Sutruedee Prathuangwong

Mode of action of AgNO3 in maximizing vase life of Dendrobium ‘Pompadour’ flowers

Abstract The effect of AgNO 3 on the vase life and bud opening of cut flowers of Dendrobium ‘Pompadour’ was investigated. AgNO 3 must be present continuously together with 8-hydroxyquinoline sulfate (HQS) and glucose in order to maximize water uptake and vase life. AgNO 3 was more effective than silver thiosulfate (STS) in controlling microbial growth and in maximizing bud opening and vase life. Bacillus sp. was found in vase water from all treatments except that containing AgNO 3 , HQS and glucose. Foliar application of AgNO 3 to the whole inflorescence did not increase vase life. Rates of ethylene production of the halved inflorescence bearing only flower buds or only open florets had no apparent relationship with vase life. This suggests that AgNO 3 in the holding solution may act as an antimicrobial agent, and not as an inhibitor of ethylene synthesis.

Role of rpfF in virulence and exoenzyme production of Xanthomonas axonopodis pv. glycines, the causal agent of bacterial pustule of soybean.

Ten strains of Xanthomonas axonopodis pv. glycines, the causal agent of bacterial pustule of soybean, which were isolated from various soybean growing regions of Thailand, produced an extracellular diffusible factor (DSF) related to a well-characterized quorum sensing molecule produced by other Xanthomonas spp. Genomic DNA of the 10 strains of X. axonopodis pv. glycines contained rpfF, a gene encoding for the biosynthesis of the DSF in X. campestris pv. campestris. The rpfF gene from one strain of X. axonopodis pv. glycines was fully sequenced, and the 289 aa product is closely related to RpfF of other Xanthomonas spp. (95 to 98% identical). Three independently generated rpfF mutants of X. axonopodis pv. glycines strain No12-2 were defective in the production of a DSF, as expected if rpfF encodes for DSF biosynthesis in X. axonopodis pv. glycines. The rpfF mutants of X. axonopodis pv. glycines exhibited reduced virulence on soybean and produced less than wild-type levels of extracellular polysaccharide and the extracellular enzymes carboxylmethylcellulase, protease, endo-beta-1,4-mannanase, and pectate lyase. Transcripts for three genes that encode for the extracellular enzymes protease, endoglucanase, and pectate lyase were at lower abundance in an rpfF mutant than in the parental strain of X. axonopodis pv. glycines. These results indicate that X. axonopodis pv. glycines produces a diffusible signal related to the DSF of X. campestris pv. campestris, which contributes to virulence and exoenzyme production by this phytopathogenic bacterium.

A Pectate Lyase Homolog, xagP, in Xanthomonas axonopodis pv. glycines Is Associated with Hypersensitive Response Induction on Tobacco.

ABSTRACT Xanthomonas axonopodis pv. glycines is the causal agent of bacterial pustule disease of soybeans. A transposon insertional mutant (KU-P-M670) of X. axonopodis pv. glycines derived from wild-type strain KU-P-34017 lost the ability to induce the hypersensitive response (HR) on tobacco and pepper but retained its HR induction capacity on cucumber, sesame, and tomato. The mutation also resulted in loss of ability to cause a potato soft rot and express pectolytic activity at pH 6.5. An approximate 1.4-kb DNA fragment carrying the transposon insertion contained a single open reading frame that showed high homology with PSTRU-3, a pectate lyase gene in X. axonopodis pv. malvacearum. Complemented KU-P-M670 regained HR induction on tobacco and also pectolytic activity. Treatment of plants with inhibitors of eukaryotic metabolism blocked HR induction by wild-type strains and by complemented KU-P-M670. The presence of the pectate lyase homolog, which we designated xagP, in 26 X. axonopodis pv. glycines strains was highly correlated with their ability to induce an HR on tobacco. To our knowledge, this is the first study indicating a role for a functional pectate lyase in induction of a plant HR.

