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Phytophthora blight, caused by Phytophthora capsici, is one of the most destructive diseases in the production of solanaceous and cucurbitaceous vegetable crops. Fluopicolide has been used to control the disease; however, reduced efficacy of the fungicide was observed in Georgia. P. capsici isolates were collected from commercial vegetable fields in Georgia in 2018 and 2019 to determine sensitivity to fluopicolide, which were phenotyped to have 43.1% of the isolates as resistant. The fitness of resistant (R) and sensitive (S) isolates was assessed through mycelial growth and sporulation assays exposed to the fungicide (0 or 50 µg/ml). Fluopicolide did not reduce mycelial growth, sporangial production, and zoospore germination of the R isolates. In the absence of fluopicolide, there was no significant difference between the R and S isolates in sporangial production but mycelial growth and zoospore germination of the R isolates was greater than the S isolates (P = 0.01 and 0.001, respectively). The R isolates had an ability similar to that of the S isolates to induce disease on Aristotle bell pepper, and most of the R and S isolates caused the same level of disease on Paladin. Inoculating squash fruit using different R:S ratios and recovering R and S isolates after five cycles of inoculation resulted in similar trends in changes of R versus S isolate ratios. Overall, it appeared that fitness and competitive ability of the R isolates were not reduced compared with the S isolates. This is the first report of the occurrence of field isolates of P. capsici resistant to fluopicolide in the world. The results have significant implications in providing guidance for growers to avoid or limit use of this fungicide in vegetable production.

Bacterial soft rot is one of the major destructive diseases affecting crop production worldwide. In summer 2017, soft rot of fruit and stem blight was observed on bell pepper in commercial fields in south Georgia, USA. Bacteria were isolated from infected fruits and stems, and 5 isolates (MPS05, MPS06, PF01–2, PF04–3 and PF05–3) were characterized in the study. The isolates were identified as Pectobacterium carotovorum subsp. brasiliense (Pcb) and P. aroidearum (Pa) by morphological characteristics, biochemical and physiological tests, PCR amplification using Pcb-specific primers, and phylogenetic analysis of the 16S rDNA sequences. Pathogenicity tests on bell pepper seedlings indicated that isolates MPS05 (Pcb) and PF05–3 (Pa) were aggressive, causing plant tissue discoloration, lesions on leaves and stems, plant wilt and death. Inoculation of bell pepper fruit with MPS05 and PF05–3 at different concentrations (105, 106, 107 and 108 CFU/ml) resulted in fruit tissue maceration and complete fruit rot. To our knowledge, this study is the first report of disease caused by P. carotovorum subsp. brasiliense on pepper in the United States and the first report of P. aroidearum causing disease on pepper in the world.

Early detection of soilborne disease is essential for prediction of disease development and successful disease management. Traditional methods of monitoring soilborne diseases based on plant growth and symptoms did not take into account the presence and inoculum potential of pathogens in the soil, which generally delay the prevention of diseases. To detect and quantify soil populations of Sclerotium rolfsii, the causal agent of southern blight of tomatoes, quantitative polymerase chain reaction (Q-PCR) was used to measure the amount of soil general fungal and specific S. rolfsii DNA. Significantly higher amounts of total fungal and S. rolfsii DNA were detected in inoculated than in uninoculated soil in a greenhouse inoculation experiment. Fluorescent in situ hybridization (FISH) was successfully developed to detect the abundance of S. rolfsii through whole cell hybridization and was further applied for visual detection of the abundance of S. rolfsii in the soil samples of greenhouse inoculation experiment. Natural abundance of S. rolfsii in soil with a DNA amount of 0.06 pg µl−1 DNA extraction, which was equivalent to 8 pg g−1 soil, was successfully detected. The hybridization signal detected in soil for S. rolfsii had a great correlation with the amount of infested DNA levels of S. rolfsii. Molecular detection and quantification of soilborne pathogens in plant roots and in the soil could provide valuable information to predict disease development and apply management practices for soilborne diseases.

