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1.
Plant Dis ; 108(2): 375-381, 2024 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-37578371

RESUMO

Sterol demethylation inhibitor (DMI) fungicides continue to be essential components for the control of brown rot of peach caused by Monilinia fructicola in the United States and worldwide. In the southeastern United States, resistance to DMIs had been associated with overexpression of the cytochrome P450 14α-demethylase gene MfCYP51 as well as the genetic element Mona, a 65 bp in length nucleotide sequence located upstream of MfCYP51 in resistant isolates. About 20 years after the first survey, we reevaluated sensitivity of M. fructicola from South Carolina and Georgia to propiconazole and also evaluated isolates from Alabama for the first time. A total of 238 M. fructicola isolates were collected from various commercial and two experimental orchards, and sensitivity to propiconazole was determined based on a discriminatory dose of 0.3 µg/ml. Results indicated 16.2, 89.2, and 72.4% of isolates from Alabama, Georgia, and South Carolina, respectively, were resistant to propiconazole. The detection of resistance in Alabama is the first report for the state. All resistant isolates contained Mona, but it was absent from most sensitive isolates. It was unclear if the resistance frequency had increased in South Carolina and Georgia. However, the resistance levels (as assessed by the isolate frequency in discriminatory dose-based relative growth categories) did not change notably, and no evidence of other resistance genotypes was found. Analysis of the upstream MfCYP51 gene region in the resistant isolate CF010 revealed an insertion sequence described for the first time in this report. Our study suggests that current fungicide spray programs have been effective against increasing resistance levels in populations of M. fructicola and suppressing development of new resistant genotypes of the pathogen.


Assuntos
Ascomicetos , Fungicidas Industriais , Triazóis , Estados Unidos , Fungicidas Industriais/farmacologia , Ascomicetos/genética , Georgia
2.
Pestic Biochem Physiol ; 197: 105642, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-38072561

RESUMO

Methyl benzimidazole carbamate (MBC) fungicides were once widely used for brown rot (Monilinia fructicola) control of peach (Prunus persica (L.) Batsch) in the southeastern US, but their use was substantially reduced and often eliminated due to widespread resistance. In this study, 233 M. fructicola isolates were collected from major peach production areas in Alabama, Georgia, and South Carolina, and sensitivity to thiophanate-methyl was examined. Isolates were also collected from one organic and two experimental peach orchards. A discriminatory dose of 1 µg/ml was used to distinguish sensitive (S) and moderately sensitive (S-LR) isolates from low resistant phenotypes, while 50 and 500 µg/ml thiophanate-methyl concentrations were used to determine high resistant (HR) phenotypes. Sequence analyses were performed to identify mutations in the ß-tubulin target gene and detached fruit assays were performed to determine the efficacy of a commercial product against isolates representing each phenotype. Results indicated 55.7%, 63.5%, and 75.9% of isolates from Alabama, Georgia, and South Carolina, respectively, were S to thiophanate-methyl; 44.3%, 36.5%, and 21.4% were S-LR; no isolates were LR; and only 3 isolates (1.3%) from South Carolina were HR. No mutations in S or S-LR isolates were found, but HR isolates revealed the E198A mutation, an amino acid change of glutamic acid to alanine conferring high resistance. The high label rate of a commercial product containing thiophanate-methyl controlled brown rot caused by S and S-LR isolates in detached fruit studies but was ineffective against HR isolates. The combinations of thiophanate-methyl with azoxystrobin or isofetamid, when mixed together and applied in an experimental orchard 14 days preharvest, significantly reduced brown rot incidence on pre and postharvest commercially ripe fruit and efficacy was comparable to that of a grower standard fungicide. These results indicate that thiophanate-methyl may again be useful to peach growers in the southeastern US for brown rot and fungicide resistance management.


