Bacterial Wilt Infection Research Articles

Natural resistance-associated macrophage proteins are involved in tolerance to heavy metal Cd2+ toxicity and resistance to bacterial wilt of peanut (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) is one of the most important oil and industrial crops. However, heavy-metal pollution and frequent soil diseases, poses a significant threat to the production of green and healthy peanuts. Herein, we investigated the effects of heavy metal Cd2+ toxicity to the peanuts, and screened out two peanut cultivars H108 and YZ 9102 with higher Cd2+-tolerance. RNA-seq revealed that Natural resistance-associated macrophage proteins (NRAMP)-like genes were involved in the Cd2+ stress tolerance in H108. Genome-wide identification revealed that 28, 13 and 9 Nramp-like genes existing in the A. hypogaea, A. duranensis and A. ipaensis, respectively. The 50 peanut NRAMP genes share conserved architectural characters, and they were classified into two groups. Expressions of AhNramps, particularly AhNramp4, AhNramp12, AhNramp19, and AhNramp25 could be greatly induced by not only cadmium toxicity, but also copper and zinc stresses. The expression profiles of AhNramp14, AhNramp16 and AhNramp25 showed significant differences in the H108 (resistance) and H107 (susceptible) under the infection of bacterial wilt. In addition, we found that the expression profiles of AhNramp14, AhNramp16, and AhNramp25 were greatly up- or down-regulated by the application of exogenous salicylic acid, methyl jasmonate, and abscisic acid. The AhNramp25, of which expression was affected by both heavy metal toxicity and bacterial wilt infection, were selected as strong candidate genes for peanut stress breeding. Our findings will provide an additional information required for further analysis of AhNramps involved in tolerance to heavy metal toxicity and resistance to bacterial wilt of peanut.

Ralstonia solanacearum differentially modulates soil physicochemical properties and rhizospheric bacteriome of resistant and susceptible tobacco cultivars

Ralstonia solanacearum is a devastating soilborne pathogen which poses significant yield and economic losses to tobacco production globally. The impact of R. solanacearum on rhizosphere bacteriome and soil physicochemical characteristics in resistant and susceptible tobacco cultivars is poorly understood. This study aims to determine the effect of R. solanacearum on soil physicochemical parameters and rhizosphere bacteriome of resistant (K326) and susceptible (Hongda) tobacco cultivars at various growth stages. Results demonstrated that the contents of available potassium and phosphorus, as well as soil pH were significantly increased in K326 soils (CK and T2) compared with Hongda (T1) after 21, 42, and 63 days post-inoculation (dpi) of R. solanacearum except for available nitrogen which showed an opposite trend. The qPCR results showed a significant decrease in R. solanacearum population in rhizosphere of K326 (T2) compared to the Hongda (T1) at 21 and 63 dpi than that after 42 dpi. The rhizosphere bacteriome analysis through 16S rRNA amplicon sequencing revealed that rhizosphere bacterial community composition was significantly different between two tobacco cultivars (Hongda and K326) and this effect was more prominent after 63 dpi (93 days after post-transplantation), suggesting that each cultivar recruits a unique set of bacterial communities. There was no obvious difference observed in the rhizosphere bacteriome of CK (K326) and T2 (K326), which might be attributed to the same genetic makeup and inherent resistance of K326 to bacterial wilt infection. Analysis of co-occurrence networks revealed that the microbial network in T1 (Hongda) was more complex than those in T2 (K326) and CK (K326), while the networks in CK and T2 were almost identical. The present research highlights the time-course relationship between environmental factors and rhizosphere bacteriome of tobacco cultivars showing different levels of resistance against R. solanacearum. Conclusively, studying the plant-soil-microbe interaction system in susceptible and resistant tobacco cultivars may enable us to develop effective integrated disease control plans for the healthy production of tobacco crops.

