cited By ~ 12

Author(s):

D. S. Egel ◽

R. Harikrishnan ◽

R. Martyn

Keyword(s):

United States ◽

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Citrullus Lanatus ◽

The United States ◽

Mineral Salts ◽

First Report ◽

Race 1 ◽

Race 2 ◽

Greenhouse Assay

Fusarium oxysporum f. sp. niveum race 1 is uniformly distributed throughout watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) growing regions, but F. oxysporum f. sp. niveum race 2 has a limited known distribution in the United States (Texas, Florida, Oklahoma, Maryland, and Delaware) (3,4). Since the spring of 2001, commercial watermelon fields in Knox and Gibson counties in southwestern Indiana have been observed with symptoms of one-sided wilt and vascular discoloration typical of Fusarium wilt. Race 2 of F. oxysporum f. sp. niveum was suspected as the casual agent since the diseased watermelon cultivars are considered resistant to races 0 and 1. Two isolates of F. oxysporum obtained from wilted watermelon plants in two different commercial fields and one isolate obtained from a wilted seedling in a transplant house were compared for pathogenicity in a greenhouse assay. Known isolates of F. oxysporum f. sp. niveum races 0, 1, and 2 were obtained from Don Hopkins (University of Florida, Apopka), Kate Everts (University of Maryland/University of Delaware, Salisbury, MD), and Ray Martyn (Purdue University, West Lafayette, IN), respectively, and were used for comparison. All isolates were grown in shake cultures in a mineral salts liquid medium. (1). After 72 hr, the predominately microconidal suspensions were filtered through cheesecloth and adjusted to 1 × 105 conidia/ml with the aid of a hemacytometer. A concentration of 1 × 105 condia/ml was shown previously to cause the desired disease reaction in the standard cultivars. Seedlings of the differential cvs, Black Diamond (universal susceptible), Charleston Gray (race 0 resistant), and Calhoun Gray (race 0 and 1 resistant) were grown in a 1:1, (v:v) sand/ vermiculite mixture to the first true-leaf stage after which the plants were uprooted and the roots carefully washed prior to root dip inoculation. Subsequent to inoculation, seedlings were planted in a sand/vermiculite/ peat mixture (4:1:1, [v:v:v]) with four seedlings to a 15-cm-diameter pot. The experimental design was a randomized complete block with five replications. Two isolates from the commercial field plants caused an average of 100% wilt on cv. Black Diamond, 95% wilt on cv. Charleston Gray, and 80% wilt on cv. Calhoun Gray, resulting in a designation of race 2. The isolate from a commercial transplant house resulted in 100, 60, and 15% wilt, respectively, on the three standard cultivars resulting in a race 1 designation. The presence of F. oxysporum f. sp. niveum race 2 in Indiana is significant because Indiana currently ranks fifth in the United States in watermelon production and there are no commercially available cultivars that possess resistance to race 2. To our knowledge, this is the first report of F. oxysporum f. sp. niveum race 2 in Indiana and the first report of race 2 from the Midwest region of the United States. Race 2, first described from the United States in 1985 (2), has now been confirmed in six states. References: (1) R. Esposito and A. Fletcher. Arch. Biochem. Biophys. 93:369, 1961. (2) R. Martyn, Plant Dis. 69:1007, 1985. (3) R. Martyn, Plant Dis. 71:233, 1987. (4) X. Zhou and K. Everts. Plant Dis. 87:692, 2003.

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First Report of Race 2 of Fusarium oxysporum f. sp. lycopersici, the Causal Agent of Fusarium Wilt on Tomato in Taiwan

Plant Disease ◽

10.1094/pd-90-0111c ◽

2006 ◽

Vol 90 (1) ◽

pp. 111-111 ◽

Cited By ~ 4

Author(s):

Z. M. Sheu ◽

T. C. Wang

Keyword(s):