Assuntos
Fungicidas Industriais , Prunus persica , Tiofanato/farmacologia , Fungicidas Industriais/farmacologia , Sudeste dos Estados Unidos
3.
Front Microbiol ; 14: 1184343, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-37808317

RESUMO

Controlling early blight of tomatoes using endophytic bacteria is an eco-friendly and sustainable approach to manage this common fungal disease caused by Alternaria solani, Alternaria alternata, and Curvularia lunata. Endophytic bacteria are microorganisms that live inside plant tissues without causing harm and can help protect the host plant from pathogens. In this work, twenty endophytic bacterial isolates from tomato healthy plants were tested against pathogenic fungal isolates that caused early blight disease in vitro. Out of the 20 tested isolates, three (B4, B7, and B17) were considered effective isolates against the growth of fungal pathogens. The three isolates were recognized as Enterobacter cloacae HS-6 (B4), Pseudomonas gessardii HS-5 (B 7), and Pseudomonas mediterranea HS-4 (B17) using 16s-rDNA sequencing. Different concentrations of bacterial cultural diltrates at 20, 40, and 60% were tested for their antagonistic effects on the development of pathogenic fungi in vitro. The lowest dry weights of pathogenic isolates in all bacterial culture filtrates were discovered at 60%. In all culture filtrates, phenolic compounds showed the largest peak area. Under greenhouse conditions, the least disease severity of tomato early blight was found for E. cloacae and its culture filtrate compared to other treatments. Real-time PCR was used to examine the expression pattern of the defense response gene ß-1.3 glucanase gene in infected tomato plants with pathogenic fungi (control) as well as its relations with efficient biocontrol agent (E. cloacae). The expression of the gene increased substantially and significantly after three days from the inoculation-infected plants with C. lunata and E. cloacae while it reached the maximum after five days from the inoculation with A. alternata, A. solani and E. cloacae. Our study concluded that the endophytic bacterial isolate E. cloacae can be considered a promising biocontrol agent for preventing tomato early blight.

4.
Plant Dis ; 107(11): 3487-3496, 2023 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-37157104

RESUMO

Frogeye leaf spot (FLS), caused by Cercospora sojina, is an economically important disease of soybean in the United States. Data from 66 uniform fungicide trials (UFTs) conducted from 2012 to 2021 across eight states (Alabama, Arkansas, Illinois, Iowa, Kentucky, Louisiana, Mississippi, and Tennessee) were gathered and analyzed to determine the efficacy and profitability of the following fungicides applied at the beginning pod developmental stage (R3): azoxystrobin + difenoconazole (AZOX + DIFE), difenoconazole + pydiflumetofen (DIFE + PYDI), pyraclostrobin (PYRA), pyraclostrobin + fluxapyroxad + propiconazole (PYRA + FLUX + PROP), tetraconazole (TTRA), thiophanate-methyl (TMET), thiophanate-methyl + tebuconazole (TMET + TEBU), and trifloxystrobin + prothioconazole (TFLX + PROT). A network meta-analytic model was fitted to the log of the means of FLS severity data and to the nontransformed mean yield for each treatment, including the nontreated. The percent reduction in disease severity (%) and the yield response (kg/ha) relative to the nontreated was the lowest for PYRA (11%; 136 kg/ha) and the greatest for DIFE + PYDI (57%; 441 kg/ha). A significant decline in efficacy over time was detected for PYRA (18 percentage points [p.p.]), TTRA (27 p.p.), AZOX + DIFE (18 p.p.), and TMET + TEBU (19 p.p.) by using year as a continuous covariate in the model. Finally, probabilities of breaking even were the greatest (>65%) for the most effective fungicide DIFE + PYDI and the lowest (<55%) for PYRA. Results of this meta-analysis may be useful to support decisions when planning fungicide programs.