Bacterial wilt and dissemination factors in tomato production areas of Benin, West Africa

Bacterial wilt caused by Ralstonia solanacearum is a major constraint for tomato production in Benin. Through this research, the distribution and incidence of bacterial wilt and its dissemination factors in tomato fields were assessed. Identification of isolates were based on morphological characterization of colonies, hypersensitivity, and pathogenicity tests. Dissemination factors were analysed through a binomial logit model. Bacterial wilt was widespread in all Benin’s eight Agro-Ecological Zones (AEZs), and mostly severe in AEZs dominated by ferralitic soils where its highest incidence was up to 100%. Other variables such as post-harvest crop residues plowed into soils, rotation practices, use of mineral fertilizer, watering practices, use of the same tools in many fields, positively influenced the probability of bacterial wilt infection in tomato fields. Dissemination of R. solanacearum is more favorited by women agricultural practices than men. Farmer’s awareness on good agricultural practices could help to reduce the pressure of the disease.

Dose-response relationship of Ralstonia solanacearum and potato in greenhouse and in vitro experiments.

Ralstonia solanacearum is the causative agent of bacterial wilt of potato and other vegetable crops. Contaminated irrigation water contributes to the dissemination of this pathogen but the exact concentration or biological threshold to cause an infection is unknown. In two greenhouse experiments, potted potato plants (Solanum tuberosum) were exposed to a single irrigation with 50mL water (non-invasive soil-soak inoculation) containing no or 102 - 108 CFU/mL R.solanacearum. The disease response of two cultivars, Kondor and HB, were compared. Disease development was monitored over a three-month period after which stems, roots and tubers of asymptomatic plants were analyzed for latent infections. First wilting symptoms were observed 15 days post inoculation in a plant inoculated with 5x109 CFU and a mean disease index was used to monitor disease development over time. An inoculum of 5x105 CFU per pot (1.3x102 CFU/g soil) was the minimum dose required to cause wilting symptoms, while one latent infection was detected at the lowest dose of 5x102 CFU per pot (0.13 CFU/g). In a second set of experiments, stem-inoculated potato plants grown in vitro were used to investigate the dose-response relationship under optimal conditions for pathogen growth and disease development. Plants were inoculated with doses between 0.5 and 5x105 CFU/plant which resulted in visible symptoms at all doses. The results led to a dose-response model describing the relationship between R.solanacearum exposure and probability of infection or illness of potato plants. Cultivar Kondor was more susceptible to brown-rot infections than HB in greenhouse experiments while there was no significant difference between the dose-response models of both cultivars in in vitro experiments. The ED50 for infection of cv Kondor was 1.1x107 CFU. Results can be used in management strategies aimed to reduce or eliminate the risk of bacterial wilt infection when using treated water in irrigation.

Genome-wide identification of long intergenic non-coding RNAs for Ralstonia solanacearum resistance in tomato (Solanum lycopersicum).

There is growing evidences indicating that long intergenic ncRNAs (lincRNAs) play key roles in plant development and stress responses. To research tomato lincRNA functions during the interaction between tomato and Ralstonia solanacearum, RNA-seq data of tomato plants inoculated with R. solanacearum was analyzed. In this study, 315 possible lincRNAs were identified from RNA-seq data. Then 23 differentially expressed lincRNAs between tomato plants inoculated with R. solanacearum and control were identified and a total of 171 possible target genes for these differentially expressed lincRNAs were predicted. Through GO and KEGG analysis, we found that lincRNA might be involved in jasmonic acid and ethylene signaling pathways to respond to tomato bacterial wilt infection. Furthermore, lincRNA may also be involved in regulating the expression of AGO protein. Subsequently, analysis of expression patterns between differentially expressed lincRNAs and adjacent mRNAs by qRT-PCR revealed that part of lincRNAs and their possible target genes exhibited positive correlation. Taken together, these results suggest that lincRNAs play potential roles in tomato against R. solanacearum infection and will provide fundamental information about the lincRNA-based plant defense mechanisms.

