Vegetative Compatibility Group Analysis Research Articles

Molecular Diagnosis and Vegetative Compatibility Group Analysis of Fusarium Wilt of Banana in Nepal

Fusarium wilt of banana (FWB), caused by Fusarium oxysporum f. sp. cubense (Foc), is the most important constraint of the banana industry globally. In Nepal, epidemics resembling FWB have been increasingly observed on the Malbhog cultivar in the past several years. However, the disease has not been officially reported yet, and consequently, little is known about the pathogen present across the country. In this study, we characterized 13 fungal strains isolated from banana plants of the Malbhog cultivar (Silk, AAB) showing symptoms similar to FWB in banana plantations in Nepal. All of the strains were typed as belonging to the F. oxysporum and caused FWB symptoms when inoculated in the Malbhog and Cachaco (Bluggoe, ABB) cultivars. No symptoms were observed in the Williams cultivar (Cavendish, AAA). Vegetative compatibility group (VCG) analysis classified the strains as VCG 0124 or VCG 0125. PCR analyses conducted with primers specific for Foc race 1 (Foc R1) or Foc tropical race 4 (TR4) revealed that all the strains reacted positively for Foc R1 and none for TR4. Altogether, our results demonstrated that the pathogen populations causing FWB of the Malbhog cultivar in Nepal were Foc R1. This work reported, for the first time, the occurrence of FWB in Nepal. Further studies with larger Foc populations are needed to better understand disease epidemiology to design sustainable disease management strategies.

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

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.

Draft Genome of Fusarium oxysporum f. sp. cubense Strain Tropical Race-4 Infecting Cavendish (AAA) Group of Banana in India.

Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. cubense, is the most serious pandemic disease of banana. In this study, we report the draft genome of F. oxysporum f. sp. cubense vegetative compatibility group (VCG) 01213/16 of strain tropical race 4 (TR4) that infects the Cavendish (AAA) group of banana collected from the subtropical region in India. The genome assembly of SFoc TR4 comprises 47,384,463 bp with 4,034 contigs and 15,508 protein-coding regions. Based on VCG analysis, the fungal isolate belongs to F. oxysporum f. sp. cubense TR4 but the genome sequence of SFoc TR4 shows differences in secreted-in-xylem (SIX) protein gene clusters (specifically, SIX8) in comparison with the reference genome of F. oxysporum f. sp. lycopersici and F. oxysporum f. sp. cubense TR4.

First detection of Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) on Cavendish banana in India

Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc), is regarded as one of the most devastating diseases of bananas globally. Foc consists of three races, of which Foc races 1 and 2 occur in India. Foc race 4 has not been found in the country despite the importance and extensive cultivation of Cavendish cultivars. In 2015, a banana grower from Barari village in the Bihar State of India reported the wilting of Cavendish banana cvs. Robusta and Grand Naine. The incidence of the disease ranged from 2 to 26.6%. Symptoms included yellowing and browning of older leaves, which progressed from the oldest to the youngest leaves. Samples were collected from pseudostems and the responsible fungus isolated. The cultures were then identified using fungal morphology, vegetative compatibility group (VCG) analysis, volatile production and PCR with Foc tropical race (TR) 4-specific primers. Pathogenicity tests were conducted using Grand Naine plantlets produced by micropropagation. The cultures were identified as volatile-producing F. oxysporum strains, and pathogenicity tests confirmed their status as the banana pathogen Foc. VCG analysis, and the use of race-specific PCR markers, identified them as members of VCG 01213/16 and Foc TR4, respectively. This indicated that the fungus responsible for Fusarium wilt in the Bihar state of India is Foc TR4. Most Indian farmers use suckers as planting material, and are not aware of the impact of the disease. If the disease spreads to other states in India it can lead to an unemployment problem for farm labourers and the change in production to non-remunerative crops that may reduce profits.

