Plant Growth Retardants Research Articles

Studies on the effects on growth and antioxidant responses of two marine microalgal species to uniconazole

Uniconazole, as a plant growth retardant, can enhance stress tolerance in plants, possibly because of improved antioxidation defense mechanisms with higher activities of superoxide dismutase (SOD) and peroxidase (POD) enzymes that retard lipid peroxidation and membrane deterioration. These years much attention has been focused on the responses of antioxidant system in plants to uniconazole stress, but such studies on aquatic organism are very few. Moreover, no information is available on growth and antioxidant response in marine microalgae to uniconazole. In this paper, the growth and antioxidant responses of two marine microalgal species, Platymonas helgolandica and Pavlova viridis, at six uniconazole concentrations (0–15 mg L−1) were investigated. The results demonstrated that 3 mg L−1 uniconazole could increase significantly chlorophyll a and carbohydrate contents of P. helgolandica (P < 0.05). Higher concentrations (≥12 mg L−1) of uniconazole could inhibit significantly the growth, dry weight, chlorophyll-a and carbohydrate contents of P. helgolandica and P. viridis (P < 0.05). Uniconazole caused a significant increase in lipid peroxidation production (MDA) at higher concentrations (≥ 9 mg L−1). The activities of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT) were enhanced remarkably at low concentrations of uniconazole. However, significant reduction of SOD and CAT activities was observed at higher concentrations of uniconazole.

Induction of dwarfing in bougainvillea cv Mahara by use of growth regulators

Bougainvillea (Bougainvillea spectabilis) is a very popular evergreen landscape plant in tropical and subtropical areas. Because of the vigorous growth habit, bougainvillea needs a lot of labor-intensive pruning when being used as a potted plant. PGRs could be alternatives to frequent pruning on bougainvillea to reduce labor costs. But, little research has been carried out on the use of plant growth retardants (PGRs) for controlling the growth and flowering. The present investigations were carried out to study the effect of growth regulators mainly; paclobutrazol, daminozide and maleic hydrazide on bougainvillea cv Mahara to induce dwarfing. The experiment was laid out in completely Randomized Block Design with 11 treatments and four replications. The rooted cuttings of bougainvillea were planted on 7 July 2012 in earthen pot (10” diameter) containing potting media consisting of sand: soil: FYM in a ratio of 1:2:1. The plants were pruned to a uniform height of 10+2 inches on 3rd September 2012. The growth regulators were applied in the form of foliar spray or drench and data was recorded for vegetative and flowering traits. After 14 weeks, it was observed that there was a significant reduction in plant height and plant spread when paclobutrazol was applied in the form of spray or drench. However, application of maleic hydrazide inhibited the plant growth, on the contrary increased plant height and plant spread over control (Distilled water spray) was observed with 5000 ppm Daminozide (B-9) application. Drench application of paclobutrazol @30 ppm resulted in highest flower index as compared to other treatments.

Suppression of transgene RNA silencing in transgenic Arabidopsis thaliana by a mild strain of Cucumber mosaic virus

The ability of Cucumber mosaic virus (CMV) subgroup II strain CMV-KT to suppress RNA silencing via posttranscriptional gene silencing (PTGS) was determined using Turnip mosaic virus (TuMV)-resistant transgenic Arabidopsis thaliana (TuR-At) carrying TuMV coat protein (CP) transgenes. CMV-KT induced only slight growth retardation in TuR-At plants, but no dwarf or mosaic symptoms, while subgroup I strain Y (CMV-Y) caused severe symptoms. Expression of the RNA-silenced TuMV-CP transgene resumed and produced TuMV-CP in either CMV-KT- or CMV-Y-infected TuR-At plants, indicating that the RNA silencing of the TuMV-CP gene was suppressed. Challenge inoculation experiments revealed that RNA silencing of the TuMV-CP transgene by CMV-KT infection is suppressed mostly in young developing leaves, but not in mature leaves, of TuR-At plants. These results demonstrated that transgene-derived virus resistance in transgenic Arabidopsis plants can be compromised by even a mild strain of CMV infection.