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Banding Pattern ◽

Vascular Tissue ◽

First Report ◽

Intergenic Spacer Region ◽

Stunted Growth ◽

Vascular Discoloration ◽

Race 1 ◽

Race 2

Fusarium wilt caused by Fusarium oxysporum Schlechtend.:Fr. f. sp. lycopersici (Sacc.) W.C. Snyder & N.H. Hans. is a destructive disease of tomato crops worldwide. The use of resistant varieties is the best strategy for disease control. There are three reported races of the pathogen. Recent surveys indicated that many of the commercial cultivars with resistance to F. oxysporum f. sp. lycopersici race 1 planted in Taiwan displayed Fusarium wilt symptoms. Yellowing on the older leaves was observed on one side of the stems close to fruit maturity. The yellowing gradually affected most of the foliage and was accompanied by wilting of the plants. The vascular tissue was usually dark brown and discoloration extended to the apex. The wilting became more extensive until plants collapsed and died. A total of 87 isolates obtained from typical diseased plants throughout Taiwan from 2002 to 2005 were analyzed to determine the race and distribution of this pathogen in Taiwan. Isolates were confirmed at the species level using F. oxysporum-specific primers FOF1 and FOR1 (4). Subsequently, isolates were characterized for pathogenicity, race and restriction fragment length polymorphisms of the intergenic spacer region of rDNA (IGS-RFLP) with two reference isolates, Fol 11A (race 1) and Fol 34-1 (race 2). Pathogenicity tests and race determination were conducted using root-dip inoculation (3) on 2-week-old seedlings of host differentials Bonny Best (no resistance), UC82-L (resistant to race 1), and Florida MH-1 (resistant to races 1 and 2). Thirty-six seedlings of each cultivar were arranged into three replications and inoculated with each isolate. Disease reaction was evaluated 3 weeks after inoculation. The disease severity rating (DSR) was determined on individual plants according to the following scale: 0 = plant healthy without external symptoms; 1 = slight vascular discoloration with or without stunted growth; 2 = severe vascular discoloration usually with stunted growth; and 3 = plant wilted beyond recovery or dead. The presence of severe vascular discoloration indicated a susceptible reaction. All isolates were race 2, and over 70% of the isolates showed strong virulence with a DSR >2 on cvs. Bonny Best and UC-82L. This result was different from a previous report of race 1 from Taiwan (2). Two IGS-RFLP haplotypes generated by EcoRI, RsaI, and HaeIII digestions (1) were identified. Eighty-six isolates displayed one banding pattern, and one unique isolate displayed a second banding pattern. The results demonstrated the predominance of race 2 and low diversity within the Taiwan population. To our knowledge, this is the first report regarding the predominant race and IGS-RFLP haplotype identification of F. oxysporum f. sp. lycopersici in Taiwan. Our study indicates that tomato varieties in Taiwan should possess resistance to race 2. References: (1) G. Cai et al. Phytopathology 93:1014, 2003. (2) K. S. Elias and R. W. Schneider. Phytopathology 82:1421, 1992. (3) J. W. Gerdemann and A. M. Finley. Phytopathology 41:238, 1951. (4) P. K. Mishra et al. FEMS Microbiol. Lett. 218:329, 2003.

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First Report of the Occurrence of Fusarium oxysporum f. sp. niveum Race 2 in Commercial Watermelon Production Areas of Maryland and Delaware

Plant Disease ◽

10.1094/pdis.2001.85.12.1291c ◽

2001 ◽

Vol 85 (12) ◽

pp. 1291-1291 ◽

Cited By ~ 12

Author(s):

X. G. Zhou ◽

K. L. Everts

Keyword(s):

