Pseudomonas syringae pv. syringae induces systemic resistance to Pyricularia oryzae in rice

Systemic resistance was induced to Pyricularia aryzae in rice by inoculation of the first leaf with the hypersensitive response causing bacterium, Pseudomonas syringae pv. syringae. Lesions caused by Pyricularia oryzae were decreased in number and size by 85% and 50%, respectively, in systemically protected leaves. Increased resistance was associated with the deposition of a dark brown material around sites of Pyricularia oryzae infection. The systemically acquired resistance was not associated with an increase in the activities of phenylalanine ammonia lyase, coniferyl alcohol dehydrogenase, peroxidase, β-1, 3-glucanase or chitinase after the challenge inocculation with Pyricularia oryzae. The levels of these enzymes were elevated by local exposure to Pseudomonas syringae pv. syringae or Pyricularia oryzae, but were not systemically induced. These data suggest that the physiological changes which occur during induced resistance in rice are different from those correlated with induced resistance in tobacco or cucumber.     

Identification and characterization of a tospovirus causing chlorotic ringspots on <Emphasis Type="Italic">Phalaenopsis</Emphasis> orchids

A putative virus-induced disease showing chlorotic ringspots on leaves of Phalaenopsis orchids has been observed in Taiwan for several years. A virus culture, 91-orchid-1, isolated from a Phalaenopsis orchid bearing chlorotic ringspot symptoms was established in Chenopodium quinoa and Nicotiana benthamiana, and characterized serologically and biologically. The virus reacted slightly with the antiserum of Watermelon silver mottle virus (WSMoV) but not with those of Tomato spotted wilt virus (TSWV), Impatiens necrotic spot virus (INSV) and Groundnut ringspot virus (GRSV). Isometric particles measuring about 70–100 nm were observed. Inoculation with isolated virus was conducted to confirm that 91-orchid-1 is the causal agent of chlorotic ringspot disease of Phalaenopsis orchids. To determine the taxonomic relationships of the virus, the conserved region of L RNA and the complete nucleocapsid gene (N gene) were cloned and sequenced. The sequence of conserved region of L RNA shares 83.8, 82.5, 64.4 and 64.9% nucleotide identities and 96.5, 97.7, 67.3 and 67.6% amino acid identities with those of Peanut bud necrosis virus (PBNV), WSMoV, TSWV and INSV, respectively, indicating that 91-orchid-1 is a tospovirus related to WSMoV. The complete nucleotide sequence of the N gene determined from a cDNA clone was found to be 828 nucleotides long encoding 275 amino acids. Sequence analyses of the N gene showed that 91-orchid-1 is an isolate of Capsicum chlorosis virus (CaCV) which has been reported to infect tomato and capsicum plants in Australia and Thailand. 91-orchid-1 is therefore designated as CaCV-Ph. To our knowledge, this is the first formal report of a tospovirus infecting Phalaenopsis orchids.     

PCR cloning, DNA sequencing and phylogenetic analysis of a xylanase gene from the phytopathogenic fungusAscochyta pisiLib.

A gene encoding a xylanase,xyl1, was isolated from the phytopathogenic fungusAscochyta pisiLib. by PCR cloning using degenerate primers. DNA sequence analysis revealed an open reading frame of 736 bp interrupted by an intron of 55 bp. The ORF encodes a predicted protein of 227 amino acids. The precise splicing site of the intron was identified from the sequence of a PCR product obtained using the same degenerated primers on a cDNA template. The cDNA product and a northern blot demonstrated that the gene is transcribed into mRNA when the fungus is cultured in media containing xylan as sole carbon source. The Neighbour-Joining method using the Clustal W(1.5) program demonstrated that theA. pisixylanase is a member of the family 11 glycosyl hydrolases, and that this family represents at least five phylogenetically consistent groups. The family 11 glycosyl hydrolases can be linked with family 10 glycosyl hydrolyses through bifunctional enzymes fromRuminococcus flavefaciensand, to a lesser extentNeocallimastix patriciarum.     