Assuntos
Fungicidas Industriais , Estados Unidos , Fungicidas Industriais/farmacologia , Glycine max , Tiofanato , Kentucky
5.
Plant Dis ; 107(11): 3422-3429, 2023 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-37093164

RESUMO

Frogeye leaf spot (FLS), caused by Cercospora sojina, is an important foliar disease affecting soybean in the United States. A meta-analytic approach including 39 fungicide trials conducted from 2012 to 2021 across eight states (Alabama, Arkansas, Illinois, Iowa, Kentucky, Louisiana, Mississippi, Tennessee) was used to assess the relationship between FLS severity and soybean yield. Correlation and regression analyses were performed separately to determine Fisher's transformation of correlation coefficients (Zr), intercept (ß0) and slope (ß1). Disease pressure (low severity, ≤34.5; high severity, >34.5%) and yield class (low, ≤3,352; high, >3,352 kg/ha) were included as categorical moderators. Pearson's [Formula: see text], obtained from back-transforming the [Formula: see text]r estimated by an overall random-effects model, showed a significant negative linear relationship between FLS severity and yield ([Formula: see text] = -0.60). The [Formula: see text]r was affected by disease pressure (P = 0.0003) but not by yield class (P = 0.8141). A random-coefficient model estimated a slope of -19 kg/ha for each percent severity for a mean attainable yield of 3,719.9 kg/ha. Based on the overall mean (95% CI) of the intercept and slope estimated by the random-coefficients model, the estimated overall relative damage coefficient was 0.51% (0.36 to 0.69), indicating that a percent increase in FLS severity reduced yield by 0.51%. The best model included yield class as a covariate, and population-average intercepts differed significantly between low (3,455.1 kg/ha) and high (3,842.7 kg/ha) yield classes. This highlights the potential impact of FLS on soybean yield if not managed and may help in disease management decisions.


Assuntos
Fungicidas Industriais , Glycine max , Estados Unidos , Doenças das Plantas , Illinois , Iowa
6.
Virol J ; 19(1): 149, 2022 09 13.
Artigo em Inglês | MEDLINE | ID: mdl-36100874

RESUMO

BACKGROUND: Viruses negatively impact soybean production by causing diseases that affect yield and seed quality. Newly emerging or re-emerging viruses can also threaten soybean production because current control measures may not be effective against them. Furthermore, detection and characterization of new plant viruses requires major efforts when no sequence or antibody-based resources are available. METHODS: In this study, soybean fields were scouted for virus-like disease symptoms during the 2016-2019 growing seasons. Total RNA was extracted from symptomatic soybean parts, cDNA libraries were prepared, and RNA sequencing was performed using high-throughput sequencing (HTS). A custom bioinformatic workflow was used to identify and assemble known and unknown virus genomes. RESULTS: Several viruses were identified in single or mixed infections. Full- or nearly full-length genomes were generated for tobacco streak virus (TSV), alfalfa mosaic virus (AMV), tobacco ringspot virus (TRSV), soybean dwarf virus (SbDV), bean pod mottle virus (BPMV), soybean vein necrosis virus (SVNV), clover yellow vein virus (ClYVV), and a novel virus named soybean ilarvirus 1 (SIlV1). Two distinct ClYVV isolates were recovered, and their biological properties were investigated in Nicotiana benthamiana, broad bean, and soybean. In addition to infections by individual viruses, we also found that mixed viral infections in various combinations were quite common. CONCLUSIONS: Taken together, the results of this study showed that HTS-based technology is a valuable diagnostic tool for the identification of several viruses in field-grown soybean and can provide rapid information about expected viruses as well as viruses that were previously not detected in soybean.


