Fusarium Oxysporum F. Sp. Vasinfectum Research Articles

Secreted in xylem (SIX) gene SIX9 is highly conserved in Fusarium oxysporum f. sp. vasinfectum race 4 isolates from cotton in the United States

Many Fusarium oxysporum formae speciales produce small, infection-dependent effector proteins called ‘secreted in xylem’ (SIX) proteins. These proteins are secreted into the xylem of a plant during the infection process and are thought to promote virulence. In this study, a collection of Fusarium oxysporum isolates composed primarily of different races of Fusarium oxysporum f. sp. vasinfectum (FOV), was screened for the presence of fourteen SIX effector genes (SIX1-SIX14). Our results showed that some of the most virulent FOV races, FOV4 and FOV7, share a common SIX effector – SIX9. This effector is largely absent in other races of FOV in North America making SIX9 a potential target for rapid detection of these highly virulent FOV strains and enabling race specific FOV quantification in infected host plants.

Enhanced phenylpropanoid metabolism underlies resistance to Fusarium oxysporum f. sp. vasinfectum race 4 infection in the cotton cultivar Pima-S6 (Gossypium barbadense L.).

Introduction: Fusarium oxysporum f. sp. vasinfectum (FOV) race 4 (FOV4) is a highly pathogenic soil-borne fungus responsible for Fusarium wilt in cotton (Gossypium spp.) and represents a continuing threat to cotton production in the southwest states of the United States, including California, New Mexico, and Texas. Pima (G. barbadense L.) cotton, which is highly valued for its fiber quality, has been shown to be more susceptible to this pathogen than Upland (G. hirsutum L.) cotton. Still, some Pima cultivars present resistance to FOV4 infection. Methods: To gain insights into the FOV4-resistance mechanism, we performed comparative transcriptional and metabolomic analyses between FOV4-susceptible and FOV4-resistant Pima cotton entries. FOV4-resistant Pima-S6 and FOV4-susceptible Pima S-7 and Pima 3-79 cotton plants were infected with FOV4 in the greenhouse, and the roots harvested 11days post-infection for further analysis. Results: We found that an enhanced root phenylpropanoid metabolism in the resistant Pima-S6 cultivar determines FOV4-resistance. Gene-ontology enrichment of phenylpropanoid biosynthesis and metabolism categories correlated with the accumulation of secondary metabolites in Pima-S6 roots. Specifically, we found esculetin, a coumarin, an inhibitor of Fusarium's growth, accumulated in the roots of Pima-S6 even under non-infected conditions. Genes related to the phenylpropanoid biosynthesis and metabolism, including phenylalanine ammonia-lyase 2 (PAL2) and pleiotropic drug resistance 12 (PDR12) transporter, were found to be upregulated in Pima-S6 roots. Discussion: Our results highlight an essential role for the phenylpropanoid synthesis pathway in FOV4 resistance in Pima-S6 cotton. These genes represent attractive research prospects for FOV4-disease resistance and breeding approaches of other cotton cultivars of economic relevance.

A high-quality whole-genome sequence, assembly, and gene annotation of Fusarium oxysporum f. sp. vasinfectum (Fov) race 1 from California.

Fusarium wilt [Fusarium oxysporum f. sp. vasinfectum (FOV)] in cotton is a widespread soilborne pathogen that causes vascular plant disease and is responsible for substantial crop losses worldwide. FOV race 1 (FOV1) is well established across almost all cotton production regions, especially in the USA. Herein, we report a high-quality whole-genome sequence, assembly, and gene annotation of a FOV1 isolate from California.

Development and validation of allele-specific PCR-based SNP typing in a gene on chromosome D03 conferring resistance to Fusarium wilt race 4 in Upland cotton (Gossypium hirsutum).