Xanthomonas axonopodis pv. glycines Soybean Cultivar Virulence Specificity Is Determined by avrBs3 Homolog avrXg1

Three races of Xanthomonas axonopodis pv. glycines were identified on pustule disease resistant and susceptible soybean cultivars based on virulence phenotype. For race 3, an avrBs3 homolog, avrXg1 was identified that conferred resistance expressed as a hypersensitive response on resistant cultivar Williams 82. Mutations in two predicted functional domains of avrXg1 resulted in gained virulence on Williams 82 and an increase in bacterial population number on susceptible cultivars. Expression of avrXg1 in race 1, that is predicted to confer a nonspecific HR, led to virulence on susceptible cultivars Spencer and PI 520733. Expression of avrXg1 in race 2, that is predicted of carrying avrBs3-like genes, resulted in gained virulence and fitness of pathogen on both resistant and susceptible cultivars. The results demonstrate multifunctions for avrXg1 dependent on pathogen and plant genetic backgrounds.

Global Pattern of Gene Expression of Xanthomonas axonopodis pv. glycines Within Soybean Leaves

To better understand the behavior of Xanthomonas axonopodis pv. glycines, the causal agent of bacterial pustule of soybean within its host, its global transcriptome within soybean leaves was compared with that in a minimal medium in vitro, using deep sequencing of mRNA. Of 5,062 genes predicted from a draft genome of X. axonopodis pv. glycines, 534 were up-regulated in the plant, while 289 were down-regulated. Genes encoding YapH, a cell-surface adhesin, as well as several others encoding cell-surface proteins, were down-regulated in soybean. Many genes encoding the type III secretion system and effector proteins, cell wall-degrading enzymes and phosphate transporter proteins were strongly expressed at early stages of infection. Several genes encoding RND multidrug efflux pumps were induced in planta and by isoflavonoids in vitro and were required for full virulence of X. axonopodis pv. glycines, as well as resistance to soybean phytoalexins. Genes encoding consumption of malonate, a compound abundant in soybean, were induced in planta and by malonate in vitro. Disruption of the malonate decarboxylase operon blocked growth in minimal media with malonate as the sole carbon source but did not significantly alter growth in soybean, apparently because genes for sucrose and fructose uptake were also induced in planta. Many genes involved in phosphate metabolism and uptake were induced in planta. While disruption of genes encoding high-affinity phosphate transport did not alter growth in media varying in phosphate concentration, the mutants were severely attenuated for growth in soybean. This global transcriptional profiling has provided insight into both the intercellular environment of this soybean pathogen and traits used by X. axonopodis pv. glycines to promote disease.

The FTIR spectroscopy investigation of the cellular components of cassava after sensitization with plant growth promoting rhizobacteria, Bacillus subtilis CaSUT007

To evaluate the response of cassava stakes to plant growth promoting rhizobacteria, Bacillus subtilis CaSUT007, the changes in cellular compositions and phytohormone were investigated using the fourier transform infrared (FTIR) and high-performance liquid chromatography (HPLC) approach. The objective of this study was to test the hypothesis that CaSUT007 stimulates production of plant cellular components and phytohormone involved in metabolism and growth development mechanisms. Cassava stake treated with CaSUT007 or with sterile distilled water were germinated in sterile soil, after incubation for 28 days, CaSUT007 treated cassava stakes had more lateral root, longer roots, shoot length and greater biomass than the control which enhanced more than 1.3 fold of the cassavas phytohormone as indole-3-acetic acid content of non-treated control. We also focused on plant cellular composition and cassava stake tissues from the two treatments were harvested for FTIR analysis. FTIR analyses revealed that higher accumulated of lipid in response to the strain CaSUT007. The cassava stake treated with the beneficial bacteria B. subtilis strain CaSUT007 showed the higher content of the lipid content as (shown in the spectral regions of CH stretching and CH bending mode associated with cell membrane structure lipids) when compared with those of the cassava stake treated with distilled water. Our results initially demonstrated that CaSUT007 can enhance plant growth under greenhouse conditions by direct stimulation of plant lipid and phytohormone as indole-3-acetic acid production.