Combining ability of tomato inbred lines to bacterial wilt resistance

Tomato is one of the most important crops worldwide. Bacterial wilt (BW), caused by Ralstonia spp., is a major disease for tomato production around the world, especially in tropical and subtropical regions. Currently in Brazil, only commercial hybrids are available as resistant rootstocks for use in infested areas, and we lack information regarding resistance to aggressive strains. Thus, the aims of this work were to estimate combining abilities of five tomato inbred lines and hybrids and to identify resistant genotypes for using as rootstocks resistant to Ralstonia solanacearum biovar 2, phylotype II, one of the most aggressive strains in Brazil. Combining abilities for BW resistance were assessed through full diallel crossings among five tomato inbred lines without reciprocals. The experiment was carried out in a greenhouse, in a complete randomized blocks design, using 15 genotypes (hybrids and parents). Additive genetic effects showed to be the most important for controlling bacterial wilt. The inbred line Hawaii 7996 exhibited the highest general combining ability among the five parents assessed. The hybrid Hawaii 7996 × Rodade was the best crossing in terms of resistance and specific combining ability, which was greater than those of all other hybrids. Although Hawaii 7996 remains as a major source for BW resistance, further researches are needed to better understand the resistance dynamics, seeking to develop hybrids with transgressive segregations and more stable resistance against aggressive strains and thrive under environmental conditions highly favorable to bacterial wilt infection.

Insect and Diseases Resistance in Tomato Entries

The study was conducted with 75 tomato entries at the farm of Olericulture Division, Horticulture Research Centre (HRC), Bangladesh Agricultural Research Institute (BARI), Gazipur, Bangladesh during the winter season of 2020-21 to evaluate insect and disease reaction. Among the various insect and diseases of tomatoes, the late blight, TYLCV, bacterial wilt infection and leaf miner, fruit borer infestation are most common in Bangladesh. The TYLCV infection was observed 0% to 27% infection, while 47 entries showed zero percent infection. The range of bacterial wilt infection was 0% to 10% and zero percent infection was observed in 62 entries. In case of leaf miner infestation and fruit borer infestation, the range was 0% to 43% and 0% to 10%, respectively. Considering tolerance to late blight, TYLCV, bacterial wilt infection and leaf miner, fruit borer infestation, fruit size, fruit shape, plant growth nature, cluster nature of fruit, type of fruit ten entries AVTO 1010, AVTO 1706, AVTO 1713, AVTO 1829, AVTO 1909, AVTO 1911, AVTO 1915, AVTO 1921, AVTO 1954 and SLA 011 were found zero percent late blight, TYLCV, bacterial wilt infection and leaf miner, fruit borer infestation. So, these ten entries can be selected for disease and insect tolerant tomato varieties development as well as developing disease and insect tolerant hybrid tomato varieties.

Evaluation of Trichodermaspp., Pseudomonasfluorescens and Bacillus subtilis for biological control of Ralstonia wilt of tomato.

Background:Ralstonia spp. is a major pathogenic microbe for tomato, which invades the roots of diverse plant hosts and colonizes xylem vessels causing wilt, especially in tropical, subtropical and warm-temperate regions. Ralstonia spp. produces several virulence factors helping it to invade the plant's natural defense mechanism. Native isolates of Trichoderma spp., Pseudomonas fluorescens and Bacillus subtilis can be used as biocontrol agents to control the bacterial wilt and combined application of these beneficial microbes can give better results. Methods: Bacterial wilt infection in the field was identified by field experts and the infected plant part was used to isolate Ralstonia spp. in CPG media and was positively identified. Subsequently, the efficacy of the biocontrol agents was tested and documented using agar well diffusion technique and digital microscopy. 2ml of the microbial concentrate (10 9 cells/ml) was mixed in one liter of water and was applied in the plant root at the rate of 100 ml per plant as a treatment method. Results: It was observed that the isolated Trichoderma spp. AA2 and Pseudomonas fluorescens PFS were most potent in inhibiting the growth of Ralstonia spp. , showing ZOI 20.67 mm and 22.33 mm, respectively. Digital microscopy showed distinct inhibitory effect on the growth and survival of Ralstonia spp . The results from the field data indicated that Trichoderma spp. and Pseudomonas fluorescens alone were able to prevent 92% and 96% of the infection and combination of both were more effective, preventing 97% of infection. Chemical control methods prevented 94% of infection. Bacillus subtilis could only prevent 84 % of the infection. Conclusions: Antagonistic effect against Ralstonia spp. shown by native isolates of Trichoderma spp. and P. fluorescens manifested the promising potential as biocontrol agents. Combined application gave better results. Results shown by Bacillus subtilis were not significant.