Fusarium Oxysporum ◽

Growth Medium ◽

Citrullus Lanatus ◽

Culture Collection ◽

Peat Moss ◽

Mineral Salts ◽

First Report ◽

Differential Cultivars ◽

Race 1 ◽

Race 2

Resistance to race 1 of Fusarium oxysporum f. sp. niveum (E.F. Sm.) W.C. Snyder & H.N. Hans) is the most widely used tool for management of Fusarium wilt of watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai). However, this resistance is ineffective against the more aggressive F. oxysporum f. sp. niveum race 2. Race 2 was first identified in Israel in 1973 (2) and was subsequently reported in Texas (1981), Oklahoma (1988), and Florida (1989) (1). From July through September 2000 in Maryland and Delaware, 123 isolates of F. oxysporum f. sp. niveum were collected from wilted plants or plants with vascular discoloration from commercial production fields with moderate to severe wilt severity. Race determination was performed in the greenhouse on five race-differential cultivars. Differential cvs. Sugar Baby, Crimson Sweet, Charleston Gray, Allsweet, and Dixielee range from susceptible to highly resistant (in the order listed) to race 1, but all are susceptible to race 2. Seeds were planted in pots containing pasteurized vermiculite and peat moss (2:3 mixture) growth medium infested with 1 × 105 conidia per g of growth medium. Conidia were harvested from 5- to 6-day-old cultures of F. oxysporum f. sp. niveum grown in a liquid mineral salts medium (2). Control pots were treated with water or diluted liquid medium. Pots were maintained in a greenhouse at 19 to 28°C. Three replicate pots containing seven plants each were used for each isolate-cultivar combination. Race 0 obtained from B. D. Bruton (USDA-ARS, Lane, OK), and races 1 and 2 obtained from the American Type Culture Collection (Manassas, VA) were included in the tests for comparative purposes. Eleven isolates from Maryland and three isolates from Delaware consistently caused 60 to 100% wilt or mortality of all cultivars, with a mean of more than 75% wilt. Percent wilt of cvs. Sugar Baby and Dixielee to races 0, 1, and 2, and the 14 isolates from Maryland and Delaware was 78, 76, 100, and 95 to 100% and 0, 14, 59, and 63 to 93%, respectively. All control plants remained healthy. In each of the three replicated tests, these 14 isolates caused an equal or greater incidence of wilt as the reference race 2 isolate, and cvs. Dixielee and Allsweet were susceptible to these isolates. Therefore, these isolates were identified as F. oxysporum f. sp. niveum race 2. This is the first report of F. oxsporum f. sp. niveum race 2 occurring in Maryland and Delaware. References: (1) R. D. Martyn and B. D. Bruton. HortScience 24:696, 1989. (2) D. Netzer. Phytoparasitica 4:131, 1976.

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First Report of Fusarium oxysporum f. sp. lycopersici Race 2 on Tomato in Italy

Plant Disease ◽

10.1094/pdis.1999.83.10.967b ◽

1999 ◽

Vol 83 (10) ◽

pp. 967-967 ◽

Cited By ~ 1

Author(s):

V. M. Stravato ◽

R. Buonaurio ◽

C. Cappelli

Keyword(s):

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Vascular Tissue ◽

Morphological Features ◽

Pathogenicity Test ◽

First Report ◽

Fungal Isolates ◽

Race 1 ◽

Race 2 ◽

I Gene

During the summer of 1997, symptoms of Fusarium wilt were observed on tomato (Lycopersicon esculentum Mill.) cvs. Monica F1 and PS 110, which bear the I gene for resistance to race 1 of Fusarium oxysporum Schlechtend.:Fr. f. sp. lycopersici (Sacc.) W.C. Snyder & H.N. Hans., in two commercial production greenhouses in Latium (Fondi) and one greenhouse in Sardinia (Oristano). Infected plants showed yellowing, stunting, vascular discoloration, and premature death. A fungus from tomato stems with discolored vascular tissue was consistently isolated on potato dextrose agar (PDA) and, based on morphological features, was identified as F. oxysporum. To verify the pathogenicity of four fungal isolates, cv. Bonny Best tomato plants, which do not carry genes for Fusarium wilt resistance, were inoculated by dipping roots of 2-week-old seedlings in a suspension of 105 microconidia per ml for 30 s. Inocula were obtained from 1-week-old fungal cultures grown on PDA. Roots of control plants were dipped in water. Seedlings were transplanted to pots containing peat and river sand (1:1, vol/vol) and placed in a greenhouse at 20 to 25°C. One month after inoculation, all fungal isolates provoked wilting of inoculated plants. No symptoms were observed on control plants. The morphological features of the fungus reisolated from diseased plants were similar to those of the original isolates. Based on the pathogenicity test, we concluded that the fungal isolates belong to F. oxysporum f. sp. lycopersici. To determine the races of the fungal isolates, differential tomato lines VFN8 (I gene for resistance to race 1), Florida MH-1 (I and I2 genes for resistance to races 1 and 2), and I3R (I, I2, and I3 genes for resistance to races 1, 2, and 3) were inoculated with the four fungal isolates, using the same procedure described for the pathogenicity test. Because disease symptoms were detected on VFN8 but not on Florida MH-1 and I3R, we deduced that the fungal isolates belong to F. oxysporum race 2. This is the first report of F. oxysporum f. sp. lycopersici race 2 in Italy. Previous research indicated that race 1 is present in Italy (1). Currently, many commercially acceptable cultivars resistant to races 1 and 2 are available to Italian greenhouse growers. Reference: (1) M. Cirulli. Phytopathol. Mediterr. 4:63, 1965.

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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 ◽

10.1094/pdis-09-20-2052-pdn ◽

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.