Assuntos
Vírus de Plantas , Potyvirus , Metagenômica , Vírus de Plantas/genética , Potyvirus/genética , Glycine max/genética
7.
Theor Appl Genet ; 135(9): 3073-3086, 2022 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-35902398

RESUMO

KEY MESSAGE: Eight soybean genomic regions, including six never before reported, were found to be associated with resistance to soybean rust (Phakopsora pachyrhizi) in the southeastern USA. Soybean rust caused by Phakopsora pachyrhizi is one of the most important foliar diseases of soybean [Glycine max (L.) Merr.]. Although seven Rpp resistance gene loci have been reported, extensive pathotype variation in and among fungal populations increases the importance of identifying additional genes and loci associated with rust resistance. One hundred and ninety-one soybean plant introductions from Japan, Indonesia and Vietnam, and 65 plant introductions from other countries were screened for resistance to P. pachyrhizi under field conditions in the southeastern USA between 2008 and 2015. The results indicated that 84, 69, and 49% of the accessions from southern Japan, Vietnam or central Indonesia, respectively, had negative BLUP values, indicating less disease than the panel mean. A genome-wide association analysis using SoySNP50K Infinium BeadChip data identified eight genomic regions on seven chromosomes associated with SBR resistance, including previously unreported regions of Chromosomes 1, 4, 6, 9, 13, and 15, in addition to the locations of the Rpp3 and Rpp6 loci. The six unreported genomic regions might contain novel Rpp loci. The identification of additional sources of rust resistance and associated genomic regions will further efforts to develop soybean cultivars with broad and durable resistance to soybean rust in the southern USA.


Assuntos
Basidiomycota , Phakopsora pachyrhizi , Genes de Plantas , Estudo de Associação Genômica Ampla , Genômica , Genótipo , Indonésia , Japão , Phakopsora pachyrhizi/genética , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Glycine max/genética , Glycine max/microbiologia , Vietnã
8.
J Nematol ; 532021.
Artigo em Inglês | MEDLINE | ID: mdl-34250503

RESUMO

LC-MS analysis of plant growth-promoting rhizobacterium (PGPR) Bacillus velezensis AP203 supernatants indicated the presence of nematode-inhibiting compounds that increased in abundance when B. velezensis AP203 was grown on orange peel. Meloidogyne incognita J2 were incubated with B. velezensis AP203 spores and orange peel, spores alone, orange peel alone, or with a non-inoculated control, and the combination of B. velezensis AP203 with orange peel resulted in 94% mortality of M. incognita juveniles (p ≤ 0.05). The J2 mortality rate for B. velezensis alone was 53%, compared to 59% mortality with orange peel, and the non-inoculated control exhibited 7% mortality. When tested on soybeans raised in a greenhouse, it was observed that when grown in the presence of orange peel, B. velezensis AP203 culture broth, cell suspension or supernatant reduced the numbers of M. incognita eggs per g of root at 45 days after planting (DAP) compared to inoculated controls in soybean and cotton (p ≤ 0.05). Likewise, soybean root length and fresh root weight significantly increased after inoculation with B. velezensis AP203 amended with orange peel. In cotton, shoot and root length significantly increased after inoculation with cell pellets of B. velezensis AP203 amended with orange peel compared to the M. incognita inoculated control. These data indicate that B. velezensis AP203 responds to growth on pectin-rich orange peel by production of biologically active secondary metabolites that can promote plant growth and inhibit root-knot nematode viability.

9.
J Nematol ; 532021.
Artigo em Inglês | MEDLINE | ID: mdl-33959722

RESUMO

Hemp (Cannabis sativa L.) is a new crop in Alabama. In 2019, symptomatic plants with stunted growth, poor root development, and numerous galls were observed in hemp plants grown in Geneva County, AL. After harvest, soil samples were collected from areas with the symptomatic plants and root-knot nematode (Meloidogyne spp.) were found in the soil. Based on morphological features and the polymerase chain reactions using species-specific primers, it was identified as Meloidogyne incognita. Further, a host differential test in a greenhouse assay confirmed it to be M. incognita race 3. The pathogenicity of the nematode to the hemp was confirmed by a modified version of Koch's postulates. To our knowledge, this is the first report of M. incognita infecting Cannabis sativa in Alabama.