Effects of Gibberellin Biosynthetic Inhibitors on Oil, Secoisolaresonolodiglucoside, Seed Yield and Endogenous Gibberellin Content in Flax

Flax (Linum usitatissimum L.) has been used for the edible oil in Korea. The evaluate the effect of plant growth retardants on flaxseed yield, oil content, and gibberellin level, chloromequat chloride (CMC), paclobutrazol (PBZ), and prohexadione-Ca (PHC) were used as plant growth retardants in this study. These plant growth retardants were foliar-sprayed to flax plant at 55 days after seeding. The concentrations of each plant growth retardant were as followed: CMC 250, 500, 1000 ppm, PBZ 40, 80, 160 ppm and PHC 500, 1000, 2000 ppm. PHC treatment to forming bolls was more stimulated than CMC and PBZ. The highest ripened seed rate was observed in PHC treatment at 2000ppm. The high see yields were obtained in PHC treatment following PBZ and CMC, in turn. Seed yield that significantly increased in PBZ and PHC was found to be increased 12.4 ~ 23.9% as compared to the control. The PHC showed higher flaxseed production and oil yield than that of CMC and PBZ. The results obtained in the present study suggest that higher concentration of plant growth retardant (PHC) increased flaxseed yield and oil content. The optimal concentration of PHC treatment was observed in 2000 ppm. It concludes that the foliar application of PHC 2000 ppm may be useful for the increasing oil and higher seed production in flax plants.

PEG-mediated osmotic stress induces premature differentiation of the root apical meristem and outgrowth of lateral roots in wheat.

Water stress is one of the major environmental stresses causing growth retardation and yield loss of plants. In the past decades, osmotic adjustment, antioxidant protection, and stomatal movement have been extensively studied, but much less attention has been paid to the study of root system reprogramming to maximize water absorption and survival under water stress. Here, it is shown that polyethylene glycol (PEG)-simulated mild and moderate osmotic stress induced premature differentiation of the root apical meristem (RAM). It is demonstrated that RAM premature differentiation is a conserved adaptive mechanism that is widely adopted by various plants to cope with osmotic stress simulated by PEG 8000, and the occurrence of RAM premature differentiation is directly related to stress tolerance of plants. It is shown that the osmotic stress-induced premature differentiation caused growth cessation of primary roots allowing outgrowth of lateral roots. This work has uncovered a key mechanism for controlling the plastic development of the root system by which plants are capable of survival, growth, or reproduction under water stress.

Drought Deceit — Can Artificial Stress Signals Be Used as Plant Growth Retardants?

Long-distance signals moving from roots to shoots in response to drought lead to reduced vegetative growth. The hypothesis that the artificial manipulation of one of these signals, alkalization of the xylem sap, can reduce problems of excessive growth in arable crops, has been tested in oilseed rape (canola; Brassica napus L.) and barley (Hordeum vulgare L.). Experiments with detached shoots have shown that both crop species can respond to artificial alkaline xylem sap with reduced leaf expansion. Applications of alkalizing agents to intact plants, either as pH buffer sprays or as solid calcium carbonate, have successfully retarded leaf expansion. The retardation has, however, either been inconsistent (possibly through difficulty in penetrating the variable epicuticular wax layer) or of very short duration (possibly through efficient buffering of internal pH). It can be inferred from these results that the greatest commercial potential for alkalizing growth retardants may be with high-value, short-duration crops that do not have a thick layer of epicuticular wax, and using either multiple applications or persistent formulations.

Cellular Mechanisms in Higher Plants Governing Tolerance to Cadmium Toxicity

Cadmium (Cd) is an inorganic mineral in the earth's crust. Cadmium entry into the environment occurs through geogenic and anthropogenic sources. Industrial activities including mining, electroplating, iron and steel plants, and battery production employ Cd during their processes and often release Cd into the environment. When disseminated into soil, Cd can be detrimental to agro-ecosystems because it is relatively mobile and phytotoxic even at low concentrations. Cadmium's phytotoxicity is due to reductions in the rate of transpiration and photosynthesis and chlorophyll concentration resulting in retardation of plant growth, and an alteration in the nutrient concentration in roots and leaves. In response to Cd toxicity, plants have developed protective cellular mechanisms such as synthesis of phytochelatins and metallothioneins, metal compartmentalization in vacuoles, and the increased activity of antioxidant enzymes to neutralize Cd-induced toxicity. While these direct protective mechanisms can help alleviate Cd toxicity, other indirect mechanisms such as microelements (zinc, iron, manganese, and selenium) interfering with Cd uptake may decrease Cd concentration in plants. This comprehensive review encompasses the significance of Cd, portals of contamination and toxicity to plants, and implications for crop production. Various mitigation strategies with the beneficial effects of zinc, iron, manganese, and selenium in activating defence mechanisms against Cd stress are discussed. Furthermore, this review systematically identifies and summarises suitable strategies for mitigating Cd-induced toxicity in plants.