First Report of Fusarium Wilt on Cavendish Bananas, Caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (VCG 01213/16), in Vietnam

Fusarium wilt of banana, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc), is a major constraint to banana production worldwide. A strain of the fungus that affects Cavendish and other dessert bananas in the tropics, called Foc tropical race 4 (TR4; VCG 01213/16), has been confined to five Asian countries (Indonesia, Malaysia, Philippines, mainland China, and Taiwan) for more than three decades. Cavendish production is now being expanded in Asia to Laos, Myanmar, and Vietnam, where local varieties still dominate the market. This is owing to an increase in Cavendish banana consumption and a decline in areas of production caused by Foc TR4 in China. The expansion of Cavendish production in Southeast Asia, however, has increased the risk of Foc TR4 being introduced into new countries. Leaf-yellowing symptoms typical of banana Fusarium wilt were observed in three provinces in northern Vietnam along the Red River that originates in the Yunnan province of China, namely Hanoi (October 2014), Hung Yen (October 2015), and Lao Cai (October 2015). When cut open, pseudostems displayed a dark-red to brown discoloration of vascular tissue, and the inner rhizome revealed a ring of yellow-brown staining. Samples of symptomatic strands from pseudostems were collected to identify the causal agent by morphological, molecular, and vegetative compatibility group (VCG) identification. The samples were first plated onto potato dextrose agar (PDA) containing streptomycin for fungal isolation. The cultures were then purified, single-spored, and maintained at the culture collection of the Department of Plant Pathology at Stellenbosch University in South Africa. Eight Fusarium isolates obtained were identified to species level on PDA and carnation leaf agar plates according to their cultural and spore morphology (Nelson et al. 1983). For molecular identification, total DNA was extracted and amplified with Foc TR4-specific primers (Dita et al. 2010) and Foc race 4-specific primers (Lin et al. 2009). VCG testing was performed according to the method of Puhalla (1985) by pairing nit-1 and nit-3 mutants of the isolates from Vietnam with nit-M testers of VCGs 01213, 01216, and 01213/16. Pathogenicity testing was performed by replanting Cavendish tissue culture plantlets at the six-leaf stage in sand mixed with corn powder, which was colonized by the individual Fusarium isolates from Vietnam, at a ratio of 19:1. Control plants were treated with sterile distilled water. The identity of the Vietnamese isolates was confirmed as F. oxysporum, whereas PCR and VCG analysis characterized six of them as VCG 01213/16 strains. After 6 weeks, plants inoculated with the VCG 01213/16 isolates produced typical symptoms of Fusarium wilt, so Koch's postulates were completed. The occurrence of Foc TR4 in Vietnam can have a significant economic impact to agricultural production, because investments were made to replace citrus, longan, and corn fields with Cavendish plantations. Foc TR4 also poses a threat to local banana varieties, and these varieties should therefore be evaluated for resistance to the fungus. The potential spread of Foc TR4 in Vietnam should be minimized by surveillance, public awareness campaigns, risk assessment, and containment efforts.

Pathogenicity and vegetative compatibility grouping among Indian populations of Fusarium oxysporum f. sp. ciceris causing chickpea wilt

Thirty-nine isolates of Fusarium oxysporum f. sp. ciceri – the causal agent of chickpea (Cicer arietinum) wilt – collected from different parts of India and representing eight races of the pathogen, were analyzed for virulence and classified on the basis of vegetative compatibility grouping (VCG). The wilt incidence ranged from 24% to 100% on a highly susceptible cultivar JG 62. Six isolates, from Delhi, Gujarat, Karnataka, Punjab and Rajasthan and belonging to six different races of the pathogen, caused 100% wilt incidence. Five isolates belonging to four different races, namely, Foc 143 from Andhra Pradesh, Foc 161 from Chhattisgarh, Foc 146 from Karnataka, Foc 158 from Madhya Pradesh and Foc 50 from Rajasthan, caused low wilt incidence. For VCG analysis, nitrate non-utilizing mutants (nit) were obtained by culturing wild-type isolates on 2.5% potassium chlorate and selecting resistant sectors. Complementary nit mutants were paired in all possible combinations to determine varying degrees of heterokaryon formation within the isolates, which showed that most of the isolates were self-compatible. Pairing of all the mutants showed that the isolates included in the present study belonged to a single VCG (0280). Thus, in spite of variability in the virulence, the Indian populations of the pathogen have only one VCG.