Colonization of Eggplant by Endophytic Bacteria Antagonistic to Ralstonia solanacearum, the Bacterial Wilt Pathogen

Bacterial wilt caused by the vascular pathogen Ralstonia solanacearum is a major constraint for cultivation of eggplant (Solanum melongena L.) in the state of Goa, India. Three strains of endophytic bacteria isolated from xylem sap of eggplant and antagonistic to R. solanacearum were evaluated for colonization of eggplant cv. Agassaim under greenhouse conditions. Results suggest that rifampicin resistant mutants XB1R (Agrobacterium tumefaciens), XB99R (Enterobacter sp.) and XB177R (Bacillus cereus) exhibit varying degree of colonization of endophytic tissues and rhizosphere soil of eggplant. XB177R colonized eggplant most efficiently and systemically from rhizosphere (6.5 Log cfu g−1) to leaves (4.34 Log cfu g−1) until 30 days after inoculation. Green fluorescent protein tagged XB177 colonized rhizoplane, cortex and xylem vessels of eggplant grown under greenhouse conditions. Studies on changes in the population of XB177R during bacterial wilt infection suggested that its endophytic population of 5.48 log cfu g−1 fresh weight and rhizosphere population of 6.18 log cfu g−1 of rhizosphere soil was necessary to control bacterial wilt in eggplant. Further, it is reported that pre-treatment of eggplant is an important pre-requisite for effective wilt prevention by the antagonistic bacteria. The present study demonstrates the importance of plant colonization ability of antagonistic bacteria for bacterial wilt control.

Evaluation of Trichoderma spp., Pseudomonas fluorescens and Bacillus subtilis for biological control of Ralstonia wilt of tomato

Background:Ralstoniaspp. is a major pathogenic microbe for tomato, which invades the roots of diverse plant hosts and colonizes xylem vessels causing wilt, especially in tropical, subtropical and warm-temperate regions.Ralstoniaspp.produces several virulence factors helping it to invade the plant’s natural defense mechanism. Native isolates ofTrichoderma spp., Pseudomonas fluorescensandBacillus subtiliscan be used as biocontrol agents to control the bacterial wilt and combined application of these beneficial microbes can give better results.Methods:Bacterial wilt infection in the field was identified by field experts and the infected plant part was used to isolateRalstoniaspp.in CPG media and was positively identified. Subsequently, the efficacy of the biocontrol agents was tested and documented using agar well diffusion technique and digital microscopy. 2ml of the microbial concentrate (109cells/ml) was mixed in one liter of water and was applied in the plant root at the rate of 100 ml per plant as a treatment method.Results:It was observed that the isolatedTrichodermaspp. AA2 andPseudomonas fluorescensPFS were most potent in inhibiting the growth ofRalstoniaspp.,showing ZOI 20.67 mm and 22.33 mm, respectively. Digital microscopy showed distinct inhibitory effect on the growth and survival ofRalstoniaspp.The results from the field data indicated thatTrichodermaspp. andPseudomonas fluorescensalone were able to prevent 92% and 96% of the infection and combination of both were more effective, preventing 97% of infection. Chemical control methods prevented 94% of infection.Bacillus subtiliscould only prevent 84 % of the infection. Conclusions:Antagonistic effect againstRalstonia spp.shown by native isolates ofTrichodermaspp. andP. fluorescensmanifested the promising potential as biocontrol agents. Combined application gave better results. Results shown byBacillus subtiliswere not significant.