Fusarium wilt of watermelon caused by Fusarium oxysporum f. sp. niveum is a serious, widespread disease of watermelon throughout the southern United States. To investigate whether soil temperature affects disease development, three cultivars of triploid watermelon were transplanted March 17 to 21, April 7 to 11, and April 26 to May 2 in 2015 and 2016 at Charleston, SC, and Tifton, GA into fields naturally infested with F. oxysporum f. sp. niveum. Incidence of Fusarium wilt was lower with late-season than with early and midseason transplanting in all four experiments (P ≤ 0.01). Cultivar Citation had more wilted plants than the cultivars Fascination and Melody in three of four experiments (P ≤ 0.05). In South Carolina, planting date did not affect weight and number of marketable fruit ≥4.5 kg apiece. In Georgia in 2016, weight and number of marketable fruit were greater with late transplanting than with early and midseason transplanting. In both states, yield and value for Fascination and Melody were higher than for Citation. Soil temperature averaged over the 4-week period after transplanting was negatively correlated with disease incidence for all four experiments (r = –0.737, P = 0.006). Transplanting after mid-April and choosing a cultivar with resistance to F. oxysporum f. sp. niveum race 1, like Fascination, or tolerance, like Melody, can help manage Fusarium wilt of watermelon and increase marketable yields in the southern United States.

Corn stalk rot, caused by Fusarium graminearum, is one of the most destructive diseases of maize in many regions of the world. A bacterial strain BV23 was isolated from corn rhizosphere tha...

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum (FON), is pathogenic only to watermelon and has become one of the main limiting factors in watermelon production internationally. Detection methods for this pathogen are limited, with few published molecular assays available to differentiate FON from other formae speciales of F. oxysporum. FON has four known races that vary in virulence but are difficult and costly to differentiate using traditional inoculation methods and only race 2 can be differentiated molecularly. In this study, genomic and chromosomal comparisons facilitated the development of a conventional polymerase chain reaction (PCR) assay that could differentiate race 3 from races 1 and 2, and by using two other published PCR markers in unison with the new marker, the three races could be differentiated. The new PCR marker, FNR3-F/FNR3-R, amplified a 511 bp region on the &ldquo, pathogenicity chromosome&rdquo, of the FON genome that is absent in race 3. FNR3-F/FNR3-R detected genomic DNA down to 2.0 pg/&micro, L. This marker, along with two previously published FON markers, was successfully applied to test over 160 pathogenic FON isolates from Florida, Georgia, and South Carolina. Together, these three FON primer sets worked well for differentiating races 1, 2, and 3 of FON. For each marker, a greater proportion (60 to 90%) of molecular results agreed with the traditional bioassay method of race differentiation compared to those that did not. The new PCR marker should be useful to differentiate FON races and improve Fusarium wilt research.

Here, we report the draft genome sequences of three Fusarium oxysporum f. sp. niveum isolates that were used to design markers for molecular race differentiation. The isolates were collected from watermelon fields in Georgia (USA) and were determined to be different races of F. oxysporum f. sp. niveum using a traditional bioassay.

Summary Drought stress conditions decrease maize growth and yield, and aggravate preharvest aflatoxin contamination. While several studies have been performed on mature kernels responding to drought stress, the metabolic profiles of developing kernels are not as well characterized, particularly in germplasm with contrasting resistance to both drought and mycotoxin contamination. Here, following screening for drought tolerance, a drought‐sensitive line, B73, and a drought‐tolerant line, Lo964, were selected and stressed beginning at 14 days after pollination. Developing kernels were sampled 7 and 14 days after drought induction (DAI) from both stressed and irrigated plants. Comparative biochemical and metabolomic analyses profiled 409 differentially accumulated metabolites. Multivariate statistics and pathway analyses showed that drought stress induced an accumulation of simple sugars and polyunsaturated fatty acids and a decrease in amines, polyamines and dipeptides in B73. Conversely, sphingolipid, sterol, phenylpropanoid and dipeptide metabolites accumulated in Lo964 under drought stress. Drought stress also resulted in the greater accumulation of reactive oxygen species (ROS) and aflatoxin in kernels of B73 in comparison with Lo964 implying a correlation in their production. Overall, field drought treatments disordered a cascade of normal metabolic programming during development of maize kernels and subsequently caused oxidative stress. The glutathione and urea cycles along with the metabolism of carbohydrates and lipids for osmoprotection, membrane maintenance and antioxidant protection were central among the drought stress responses observed in developing kernels. These results also provide novel targets to enhance host drought tolerance and disease resistance through the use of biotechnologies such as transgenics and genome editing.