10.
Mycologia ; 113(2): 326-347, 2021.
Artigo em Inglês | MEDLINE | ID: mdl-33555993

RESUMO

Taproot decline (TRD) is a disease of soybean that has been reported recently from the southern United States (U.S.). Symptoms of TRD include foliar interveinal chlorosis followed by necrosis. Darkened, charcoal-colored areas of thin stromatic tissue are evident on the taproot and lateral roots along with areas of necrosis within the root and white mycelia within the pith. Upright stromata typical of Xylaria can be observed on crop debris and emerging from infested roots in fields where taproot decline is present, but these have not been determined to contain fertile perithecia. Symptomatic plant material was collected across the known range of the disease in the southern U.S., and the causal agent was isolated from roots. Four loci, ⍺-actin (ACT), ß-tubulin (TUB2), the nuclear rDNA internal transcribed spacers (nrITS), and the RNA polymerase subunit II (RPB2), were sequenced from representative isolates. Both maximum likelihood and Bayesian phylogenetic analyses showed consistent clustering of representative TRD isolates in a highly supported clade within the Xylaria arbuscula species complex in the "HY" clade of the family Xylariaceae, distinct from any previously described taxa. In order to understand the origin of this pathogen, we sequenced herbarium specimens previously determined to be "Xylaria arbuscula" based on morphology and xylariaceous endophytes collected in the southern U.S. Some historical specimens from U.S. herbaria collected in the southern region as saprophytes as well as a single specimen from Martinique clustered within the "TRD" clade in phylogenetic analyses, suggesting a possible shift in lifestyle. The remaining specimens that clustered within the family Xylariaceae, but outside of the "TRD" clade, are reported. Both morphological evidence and molecular evidence indicate that the TRD pathogen is a novel species, which is described as Xylaria necrophora.


Assuntos
Glycine max/microbiologia , Doenças das Plantas/microbiologia , Raízes de Plantas/microbiologia , Xylariales/genética , Xylariales/patogenicidade , Teorema de Bayes , DNA Fúngico/genética , DNA Ribossômico/genética , Variação Genética , Filogenia , Estados Unidos , Xylariales/classificação
11.
Plant Physiol Biochem ; 156: 146-154, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32947123

RESUMO

In recent decades, drought has become a global problem for food security and agricultural production. A variety of strategies have been developed to enhance drought tolerance, but largely unsuccessful since most drought-responsive genes (DRGs) stimulate a stomata closure and in turn suppress plant growth and yield. To access if and/or how plants could enhance drought tolerance without trading off growth and development, we screened and isolated a plant growth-promoting rhizobacterium, Paenibacillus polymyxa CR1, capable of 1) priming drought tolerance and concurrently 2) increasing root growth in plants, e.g., Arabidopsis and soybean. In parallel, we uncovered that P. polymyxa CR1 3) induces the expression of two DRGs, Response to Desiccation (RD)29A and RD29B, 4) of which pattern upregulations are controlled by a diurnal rhythm. Besides, RD29A and RD29B act as 5) 'memory' genes; their transcript levels are increased to a greater extent when plants encountered P. polymyxa CR1 for the second time compared to an initial exposure. In line with these findings, T-DNA insertion mutant Arabidopsis of RD29A or RD29B displayed enhanced susceptibility to drought, without any change in stomata behaviors or growth rates, than wild-type plants. Hence, we conclude that RD29A or RD29B are unique, efficacious generic materials that can potentially aid in upgrading the plants own survival capacity against drought without reducing yield potential.


Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis , Secas , Paenibacillus polymyxa/fisiologia , Estresse Fisiológico , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Proteínas e Peptídeos de Choque Frio , Desidratação , Regulação da Expressão Gênica de Plantas , Plantas Geneticamente Modificadas/metabolismo
12.
Environ Microbiol ; 22(7): 2693-2708, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32207218