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Current Classification and Diversity of Fusarium Species Complex, the Causal Pathogen of Fusarium Wilt Disease of Banana in Malaysia

Agronomy ◽

10.3390/agronomy11101955 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1955

Author(s):

Anysia Hedy Ujat ◽

Ganesan Vadamalai ◽

Yukako Hattori ◽

Chiharu Nakashima ◽

Clement Kiing Fook Wong ◽

...

Keyword(s):

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Species Complex ◽

Phylogenetic Trees ◽

Fusarium Species ◽

Morphological Characteristics ◽

Pathogenicity Test ◽

Fusarium Spp ◽

Specific Primers ◽

Fusarium Oxysporum Species Complex

The re-emergence of the Fusarium wilt caused by Fusarium odoratissimum (F. odoratissimum) causes global banana production loss. Thirty-eight isolates of Fusarium species (Fusarium spp.) were examined for morphological characteristics on different media, showing the typical Fusarium spp. The phylogenetic trees of Fusarium isolates were generated using the sequences of histone gene (H3) and translation elongation factor gene (TEF-1α). Specific primers were used to confirm the presence of F. odoratissimum. The phylogenetic trees showed the rich diversity of the genus Fusarium related to Fusarium wilt, which consists of F. odoratissimum, Fusarium grosmichelii, Fusarium sacchari, and an unknown species of the Fusarium oxysporum species complex. By using Foc-TR4 specific primers, 27 isolates were confirmed as F. odoratissimum. A pathogenicity test was conducted for 30 days on five different local cultivars including, Musa acuminata (AAA, AA) and Musa paradisiaca (AAB, ABB). Although foliar symptoms showed different severity of those disease progression, vascular symptoms of the inoculated plantlet showed that infection was uniformly severe. Therefore, it can be concluded that the Fusarium oxysporum species complex related to Fusarium wilt of banana in Malaysia is rich in diversity, and F. odoratissimum has pathogenicity to local banana cultivars in Malaysia regardless of the genotype of the banana plants.

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Suppression of Fusarium Wilt Caused by Fusarium oxysporum f. sp. niveum Race 2 on Grafted Triploid Watermelon

Plant Disease ◽

10.1094/pdis-01-14-0005-re ◽

2014 ◽

Vol 98 (10) ◽

pp. 1326-1332 ◽

Cited By ~ 13

Author(s):

Anthony P. Keinath ◽

Richard L. Hassell

Keyword(s):

Fusarium Oxysporum ◽

Fusarium Wilt ◽

Disease Incidence ◽

The United States ◽

Infested Soil ◽

Marketable Yield ◽

Race 1 ◽

Susceptible Control ◽

Triploid Watermelon ◽

Race 2

Fusarium wilt of watermelon, caused by the soilborne fungal pathogen Fusarium oxysporum f. sp. niveum race 2, is a serious, widespread disease present in major watermelon-growing regions of the United States and other countries. ‘Fascination,’ a high yielding triploid resistant to race 1, is grown in southeastern states in fields that contain a mixture of races 1 and 2. There is some benefit to using cultivars with race 1 resistance in such fields, even though Fascination is susceptible to Fusarium wilt caused by race 2. Experiments in 2012 and 2013 were done in fields infested primarily with race 2 and a mixture of races 1 and 2, respectively. Fascination was grafted onto four rootstock cultivars: bottle gourd (Lagenaria siceraria) ‘Macis’ and ‘Emphasis’ and interspecific hybrid squash (Cucurbita maxima× C. moschata) ‘Strong Tosa’ and ‘Carnivor.’ Nongrafted and self-grafted Fascination were used as susceptible control treatments. In both experiments, mean incidence of plants with symptoms of Fusarium wilt was ≥52% in the susceptible control treatments and ≤6% on the grafted rootstocks. Disease incidence did not differ between rootstock species or cultivars. In both years, Fascination grafted onto Strong Tosa and Macis produced more marketable-sized fruit than the susceptible control treatments. Grafted Emphasis and Carnivor also produced more fruit than the control treatments in 2012. The cucurbit rootstocks suppressed Fusarium wilt caused by race 2 and increased marketable yield of triploid watermelon grown in infested soil.

