Spotted wilt disease, caused by Tomato spotted wilt virus (TSWV), is an economically important disease in peanut, pepper, tobacco, and tomato in the southeastern United States. However, very little is known about the biological variability existent in the virus population. Fourteen isolates of TSWV collected in Georgia were evaluated for symptom severity. The majority of the isolates produced severe systemic necrosis. One mild (GATb-1) and one severe (GAL) isolate were further examined because of the distinct differences in their virulence and symptomatology on tobacco. GATb-1 caused a few chlorotic spots and mild systemic symptoms, whereas GAL produced a large number of local lesions and severe systemic necrosis. Distinct differences in the response of selected commercial cultivars of peanut, tobacco, and tomato to GATb-1 and GAL infection were observed. GAL was lethal to a widely grown tobacco cultivar, K326. Georgia Green, a field resistant peanut cultivar, and C11-2-39, a breeding line with the highest level of known resistance to TSWV, were more susceptible to GAL than to GATb-1. BHN 444, a newly released TSWV-resistant tomato cultivar, showed a resistant reaction, whereas Stiletto, a newly released TSWV-resistant pepper cultivar, was susceptible to both GATb-1 and GAL isolates. Information on the biological diversity of TSWV may be useful in developing more durable TSWV-resistant crops.

The efficacy of two fungicides, azoxystrobin and trifloxystrobin, and a plant defense activator, acibenzolar-S-methyl, for the control of tomato corky root and eggplant verticillium wilt, was evaluated under greenhouse and field conditions by means of dips, soil drenches or foliar sprays. The strobilurins provided excellent control of the two diseases under greenhouse conditions. Azoxystrobin was more effective than trifloxystrobin and reduced the severity of tomato corky root and eggplant verticillium wilt by 98% and 95%, respectively. Acibenzolar-S-methyl caused plant stunting and severe leaf chlorosis in the greenhouse experiments. In the field, azoxystrobin provided the best control. Tomato corky root severity was reduced by 83% and eggplant verticillium wilt severity by 29%. At the dosage used, acibenzolar-S-methyl was effective only in controlling tomato corky root. No phytotoxic symptoms were observed by any material in the field.

In order to study the agent of Early blight disease of tomato and determine isolates causing severe disease for using in evaluation of tomato germplasms, infected samples from tomato in central and southern regions of country collected and agent of disease isolated and purified in laboratory during first year.Macroscopic characters of isolates like shape,color and growth rate of colony as well as microscopic characters of them such as type of mycellium,conidiofore and conidium were studied carefully. According to the characteristics of Alternaria species mentioned in the Ellis keys the isolates belonged to two species. most of ones caused early blight disease on tomato were detected as A .alternata which produce conidia with obclavate in shape and short narrow beak.Few isolate that caused early blight disease on tomato were detected as A .tenuissima which produced conidia with ellipsoid body tapering gradually to fairly long beak. pathogenicity of first type of isolates were tested on Imperial cultivar in greenhouse and percent of blight and defoliation were determined .the result showed that isolates B-8 from Booshehr DKA-5 , DKA-10 from Desfol with means of %98.3 , %89.56 ,%87.76 disease severity respectively were the most virulent isolates on tomato.In this study the disease caused by virulent fungi responsible for Alternaria blight (DKA-5) Was evaluated in the field and greenhouse on 21 varieties and genotypes of tomato simultaneously. Progress of disease infection and disease index in the field and also percent of infected leaves , leaf blight area and disease index in the greenhouse was determined.Infection was based on artificial inoculation by SB-3 and DSF-2 isolates. Further evaluation showed that varieties and genotypes of super 2270 ,Kingstone ,Early orbano and 8402 had the least disease progress and index in the field.Syria variety showed a considerable disease spot but could produce the highest means of yield of 91.64 ton/ha. compared to other varieties and genotypes ,hence considered to be tolerant variety. Super 2270 ,Kingstone Kalgi and genotype 8403 had the least infection in the greenhouse ,where as variety Peto early CH and genotypes 8406 ,8405 ,8407 in the field and variety Imperial with the genotype 8406 in the greenhouse had the maximum infection.In both field and greenhouse experiment varieties Super 2270 ,King stone with very low infection to the disease considered as resistant , where as genotypes 8406 with maximum disease infection were considered as susceptible genotype.

In a search for plant extracts with potent in vivo antifungal activity against various plant pathogenic fungi, the methanol extract of the Curcuma longa rhizomes effectively controlled the development of rice blast caused by Magnaporthe grisea and tomato late blight caused by phytophthora infestans. Three curcuminoids such as curcumin, demethoxycurcumin, and bisdemethoxycurcumin were purified from the methanol extract of C. longa rhizomes as antifungal principles.

Norwalk virus (NV) is an important agent of epidemic gastroenteritis, and an oral subunit vaccine shows potential for protection. Recombinant Norwalk virus (rNV) capsid protein expressed in plants assembles virus-like particles (VLPs) that are orally immunogenic in mice and humans. In this article we examine rNV expression in tomato and potato using a plant-optimized gene, and test the immunogenicity of dried tomato fruit and potato tuber fed to mice. The synthetic gene increased rNV expression fourfold in tomato and potato plants, which assembled VLP. Four doses of 0.4 g freeze-dried tomato fruit containing 64 μg rNV (40 μg VLPs) induced NV-specific serum IgG and mucosal IgA in >= 80% of mice, while doses of 0.8 g elicited systemic and mucosal antibody responses in all mice. Feedings of 1 g freeze-dried potato tuber containing 120 μg rNV (90 μg VLPs) were required to produce 100% responsiveness. Oxidation of phenolic compounds upon rehydration of dried tuber caused significant VLP instability, thus decreasing immunogenicity. Air-dried tomato fruit stimulated stronger immune responses than freeze-dried fruit of the same mass, perhaps by limiting the destruction of plant cell matrix and membrane systems that occurs with freeze-drying. Thus, rNV in dried transgenic tomato fruit was a more potent immunogen than that in dried potato tubers, based on the total VLPs ingested. These findings support the use of stabilized, dried tomato fruit for oral delivery of subunit vaccines.