English

Effect of banana bunchy top virus (BBTV) on morpho-physiological characteristics of banana (Musa sp.) cv., Basrai plants was assessed. Healthy and BBTV infected samples of banana were collected from its open fields and micro-propagated aseptically. These plantlets were established in wire-house for three months. Presence of BBTV was confirmed by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Micro-propagation efficiency of BBTV-infected plants was observed in less than healthy plants under in-vitro as well as in-vivo. Significant reduction in plant height, fresh weight (F wt) and dry weight (D wt) of leaf was observed in BBTV infected plants. A co-relation of peroxidase (POX) activity was observed with total carotenoids that increased in BBTV infected plants, while chlorophyll contents decreased significantly. Nitrate reductase activity also decreased with increase in proline contents in BBTV-stresses plants (p&lt;0.05). Meanwhile, reducing sugars also increased but not-significantly. Bunchy top virus infection in banana therefore resulted in alteration of growth related physiological traits that led to retardation of plant growth. &nbsp; Key words: Ex-vitro, Musa sp., micro-propagation, photosynthetic pigments, BBTV, peroxidases, total proteins, reducing sugars, cell size.

Effect of two plant growth retardants on steviol glycosides content and antioxidant capacity in Stevia (Stevia rebaudiana Bertoni)

Two greenhouse experiments were conducted to study the effect of two plant growth retardants, Chlorocholine chloride (CCC) and Paclobutrazol (PBZ), on growth, Steviol glycosides (SVglys) content and antioxidant capacity in Stevia (Stevia rebaudiana Bertoni). Five concentrations of CCC (0, 250, 500, 750 and 1,000 ppm) and PBZ (0, 6, 12, 18 and 24 ppm) with three replications were applied to Stevia plants as treatments based on completely randomized design. CCC was sprayed on Stevia shoots, but PBZ was applied as a drench. The obtained results showed that CCC reduced plant height but improved leaf and stem dry weight, especially with 750 ppm concentration. Total SVgly content and consequently SVglys yield were significantly reduced by CCC application, and 1,000 ppm of CCC concentration was more effective than other treatments. PBZ had no effect on Stevia height while it significantly enhanced stem and dry weight at 12 ppm. Moreover, PBZ remarkably increased total SVglys contents, SVglys yield, and Rebaudioside A/Stevioside ratio. Total antioxidant capacity significantly varied with CCC and PBZ and the highest activity was obtained with 1,000 and 12 ppm of CCC and PBZ, respectively. The results of these experiments indicated that, although CCC and PBZ are plant growth retardants and act as anti-gibberellins, only CCC reduced plant height and SVglys production in Stevia. On the contrary, PBZ at 12 ppm concentration, improved Stevia growth, SVglys production, and antioxidant capacity.

Effect of Some Plant Growth Retardants on Vegetative Growth, Spurs and Fruiting of 'Le - Conte' Pear Trees

This study was carried out during two successive seasons 2012 and 2013 on 5 -years old 'Le Conte' pear trees grown under two types of soil. Selected trees were sprayed by some plant growth retardants such as, Paclobutrazol (Cultar) at 200 & 300 ppm conc., Mepiquat chloride at 150 & 250 ppm, Succinic acid at 150 & 300 ppm and control. Treatments were sprayed with the specified solutions till run off at three times: before flowering, after fruit set stage and two months after fruit set. That was at early March, mid April and mid May. Herein, fruit quality and vegetative growth parameters were determined at the time of harvest. Results showed that significantly increased fruit set and improved fruit quality compared with the control. It should be noted that the best results were recorded in sandy soil compared with the clay soil. The highest concentration in all treatments improved fruit set, yield and fruit quality.

Cloning of Three Antiporter Genes from Arabidopsis and Rice for Over-Expressing Them in Farmer Popular Tomato Varieties of Bangladesh

Salinity is one of the most critical environmental problems, which causes plant growth retardation by disturbing intracellular ion homeostasis. The Na+/H+ antiporter plays an important role in resistance to salt stress by sequestering Na+ in exchange for H+ across the vacuolar membranes. In the current study, the coding regions of two Arabidopsis antiporters (AtNHX1 and AtNHX2) and one rice antiporter (OsNHX1) were amplified by target specific PCR. PCR amplicons were first cloned into pENTR/D-TOPO and later recombined with a destination vector (pK7WG2.0) by LR reaction. Positive clones were selected by PCR, restriction digestion (RD) and sequencing. They were then transformed into Agrobacterium tumefaciens (LBA4404 strain) for subsequent transformation of farmer popular tomato varieties.