Fusarium wilt, incited by the fungus Fusarium oxysporum f. sp. niveum, is a soilborne disease that affects watermelon production worldwide. Approaches for effective management of Fusarium wilt in watermelon are limited. Studies conducted in recent years indicated that prothioconazole and thiophanate-methyl reduced the disease significantly under field conditions. However, effects of the fungicides on different life stages of F. oxysporum f. sp. niveum and potential existence of fungicide resistance in F. oxysporum f. sp. niveum populations are unknown. In the present study, effects of prothioconazole and thiophanate-methyl on mycelium growth and spore germination of F. oxysporum f. sp. niveum isolates collected in watermelon fields in Georgia were determined. In vitro mycelium growth studies indicated that all 100 isolates evaluated were sensitive to prothioconazole; the effective concentration that suppressed mycelium growth by 50% ranged from 0.75 to 5.69 μg/ml (averaged 1.62 μg/ml). In contrast, 33 and 4% of the isolates were resistant to thiophanate-methyl at 10 and 100 μg/ml, respectively. Microconidial germination assays showed that 36 and 64% of the isolates tested were sensitive or intermediately sensitive to prothioconazole at 100 μg/ml but the fungicide did not inhibit spore germination at 10 μg/ml. Sequencing a portion of the β-tubulin gene of eight isolates resistant or sensitive to thiophanate-methyl indicated that fungicide resistance was associated with a point mutation at nucleotide position 200, resulting in a substitution of phenylalanine by tyrosine. This is the first report of isolates of F. oxysporum resistant to thiophanate-methyl. Results of the research suggest that prothioconazole may be a viable option for management of Fusarium wilt of watermelon whereas thiophanate-methyl should be used judiciously due to the existence of isolates resistant to the fungicide.

About 50% of the watermelons in the United States are produced in the southeastern states, where optimal conditions for development of Phytophthora fruit rot prevail. Phytophthora fruit rot significantly limits watermelon production by causing serious yield losses before and after fruit harvest. Efficacy of fungicide rotation programs and Melcast-scheduled sprays for managing Phytophthora fruit rot was determined by conducting experiments in Phytophthora capsici-infested fields at three locations in southeastern United States (North Carolina, South Carolina, and Georgia). The mini seedless cultivar Wonder and seeded cultivar Mickey Lee (pollenizer) were used. Five weekly applications of fungicides were made at all locations. Significant fruit rot (53 to 91%, mean 68%) was observed in the nontreated control plots in all three years (2013 to 2015) and across locations. All fungicide rotation programs significantly reduced Phytophthora fruit rot compared with nontreated controls. Overall, the rotation of Zampro alternated with Orondis was highly effective across three locations and two years. Rotations of Actigard followed by Ranman+Ridomil Gold, Presidio, V-10208, and Orondis, or rotation of Revus alternated with Presidio were similarly effective. Use of Melcast, a melon disease-forecasting tool, may occasionally enable savings of one spray application without significantly impacting control. Although many fungicides are available for use in rotations, under very heavy rain and pathogen pressure, the fungicides alone may not offer adequate protection; therefore, an integrated approach should be used with other management options including well-drained fields.

Black shank incited by Phytophthora nicotianae is a devastating disease in the production of tobacco. Fungicides have been commonly used for managing the disease; however, there is only a narrow pool of effective fungicides. A few new fungicides became available in recent years, including fluopicolide, mandipropamid, and oxathiapiprolin, which reduced diseases incited by oomycetes under field conditions. Limited information is available regarding sensitivity of P. nicotianae isolates to these new fungicides. Research was conducted to determine effects of the three new fungicides on P. nicotianae isolates from tobacco in Georgia. Studies with 106 isolates indicated that they did not grow when agar medium was amended with the fungicides at the rate of 1 μg/ml. Twenty isolates were used for in vitro studies to determine sensitivity to the fungicides. Fluopicolide, mandipropamid, and oxathiapiprolin inhibited mycelial growth of the isolates with mean EC50 values (effective concentrations that provide 50% growth reduction) of 0.09, 0.04, and 0.001 μg/ml, respectively. EC50 values of fluopicolide, mandipropamid, and oxathiapiprolin for inhibiting sporangial formation were 0.15, 0.03, and 0.0002 μg/ml, respectively. EC50 values for suppressing zoospore germination averaged 0.16, 0.04, and 0.002 μg/ml for fluopicolide, mandipropamid, and oxathiapiprolin, respectively. Results from the study indicated that P. nicotianae isolates from tobacco in Georgia were sensitive to the fungicides, with lower EC50 for oxathiapiprolin than for fluopicolide and mandipropamid. The information on effectiveness and baseline sensitivity of fungicides on P. nicotianae will facilitate monitoring of resistance development in the pathogen population.