Characterization of the first two viruses described from wild populations of hammer orchids (Drakaea spp.) in Australia

Sequences representing the genomes of two distinct virus isolates infecting wild plants of two members of the genus Drakaea (hammer orchids) in Western Australia are described. The virus isolated from Drakaea livida has a bipartite genome of 4490 nt (RNA1) and 2905 nt (RNA2) that shares closest sequence and structural similarity to members of the genus Pecluvirus, family Virgaviridae, described from legumes in the Indian subcontinent and West Africa. However, it differs from pecluviruses by lacking a P39 protein on RNA2 and having a cysteine‐rich protein gene located 3′ of the triple gene block protein genes. It is the first peclu‐like virus to be described from Australia. The name Drakaea virus A is proposed (DVA; proposed member of the family Virgaviridae, genus unassigned). The second virus isolate was identified from Drakaea elastica, a species classed as endangered under conservation legislation. The genome sequence of this virus shares closest identity with isolates of Donkey orchid symptomless virus (DOSV; proposed member of the order Tymovirales, family and genus unassigned), a species described previously from wild Caladenia and Diuris orchids in the same region. These viruses are the first to be isolated from wild Drakaea populations and are proposed to have an ancient association with their orchid hosts.     

Putative new species of the genus Dickeya as major soft rot pathogens in Phalaenopsis orchid production

Bacterial soft rots are a serious limitation to the production of orchids and other horticultural plants. Here, the characterization of causative bacteria isolated from Phalaenopsis orchids showing symptoms, from a commercial production site, is reported. The most commonly isolated bacteria were identified as Dickeya spp. Partial sequencing of 16S rDNA, fliC and dnaX showed diversity among the isolates and divided the isolates into two groups, with greatest similarity to previously reported undefined Dickeya lineages from orchids (UDL‐3 and UDL‐4). Two isolates (B16, S1) were sequenced using next‐generation sequencing, which has provided draft genomes of these two isolates for further studies (Ali? et al., 2015 ). Newly developed fliC‐based lineage‐specific quantitative real‐time PCR assays were used to distinguish among the lineages and to assess their relative abundances in diseased tissues. Virulence and aggressiveness comparison tests in vivo on Phalaenopsis orchids, potato plants and witloof chicory leaves indicated high virulence and extreme maceration potential of these novel Dickeya isolates, compared to a reference panel of other Dickeya spp. Pantoea cypripedii (formerly Pectobacterium cypripedii), which has previously been reported as a soft rot pathogen of orchids, was not detected, and isolates obtained from culture collections did not cause symptoms on artificially infected Phalaenopsis orchids.     

<Emphasis Type="Italic">Odontoglossum ringspot virus</Emphasis> causing flower crinkle in <Emphasis Type="Italic">Phalaenopsis</Emphasis> hybrids

A new disorder exhibiting flower crinkle on Phalaenopsis orchids bearing white flowers has been observed in Taiwan, China and Japan for several years. This disorder decreased the flower longevity and was considered as a physiological syndrome. The objective of this study was to identify and characterize the real causal agent of this new Phalaenopsis disorder. Five plants of Phalaenopsis hybrids “V3” (Phal. Yukimai × Phal. Taisuco Kochdian) with flower crinkle symptoms were collected and tested by enzyme-linked immunosorbent assay with antisera against 18 viruses. The extract of leaves and flowers from one diseased plant (96-Ph-16) reacted positively only to antiserum against Odontoglossum ringspot virus (ORSV), while those from the other four plants (96-Ph-7, 96-Ph-17, 96-Ph-18 and 96-Ph-19) reacted positively to the antisera against ORSV and Cymbidium mosaic virus (CymMV). Five ORSV isolates, one each from flowers of those five diseased Phalaenopsis orchids, were established in Chenopodium quinoa. A CymMV culture was isolated from the flowers of one of the ORSV/CymMV mix-infected Phalaenopsis orchids (96-Ph-19). To determine the causal agent of the flower crinkle disease, healthy Phalaenopsis seedlings were singly or doubly inoculated with the isolated ORSV and/or CymMV. Results of back inoculation indicated that ORSV is the sole causal agent of the crinkle symptom on petals of Phalaenopsis orchid. The CP gene of the ORSV isolates from this study shared 97.3–100% nucleotide identity and 96.2–100% amino acid identity with those of 41 ORSV isolates available in GenBank. This is the first report demonstrating ORSV as the sole virus causing flower crinkle disease on Phalaenopsis orchids.     