Upland cotton (Gossypium hirsutum) is the most important fiber crop for the global textile industry. Fusarium oxysporum f. sp. vasinfectum (FOV) is one of the most destructive soil-borne fungal pathogens in cotton. Among eight pathogenic races and other strains, FOV race 4 (FOV4) is the most virulent race in US cotton production. A single nucleotide polymorphism (SNP) in a glutamate receptor-like gene (GhGLR4.8) on chromosome D03 was previously identified and validated to confer resistance to FOV race 7, and targeted genome sequencing demonstrated that it was also associated with resistance to FOV4. The objective of this study was to develop an easy and convenient PCR-based marker assay. To target the resistance SNP, a forward primer for the SNP with a mismatch in the 3rd position was designed for both the resistance (R) and susceptibility (S) alleles, respectively, with addition of 20-mer T7 promoter primer to the 5' end of the forward primer for the R allele. The two forward primers, in combination with each of five common reverse primers, were targeted to amplify amplicons of 50-260bp in size with R and S alleles differing in 20bp. Results showed that each of three common reverse primers in combination with the two forward primers produced polymorphic markers between R and S plants that were consistent with the targeted genome sequencing results. The polymorphism was distinctly resolved using both polyacrylamide and agarose gel electrophoreses. In addition, a sequence comparative analysis between the resistance gene and homologous sequences in sequenced tetraploid and diploid A and D genome species showed that none of the species possessed the resistance gene allele, suggesting its recent origin from a natural point mutation. The allele-specific PCR-based SNP typing method based on a three-primer combination provides a fast and convenient marker-assisted selection method to search and select for FOV4-resistant Upland cotton.

GBSOT4 Enhances the Resistance of Gossypium barbadense to Fusarium oxysporum f. sp. vasinfectum (FOV) by Regulating the Content of Flavonoid.

Sulfotransferases (SOTs) (EC 2.8.2.-) are sulfate regulatory proteins in a variety of organisms that have been previously shown to be involved in regulating a variety of physiological and biological processes, such as growth, development, adaptation to land, stomatal closure, drought tolerance, and response to pathogen infection. However, there is a lack of comprehensive identification and systematic analysis of SOT in cotton, especially in G. barbadense. In this study, we used bioinformatics methods to analyze the structural characteristics, phylogenetic relationships, gene structure, expression patterns, evolutionary relationships, selection pressure and stress response of SOT gene family members in G. barbadense. In this study, a total of 241 SOT genes were identified in four cotton species, among which 74 SOT gene members were found in G. barbadense. According to the phylogenetic tree, 241 SOT protein sequences were divided into five distinct subfamilies. We also mapped the physical locations of these genes on chromosomes and visualized the structural information of SOT genes in G. barbadense. We also predicted the cis-acting elements of the SOT gene in G. barbadense, and we identified the repetitive types and collinearity analysis of SOT genes in four cotton species. We calculated the Ka/Ks ratio between homologous gene pairs to elucidate the selective pressure between SOT genes. Transcriptome data were used to explore the expression patterns of SOT genes, and then qRT-PCR was used to detect the expression patterns of GBSOT4, GBSOT17 and GBSOT33 under FOV stress. WGCNA (weighted gene co-expression network analysis) showed that GB_A01G0479 (GBSOT4) belonged to the MEblue module, which may regulate the resistance mechanism of G. barbadense to FOV through plant hormones, signal transduction and glutathione metabolism. In addition, we conducted a VIGS (virus-induced gene silencing) experiment on GBSOT4, and the results showed that after FOV inoculation, the plants with a silenced target gene had more serious leaf wilting, drying and cracking than the control group, and the disease index of the plants with the silenced target gene was significantly higher than that of the control group. This suggests that GBSOT4 may be involved in protecting the production of G. barbadense from FOV infection. Subsequent metabolomics analysis showed that some flavonoid metabolites, such as Eupatorin-5-methylether (3'-hydroxy-5,6,7,4'-tetramethoxyflavone, were accumulated in cotton plants in response to FOV infection.

In Vitro Antagonistic Action by Bacillus Velezensis Strain LP16S Against Cotton Wilt Pathogens

Cotton productivity and profitability are hampered by several biotic stresses, including the two most destructive wilt pathogens Verticillium dahliae and Fusarium oxysporum f. sp. vasinfectum (FOV). In this study, an in vitro assay was conducted to determine the activity of Bacillus velezensis LP16S against three V. dahliae isolates and six F. oxysporum f. sp. vasinfectum isolates. Among the fungal isolates, the response when exposed to the B. velezensis LP16S strain in a half-strength potato dextrose agar plate varied markedly. Fusarium oxysporum f. sp. vasinfectum isolates FOV11, FOV 944, and FOV Tx8 were tolerant, while FOV Tx39, FOV 1073, and the three V. dahliae isolates were highly sensitive to B. velezensis LP16S. In conclusion, this Bacillus sp. strain has potential for use in managing these damaging cotton diseases.