Pasteuria penetrans is an obligate parasite of root-knot nematodes (Meloidogyne spp.). Endospores of P. penetrans attach to the cuticle of second-stage juveniles (J2) and complete their life cycle within the nematode female body. Infected females will be filled with spores and will be sterilized. Studies with Daphnia magna and its parasite Pasteuria ramosa showed that a poor maternal environment can lead to offspring resistant to P. ramosa. Therefore, we hypothesized that Meloidogyne arenaria females raised under a stressed environment would produce offspring that were more resistant to P. penetrans. Females were exposed to a stressed environment created by crowding and low-food supply, or a non-stressed environment and their offspring evaluated for endospore attachment and infection by P. penetrans. No difference in spore attachment was observed between the two treatments. However, infection rate of P. penetrans in the stressed treatment was significantly lower than that in the non-stressed treatment (8 vs 18%). Mothers raised under stressed conditions appeared to produce more resistant offspring than did mothers raised under favorable conditions. Under stressful conditions, M. arenaria mothers may provide their progeny with enhanced survival traits. In the field, when nematode populations are not managed, they often reach the carrying capacity of their host plant by the end of the season. This study suggests that the next generation of inoculum may be more resistant to infection by P. penetrans.

Black shank, caused by Phytophthora nicotianae, occurs worldwide and is responsible for significant yield loss in tobacco production in Georgia. Management of the disease has primarily relied on utilization of tobacco cultivars with resistance to race 0 of the pathogen and application of the fungicide mefenoxam. Races of P. nicotianae currently prevalent in tobacco production in Georgia, their sensitivity to mefenoxam, and genetic diversity of the pathogen are largely unknown. To determine population structure and genetic diversity of the pathogen, simple sequence repeat (SSR) markers were used. Three races of P. nicotianae (races 0, 1, and 3) were isolated from infected tobacco plants, with race 3 identified in Georgia for the first time. The majority of isolates were identified as A2 mating type and all isolates were sensitive or intermediately sensitive to mefenoxam at 1 or 10 μg/ml, with effective concentration of mefenoxam for 50% mycelial growth reduction values ranging from

Production of bell pepper is seriously affected by Phytophthora capsici, the causal agent of Phytophthora blight. Limited approaches are available for effective management of the disease. Oxathiapiprolin is a fungicide recently registered in the United States that suppressed P. capsici and reduced Phytophthora blight on bell pepper significantly in our previous studies. It is unknown whether oxathiapiprolin translocates in bell pepper plants systemically after application. Experiments were conducted to determine uptake of oxathiapiprolin by bell pepper plants and its systemic movement in the plant. Quantification of oxathiapiprolin in plant tissues was conducted by high-performance liquid chromatography (HPLC) that detected the compound sensitively and selectively. Percentage of recovery of oxathiapiprolin from plant tissues was calculated by comparing the quantities in plant tissues determined by HPLC with known quantities of the compound added to the plant tissues. Recovery rates of oxathiapiprolin from pepper plant tissues ranged from 87.0 to 119.3%. When oxathiapiprolin was applied to roots of bell pepper plants grown in hydroculture, the compound was detected in the root within 4 h and in the cotyledon, first true leaf, and second true leaf within 8 h. It was detectable in the top new leaf 48 h after application to the root. In greenhouse studies with bell pepper plants grown in pots, oxathiapiprolin was applied as a soil drench at 100 and 400 μg/ml. The compound was detected in the root within 3 days and in the stem and first true leaf within 6 days when applied at 100 μg/ml. It was detected in the root, stem, first true leaf, and top new leaf within 3 days when applied at 400 μg/ml. Phytophthora blight on pepper foliage was significantly reduced when oxathiapiprolin was applied as a soil drench at 100 or 400 μg/ml under greenhouse conditions. This is the first report indicating systemic movement of oxathiapiprolin in pepper plants that provides useful information for designing fungicide application programs for effective management of the disease.