Characterization of Fusarium oxysporum f. sp. melongenae isolates from eggplant in Turkey by pathogenicity, VCG and RAPD analysis

Fusarium wilt is an economically important fungal disease of common eggplant (Solanum melongena) cultivated in the eastern Mediterranean region of Turkey. Seventy-four isolates of Fusarium oxysporum isolated from diseased eggplant displaying typical Fusarium wilt symptoms were screened for pathogenicity on the highly susceptible cv. ‘Pala’. All the isolates tested were pathogenic to eggplant and designated as Fusarium oxysporum f. sp. melongenae (Fomg). Genetic diversity among a core set of 20 Fomg isolates that were selected based upon geographic locations, were characterized by using pathogenicity, vegetative compatibility grouping (VCG), and random amplified polymorphic DNA (RAPD) analysis. The area under the disease progress curve (AUDPC) was calculated for each Fomg isolate until 21 days after inoculation (DAI). The most virulent isolate was identified as Fomg10 based on AUDPC, disease severity and vascular discoloration measurements at 21 DAI. At this date, a good correlation was observed between disease severity and AUDPC values for all isolates (r = 0.73). UPGMA (unweighted pair group method with arithmetic average) cluster analysis of RAPD data using Dice’s coefficient of similarity differentiated all the Fomg isolates tested, and indicated considerable genetic variation among Fomg isolates, but isolates from the same geographic region were grouped together. There was no direct correlation between clustering in the RAPD dendrogram and pathogenicity testing of Fomg isolates. Twenty isolates of Fomg were assigned to VCG 0320.

Lamb’s lettuce (Valerianella olitoria): new host of Fusarium oxysporum f. sp. conglutinans

A new wilt of lamb’s lettuce (Valerianella olitoria) was detected in northern Italy in 2003 and the causal agent of the disease was identified as Fusarium oxysporum. Pathogenicity tests and vegetative compatibility analysis were carried out on different isolates of the fungus. The pathogenicity of six isolates was tested on radish (Raphanus sativus), wild (Diplotaxis tenuifolia) and cultivated (Eruca sativa) rocket, cabbage (Brassica oleracea var. sabauda), cauliflower (Brassica oleracea var. botrytis), Brussels sprout (Brassica oleracea var. gemmifera), broccoli (Brassica oleracea var. italica), and turnip (Brassica rapa var. rapa). The results indicated that isolates of F. oxysporum from lamb’s lettuce belong to the forma specialis conglutinans. Vegetative compatibility grouping analysis showed the presence of VCG 0101 pathogenic on lamb’s lettuce. Among the 12 isolates from lamb’s lettuce tested, 10 belongs to VCG 0101 and are classified as F. oxysporum f. sp. conglutinans, while two are self-incompatible.

Vegetative Compatibility of Fusarium graminearum Isolates and Genetic Study on Their Carbendazim-Resistance Recombination in China

ABSTRACT Monoconidial isolates of 33 carbendazim-sensitive isolates and 31 carbendazim-resistant isolates of Fusarium graminearum were selected from three regions of China for vegetative compatibility group (VCG) analysis. A total of 213 and 224 nit mutants were recovered from the 33 sensitive and the 31 resistant isolates, respectively. Of all the nit mutants, the frequency of the different phenotypes was 44.6, 46.5, 5.7, and 3.2% for nit1, nit3, nitM, and nitA, respectively. VCG analysis identified 30 different VCGs among the 33 sensitive- and the 31 carbendazim-resistant isolates, with VCG diversity 0.91 and 0.97, respectively. Both, a carbendazim-sensitive and a -resistant isolate from the same field belonged to the same VCG. In all then, a total of 59 VCGs were identified among the 64 isolates with an overall VCG diversity 0.92. Direct hyphal fusion was observed in six pairs of vegetatively compatible complements, which is evidence of heterokaryon formation. It was hypothesized that carbendazim resistance could not be transferred by hyphal fusion or there is a small chance to be transferred between two compatible isolates. Three stable sexual recombinants of F. graminearum were randomly chosen from each of the three genetic crosses to study their biological properties. There were no significant differences in mycelial linear growth and pathogenicity between recombinants and their parents, but they differ in sporulation ability and capacity to produce perithecia. We concluded that sexual recombination presumably played a role in the development of carbendazim resistance under field conditions.

Vegetative Compatibility Grouping of the Fusarium Wilt Pathogen of Paris Daisy (Argyranthemum frutescens L.)