Hemin transported protein of Xanthomonas axonopodis pv. glycines functions on leaf colonization and virulence on soybean

Xanthomonas axonopodis pv. glycines (Xag) causes bacterial pustule disease on soybean. This bacterium is present worldwide around hot and humid growing regions such as Southeast Asia. To understand if the gene coding for hemin transport protein (hem) is involved in virulence of the pathogen in soybean, we generated a hem mutant in Xag by overlapping PCR mutagenesis. Disruption of hem significantly reduced the population size and the disease incidence when sprayed on soybean but not when injected directly to soybean. The hem mutant caused the hypersensitive response induction on tobacco as an Xag wildtype. Interestingly, the hem expression was also reduced when the Xag wildtype grow in planta. The hemin transporter protein involved in the production of extracellular polysaccharide, biofilm formation, motility and attachment but not for extracellular enzymes. This confirmed that epiphytic fitness of Xag strongly required hem functions. These results suggest that hem gene is essential for virulence of Xag on soybean during the infection process.

Effects of Bacterial Leaf Spot on Yield, Resistance, and Seedborne Infection of Sesame in Thailand

The relationship between yield loss and bacterial leaf spot severity caused by Pseudomonas syringae pv. sesami in 14 sesame cultivars (cv’s) was evaluated under greenhouse and field conditions. Plants were sprayed with a mixture of five locally obtained strains. The average yield losses from all cv’s tested were 1.30 and 0.92% under greenhouse and field experiments for every 1% increment of disease severity, respectively. Based on the amount of infected leaf area, cv Col 55 was resistant while cv’s Buriram, Dam-Damg-Phitsanuiok, Col 30/nw-3, Nakhonsawan, and Roi-et 1 were susceptible. Other cv’s showed an intermediate reaction. The pathogen was seedborne in all cv’s tested, and the mean percentage of infected seed was 62%. The causal bacterium was found in the seed coat but not associated with the embryo or endosperm. The results showed that a seed health program would be useful for controlling the disease.

Efficiency of new plant growth promoting rhizobacteria on corn diseases control

The efficacy of two plant growth promoting rhizobacteria (PGPR) strains including Bacillus subtilis TU-Orga1 and Pseudomonas fluorescens TU-Orga2 obtained from rice rhizosphere against naturally occurring diseases as well as their capacity to improve crop yield of sweet corn cv. Insee2 was studied. TU-Orga1 was significantly greater in inhibition of Acidovorax avenae subsp. avenae (Aaa) and Erwinia chrysanthemi pv. zeae (Ecz), caused bacterial leaf streak and stalk rot of corn, respectively by antibiosis. Greenhouse experiments using TU-Orga1 and TU-Orga2 treatments increased highest salicylic acid accumulation in corn leaves with 7.85 and 6.98 mg g-1 fresh weight, respectively to protect Ecz infection. Each PGPR strain was single applied in the field through seed treatment and 3-foliar-spray-intervals at 14, 21, and 28 days after planting. Two PGPR treatments resulted in reduced severity of all diseases and increased yields when compared with the control treatment. There were differences among the treatments in that the highest level of disease suppression of bacterial stalk rot resulted with treatments TU-Orga1 (P = 0.05), whereas TU-Orga2 showed the highest level of disease suppression of bacterial leaf streak and sugarcane mosaic virus and provided significantly greater marketable yield increases than the other treatments. This illustrates the potential of these new biocontrol agents to suppress multiple diseases. They could become a component of an integrated program or an organic farming for corn disease management. Key words: Plant growth promoting rhizobacteria (PGPR), Acidovorax avenae subsp. avenae, Erwinia chrysanthemi pv. zeae, SCMV, systemic acquired resistant.

Approach to Control Measure of Sesame Bacterial Leaf Spot in Thailand

A preliminary seed treatment with both physical and chemical methods for efficient control of sesame bacterial leaf spot (caused by Pseudomonas syringae pv. sesami) in the laboratory indicated that either 35 min duration In 50 °C hot water or 30 min soaking in aqueous solution of 75 ml/I streptomycin fitted to our test criteria of 25 or 100% disease reduction with 79.4 or 88.6% seed germination, respectiveiy. Additional experiments with foliar sprays on sesame (KU7118) under greenhouse and field conditions were also carried out. The results from two locations tested revealed that all bactericide and antibiotic treatments could reduce the disease incidence compared to non-treated controls. In the field experiments however, the best control of bacterial leaf spot in two growing seasons was achieved by 10 times spraying of 250 ml/L streptomycin at 7-day intervals starting 7 days after sesame emergence giving 72.5% increased yield when compared to that of non-treated controis. The data obtained would seemingly be the method of choice for controlling the disease.