The essential amino acid methionine is a substrate for the synthesis of S-adenosyl-methionine (SAM), that donates its methyl group to numerous methylation reactions, and from which polyamines and ethylene are generated. To study the regulatory role of methionine synthesis in tomato fruit ripening, which requires a sharp increase in ethylene production, we cloned a cDNA encoding cystathionine γ-synthase (CGS) from tomato and analysed its mRNA and protein levels during tomato fruit ripening. CGS mRNA and protein levels peaked at the “turning” stage and declined as the fruit ripened. Notably, the tomato CGS mRNA level in both leaves and fruit was negatively affected by methionine feeding, a regulation that Arabidopsis, but not potato CGS mRNA is subject to. A positive correlation was found between elevated ethylene production and increased CGS mRNA levels during the ethylene burst of the climacteric ripening of tomato fruit. In addition, wounding of pericarp from tomato fruit at the mature green stage stimulated both ethylene production and CGS mRNA level. Application of exogenous methionine to pericarp of mature green fruit increased ethylene evolution, suggesting that soluble methionine may be a rate limiting metabolite for ethylene synthesis. Moreover, treatment of mature green tomato fruit with the ethylene-releasing reagent Ethephon caused an induction of CGS mRNA level, indicating that CGS gene expression is regulated by ethylene. Taken together, these results imply that in addition to recycling of the methionine moieties via the Yang pathway, operating during synthesis of ethylene, de novo synthesis of methionine may be required when high rates of ethylene production are induced.

Integration of foliar bacterial biological control agents and plant growth promoting rhizobacteria (PGPR) was investigated to determine whether biological control of bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, and bacterial spot of tomato, caused by Xanthomonas campestris pv. vesicatoria and Xanthomonas vesicatoria, could be improved. Three foliar biological control agents and two selected PGPR strains were employed in pairwise combinations. The foliar biological control agents had previously demonstrated moderate control of bacterial speck or bacterial spot when applied as foliar sprays. The PGPR strains were selected in this study based on their capacity to induce resistance against bacterial speck when applied as seed and soil treatments in the greenhouse. Field trials were conducted in Alabama, Florida, and California for evaluation of the efficacy in control of bacterial speck and in Alabama and Florida for control of bacterial spot. The foliar biological control agent P. syringae strain Cit7 was the most effective of the three foliar biological control agents, providing significant suppression of bacterial speck in all field trials and bacterial spot in two out of three field trials. When applied as a seed treatment and soil drench, PGPR strain Pseudomonas fluorescens 89B-61 significantly reduced foliar severity of bacterial speck in the field trial in California and in three of six disease ratings in the field trials in Alabama. PGPR strains 89B-61 and Bacillus pumilus SE34 both provided significant suppression of bacterial spot in the two field trials conducted in Alabama. Combined use of foliar biological control agent Cit7 and PGPR strain 89B-61 provided significant control of bacterial speck and spot of tomato in each trial. In one field trial, control was enhanced significantly with combined biological control agents compared to single agent inoculations. These results suggest that some PGPR strains may induce plant resistance under field conditions, providing effective suppression of bacterial speck and spot of tomato, and that there may be some benefit to the integration of rhizosphere-applied PGPR and foliar-applied biological control agents.

Fecha de presentación internacional: 27.07.2005.- Titulares: Consejo Superior de Investigaciones Científicas (CSIC).- Universidad Politécnica de Valencia. | [EN]The bacterial spot caused by pathogen Pseudomonas syringae pv. tomato (P.s. tomato) is a devastating disease affecting tomato plants. The invention shows that the mere inhibition of the expression of gene Ep5C, coding an extracellular cationic peroxidase is sufficient to impart marked resistance to P.s. tomato. Said inhibition found in tomato plants provides a resistance with no need for activation of defense pathways currently described and controlled by salicylic acid and jasmonic acid. In addition the invention shows that Ep5C is repressed at the transcription level in healthy plants through the formation of a stable complex including proteins and one cis acting element identified within the 5' region of the gene promoter. Said complex is disabled in tissue infected with P.s. tomato and shows maximum expression in the gene. Thus Ep5C gene as well as its promoter provides a new genetic asset to develop plants resisting to the bacterial spot disease. | [ES]La mancha bacteriana causada por el patógeno Pseudomonas syringae pv. tomato (Es. tomato) es una enfermedad devastadora de las plantas del tomate. La invención muestra que la sola inhibición de la expresión del gen Ep5C, que codifica una peroxidasa catiónica extracelular, es suficiente para conferir una marcada resistencia a Es. tomato. Esta inhibición encontrada en las plantas de tomate produce una resistencia que no requiere la activación de las rutas de defensa descritas hasta ahora, controladas por el ácido salicílico y el ácido jasmónico. La invención demuestra además, que Ep5C está reprimido a nivel de la transcripción, en plantas sanas, por la formación de un complejo estable entre proteínas y un elemento que actúa en cis identificado dentro de la región 5' del promotor del gen. Este complejo se ve anulado en los tejidos infectados con P.s. tomato y coexiste con una expresión máxima del gen. Así, el gen Ep5C y su promotor proporciona un nuevo recurso genético para desarrollar plantas resistentes a la enfermedad de la mancha bacteriana. | Peer reviewed