Cottonseed yield and its quality as affected by mineral fertilizers and plant growth retardants

The increase in the population in Egypt makes it imperative to explore promising approaches to increase food supply, including protein and oil, to meet the needs of the Egyptian people. Cotton is the principal crop of Egyptian agriculture, it is grown mainly for its fiber, but cottonseed products are also of economic importance. Cottonseed is presently the main source of edible oil and meal for livestock in Egypt. Economic conditions in modern agriculture demand high crop yields in order to be profitable and consequently meet the high demand for food that comes with population growth. Oil crop production can be improved by development of new high yielding varieties, and the application of appropriate agronomic practices. There is limited information about the most suitable management practice for application of N, P, K, Zn, Ca and PGRs in order to optimize the quantity and quality of oil and protein of cottonseed. In maximizing the quantity and quality of a crop’s nutritional value in terms of fatty acids and protein, field experiments were conducted to investigate the effect of nitrogen, phosphorus, potassium, foliar application of zinc and calcium, the use of plant growth retardants (Pix, Cycocel or Alar), on cottonseed, protein, oil yields, and oil properties of Egyptian cotton. From the findings of this study, it seems rational to recommend that application of N, P, K, foliar application of Zn and Ca, the use of PGRs (Pix, Cycocel or Alar), could bring about better impact on cottonseed yield, seed protein content, oil and protein yields, oil refractive index, unsaponifiable matter, and unsaturated fatty acids in comparison with the ordinary cultural practices adopted by Egyptian cotton producers.

Discovery of a new lead compound for plant growth retardants through compound library screening

Discovery of a new lead compound for plant growth retardants through compound library screening

The effect of the plant growth retardants AMO-1618 and CCC on the synthesis of ribonucleic acids and proteins in triticale embryos during the initial phase of germination

Triticale var. Grado caryopses were subjected to imbibition and germination in the presence of the growth retardants, AMO-1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidinecarboxylate methyl chloride) and CCC (2-chloroethyl)-trimethylammonium chloride) at the following concentrations, 3 x 10&lt;sup&gt;-4&lt;/sup&gt; M and 10&lt;sup&gt;-3&lt;/sup&gt; M. These compounds exerted a very strong inhibitory effect on the initiation of germination processes, growth of embryos and the germination capacity of the caryopses. At the concentration of 10&lt;sup&gt;-3&lt;/sup&gt; M, AMO-1618 showed an especially strong effect, lowering the germination capacity of the caryopses to about 50%. It was also shown that both retardants are decidedly more effective on the germination of whole, intact caryopses than on that of isolated embryos. During the very earliest hours of germination, these retardants already inhibited RNA synthesis. The participation of the polyribosome fraction in the total ribosome fraction of embryos in the control sample after 24 hrs of germination of caryopses equalled about 70%, while in the samples treated with CCC (10&lt;sup&gt;-3&lt;/sup&gt; M)- about 57%, in the samples treated with AMO-1618 (10&lt;sup&gt;-3&lt;/sup&gt; M) about 35%,. The inhibition of incorporation of &lt;sup&gt;14&lt;/sup&gt;C-amino acids into ribosomal proteins in the polyribosome fraction was in the case of CCC about 13%, while in the samples treated with AMO-1618, about 55%. In the monosome fraction (80S), the inhibition by CCC was about 23%, whereas in the samples treated with AMO-1618 it reached around 73%. From this data it is evident that the studied retardants have a significant influence on the synthesis of ribonucleic acids as well as on ribosome proteins. These results also suggest the existance of another mechanism, aside from that of inhibition of gibberellin biosynthesis, inhibiting the growth and development of cells. The high percentage of ribosome subunits in the samples treated with CCC, in comparison with controls and samples treated with AMO-1618, points to different mechanisms by which these two compounds affect protein biosynthesis.