Abstract Fusarium oxysporum isolates, pathogenic on Paris daisy (Argyranthemum frutescens), were classified by vegetative compatibility grouping analysis. They were compared with isolates of the formae speciales chrysanthemi and tracheiphilum, and with f. sp. dianthi as a genetically distant control. The results show the uniformity of the pathogenic isolates from Paris daisy, except for one which was of a different geographic origin. They were classified as a new VC group (0052). We report also the efficacy of different media in obtaining nit mutants.

Analysis of population structure of Aspergillus flavus from peanut based on vegetative compatibility, geographic origin, mycotoxin and sclerotia production

Isolates of Aspergillus flavus obtained from a new growing peanut region in Argentina (Formosa province) were examined for aflatoxin types B and G and cyclopiazonic acid (CPA) production. Sclerotia diameters and the number of sclerotia produced per square centimetre were also determined for each isolate. They were tested by vegetative compatibility group analysis to investigate their genetic relatedness and correlate the results with vegetative compatibility groups previously described from the major peanut-growing area (Córdoba province) in our country. Two isolates were considered atypical because they simultaneously produce aflatoxins B and G and CPA. A. flavus population from Formosa province was very diverse genetically. Vegetative compatibility groups (VCGs) formed by typical isolations of A. flavus were different among agroecological sites. Formosa isolates could not be grouped to any of the Córdoba VCGs, while that one of the VCGs that contain atypical isolates included strains from the two geographical regions. Each VCG included isolates of the same mycotoxin and sclerotia production pattern. The two regions analysed have different climatic conditions, soil type, crop sequence history and also are in different latitude. These parameters may reflect different geographic adaptation between isolates from both sites.

Distribution of Fumonisins in Maize Ears Infected with Strains of Fusarium moniliforme that Differ in Fumonisin Production.

Strains of Fusarium moniliforme (Gibberella fujikuroi mating population A) that differ in fu-monisin production in vitro were previously identified in a Kansas field population. One strain that produced high levels of fumonisins and two strains that produced very low levels of fu-monisins were applied to maize kernels at planting at the Rocky Ford Farm near Manhattan, Kansas. The distribution of fumonisins in symptomatic and symptomless kernels from individual harvested ears was determined by high performance liquid chromatography, and the distribution of the three applied strains in the kernels was determined by vegetative compatibility group analysis. Both symptomatic and symptomless kernels were extensively colonized with F. moniliforme, but the highest levels of fumonisins were in the symptomatic kernels. All three applied strains were recovered from kernels in 1993, and two of them were recovered from kernels in 1994. However, a high frequency of ear and kernel infection with a strain that produced little fumonisin in vitro did not consistently decrease the level of fumonisins. The frequency of infection with fumonisin low-producing strains may have been too low for competitive exclusion of naturally occurring fumonisin high-producing strains. Also, strains that are low-fumonisin producers under laboratory conditions may be high producers in the field.

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

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.

Genetic diversity of Fusarium moniliforme detected by vegetative compatibility groups and random amplified polymorphic DNA markers

Genetic diversity among Fusarium moniliforme isolates was analysed using vegetative compatibility group (VCG) and random amplified polymorphic DNA (RAPD) techniques. In the first experiment, RAPD was used to analyse a set of 43 isolates collected from different corn growing areas in Israel and the US. The isolates were assigned to 27 different VCGs. Thirty‐two RAPD haplotypes were also detected by analysing 48 polymorphic bands. RAPD could differentiate all the VCGs, except in two cases where two VCGs were assigned a single RAPD haplotype. In six cases, however, molecular variation was detected among isolates belonging to the same VCG. Cluster analysis of the RAPD data showed a very good agreement with the VCG grouping, e.g. isolates of the same VCG were always closely clustered by the molecular data. In a second experiment, 63 isolates of Fusarium moniliforme were collected from six corn lines growing in a single corn field. Extensive genetic variation was observed among the isolates: 42 different VCGs and 37 RAPD haplotypes were identified. Once again, RAPD patterns could differentiate nearly all the VCGs. However, in four cases, two different VCGs were grouped into a single RAPD haplotype, while in another three cases, isolates of the same VCG could be differentiated by distinct molecular haplotypes. The variation data was used to gain insight on the population structure and the patterns of genetic variation among geographical locations and within a single field. Hierarchical gene diversity analysis of the RAPD data indicated that most of the genetic variability (81%) was distributed within corn lines in the same field, suggesting that RAPD haplotype, or VCG frequencies, were not significantly affected by the plant genotypes grown in this experiment. Most of the RAPD band combinations did not display significant gametic phase disequilibrium, suggesting that active recombination might be occurring in the field. Our results indicate that by using a small number of primers, similar resolution was obtained by RAPD and VCG analysis, respectively. RAPD analysis is however, simpler to perform and its sensitivity in genotyping individuals within Fusarium moniliforme can be increased by analysing more primers, enabling a more detailed population genetic analysis of this important pathogen.