RESUMO

Assessment of pathogen diversity in agricultural fields is essential for informing management decisions and the development of resistant plant varieties. However, many population genomic studies have relied on culture-based approaches that do not provide quantitative assessment of pathogen populations at the field-level or the associated host microbiome. Here, we applied whole-genome shotgun sequencing of microbial DNA extracted directly from the washings of pooled leaf samples, collected from individual tomato and pepper fields in Alabama that displayed the classical symptoms of bacterial spot disease caused by Xanthomonas spp. Our results revealed that while the occurrence of both X. perforans and X. euvesicatoria within fields was limited, evidence of co-occurrence of up to three distinct X. perforans genotypes was obtained in 7 of 10 tomato fields sampled. These population dynamics were accompanied by the corresponding type 3 secreted effector repertoires associated with the co-occurring X. perforans genotypes, indicating that metapopulation structure within fields should be considered when assessing the adaptive potential of X. perforans. Finally, analysis of microbial community composition revealed that co-occurrence of the bacterial spot pathogens Pseudomonas cichorii and Xanthomonas spp. is common in Alabama fields and provided evidence for the non-random association of several other human and plant opportunists.


Assuntos
Genoma Bacteriano/genética , Doenças das Plantas/microbiologia , Pseudomonas/genética , Solanum lycopersicum/microbiologia , Xanthomonas/genética , Sequência de Bases , Genômica , Genótipo , Humanos , Metagenômica , Microbiota/genética , Folhas de Planta/microbiologia , Análise de Sequência de DNA
13.
J Econ Entomol ; 111(6): 2562-2569, 2018 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-30124887

RESUMO

Soybean vein necrosis virus (SVNV), a new virus in the genus Orthotospovirus, has been found in all soybean-growing regions in the United States and Ontario, Canada. Soybean thrips, Neohydatothrips variabilis (Beach) (Thysanoptera: Thripidae), tobacco thrips, Frankliniella fusca (Hinds) (Thysanoptera: Thripidae), and eastern flower thrips, Frankliniella tritici (Fitch) (Thysanoptera: Thripidae) are reported vectors of this virus, but there are no reports on their distribution in Alabama. A monitoring study was conducted in 2015 and 2016 to determine thrips species composition and abundance in Alabama soybean agroecosystems. Thrips were monitored weekly by collecting them on yellow sticky traps and soybean plant parts including foliage and reproductive structures. All three reported vectors of SVNV were identified in Alabama, with N. variabilis and F. tritici as the predominant species, while F. fusca was not consistently collected from soybean plants. Four additional thrips species were collected, of which Echinothrips americanus (Morgan) (Thysanoptera: Thripidae) was commonly found on soybean at all three locations. Results presented in this study provide new information about seasonal thrips species abundance in soybean agroecosystems in Alabama, and is an important first step to understanding thrips vector species of epidemiological importance in the Southern United States.


Assuntos
Distribuição Animal , Glycine max/virologia , Insetos Vetores , Tisanópteros , Alabama , Animais , Doenças das Plantas
14.
Data Brief ; 17: 129-133, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29349107

RESUMO

The draft genome of Xylaria sp. isolate MSU_SB201401, causal agent of taproot decline of soybean in the southern U.S., is presented here. The genome assembly was 56.7 Mb in size with an L50 of 246. A total of 10,880 putative protein-encoding genes were predicted, including 647 genes encoding carbohydrate-active enzymes and 1053 genes encoding secreted proteins. This is the first draft genome of a plant-pathogenic Xylaria sp. associated with soybean. The draft genome of Xylaria sp. isolate MSU_SB201401 will provide an important resource for future experiments to determine the molecular basis of pathogenesis.