Effects of Hydrogels on Soil Moisture and Growth of &amp;lt;i&amp;gt;Cajanus cajan&amp;lt;/i&amp;gt; in Semi Arid Zone of Kongelai, West Pokot County

Studies on the effects of hydrogels on soil amendments, moisture conservation and growth of Cajanus cajan in arid and semi-arid lands were carried out. Seedlings of C. cajan were established both in the nursery and in the field with and without hydrogels. In the field, three replications were used with three levels of hydrogels concentration (7 g, 11 g, and 15 g). Control seedlings were established in soils without hydrogels. In the nursery, root collar diameters and heights were measured every two weeks up to eight weeks. Seedlings established without hydrogels in the nursery were transplanted into field soils with none, 7 g, 11 g and 15 g of hydrogels. Root collar diameters and heights were again measured every month for three months. In addition, soil was collected randomly once every month from the base of each seedling and analyzed for soil moisture using standard laboratory procedures. All data were subjected to analysis of variance. The results show that growth in both the height and root collar diameter of the species was significantly different at the three levels of hydrogels. This suggests that use of hydrogels retards plant growth in nursery soils but improves growth in the field. Hydrogels increased soil moisture volume from 8.3% to 10% in H15g level of hydrogels under C. cajan after transplanting. It was concluded that hydrogels do not contribute to growth of seedlings in the nursery but they do so after transplanting. Hydrogels increase soil moisture in the soil, so they are recommended for use in semi-arid lands to boost the survival and growth of seedlings.

Combined Effects of Mepiquat Chloride and Trinexapac-ethyl on Oil Content, Lignan, Seed Yield and Endogenous Gibberellins in Flax (Linum usitatissimum L.)

Flax (Linum usitatissimum L.) has been used for the only edible oil in Korea. We carried out the field experiment in order to investigate the possibly combined effects of mepiquat chloride (MC) and trinexapac-ethyl (TE) on oil composition, lignan content, seed yield and endogenous gibberellins content of flax cultivar. Plant growth retardants mepiquat chloride (300 and 600 ppm) and trinexapac-ethyl (100, 200 and 300 ppm) were foliar-sprayed to flax plant at 50days after seeding. The plant height was decreased in the combination of mepiquat chloride 600 ppm with trinexapac-ethyl 100, 200 and 300 ppm. Mepiquat chloride treatment combined with trinexapac-ethyl observed the highest response on seed yield, followed by mepiquat chloride 300 ppm with trinexapac-ethyl 100 ppm, mepiquat chloride 300 ppm with trinexapac-ethyl 200 ppm and mepiquat chloride 300 ppm with trinexapac-ethyl 300 ppm. Lignan content was increased in all of the combination treatments. It concludes that the combination of mepiquat chloride 300 ppm with trinexapac-ethyl 300 ppm will be useful to increasing oil and lignan content in flax plants.

Plant Growth Retardation and Conserved miRNAs Are Correlated to Hibiscus Chlorotic Ringspot Virus Infection

Virus infection may cause a multiplicity of symptoms in their host including discoloration, distortion and growth retardation. Hibiscus chlorotic ringspot virus (HCRSV) infection was studied using kenaf (Hibiscus cannabinus L.), a non-wood fiber-producing crop in this study. Infection by HCRSV reduced the fiber yield and concomitant economic value of kenaf. We investigated kenaf growth retardation and fluctuations of four selected miRNAs after HCRSV infection. Vegetative growth (including plant height, leaf size and root development) was severely retarded. From the transverse and radial sections of the mock and HCRSV-infected kenaf stem, the vascular bundles of HCRSV-infected plants were severely disrupted. In addition, four conserved plant developmental and defence related microRNAs (miRNAs) (miR165, miR167, miR168 and miR171) and their respective target genes phabulosa (PHB), auxin response factor 8 (ARF8), argonaute 1 (AGO1) and scarecrow-like protein 1 (SCL1) displayed variation in expression levels after HCRSV infection. Compared with the mock inoculated kenaf plants, miR171 and miR168 and their targets SCL1 and AGO1 showed greater fluctuations after HCRSV infection. As HCRSV upregulates plant SO transcript in kenaf and upregulated AGO1 in HCRSV-infected plants, the expression level of AGO1 transcript was further investigated under sulfite oxidase (SO) overexpression or silencing condition. Interestingly, the four selected miRNAs were also up- or down-regulated upon overexpression or silencing of SO. Plant growth retardation and fluctuation of four conserved miRNAs are correlated to HCRSV infection.