Induced accessibility and enhanced inaccessibility at the cellular level in barley coleoptiles. XIV. Evidence for elicitor(s) and suppressor(s) of host inaccessibility from Erysiphe graminis

The release of elicitors and suppressors by Erysiphe graminis, the powdery mildew pathogen of barley, was investigated by microscopy in combination with micromanipulation. The elicitors enhance inaccessibility whereas the suppressors prevent the action of the elicitors. Conidia were deposited onto barley coleoptiles and incubated for intervals that varied from 1-8 h. These conidia were termed the inducer conidia since they determined whether their presence would induce the cells of the host to become inaccessible to subsequent inoculations with the fungus. At specified intervals after inoculation the conidial germlings were removed from cells with a micromanipulator. The coleoptiles were then incubated for an additional 8 h after which, a new germling of the fungus was transferred to the same cell from which the inducer germling had been removed. This new germling was called the challenge germling since it was used to determine if it could challenge the host cell to express either induced accessibility or enhanced inaccessibility. The ability of these challenge germlings to penetrate the barley host cell was then assessed after they had been incubated on the cell for an additional 19 h. This allowed the determination of whether inaccessibility had been enhanced in the host. Inaccessibility was enhanced in the host only when the inducer conidia were incubated on host cells for more than 7 h. Scanning electron microscopy revealed that these challenge germlings did not penetrate into the host cell. Thus, enhanced inaccessibility had occurred. The results indicate that the E. graminis germling released a material that enhanced the inaccessibility of the barley host cells. We refer to this material as an elicitor. The transfer of a challenge germling to a coleoptile was made at various times after the removal of the inducer germling from the tissue. This allowed us to determine that more than 2 h is required for the enhancement of inaccessibility after the removal of the inducer germling from the tissue. If a germling, either the same or a different germling, was left on the host cell continuously, then enhanced inaccessibility did not occur. Rather, susceptibility occurred. These results suggest that the E. graminis germling releases a material that suppresses inaccessibility. We refer to this material as a suppressor. Thus, the results indicate that E. graminis conidia release an elicitor that enhances inaccessibility of barley cells and that they also release a suppressor that prevents enhanced inaccessibility in the barley cell.     

Histochemical and chemical evidence for lignin accumulation during the expression of resistance to leaf rust fungi in wheat

Levels of individual phenolic acids were examined in primary leaves of wheat (Triticum aestivum) after inoculation with avirulent and virulent strains of the leaf rust fungus (Puccinia recondita f. sp. tritici) at stages when previous work had shown fungal and host cells to be affected by expression of the Lr20 or Lr28 alleles for resistance. The predominant phenolic acid, ferulic acid, as well as p-coumaric and syringic acids were detected in primary leaves in both unbound and bound forms. They were not detected in germinating urediniospores of either rust strain. Levels of unbound phenolic acids changed little in response to infection. In Lr28-bearing leaves inoculated with an avirulent strain, increased concentrations of bound phenolic acids and three other unidentified compounds were observed about 4 h after many single or small groups of cells had undergone hypersensitive collapse. In an Lr20-bearing cultivar, levels of bound phenolic acids fell in leaves inoculated with either a virulent or avirulent rust strain. Coniferyl aldehyde and coniferyl alcohol were not detected in healthy or inoculated leaves of either wheat cultivar. Attempts to affect expression of resistance by application of inhibitors of phenylalanine ammonia-lyase were not successful and both wheat cultivars remained resistant to avirulent rust strains. The bound phenolic acids which accumulate in cells undergoing a hypersensitive response may play a role in resistance of Lr28-bearing wheat to the leaf rust fungus.     

Identification and characterization of a potyvirus causing chlorotic spots on <Emphasis Type="Italic">Phalaenopsis</Emphasis> orchids

A putative virus-induced disease showing chlorotic spots on leaves of Phalaenopsis orchids was observed in central Taiwan. A virus culture, phalaenopsis isolate 7-2, was isolated from a diseased Phalaenopsis orchid and established in Chenopodium quinoa and Nicotiana benthamiana. The virus reacted with the monoclonal antibody (POTY) against the potyvirus group. Potyvirus-like long flexuous filament particles around 12–15 × 750–800 nm were observed in the crude sap and purified virus preparations, and pinwheel inclusion bodies were observed in the infected cells. The conserved region of the viral RNA was amplified using the degenerate primers for the potyviruses and sequence analysis of the virus isolate 7-2 showed 56.6–63.1% nucleotide and 44.8–65.1% amino acid identities with those of Bean yellow mosaic virus (BYMV), Beet mosaic virus (BtMV), Turnip mosaic virus (TuMV) and Bean common mosaic virus (BCMV). The coat protein (CP) gene of isolate 7-2 was amplified, sequenced and found to have 280 amino acids. A homology search in GenBank indicated that the virus is a potyvirus but no highly homologous sequence was found. The virus was designated as Phalaenopsis chlorotic spot virus (PhCSV) in early 2006. Subsequently, a potyvirus, named Basella rugose mosaic virus isolated from malabar spinach was reported in December 2006. It was found to share 96.8% amino acid identity with the CP of PhCSV. Back-inoculation with the isolated virus was conducted to confirm that PhCSV is the causal agent of chlorotic spot disease of Phalaenopsis orchids in Taiwan. This is the first report of a potyvirus causing a disease on Phalaenopsis orchids.     