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Race 3, a New and Highly Virulent Race of Fusarium oxysporum f. sp. niveum Causing Fusarium Wilt in Watermelon

Plant Disease ◽

10.1094/pdis-94-1-0092 ◽

2010 ◽

Vol 94 (1) ◽

pp. 92-98 ◽

Cited By ~ 51

Author(s):

X. G. Zhou ◽

K. L. Everts ◽

B. D. Bruton

Keyword(s):

Fusarium Oxysporum ◽

Host Range ◽

Fusarium Wilt ◽

Citrullus Lanatus ◽

Genetic Difference ◽

Infested Soil ◽

Reference Isolate ◽

New Race ◽

Race 2 ◽

Highly Virulent

Three races (0, 1, and 2) of Fusarium oxysporum f. sp. niveum have been previously described in watermelon (Citrullus lanatus) based on their ability to cause disease on differential watermelon genotypes. Four isolates of F. oxysporum f. sp. niveum collected from wilted watermelon plants or infested soil in Maryland, along with reference isolates of races 0, 1, and 2, were compared for virulence, host range, and vegetative compatibility. Race identification was made on the watermelon differentials Sugar Baby, Charleston Gray, Dixielee, Calhoun Gray, and PI-296341-FR using a root-dip, tray-dip, or pipette inoculation method. All four Maryland isolates were highly virulent, causing 78 to 100% wilt on all differentials, one of which was PI-296341-FR, considered highly resistant to race 2. The isolates also produced significantly greater colonization in the lower stems of PI-296341-FR than a standard race 2 reference isolate. In field microplots, two of the isolates caused over 90% wilt on PI-296341-FR, whereas no disease was caused by a race 2 isolate. All four isolates were nonpathogenic on muskmelon, cucumber, pumpkin, and squash, confirming their host specific pathogenicity to watermelon. The Maryland isolates were vegetatively compatible to each other but not compatible with the race 2 isolates evaluated, indicating their genetic difference from race 2. This study proposes that the Maryland isolates belong to a new race, race 3, the most virulent race of F. oxysporum f. sp. niveum described to date.

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Control of Fusarium Wilt of Watermelon by Grafting onto Bottlegourd or Interspecific Hybrid Squash Despite Colonization of Rootstocks by Fusarium

Plant Disease ◽

10.1094/pdis-01-13-0100-re ◽

2014 ◽

Vol 98 (2) ◽

pp. 255-266 ◽

Cited By ~ 21

Author(s):

A. P. Keinath ◽

R. L. Hassell

Keyword(s):

Fusarium Wilt ◽

Interspecific Hybrid ◽

Citrullus Lanatus ◽

Disease Incidence ◽

Field Performance ◽

Control Treatment ◽

Infested Field ◽

Race 1 ◽

Seedless Watermelon ◽

Race 2

Grafting watermelon (Citrullus lanatus var. lanatus) onto rootstocks of interspecific hybrid squash (Cucurbita moschata × C. maxima), bottle gourd (Lagenaria siceraria), or citron (Citrullus lanatus var. citroides) has been used in Asia and Israel to mange Fusarium wilt of watermelon caused by Fusarium oxysporum f. sp. niveum. The objectives of this study were to determine the frequency of infection of six rootstocks by F. oxysporum f. sp. niveum races 1 and 2 and the field performance of grafted rootstocks in Charleston, SC. Grafted and nongrafted watermelon and rootstock plants were inoculated in the greenhouse with race 1, race 2, or water (the control treatment). With both races, the frequency of recovery of F. oxysporum from scion and rootstock portions of inoculated watermelon plants grafted onto ‘Ojakkyo’ citron was greater than from watermelon plants grafted onto ‘Shintosa Camel’ and ‘Strong Tosa’ interspecific hybrid squash, and from plants grafted onto ‘Emphasis’, ‘Macis’, and ‘WMXP 3945’ bottlegourd. For nongrafted plants inoculated with race 1, percent recovery also was greater from Ojakkyo than from interspecific hybrid squash and bottlegourd. For nongrafted plants inoculated with race 2, F. oxysporum was recovered from the base of ≥79% of all inoculated plants. More than two-thirds (15) of 21 isolates recovered from the tops or scions of inoculated plants were pathogenic on watermelon. In spring 2010 and 2011, the six rootstocks were grafted with seedless watermelon ‘Tri-X 313’, which is susceptible to both races, and transplanted in a field infested with races 1 and 2 of F. oxysporum f. sp. niveum. Disease incidence for nongrafted and self-grafted Tri-X 313 (the control treatments) and Tri-X 313 grafted onto Ojakkyo citron did not differ significantly. Grafted watermelon plants produced greater weights and numbers of fruit than plants of the two control treatments. Nonpathogenic isolates of F. oxysporum and isolates of F. oxysporum f. sp. niveum colonized interspecific hybrid squash, bottlegourd, and grafted watermelon. The rootstocks evaluated, however, restricted movement of F. oxysporum f. sp. niveum into the watermelon scion, suppressed wilt symptoms, and increased fruit yields in an infested field.