Evaluation of Trichoderma spp., Pseudomonas fluorescens and Bacillus subtilis for biological control of Ralstonia wilt of tomato

Background: Ralstonia spp. is a major pathogenic microbe for tomato, which invades the roots of diverse plant hosts and colonizes xylem vessels causing wilt, especially in tropical, subtropical and warm-temperate regions. Ralstonia spp. produces several virulence factors helping it to invade the plant’s natural defense mechanism. Native isolates of Trichoderma spp., Pseudomonas fluorescens and Bacillus subtilis can be used as biocontrol agents to control the bacterial wilt and combined application of these beneficial microbes can give better results. Methods: Bacterial wilt infection in the field was identified by field experts and the infected plant part was used to isolate Ralstonia spp. in CPG media and was positively identified. Subsequently, the efficacy of the biocontrol agents was tested and documented using agar well diffusion technique and digital microscopy. 2ml of the microbial concentrate (10 9 cells/ml) was mixed in one liter of water and was applied in the plant root at the rate of 100 ml per plant as a treatment method. Results: It was observed that the isolated Trichoderma spp. AA2 and Pseudomonas fluorescens PFS were most potent in inhibiting the growth of Ralstonia spp. , showing ZOI 20.67 mm and 22.33 mm, respectively. Digital microscopy showed distinct inhibitory effect on the growth and survival of Ralstonia spp . The results from the field data indicated that Trichoderma spp. and Pseudomonas fluorescens alone were able to prevent 92% and 96% of the infection and combination of both were more effective, preventing 97% of infection. Chemical control methods prevented 94% of infection. Bacillus subtilis could only prevent 84 % of the infection. Conclusions: Antagonistic effect against Ralstonia spp. shown by native isolates of Trichoderma spp. and P. fluorescens manifested the promising potential as biocontrol agents. Combined application gave better results. Results shown by Bacillus subtilis were not significant.

Comparison between gold nanoparticles and FITC as the labelling in lateral flow immunoassays for rapid detection of Ralstonia solanacearum

ABSTRACT Early prevention and monitoring of Ralstonia solanacearum (Rs) on nightshade is extremely critical for potent prevention and treatment of bacterial wilt disease. We developed two kinds of lateral flow immunochromatographic strip (LFICS) using gold nanoparticles (GNPs) and fluorescein isothiocyanate (FITC) for rapid diagnosis of plant bacterial wilt, caused by Ralstonia solanacearum (Rs), which both were based on double antibody sandwich method. Three monoclonal antibodies (McAb) highly specific to Rs were obtained by cell fusion and screening after four times of immunization with the strain GIM 1.76. Under optimized conditions, the limit of detection (LOD) with GNPs and FITC were 104 colony forming units per millilitre (CFU/mL) and 106 CFU/mL respectively, then the range detection correspondingly were 104–109 CFU/mL and 106–109 CFU/mL. On top of that, the developed immunoassay could be used for spot and point-of-care testing Rs on tomato seed, ginger seed, casuarina seed and display no cross-reaction with 43 other phytopathogenic strains that also could infect plants so as to cause plants diseases. These results demonstrated that we sucessfully developed two simple, effective and sensitive strips for monitoring bacterial wilt infection. Meanwhile, this is the first report about LFICS labelled by FITC for rapid detection of Rs, and it is the first time conformed that the sensitive of the LFICS with GNPs is significantly higher than FITC.

Evaluation of Trichodermaspp., Pseudomonas fluorescence and Bacillus subtilis for biological control of Ralstonia wilt of tomato.