Diversity and temporal distribution of Fusarium oxysporum f. sp. vasinfectum races and genotypes as influenced by Gossypium cultivar.

This study assess the population diversity and temporal variability of caused by Fusarium oxysporum f. sp. vasinfectum (FOV) races/genotypes infecting cotton cultivars with either FOV or Meloidogyne incognita resistance. All plants sampled demonstrated typical symptoms of FOV including wilting, chlorosis and necrosis of the leaves, and discoloration of the vascular tissue in the stem. A diverse population of FOV was characterized. Eight races/genotypes of FOV were collected throughout the three site years. FOV race 1 was the most predominant in all tests (AUDPC=101.1); statistically higher numbers of isolates from LA-108 (AUDPC=59.9), race 8 (AUDPC=47.5), and race 2 (AUDPC=38.6) were also found compared to other races and genotypes collected. FOV race 1, race 2, race 8, and 108 were the most virulent races identified. The genotypes MDS-12, LA-110, and LA-127/140 were found in all tests but at a low incidence, and LA-112 was only found in trace amounts. MDS-12, LA-110, LA-112, and LA-127/140 produced less disease pressure. FOV race 4 which is highly virulent and present in California and Texas was not found in Alabama. A positive correlation was observed between the accumulation of growing degree days and FOV race 1, race 2, race 8, LA-108, and LA-110. Later symptom expression influenced by seasonal heat partially mitigates damage allowing cotton to produce bolls though they may be reduced in number and lint quality. Plant resistance to the FOV as expressed in these cultivars appears to provide better protection than M. incognita resistance. PhytoGen 72, which is resistant to FOV races/genotypes had low levels of FOV infection even though it sustained a high level of M. incognita root population density. The M. incognita resistant cultivars Deltapine 1558NR B2RF and PhytoGen 480 W3FE supported a lower nematode population density, however, FOV disease incidence was not reduced. FOV races/genotypes did not vary significantly between the nematode resistant and nematode susceptible cultivars.

Quantitative Trait Locus Mapping for Fusarium Wilt Race 4 Resistance in a Recombinant Inbred Line Population of Pima Cotton (Gossypium Barbadense).

Fusarium oxysporum f. sp. vasinfectum (FOV) race 4 (FOV4) causes seedling death immediately after emergence, in addition to leaf chlorosis and necrosis, vascular discoloration, plant wilting, defoliation, and plant death at late stages. Breeding for FOV4 resistance is the most cost effective management method. In this study, 163 recombinant inbred lines (RILs) of FOV4-resistant Pima S-6 × susceptible 89590, together with the two parents (Gossypium barbadense), were artificially inoculated with FOV4 and assayed for resistance based on foliar disease severity ratings (DSR) at 30 days post inoculation (dpi) in two replicated tests in the greenhouse or controlled conditions. Significant genotypic variations were detected for FOV4 resistance in a combined analysis of variance. Although a significant genotype × test interaction was detected for DSR, the 10 most resistant RILs had significantly and consistently lower DSR than the susceptible parent in both tests. The heritability estimate for DSR was 0.65, indicating that two-thirds of the phenotypic variation for FOV4 resistance in this Pima RIL population was due to genetic factors. Based on 404 polymorphic SSR markers, five and four quantitative trait loci (QTL) on six chromosomes (c14, c17, c19, c21, c24, and c25) were detected in Tests 1 and 2, respectively, and each explained 15 to 29% of the phenotypic variation. Three QTL on c17, c24, and c25 were in common between the two tests, accounting for 60% and 75% of the QTL detected in Tests 1 and 2, respectively. The three QTL were also reported in previous studies and will be useful for marker-assisted selection for FOV4 resistance in Pima cotton.

Response of the plant core microbiome to Fusarium oxysporum infection and identification of the pathobiome.