15.
Biol Invasions ; 15(7): 1431-1438, 2013 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-23853520

RESUMO

Hosts of soybean rust (Phakopsora pachyrhizi) are sensitive to low temperatures, limiting this obligate parasite in the United States to overwintering sites in a restricted area along the Gulf Coast. This temperature sensitivity of soybean rust hosts allowed us to study spatial spread of epidemic invasions over similar territory for seven sequential years, 2005-2011. The epidemic front expanded slowly from early April through July, with the majority of expansion occurring from August through November. There was a 7.4-fold range of final epidemic extent (0.4 to 3.0 million km2) from the year of smallest final disease extent (2011) to that of the largest (2007). The final epidemic area of each year was regressed against epidemic areas recorded at one-week intervals to determine the association of final epidemic extent with current epidemic extent. Coefficients of determination for these regressions varied between 0.44 to 0.62 during April and May. The correlation coefficients varied between 0.70 and 0.96 from early June through October, and then increased monotonically to 1.0 by year's end. Thus, the spatial extent of disease when the epidemics began rapid expansion may have been a crucial contributor to subsequent spread of soybean rust. Our analyses used presence/absence data at the county level to evaluate the spread of the epidemic front only; the subsequent local intensification of disease could be strongly influenced by other factors, including weather.

16.
Plant Dis ; 84(7): 779-784, 2000 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30832108

RESUMO

Tomato plants treated with plant growth-promoting rhizobacteria (PGPR), applied as an industrially formulated seed treatment, a spore preparation mixed with potting medium (referred to as powder), or a combined seed-powder treatment, were evaluated under field conditions for induced resistance to Tomato mottle virus (ToMoV). The PGPR strains used, based on their ability to induce resistance in previous experiments, included Bacillus amyloliquefaciens 937a, B. subtilis 937b, and B. pumilus SE34. Experiments were conducted in the fall of 1997 and the spring and fall of 1998 at the University of Florida's Gulf Coast Research & Education Center, Bradenton. All plants were rated for symptoms and analyzed for the presence of ToMoV DNA at 40 days after transplant (dat). Whitefly densities were determined on individual plants in each trial, and marketable fruit yields were determined at least two times during each trial. The highest level of protection occurred in the fall 1997 trial when, at 40 dat, ToMoV disease severity ratings were significantly less in all PGPR powder-based treatments than in either of the seed or control treatments. Detection of viral DNA using Southern dot blot analyses correlated with symptom severity ratings, as did fruit yields. A reduction in ToMoV symptom severity ratings and incidence of viral DNA were also observed for some PGPR treatments in the spring 1998 trial, although corresponding yield responses were not apparent. Little or no resistance was observed in the fall 1998 trial. No differences in disease severity, detection of ToMoV DNA, or yield occurred among treatments in any of the trials at 80 dat. These data show that up to 40 dat under natural conditions of high levels of vector-virus pressure, some PGPR treatments resulted in reduced ToMoV incidence and disease severity and, in some cases, a corresponding increase in fruit yield. The use of PGPR could become a component of an integrated program for management of this virus in tomato.

17.
Plant Dis ; 82(1): 117-120, 1998 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30857044

RESUMO

During 1992, a multivirus epidemic reduced tomato production by as much as 25% in the major tomato-growing region of Alabama. Estimated yield losses of 100% resulted from the epidemic in over 250 ha in two counties of North Alabama. Cucumber mosaic cucumovirus (CMV), alone or in combination with potato potyvirus Y (PVY) and/or tobacco etch potyvirus (TEV), was responsible for the crop failure. CMV was detected alone or in combination with PVY and/or TEV in over 70% of the samples tested and was present in 90% of the fields surveyed. In 1993, 21 tomato fields were monitored weekly from transplanting through harvest for CMV, PVY, TEV, tobacco mosaic tobamovirus, and tomato spotted wilt tospovirus. All 5 viruses were detected, with CMV occurring most frequently. Incidence of CMV at the 61% level or higher was found in 16 of the 21 fields surveyed. Tomatoes transplanted in April and May were least effected and had relatively low virus incidence until late in their development. Tomatoes transplanted in June and July were infected at an earlier age, had the highest virus incidence, were the most severely affected, and suffered the greatest loss in yield. In 1994,Aphis gossypii, the cotton aphid, was the most common virus vector found during an aphid monitoring/virus spread study. Populations of A. gossypii peaked in late June, immediately preceding a period of rapid CMV incidence and spread.

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