Background:Ralstonia solanacearum is the major bacterial disease in tomato, which invades the roots of diverse plant hosts and colonizes xylem vessels causing wilt, especially in tropical, subtropical and warm-temperate regions. R. solanacearum produces several toxins helping it to invade the plant's natural defense mechanism. Native isolates of Trichoderma spp., Pseudomonas fluorescence and Bacillus subtilis can be used as biocontrol agents to control the bacterial wilt and combined application of these beneficial microbes can give better results. Methods: Bacterial wilt infection in the field was identified by field experts and the infected plant part was used to isolate Ralstonia solanacearum in CPG media and was positively identified. Subsequently, the efficacy of the biocontrol agents was tested and documented using agar well diffusion technique and digital microscopy. 2ml of the microbial concentrate (10 9 cfu/ml) was mixed in one liter of water and was applied in the plant root at the rate of 100 ml per plant as a treatment method. Results: It was observed that the isolated Trichoderma spp. AA2 and Pseudomonas fluorescence PFS were most potent in inhibiting the growth of R. solanacearum, showing ZOI 20.67 mm and 22.33 mm, respectively. Digital microscopy showed distinct inhibitory effect on the growth and survival of R. solanacearum. The results from the field data indicated that Trichoderma spp. and Pseudomonas fluorescence alone were able to prevent 92% and 96% of the infection and combination of both were more effective, preventing 97% of infection. Chemical control methods prevented 94% of infection. Conclusions: Results showed the bio-efficacy of the native isolates. The various level of antagonistic effect against R. solanacearum shown by all 13 isolates, including the results shown by native isolates in the field, manifested the promising potential of the biocontrol agents, like Trichoderma and Pseudomonas against controlling the bacterial wilt infection.

Growth and yield of non-grafted and grafted tomato (Solanum lycopersicum L.) cultivars grown in two cultivation systems

Tomato is a high-value vegetable crop because of its broad culinary uses and nutritional values. Its production however is inhibited in some areas with soil-borne disease problems, particularly bacterial wilt. This study was conducted to evaluate the yield, bacterial wilt infection, and profitability of non-grafted and grafted tomato cultivars planted in open field and protected cultivation. Protected cropping of tomato increased number of marketable fruits and total yield by approximately 2 times fold than those grown in open field. Grafting of the cultivars to eggplant significantly reduced bacterial wilt infection such that increased survival among plants resulted to higher yield than non-grafted. The cultivar with biggest fruits was from ‘Kingkong’ while season red had the smallest and other cultivars were in average size of the two. Grafted ‘Diamante max’ cultivar yielded the highest followed by ‘Season red’. Net return of protected cropping tomato was higher than in open field. Non-grafted tomato grown in bacterial wilt infected area was unprofitable. On the other hand, grafting and protected resulted in better yield, gross income and a positive net return. Season red produced the highest income in the open field while Diamante max for protected cultivation. The use of grafted tomato and protective structure are strongly recommended for planting in areas known to have high bacterial wilt.

Growth and yield of tomato (Solanum lycopersicum) as influenced by different soil organic amendments and types of cultivation

Tomato is one of the most profitable crops in the Philippines and is extensively cultivated throughout the world. However, its production faces different pest and disease problems, particularly bacterial wilt which greatly reduces yield. Two separate studies were conducted simultaneously in a single factor experiment arranged in randomized complete block design (RCBD) with three (3) replications. The studies were conducted to evaluate the effects of the different soil organic amendments on the growth and yield of tomato in the open field (Study I) and under protective structure (Study II) with the following treatments: control, cabbage waste, carbonized rice hull, chicken dung, hagonoy, wedelia, and wild sunflower. Protective structure grown plants had better protection against detrimental heavy rain and strong light intensity, thus had better performance in terms of lower bacterial wilt infection and weed incidence, higher percentage survival, enhanced flowering, and a higher yield than those grown in the open field. On the other hand, only the weight of marketable fruits and total yield were enhanced by the application of the different soil organic amendments. All amendments had similar effects but were superior than the control. Protected cultivation gave a higher net return than the open field. In particular, sunflower amended plants under structure were the most profitable, by almost 8 times compared to the open field.