Effect of 4-amino-6-methyl-3-phenylamino-l,2,4-triazin-5(4H)-one on the lignification process catalysed by peroxidase from lupin (lupinus albus)

The molecular action of herbicides with a triazine structure, such as atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) and metribuzin (4-amino-6-tert-butyl-3-methylthio-1,2,4-triazin-5(4H)-one), has been related to their inhibition of the electron carrier system between chloroplastic photosystems II and I. This report provides evidence that 4-amino-6-methyl-3-phenylamino-1,2,4-triazin-5(4H)-one, a recently synthesised triazine, structurally analogous to metribuzin, causes a powerful inhibition of the cell-wall lignification catalysed by peroxidase from lupin. The two reactions involved in this lignification process are: oxidative polymerisation of coniferyl alcohol and the generation of hydrogen peroxide at the expense of NADH oxidation.     

Plant amphipathic proteins delay the hypersensitive response caused by harpinPssandPseudomonas syringaepv.syringae

Harpin_Pssfrom the plant pathogenPseudomonas syringaepv.syringaeis a proteinaceous elicitor that induces a hypersensitive response (HR) in non-host plants. The plant products which recognize harpin_Pssin the triggering of the HR are not yet known. According to the elicitor-receptor model, we hypothesize that an exogenous cell membrane receptor infiltrated into the intercellular space will interfere with the interaction between harpin_Pssand the putative receptor. We demonstrate a plant amphipathic protein (AP1) which can postpone the HR induced by harpin_Pssas well asP. syringaepv.syringae.AP1 was extracted by solubilizing proteins from healthy leaves in the non-polar n-octanol buffer followed by a polar Tris buffer. The amphipathic extracts were then further separated by gel filtration and anion exchange chromatography to obtain highly purified AP1. Similar proteins can be extracted from cotton, tomato, and sweet pepper. The N-terminal amino acid sequence of AP1 is conserved among cotton, tomato, and sweet pepper. The postponement of the harpin_Pss-mediated HR was characterized as a competitive dosage-dependent pattern of AP1. An analysis of the bacterial population development indicates that the effect of AP1 on the postponement of bacteria-mediated HR was attributed to the suppression of bacterial growth during the early stages of the HR. The time course analysis of the infiltration indicates that the postponement of HR resulted from the co-interaction between AP1 and the bacteria. Based on these results, we suggest that the postponement of bacteria-mediated HR is due to the interference of the interaction between harpin_Pssand the putative receptor in the plant. Our research provides a new approach to elucidating the role that plants may play in the nonhost response caused by pathogens.     

Bacterial black spot caused by <Emphasis Type="Italic">Burkholderia andropogonis</Emphasis> on <Emphasis Type="Italic">Odontoglossum</Emphasis> and intergeneric hybrid orchids

A new bacterial black spot disease was observed on Odontoglossum, Odontioda, Odontocidium, and Vuylstekeara orchids in Japan. Typical symptoms on the leaves were dark or black spots (or both) with a yellow halo. The causal agent was identified as Burkholderia andropogonis (Smith 1911) Gillis, Van Van, Bardin, Goor, Hebbar, Willems, Segers, Kersters, Heulin and Fernandez 1995. The isolates were pathogenic on four original host orchids, Phalaenopsis orchid, and tulip; they were not pathogenic on white clover or corn after needle stab inoculation. An antibiotic bactericide (oxytetracycline/streptomycin mixture WP) was most effective for controlling the disease.     

Identification and in planta detection of Pseudomonas syringae pv. tomato using PCR amplification of hrpZPst

A rapid detection method based on PCR amplification of Pseudomonas syringae pv. tomato chromosomal sequences was developed. Primer design was based on the P. syringae DC3000 hrpZ_Pst gene, which maps on a pathogenicity-associated operon of the hrp/hrc pathogenicity island.A 532 bp product corresponding to an internal fragment of hrpZ_Pst was amplified from 50 isolates of P. syringae pv. tomato belonging to a geographically representative collection. The amplification product was also obtained from three coronatine-deficient strains of P. syringae pv. tomato.On the other hand, PCR did not produce any such products from 100 pathogenic and symbiotic bacterial strains of the genera Pseudomonas, Xanthomonas, Erwinia, and Rhizobium and 75 unidentified bacterial saprophytes isolated from tomato plants. The method was tested using leaf and fruit spots from naturally-infected tomato plants and asymptomatic nursery plants and artificially contaminated tomato seeds. The results confirmed the high specificity observed using pure cultures.     