Fusarium wilt caused by Fusarium oxysporum f. sp. niveum (FON) is a destructive soilborne disease commonly found in watermelon producing areas throughout the world. At present, the control of Fusarium wilt depends heavily on host resistance and chemical fungicide application. In this study, we isolated fluorescent pseudomonads from the rhizosphere of healthy watermelon and evaluated their biocontrol capacity against FON race 2. Biochemical assays indicated that all 14 fluorescent Pseudomonas strains were able to produce indole-3-acetic acid and at least one type of biosurfactants. Both sulphur oxidising and proteolytic activities were exhibited in 2 of the 14 strains. However, none of them could synthesise phenazine antibiotics. Seven strains with different morphological and biochemical characteristics were identified by sequencing the rpoB gene. Among those, one was Pseudomonas resinovorans (WMT16-1-1), two were P. putida (WMC16-1-1 and WMC16-2-5), one was P. fluorescens (WMC16-1-8) and others were Pseudomonas sp. In vitro studies indicated that WMC16-1-1, WMC16-1-8 and WMC16-2-5 inhibited mycelial growth of FON significantly. Detection of biosynthetic loci of 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin and pyoluteorin using specific primers indicated that the three strains could not produce the antibiotics. In greenhouse studies, WMC16-1-1, WMC16-1-8 and WMC16-2-5 reduced the severity of Fusarium wilt significantly with WMC16-1-1 being the most effective. Inoculation with WMC16-2-5 resulted in the significantly greater weight of both stems and roots compared to the nontreated control, while WMC16-1-1 resulted in greater stem weight. Pseudomonas strains WMC16-1-1, WMC16-1-8 and WMC16-2-5 are potential candidates for controlling Fusarium wilt and promoting the growth of watermelon.

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum (FON), is a devastating soil-borne disease in watermelon production. Race 1 and race 2 of the pathogen are widely distributed in different watermelon producing regions. To investigate whether the root-knot nematodes break resistance of watermelon genotypes with resistance to FON race 1 and race 2, four greenhouse experiments were conducted on two watermelon cultivars ‘Calhoun Gray’ and ‘Fascination’ that are resistant to race 1, and an accession PI 296 341-FR that is resistant to race 2. The treatments included seedlings of ‘Calhoun Gray’ and ‘Fascination’ inoculated with Meloidogyne incognita (1000 J2/plant) or FON race 1 alone, nematodes 5 days before FON, FON 5 days before nematodes, nematodes and FON simultaneously, and non-inoculated control. PI 296 341-FR was inoculated with FON race 2, with or without M. incognita inoculation. The presence of M. incognita enhanced the susceptibility of all watermelon genotypes to Fusarium wilt. Co-inoculation with M. incognita led to an early development of wilt symptoms and increased disease severity. Galls were observed on roots of all nematode-inoculated plants, and sequential inoculation of FON followed by nematodes resulted in numerically lower galling indices compared with other inoculation methods. Whereas inoculation of the nematodes alone did not reduce plant growth, growth suppression was evident when seedlings were inoculated with both pathogens. The results indicated that M. incognita could enhance susceptibility of resistant watermelon genotypes to respective FON races, and host resistance alone is not sufficient for managing Fusarium wilt on watermelon in soils infested with root-knot nematodes.

The root-knot nematode, Meloidogyne incognita, and the Phytophthora blight pathogen, Phytophthora capsici, cause root diseases in bell pepper under field conditions. However, limited information is available about the interactions between these two pathogens on different bell pepper cultivars. Greenhouse experiments were conducted on cultivars of bell pepper with different levels of resistance to P. capsici (‘Aristotle’, ‘Paladin’ and ‘Intruder’), by concomitant and sequential inoculation of both pathogens. The treatments included inoculating both pathogens simultaneously into the root zone, inoculating M. incognita 7 days before P. capsici, inoculating P. capsici 7 days before M. incognita, inoculating M. incognita or P. capsici alone, and an untreated control without any pathogens. In ‘Aristotle’ and ‘Intruder’, P. capsici inoculation with M. incognita simultaneously or 7 days before or after M. incognita reduced gall index significantly as compared with M. incognita alone. In ‘Paladin’, P. caps...

Bacteria were isolated from corn plants and efficacy of a selected isolate for control of corn stalk rot caused by Fusarium graminearum was evaluated. The bacterial isolate provided the greatest suppression of F. graminearum in lab studies and reduced corn stalk rot significantly in 2013 and 2014 field experiments.