Plant core microbiomes consist of persistent key members that provide critical host functions, but their assemblages can be interrupted by biotic and abiotic stresses. The pathobiome is comprised of dynamic microbial interactions in response to disease status of the host. Hence, identifying variation in the core microbiome and pathobiome can significantly advance our understanding of microbial-microbial interactions and consequences for disease progression and host functions. In this study, we combined glasshouse and field studies to analyse the soil and plant rhizosphere microbiome of cotton plants (Gossypium hirsutum) in the presence of a cotton-specific fungal pathogen, Fusarium oxysporum f. sp. vasinfectum (FOV). We found that FOV directly and consistently altered the rhizosphere microbiome, but the biocontrol agents enabled microbial assemblages to resist pathogenic stress. Using co-occurrence network analysis of the core microbiome, we identified the pathobiome comprised of the pathogen and key associate phylotypes in the cotton microbiome. Isolation and application of some negatively correlated pathobiome members provided protection against plant infection. Importantly, our field survey from multiple cotton fields validated the pattern and responses of core microbiomes under FOV infection. This study advances key understanding of core microbiome responses and existence of plant pathobiomes, which provides a novel framework to better manage plant diseases in agriculture and natural settings.

Gb_ANR-47 Enhances the Resistance of Gossypium barbadense to Fusarium oxysporum f. sp. vasinfectum (FOV) by Regulating the Content of Proanthocyanidins.

Anthocyanidin reductase (ANR) is an important regulator of flavonoid metabolism, and proanthocyanidins, the secondary metabolites of flavonoids, play an important role in the response of plants to pathogenic stress. Therefore, in this study, the expression analysis of the ANR gene family of Gossypium barbadense after inoculation with Fusarium oxysporum f. sp. vasinfectum (FOV) was performed at different time points. It was found that Gb_ANR-47 showed significant differences in the disease-resistant cultivar 06-146 and the susceptible cultivar Xinhai 14, as well as in the highest root expression. It was found that the expression of Gb_ANR-47 in the resistant cultivar was significantly higher than that in the susceptible cultivar by MeJA and SA, and different amounts of methyl jasmonate (MeJA) and salicylic acid (SA) response elements were found in the promoter region of Gb_ANR-47. After silencing GbANR-47 in 06-146 material by VIGS technology, its resistance to FOV decreased significantly. The disease severity index (DSI) was significantly increased, and the anthocyanin content was significantly decreased in silenced plants, compared to controls. Our findings suggest that GbANR-47 is a positive regulator of FOV resistance in Gossypium barbadense. The research results provide an important theoretical basis for in-depth analysis of the molecular mechanism of GbANR-47 and improving the anti-FOV of Gossypium barbadense.

The Pre-treatment of Cotton with Polysaccharide Biocontrols Inducing Tolerance to Fusarium oxysporum f. sp. Vasinfectum Causal Agent of Fusarium Wilt in Cotton (Gossypium hirsutum L.)

Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum (FOV) is a major damaging disease of cotton. Chemical control is currently ineffective and has led to resistance of the pathogen. In addition, pesticides are indexed for their negative impact on the environment and on human health. The objective of this study was to evaluate the impact of sugarcane stem residue filtrate (FCS) and cotton stem residue filtrate (FTC) residue filtrate on FOV causal agent of the disease. These two polysaccharide biocontrols allowed a good accumulation of gallic acid, caffeoyl D-glucose, catechin, gossypetin and 3-p-coumaroylquinic acid and the de novo synthesis of epicatechin, protocatechic acid, ferulic acid, trans-resveratrol, trans-piceide, pterosilbene, 5-caffeylquinic acid, rutin, astringin and isoquercetin. However, 5-caffeylquinic acid and rutin are specific to FCS while astringin and isoquercetin are specific only to FTC. This difference in polyphenol synthesis caused 1% mortality in FTC and 8% in FCS. This indicates that astringin and isoquercetin are phenolic markers of resistance to FOV followed by 5-caffeylquinic acid and rutin. FTC can be used as a preventive control of Fusarium wilt in cotton.