Population structure ofGibberella pulicaris (AnamorphFusarium sambucinum) from potato tuber dry rot in North America and Europe

Gibberella pulicaris is the sexual stage ofFusarium sambucinum, the major cause of potato tuber dry rot in North America and Europe. In a previous study 42 strains from dry-rotted tubers in North America were analyzed for genetic diversity by mating type and vegetative compatibility group (VCG) tests. In the present study, an additional 96 strains from North America, 21 strains from Europe, and six strains from other geographic areas were analyzed. Both mating types, MAT1-1 and MAT1-2, occur widely outside North America. In contrast, all but two, Canadian, strains of the 138 North American strains analyzed to date are MAT1-1. VCG analysis provides additional evidence that genetic diversity ofG. pulicaris from potato tubers is high in Europe but low in the United States. These results suggest that the potential for pathogen change due to sexual recombination is low in the United States, but may be higher in Europe. Limited genetic diversity ofG. pulicaris in the United States indicates that there are likely to be few barriers to heterokaryon formation and asexual recombination in the field. Thus, the potential exists for rapid spread and persistence of advantageous mutations throughout theG. pulicaris population, which may have contributed to the recent proliferation of strains resistant to the fungicide thiabendazole which has been widely used to control tuber dry rot.

Variation Among Isolates ofFusarium lateritiumfrom Sweetpotato for Pathogenicity and Vegetative Compatibility

Isolates (132) of Fusarium lateritium from sweetpotato and from other hosts (20) were compared for pathogenicity to sweetpotato vines and vegetative compatibility grouping (VCG) using complementation among nitrate nonutilizing (nit) mutants. Isolates from sweetpotato were either nonpathogenic or fell into one of two pathotypes: the chlorotic leaf distortion (CLD) pathotype, which induced all symptoms of CLD, or the epiphytic mycelial growth pathotype, which produced the typical epiphytic, systemic mycelial growth but did not induce chlorosis. With one possible exception, isolates from other hosts were nonpathogenic to sweetpotato. All isolates from sweetpotato produced nor mutants, and 44 VCGs were identified. Only 16 of 20 isolates from other hosts could be induced to produce nor mutants, only 10 of these were self-compatible, and none of these were compatible with any other isolate. Sweetpotato isolates from the United States appeared less diverse by VCG analysis than isolates from Africa

Fusarium oxysporum associated with wilt and root rot of tomato in Queensland; races and vegetative compatibility groups

Twenty-two isolates of Fusarium oxysporum, from Queensland's major tomato growing areas, were studied in glasshouse pathogenicity tests and assessed for vegetative compatibility. Isolates of Fusarium oxysporum f. sp. lycopersici were identified to race using pathogenicity tests with 4 differential tomato cultivars: Grosse Lisse, Scorpio, moradade and Delta Tristar. The occurrence of race 3 in the Bundaberg district in 1988 was established. In glasshouse experiments, Fusarium wilt severity was influenced by inoculum concentration (1 x 106 v. 5 x 106 conidia/ml). Pathogenic and non-pathogenic isolates were distinguished by vegetative compatibility group analysis. However, all races were in a single vegetative compatibility group and could not be differentiated using this technique. Isolates collected from discoloured vascular tissue in the lower stems of plants with severe root rot (Pythium spp. associated), were non-pathogenic to tomato, bean and pea, although some isolates caused slight damage to cucumber. These isolates were distinctly different from Fusarium oxysporum f. sp. radicis-lycopersici, the cause of root and crown rot.