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First Report on Ovate-leaf Atractylodes Damping-off Caused by Fusarium oxysporum species Complex in South Korea

Plant Disease ◽

10.1094/pdis-05-21-1107-pdn ◽

2021 ◽

Author(s):

Oliul Hassan ◽

Taehyun Chang

Keyword(s):

South Korea ◽

Fusarium Oxysporum ◽

Species Complex ◽

Disease Incidence ◽

Fusarium Species ◽

Morphological Characteristics ◽

Conidial Suspension ◽

Sterile Water ◽

Damping Off ◽

First Report

In South Korea, ovate-leaf atractylodes (OLA) (Atractylodes ovata) is cultivated for herbal medicine. During May to June 2019, a disease with damping off symptoms on OLA seedlings were observed at three farmer fields in Mungyeong, South Korea. Disease incidence was estimated as approximately 20% based on calculating the proportion of symptomatic seedlings in three randomly selected fields. Six randomly selected seedlings (two from each field) showing damping off symptoms were collected. Small pieces (1 cm2) were cut from infected roots, surface-sterilized (1 minute in 0.5% sodium hypochlorite), rinsed twice with sterile water, air-dried and then plated on potato dextrose agar (PDA, Difco, and Becton Dickinson). Hyphal tips were excised and transferred to fresh PDA. Six morphologically similar isolates were obtained from six samples. Seven-day-old colonies, incubated at 25 °C in the dark on PDA, were whitish with light purple mycelia on the upper side and white with light purple at the center on the reverse side. Macroconidia were 3–5 septate, curved, both ends were pointed, and were 19.8–36.62 × 3.3–4.7 µm (n= 30). Microconidia were cylindrical or ellipsoid and 5.5–11.6 × 2.5–3.8 µm (n=30). Chlamydospores were globose and 9.6 –16.3 × 9.4 – 15.0 µm (n=30). The morphological characteristics of present isolates were comparable with that of Fusarium species (Maryani et al. 2019). Genomic DNA was extracted from 4 days old cultures of each isolate of SRRM 4.2, SRRH3, and SRRH5, EF-1α and rpb2 region were amplified using EF792 + EF829, and RPB2-5f2 + RPB2-7cr primer sets, respectively (Carbone and Kohn, 1999; O'Donnell et al. 2010) and sequenced (GenBank accession number: LC569791- LC569793 and LC600806- LC600808). BLAST query against Fusarium loci sampled and multilocus sequence typing database revealed that 99–100% identity to corresponding sequences of the F. oxysporum species complex (strain NRRL 28395 and 26379). Maximum likelihood phylogenetic analysis with MEGA v. 6.0 using the concatenated sequencing data for EF-1α and rpb2 showed that the isolates belonged to F. oxysporum species complex. Each three healthy seedlings with similar sized (big flower sabju) were grown for 20 days in a plastic pot containing autoclaved peat soil was used for pathogenicity tests. Conidial suspensions (106 conidia mL−1) of 20 days old colonies per isolate (two isolates) were prepared in sterile water. Three pots per strain were inoculated either by pouring 50 ml of the conidial suspension or by the same quantity of sterile distilled water as control. After inoculation, all pots were incubated at 25 °C with a 16-hour light/8-hour dark cycle in a growth chamber. This experiment repeated twice. Inoculated seedlings were watered twice a week. Approximately 60% of the inoculated seedlings per strain wilted after 15 days of inoculation and control seedlings remained asymptomatic. Fusarium oxysporum was successfully isolated from infected seedling and identified based on morphology and EF-1α sequences data to confirm Koch’s postulates. Fusarium oxysporum is responsible for damping-off of many plant species, including larch, tomato, melon, bean, banana, cotton, chickpea, and Arabidopsis thaliana (Fourie et al. 2011; Hassan et al.2019). To the best of our knowledge, this is the first report on damping-off of ovate-leaf atractylodes caused by F. oxysporum in South Korea. This finding provides a basis for studying the epidemic and management of the disease.

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