DNA-Based Quantification of Fusarium oxysporum f. sp. vasinfectum in Environmental Soils to Describe Spatial Variation in Inoculum Density

Fusarium wilt of cotton, caused by the soilborne fungal pathogen Fusarium oxysporum f. sp. vasinfectum (FOV), occurs in regions of the United States where cotton (Gossypium spp.) is grown. Race 4 of this pathogen (FOV4) is especially aggressive, and does not require the co-occurrence of the root knot nematode (Meloidogyne incognita) to infect cotton. Its sudden appearance in far-west Texas in 2016 after many years of being restricted to California is of great concern, as is the threat of its continued spread through the cotton-producing regions of the United States. The aim of this research was to analyze the spatial variability of FOV4 inoculum density in the location where FOV4 is locally emerging, using quantitative and droplet digital PCR methods. Soil samples collected from a field with known FOV4 incidence in Fabens, Texas, were analyzed. Appreciable variation in inoculum density was found to occur at spatial scales smaller than the size of plots involved in cultivar trial research, and was spatially autocorrelated (Moran's I, Z = 17.73, P < 0.0001). These findings indicate that, for cultivar trials, accounting for the spatial distribution of inoculum, either by directly quantifying it or through the use of densely distributed calibration checks, is important to the interpretation of results.

Quantitative Trait Locus Mapping and Identification of Candidate Genes for Resistance to Fusarium Wilt Race 7 Using a Resequencing-Based High Density Genetic Bin Map in a Recombinant Inbred Line Population of Gossypium barbadense.

Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum (FOV) is one of the most destructive diseases in cotton (Gossypium spp.) production, and use of resistant cultivars is the most cost-effective method managing the disease. To understand the genetic basis of cotton resistance to FOV race 7 (FOV7), this study evaluated a recombinant inbred line (RIL) population of 110 lines of G. barbadense from a cross between susceptible Xinhai 14 and resistant 06-146 in eight tests and constructed a high-density genetic linkage map with resequencing-based 933,845 single-nucleotide polymorphism (SNP) markers covering a total genetic distance of 2483.17 cM. Nine quantitative trait loci (QTLs) for FOV7 resistance were identified, including qFOV7-D03-1 on chromosome D03 in two tests. Through a comparative analysis of gene expression and DNA sequence for predicted genes within the QTL region between the two parents and selected lines inoculated with FOV7, GB_D03G0217 encoding for a calmodulin (CaM)-like (CML) protein was identified as a candidate gene. A further analysis confirmed that the expression of GB_D03G0217 was suppressed, leading to increased disease severity in plants of the resistant parent with virus induced gene silencing (VIGS).

Importance of temperature in evaluating cotton for resistance to Fusarium wilt caused by Fusarium oxysporum f. sp. vasinfectum race 4

AbstractFusarium wilt of cotton (Gossypium spp.) is caused by a soil‐ and seed‐borne fungal pathogen Fusarium oxysporum f. sp. vasinfectum (FOV). Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) is a significant threat to cotton production in the United States. The effect of temperature and soil on disease symptoms in cultivars with a range of susceptibility to FOV4 was examined in growth chamber trials. Three upland (G. hirsutum L.) and three pima (G. barbadense L.) cultivars were planted in three types of soils (potting mix and farm soils with and without FOV4 preinfestation) and maintained at four constant temperature regimes (20, 23, 26, and 29 °C). After seedling emergence, each pot was inoculated with conidial suspensions of FOV4 and scored for resistance based on disease incidence (DI), foliar disease severity rating (DSR), and mortality rate (MR) at 7, 14, 21, and 28 d post‐inoculation (dpi). The area under the disease progress curve (AUDPC) based on DSR across the four evaluation dpi was also analyzed. Among the six cultivars tested, Pima PHY 841 RF, Pima S‐6, and the uplands Acala 1517‐08 and FM 2334GLT were the most resistant, whereas upland PHY 725 RF and Pima S‐7 were the most susceptible. The genotypic responses to FOV4 were not significantly (P &gt; .05) affected by differences in temperature regime or soil type. Cotton seedlings manifested more severe symptoms and higher mortality when maintained at 23 °C, followed by 20/26 °C and 29 °C in descending order. The mycelial growth rate was greater at 23/26 °C, whereas plants grew slower at 20/23 °C. There were no differences (P &gt; .05) in DI, DSR, MR, and AUDPC between the inoculated farm soil (with no FOV4 preinfestation) and the inoculated FOV4‐preinfested farm soil, suggesting the unnecessity of using the latter in artificial inoculations. However, the potting soil produced higher (P &lt; .05) DI and DSR at 7 and 14 dpi but lower (P &lt; .05) AUDPC. This growth chamber study demonstrated that 23 °C produced the highest DI, severity, and plant death, providing an important piece of information for screening cotton for FOV4 resistance in breeding and FOV4 disease management in cotton production.