Phomopsis longicolla T. W. Hobbs (syn. Diaporthe longicolla) is the primary cause of Phomopsis seed decay (PSD) in soybean, Glycine max (L.) Merrill. This disease results in poor seed quality and is one of the most economically important seed diseases in soybean. The objectives of this study were to infer protein-protein interactions (PPI) and to identify conserved global networks and pathogenicity subnetworks in P. longicolla including orthologous pathways for cell signaling and pathogenesis. The interlog method used in the study identified 215,255 unique PPIs among 3,868 proteins. There were 1,414 pathogenicity related genes in P. longicolla identified using the pathogen host interaction (PHI) database. Additionally, 149 plant cell wall degrading enzymes (PCWDE) were detected. The network captured five different classes of carbohydrate degrading enzymes, including the auxiliary activities, carbohydrate esterases, glycoside hydrolases, glycosyl transferases, and carbohydrate binding molecules. From the PPI analysis, novel interacting partners were determined for each of the PCWDE classes. The most predominant class of PCWDE was a group of 60 glycoside hydrolases proteins. The glycoside hydrolase subnetwork was found to be interacting with 1,442 proteins within the network and was among the largest clusters. The orthologous proteins FUS3, HOG, CYP1, SGE1, and the g5566t.1 gene identified in this study could play an important role in pathogenicity. Therefore, the P. longicolla protein interactome (PiPhom) generated in this study can lead to a better understanding of PPIs in soybean pathogens. Furthermore, the PPI may aid in targeting of genes and proteins for further studies of the pathogenicity mechanisms.

Fusarium wilt incited by Fusarium oxysporum f. sp. niveum is a seed-transmitted disease that causes significant yield loss in watermelon production. The pathogen may infect watermelon seeds latently, which can be an important inoculum source and contribute to severe disease outbreak. However, information regarding infection courts of F. oxysporum f. sp. niveum leading to infestation of watermelon seeds is limited. To determine how seeds in watermelon fruit can be infested by F. oxysporum f. sp. niveum during the watermelon growing season, greenhouse and field experiments were conducted in 2014 and 2015 where watermelon flowers and immature fruit were inoculated with F. oxysporum f. sp. niveum. Seeds were extracted from mature watermelon fruit, and infestation of watermelon seeds was determined by isolation of F. oxysporum f. sp. niveum and further confirmed by real-time polymerase chain reaction (PCR) analysis. Inoculation of the pericarp of immature fruit resulted in 17.8 to 54.4% of infested seeds under field conditions and 0.6 to 12.8% of infested seeds under greenhouse conditions when seeds were not surface disinfested prior to isolation. Seed infestation was also detected in 0 to 4.5% of the seeds when seeds were surface disinfested prior to isolation. Inoculation of pistil resulted in 0 to 7.2% and 0 to 18.3% of infested seeds under greenhouse and field conditions when seeds were surface disinfested or not disinfested before isolation, respectively. Inoculation of peduncle resulted in 0.6 to 6.1% and 0 to 10.0% of infested seeds in the greenhouse and field experiments when seeds were surface disinfested or not disinfested before isolation, respectively. Seed infestation was also detected in all the experiments using real-time PCR assay when pericarp or pistil was inoculated, and in three of four experiments when peduncle was inoculated, regardless of whether seeds were surface disinfested or not disinfested. Pericarp and peduncle of immature watermelon fruit and pistil of watermelon flowers could be potential infection courts for F. oxysporum f. sp. niveum leading to infestation of seeds in asymptomatic watermelon fruit.

Bacterial leaf scorch, caused by Xylella fastidiosa, is a major threat to blueberry production in the southeastern United States. Management of this devastating disease is challenging and often requires early detection of the pathogen to reduce major loss. There are several different molecular and serological detection methods available to identify the pathogen. Knowing the efficiency and suitability of these detection techniques for application in both field and laboratory conditions is important when selecting the appropriate detection tool. Here, we compared the efficiency and the functionality of four different molecular detection techniques (PCR, real-time PCR, LAMP and AmplifyRP® Acceler8™) and one serological detection technique (DAS-ELISA). The most sensitive method was found to be real-time PCR with the detection limit of 25 fg of DNA molecules per reaction (≈9 genome copies), followed by LAMP at 250 fg per reaction (≈90 copies), AmplifyRP® Acceler8™ at 1 pg per reaction (≈350 copies), conventional PCR with nearly 1.25 pg per reaction (≈ 440 copies) and DAS-ELISA with 1x105 cfu/mL of Xylella fastidiosa. Validation between assays with 10 experimental samples gave consistent results beyond the variation of the detection limit. Considering robustness, portability, and cost, LAMP and AmplifyRP® Acceler8™ were not only the fastest methods but also portable to the field and didn’t require any skilled labor to carry out. Among those two, AmplifyRP® Acceler8™ was faster but more expensive and less sensitive than LAMP. On the other hand, real-time PCR was the most sensitive assay and required comparatively lesser time than C-PCR and DAS-ELISA, which were the least sensitive assays in this study, but all three assays are not portable and needed skilled labor to proceed. These findings should enable growers, agents, and diagnosticians to make informed decisions regarding the selection of an appropriate diagnostic tool for X. fastidiosa on blueberry.

Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum (FON), occurs worldwide and is responsible for substantial yield losses in watermelon-producing areas of the southeastern United States. Management of this disease largely relies on the use of integrated pest management (i.e., fungicides, resistant cultivars, crop rotation, etc.). Knowledge about race structure and genetic diversity of FON in the southeastern US is limited. To determine genetic diversity of the pathogen, FON isolates were collected from symptomatic watermelon plants in commercial fields in Georgia and Florida, USA, and identified based on morphological characteristics and PCR analysis using FON-specific primers. Discriminant analysis of principal components (DAPC) of 99 isolates genotyped with 15 simple sequence repeat (SSR) markers grouped the isolates in eight distinct clusters with two prominent clusters (clusters 1 and 8). Cluster 1 consisted of a total of 14 isolates, out of which 85.7% of the isolates were collected in Florida. However, most of the isolates (92.4%) in cluster 8 were collected in Georgia. Both DAPC and pairwise population differentiation analysis (ФPT) revealed that the genetic groups were closely associated with geographical locations of pathogen collection. Three races of FON (races 0, 2 and 3) were identified in the phenotypic analysis; with race 3 identified for the first time in Georgia. Overall, 5.1%, 38.9% and 55.9% of the isolates were identified as race 0, race 2 and race 3, respectively. The majority of the isolates in cluster 1 and cluster 8 belonged to either race 2 (35.6%) or race 3 (45.8%). Additionally, no relationship between genetic cluster assignment and races of the isolates was observed. The information obtained on genotypic and phenotypic diversity of FON in the southeastern US will help in development of effective disease management programs to combat Fusarium wilt.

Soybean is an important edible legume cultivated around the world. However, soybean production is seriously impacted by the widespread of root rot disease. In this study, genetic diversity and pathogenicity of Fusarium oxysporum associated with root rot of soybean in Heilongjiang province, China, were examined. A total of 50 F. oxysporum strains were isolated from diseased soybean plants grown in Harbin, Heihe, Jixi, Jiamusi and Qiqihar of Heilongjiang province. Pathogenicity study indicated that all F. oxysporum strains were able to induce root rot disease on soybean in which 28% of the isolates were highly aggressive, 42% were moderately aggressive, and 30% were weakly aggressive. Aggressiveness of the isolates did not appear to be associated with geographic location or plant age of isolation. Genomic DNA of the isolates was analyzed by polymerase chain reaction using eight amplified fragment length polymorphism (AFLP) primers that generated 1728 bands, of which 99% were polymorphic. Cluster analysis using UPGMA showed that the similarity values ranged from 0.15 to 0.47. At a similarity coefficient of 0.2, the isolates were separated into 7 groups. Analysis of molecular variance indicated that about 92% of the genetic variation resided within populations. No correlation was found between genetic diversity and aggressiveness or the geographic origin of the isolates. Results of the study indicate that pathogenic F. oxysporum are commonly associated with root rot of soybean with various aggressiveness and they are genetically diverse.

Root rot was observed on cowpea [Vigna unguiculata (Linn.) Walp] in Tift County, Georgia, in May of 2015. The disease occurred on approximately 10% of cowpea plants in 2 fields (2 ha), a distance of about 5 miles apart. Symptoms appeared as yellowing lower leaves, dwarfed growth, sunken reddish brown lesions on roots and stems under the soil line, secondary roots became dark brown and rotted, and infected plants eventually wilted and died. Infected plants were collected from each field and roots were surface disinfested in 0.5% NaOCl for 2 min, rinsed in sterile distilled water, and cultured on potato dextrose agar (Full-strength PDA) at 26°C. A fungus was isolated on all plates, which produced whitish aerial mycelium with pale brown pigments in the agar. Macroconidia were produced on PDA at 26°C after 7 days. Macroconidia were produced from monophialides on branched conidiophores in sporadochia and had pronounced dorsiventral curvature, with a tapered and elongated apical cell and prominent foot-shaped b...