Proteomic analysis of salicylic acid enhanced disease resistance in bacterial wilt affected chilli (Capsicum annuum) crop

Salicylic acid (SA) is an important endogenous chemical signal that plays a key role in enhancing plant defense responses. Exogenous application of 0.5 mM SA for 3 days enhanced resistance to bacterial wilt (BW) disease (by reduction in disease incidence level upto 64% under greenhouse conditions) without any detrimental effect on plant growth. To understand the dynamics of protein in SA-primed chilli during BW infection, proteomic approach using 2DE-SDS PAGE was performed. Proteomic analysis revealed 25 differentially expressed proteins (which were more prominent in SA primed-challenge inoculated chilli samples), of which 20 were successfully identified by Nano-LC MS/MS analysis. The differential expression pattern revealed that proteins associated with stress and defense, energy and metabolism, protein synthesis, protein destination and storage and transcription related were upregulated indicating the involvement of SA induced disease resistance in chilli seedlings. This suggests the complexity of the proteome and inter-connected pathways responsible for SA induced resistance in chilli. Correlation in the differential expression of catalase and EF-1A from proteomic as well as semiquantitative RT-PCR suggests this probable use as biomarkers in screening susceptibility of chilli cultivars for wilt disease. Findings from this study will serve as basis for designing disease-management strategies based on resistance conferred by SA, which could applicable to other biotic stress affected staple crops.

An Early Detection of Latent Infection of Ralstonia solanacearum on Potato Tubers

Ralstonia solanacearum is not only a soil-borne pathogen but also a seedborne bacterial pathogen. National Seed Agency require that seed-source (G0) must free from bacterial wilt infection (0%) in potato seed certification process. This study aimed to determine an early and accurately detection of Ralstonia solanacearum in potato seedsource production (G0) on aeroponics cultivation system, which previously treated with microbial antagonists and artificialy infected with Ralstonia solanacearum. Seed potatoes were obtained from the previous study. Antagonist isolates NS01, S04, G06, and NG02 were applied separately in aeroponic system in nutrient solution, then artificially infected with R. solanacearum. These four isolates is quite effective inhibite R. solanacearum infection in potato aeroponic system with the intensity attach of 5, 7, 9 and 21% respectively, compared to 100% in control. Although the symptoms of wilt disease were appeared in plants, but the seeds did not show typical symptoms. In the positive control that inoculated with R. solanacearum without antagonists, revealing immediately wilt and death of plants, 14 days after inoculation. The result of polymerace chain reaction (PCR) using OLI1 and Y2 primers on tubers without antagonist with 100% disease incidence showed, that all of the tuber have positive results indicated by the appearance of DNA bands in the size of 287 bp. From visually healthy seeds sample resulted from antagonist treatment, only few of them have positive result and mostly other tubers showed negative result. This means that the role of antagonists on suppression of wilt disease, cannot totally guarantee the tubers free from latent infection of R. solanacearum.

Identification of Suitable Planting Method for Potato + Maize Intercropping System in the Hill of Eastern Nepal

Field experiments to identify suitable planting method under potato + maize system in the high hill (2200 m) of eastern Nepal Sindhuwa, Dhankuta, was conducted during 2000 and 2001 seasons for the potato variety Hale and maize variety Ganesh 1. Of the different planting methods tested, significantly the highest yield of potato (15.5 t/ha) was recorded from the alternate row planting followed by recommended practice and flat row planting. Early emergence (by 7-12 days) was in farmers' practice, whereas uniform plants (1-5 scale) observed in flat row and double row planting. Maize did not follow this trend. Double row and farmer's practice favored good ground coverage (80-95%) by potato plants, which attained height from 49.8cm (farmer's practice) to 56.8 cm (flat row). Number of main stems/plant was higher in all treatments, except farmer's practice. Similar trend was followed in tuber numbers. Maturity of crops did not depend on planting methods. Final stand of potato ranged between 46.9 (alternate row) and 68.6 thousand/ha (farmer's practice). Late blight and bacterial wilt infection was higher in the farmers' practice. The height of maize plants was significantly differed between sole cropping (220 cm), which yielded higher followed by alternate row (183 cm) and flat row plantings. Gross income from maize and potato was higher in flat row planting. The data revealed that alternate row and flat row planting methods were superior over the common farmers' practice and the recommended practice, so the identified planting methods were recommended.Nepal Agric. Res. J. Vol. 8, 2007, pp. 113-119DOI: http://dx.doi.org/10.3126/narj.v8i0.11604