Evaluation of different biocontrol agents against Fusarium oxysporum f. sp. vasinfectum (FOV) under in vitro condition of South Gujarat

Cotton (Gossypium spp.) is one of the most important fiber crops playing a key role in economic globe. The symptoms of Fusarium oxysporum f. sp. vasinfectum is both seed borne and soil borne and colonizes the roots and vascular system of susceptible cotton cultivars, causing root and vascular discoloration, wilting and sometimes death of the plant. As the wilt disease is becoming an important and destructive disease in the cotton growing areas. Here in this experiment, in vitro evaluation of native isolated antagonists were tested under dual culture method revealed the growth inhibition of test fungus (Fusarium oxysporum f. sp. vasinfectum) by the test antagonists. Five different biocontrol agents were screened in vitro for the growth inhibition of Fusarium oxysporum f. sp. vasinfectum by dual culture method and found that all the Trichoderma isolates were more effective than bacterial isolates. Among the Trichoderma isolates Trichoderma harzianum showed most promising results compared to other isolates. The highest growth inhibition of Fusarium oxysporum f. sp. vasinfectum was caused by Trichodermaharzianum (71.70%). While, the least growth inhibition was showed by Bacillus substillis (47.29%).

Evaluation of various combi product fungicides for the control of wilt (FOV) disease of cotton under in vitro condition of south Gujarat (India)

In this experiment, different districts of South Gujarat were closely examined for the presence of wilt disease in different cultivars/ Bt hybrids during the crop season to know the current scenario of wilt disease. The respective FOV wilt pathogen was purified, identified and isolated. Here, different combi fungicides were tested for their effect on the growth of Fusarium oxysporum f. sp. vasinfectum (FOV) using poisoned food technique. The technique involves cultivation of test organism on a medium containing the test chemicals. In this experiment, PDA was used as basal medium. Six combination products of fungicides were evaluated at three different concentrations by poisoned food technique for evaluating their efficacy against the Fusarium oxysporum f. sp. vasinfectum. Among them, combination products of fungicides, carbendazim 12% + mancozeb 63% significantly inhibited the growth of the Fusarium oxysporum f. sp. vasinfectum and proved strongly fungitoxic in nature.

Screening of different fungicides and biocontrol agents against Fusarium oxysporum f. sp. vasinfectum (FOV) under pot condition

Cotton (Gossypium spp.) is one of the most important fiber crops playing a key role in economic and social scenario of the globe. It is oldest among the commercial crops of the world providing fiber for clothing of the mankind. A pot experiment was conducted to test the efficacy of the fungicides and bioagents under in vitro condition. Among these, soil drenching with 0.20% pyraclostrobin 5%+ mitiram 55% (84.07%) proved effective which is followed by 0.20% captan 70%+ hexaconazole 5% (80.52%) in managing the wilt of cotton.

Genetic Diversity and Population Structure of Races of Fusarium oxysporum Causing Cotton Wilt.

To better understand the evolution of virulence we are interested in identifying the genetic basis of this trait in pathogenic fungi and in developing tools for the rapid characterization of variation in virulence among populations associated with epidemics. Fusarium oxysporum f. sp. vasinfectum (FOV) is a haploid fungus that causes devastating outbreaks of Fusarium wilt of cotton wherever it is grown. In the United States, six nominal races and eleven genotypes of FOV have been characterized based on the translation elongation factor (EF-1α) gene and intergenic spacer region (IGS), but it is unclear how race or genotype based on these regions relates to population structure or virulence. We used genotyping-by-sequencing to identify SNPs and determine genetic diversity and population structure among 86 diverse FOV isolates. Six individuals of Fusarium oxysporum closely related to FOV were genotyped and included in some analyses. Between 193 and 354 SNPs were identified and included in the analyses depending on the pipeline and filtering criteria used. Phylogenetic trees, minimum spanning networks (MSNs), principal components analysis (PCA), and discriminant analysis of principal components (DAPC) demonstrated that races and genotypes of FOV are generally not structured by EF-1α genotype, nor are they monophyletic groups with the exception of race 4 isolates, which are distinct. Furthermore, DAPC identified between 11 and 14 genetically distinct clusters of FOV, whereas only eight EF-1α genotypes were represented among isolates; suggesting that FOV, especially isolates within the widely distributed and common race 1 genotype, is more genetically diverse than currently recognized.