The effects of flurprimidol concentrations and application methods on Ornithogalum saundersiae Bak. grown as a pot plant

Ornithogalum saundersiae is an ornamental bulb plant originating from South Africa that is mostly grown for cut flowers. The aim of the study was to assess the possibility of producing O. saundersiae as a pot plant using flurprimidol. A retardant in the form of the Topflor 015 preparation was used at concentrations of 15 and 30 mgE–dm-3 as a pre-plant bulb soak, a soil drench or a foliar spray. Retardant applied as a foliar spray at a concentration of 30 mg·dm-3 inhibited plant growth most effectively (by 52.5%), caused flowering delay and reduced the inflorescence and flower diameter. The plants obtained from the bulbs soaked in the retardant solution at a concentration of 30 mg·dm-3 had the smallest plant diameter and the shortest leaves. The use of flurprimidol resulted plants with an increased relative chlorophyll content. Retardant used as a foliar spray increased the stomatal conductance, regardless of the solution concentration. Key words: Geophytes, plant growth retardants, relative chlorophyll content (SPAD), stomatal conductance (gs), Topflor.

Responses of Root Growth and Nitrogen Transfer Metabolism to Uniconazole, a Growth Retardant, during the Seedling Stage of Soybean under Relay Strip Intercropping System

Relay strip intercropping of soybean has been widely developed in the southwest of China to secure China's soybean production. However, due to the shading from maize, soybean plants are thin and have a poor root system. Uniconazole is a plant-growth retardant that could enhance root vigor; increase root length, root volume, and root dry weight; and affect nitrogen (N) metabolism. To understand the effects of uniconazole on the root growth and N-transfer metabolism of soybean seedlings under relay strip intercropping, the changes in some morphological characteristics of root, dry-matter weight, root vigor, nitrate (NO3 −)-N, ammonium (NH4 +)-N, and amino acid of xylem sap after seed treatment with uniconazole powder (0, 2, 4, and 8 mg kg−1 seed) were investigated. Main root length, total lateral root lengths, first lateral root numbers, root nodule numbers, root vigor together with bleeding sap, bleeding sap–top ratio, root dry weight, and root/shoot ratio were increased, indicating uniconazole improved soybean root system in relay strip intercropping. Uniconazole powder treatment could increase NO3 −-N, NH4 +-N, and total amino acid of xylem sap, to increase the potential of leaf and root N reduction and assimilation, and increase of leaf and root N contents. Thus, results suggested that uniconazole treatment can improve root growth and N transfer mechanism of soybean to support its further growth.

Xanthomonas Filamentous Hemagglutinin-Like Protein Fha1 Interacts with Pepper Hypersensitive-Induced Reaction Protein CaHIR1 and Functions as a Virulence Factor in Host Plants

Pathogens have evolved a variety of virulence factors to infect host plants successfully. We previously identified the pepper plasma-membrane-resident hypersensitive-induced reaction protein (CaHIR1) as a regulator of plant disease- and immunity-associated cell death. Here, we identified the small filamentous hemagglutinin-like protein (Fha1) of Xanthomonas campestris pv. vesicatoria as an interacting partner of CaHIR1 using yeast two-hybrid screening. Coimmunoprecipitation and bimolecular fluorescence complementation experiments revealed that Fha1 specifically interacts with CaHIR1 in planta. The endocytic tracker FM4-64 staining showed that the CaHIR1-Fha1 complex localizes in the endocytic vesicle-like structure. The X. campestris pv. vesicatoria Δfha1 mutant strain exhibited significantly increased surface adherence but reduced swarming motility. Mutation of fha1 inhibited the growth of X. campestris pv. vesicatoria and X. campestris pv. vesicatoria ΔavrBsT in tomato and pepper leaves, respectively, suggesting that Fha1 acts as a virulence factor in host plants. Transient expression of fha1 and also infiltration with purified Fha1 proteins induced disease-associated cell death response through the interaction with CaHIR1 and suppressed the expression of pathogenesis-related (PR) genes. Silencing of CaHIR1 in pepper significantly reduced ΔavrBsT growth and Fha1-triggered susceptibility cell death. Overexpression of fha1 in Arabidopsis retarded plant growth and triggered disease-associated cell death, resulting in altered disease susceptibility. Taken together, these results suggest that the X. campestris pv. vesicatoria virulence factor Fha1 interacts with CaHIR1, induces susceptibility cell death, and suppresses PR gene expression in host plants.