Disease Interactions in a Shared Host Plant: Effects of Pre-Existing Viral Infection on Cucurbit Plant Defense Responses and Resistance to Bacterial Wilt Disease

Both biotic and abiotic stressors can elicit broad-spectrum plant resistance against subsequent pathogen challenges. However, we currently have little understanding of how such effects influence broader aspects of disease ecology and epidemiology in natural environments where plants interact with multiple antagonists simultaneously. In previous work, we have shown that healthy wild gourd plants (Cucurbita pepo ssp. texana) contract a fatal bacterial wilt infection (caused by Erwinia tracheiphila) at significantly higher rates than plants infected with Zucchini yellow mosaic virus (ZYMV). We recently reported evidence that this pattern is explained, at least in part, by reduced visitation of ZYMV-infected plants by the cucumber beetle vectors of E. tracheiphila. Here we examine whether ZYMV-infection may also directly elicit plant resistance to subsequent E. tracheiphila infection. In laboratory studies, we assayed the induction of key phytohormones (SA and JA) in single and mixed infections of these pathogens, as well as in response to the feeding of A. vittatum cucumber beetles on healthy and infected plants. We also tracked the incidence and progression of wilt disease symptoms in plants with prior ZYMV infections. Our results indicate that ZYMV-infection slightly delays the progression of wilt symptoms, but does not significantly reduce E. tracheiphila infection success. This observation supports the hypothesis that reduced rates of wilt disease in ZYMV-infected plants reflect reduced visitation by beetle vectors. We also documented consistently strong SA responses to ZYMV infection, but limited responses to E. tracheiphila in the absence of ZYMV, suggesting that the latter pathogen may effectively evade or suppress plant defenses, although we observed no evidence of antagonistic cross-talk between SA and JA signaling pathways. We did, however, document effects of E. tracheiphila on induced responses to herbivory that may influence host-plant quality for (and hence pathogen acquisition by) cucumber beetles.

Detection of bacterial wilt infection caused by Ralstonia solanacearum in potato (Solanum tuberosum L.) through multifractal analysis applied to remotely sensed data

Potato bacterial wilt, caused by the bacterium Ralstonia solanacearum race 3 biovar 2 (R3bv2), affects potato production in several regions in the world. The disease becomes visually detectable when extensive damage to the crop has already occurred. Two greenhouse experiments were conducted to test the capability of a remote sensing diagnostic method supported by multispectral and multifractal analyses of the light reflectance signal, to detect physiological and morphological changes in plants caused by the infection. The analysis was carried out using the Wavelet Transform Modulus Maxima (WTMM) combined with the Multifractal (MF) analysis to assess the variability of high-resolution temporal and spatial signals and the conservative properties of the processes across temporal and spatial scales. The multispectral signal, enhanced by multifractal analysis, detected both symptomatic and latently infected plants, matching the results of ELISA laboratory assessment in 100 and 82%, respectively. Although the multispectral method provided no earlier detection than the visual assessment on symptomatic plants, the former was able to detect asymptomatic latent infection, showing a great potential as a monitoring tool for the control of bacterial wilt in potato crops. Applied to precision agriculture, this capability of the remote sensing diagnostic methodology would provide a more efficient control of the disease through an early and full spatial assessment of the health status of the crop and the prevention of spreading the disease.