Pathogenicity of Meloidogyne incognita and Fusarium oxysporum f. sp. vasinfectum on Growth and Yield of Two Okra Varieties Cultivated in Ghana

The interaction of the fungus, Fusarium oxysporum f. sp. vasinfectum (FOV), and the nematode, Meloidogyne incognita, on wilt disease on “Essoumtem” and Clemson spineless okra varieties, was examined in pot and field experiments from September 2016 to June 2017, in the University of Ghana farms. Four-week-old “Essoumtem” and Clemson spineless seedlings for pot experiment and one-week-old “Essoumtem” and Clemson spineless seedlings for field experiment were inoculated with fungus, Fusarium oxysporum, and nematode, Meloidogyne incognita. The individual, simultaneous, and sequential inoculation of second stage juveniles (at 1000 J2/kg soil) of Meloidogyne incognita and Fusarium oxysporum (1.1 × 106 cells/kg soil) resulted in significant reduced plant growth parameters (plant height, plant girth, chlorophyll content, fresh and dry shoot weights, and fresh and dry root weights). Maximum suppression in plant growth parameters was observed in plants that received NF21 (Fusarium oxysporum inoculated 21 days after Meloidogyne incognita on okra) and F21 (fungus inoculated 21 days after seedling emergence) treatments for pot and field experiments, respectively. The least suppression of plant growth parameters was observed in separate inoculations of the two pathogens for both pot and field experiments. Maximum suppression in yield parameters was observed in okra plants that received NF21 and F21 treatments for pot and field experiments, respectively. Minimal yield suppression was observed for individual inoculations (N and F treatments) in both pot and field experiments. The highest severity of wilt disease was observed on okra plants that received NF21 and F21 treatment in both pot and field experiments. Plants in control plots had higher yields and the least wilt incidences (0.0%).

Assessing genetic variation for Fusarium wilt race 4 resistance in tetraploid cotton by screening over three thousand germplasm lines under greenhouse or controlled conditions

Cotton (Gossypium spp.) is the most widely-grown natural fiber crop used by the textile industry. Fusarium wilt, caused by Fusarium oxysporum f. sp. vasinfectum (FOV) comprised of eight nominal pathogenic races, is one of the most destructive diseases in cotton. FOV race 4 (FOV4) is an emerging threat to cotton production in the US. In this study, a total of 3258 lines including 3080 Upland (G. hirsutum) and 178 Pima (G. barbadense) germplasm lines were evaluated in 21 tests under greenhouse or temperature-controlled conditions for resistance to FOV4. A total of 2224 lines from 13 tests were screened in a commercial potting soil in the greenhouse under higher temperature (HT) conditions (24–32 °C), while 1204 lines from 8 tests were screened in a naturally FOV4-infected farm soil at a lower temperature (LT) setting (20–21 °C), both with artificial inoculations. The 170 Pima lines were evaluated in both temperature regimes. The results showed that, at 30 days post inoculation, both temperature regimes produced similar disease incidence (81.2% for HT vs. 86.8% for LT), but LT caused significantly higher disease severity ratings (DSR, 3.86 vs. 1.94) and plant mortality (81.7% vs. 7.5%) than did HT. DSR and morality rate were highly significantly correlated (r = 0.849–0.941) at LT. Significant genotypic variations in DSR were detected in all studies except two, and the broad-sense heritability estimates for DSR were 0.59–0.83 with an average of 0.70 at HT and 0.61–0.72 with an average of 0.69 at LT, indicating that 70% the phenotypic variation in FOV4 resistance was determined by genetic variation. Using the naturally FOV4-infected farm soil and LT to screen 1034 Upland and 170 Pima germplasm lines (with 20–40 plants for each line) with artificial inoculations, 48% showed 100% mortality; 22% had a mortality rate between 70 and 99%; 5% had mortality below 30%; and 0.5% (6 lines) did not display any apparent FOV4 symptoms. The results indicated that many existing available germplasm lines may be heterogeneous for FOV4 resistance and pedigree selection within germplasm may increase frequencies of resistant plants. This study represents one of the first publicly reported large-scale screenings of cotton for FOV4 resistance in the US and provides useful information for breeding cotton with resistance to FOV4.