Characterization of Fusarium diseases on commercially grown orchids in Hawaii

A decline of unknown aetiology has become a major problem for commercial orchid production in Hawaii, one of the primary orchid‐producing states in the USA. The major symptoms of decline include root degradation, foliar blight, pseudobulb rot and sheath rot. It was unclear whether all these symptoms are caused by the same or different pathogens, but preliminary research indicated that Fusarium species may be involved. In this study, the incidence of Fusarium species was examined across 186 plants, from 29 orchid genera and intergeneric hybrids across three islands in the state of Hawaii. The main five species associated with diseased orchids were F. proliferatum (38% of samples), F. solani (16%), F. oxysporum (16%) and two previously undescribed species (8% for both species combined). The two undescribed species were similar in appearance to F. subglutinans, and were designated FS‐A and FS‐B. Pathogenicity tests established that both F. proliferatum and FS‐B caused foliar spots, foliar blight and pseudostem rot on Dendrobium orchids, and that F. proliferatum isolates from diseased tissue of several genera could also induce symptoms on Dendrobium orchids. Although orchids have increasing importance in floriculture, relatively little is known about orchid pathogens, and previous studies focused primarily on Cymbidium and Phalaenopsis. This study provides new information concerning Dendrobium orchid pathogens and suggests a much wider host range than previously recognized for the five Fusarium species recovered from tissue with symptoms. These findings can contribute to better management of Fusarium diseases, which represent a significant challenge to orchid production in Hawaii.     

Orchid fleck symptoms may be caused naturally by two different viruses transmitted by <Emphasis Type="Italic">Brevipalpus</Emphasis>

Brevipalpus-transmitted viruses (BTV) cause chlorotic, necrotic and/or ringspot lesions in leaves and stems of orchids, citrus, coffee and several other plant species. There are two different types of BTVs, the nuclear and the cytoplasmic, based on maturation locale in the cell and particle morphology. The orchid fleck virus (OFV) is a BTV that infects orchids. Its short rodlike particles are 32–40 nm in diameter, 100–150 nm in length. OFV is found in the nucleus and is associated with intranuclear electronlucent viroplasms. In 1999, transmission electron microscopy analysis revealed a distinct type of virus causing orchid fleck symptoms. The bacilliform particles, 70–80 nm in diameter and 110–120 nm in length, induced electron-dense viroplasm inclusions in infected cells and resembled the cytoplasmic type associated with BTV, such as the citrus leprosis virus C. Our objective in the present study was to verify whether the cytoplasmic type virus found in orchids could be amplified using primers for other cytoplasmic BTVs, such as CiLV-C and Solanum violaefolium ringspot virus (SvRSV). Additionally, we aimed to differentiate the two BTVs found in orchids: the nuclear and the cytoplasmic types of OFV using microscopy and molecular and serological tools. This virus was not amplified by the CiLV-C and SvRSV primers, and neither the molecular nor the serological tools available to the OFV diagnosis reacted with it, demonstrating that they are definitely different viruses.     

Ozone for control of post-harvest decay of table grapes caused byRhizopus stolonifer

The effect of ozone on post-harvest decay of table grapes was studied both with regard to its effectiveness and its possible mode of action. Ozone concentrations fell rapidly upon contact with organic matter and the amount which reacted with grape berries and the microflora on their surface was about 0.1mgg^-1, when supplied at a rate of 8mgmin^-1for 20min. The dose applied could be increased by longer periods of exposure, but symptoms of toxicity were observed on certain cultivars. The number of colony forming units (cfu) of fungi, yeasts and bacteria naturally present on the berry surface was considerably reduced by a 20min exposure to ozone. Ozone treatments significantly reduced the extent of berry decay caused by fungi following cold storage and increased shelf-life. A significant decrease in decay was observed in berries that were treated with ozone either before or after being inoculated withRhizopus stolonifer.This finding indicates that, in addition to its sterilizing effect, ozone also induced resistance to post-harvest decay development. The phytoalexins resveratrol and pterostilbene were elicited by ozone treatments, at levels similar to those produced by uv-c irradiation. Resveratrol accumulated in greater quantities than pterostilbene. Inoculation withR. stoloniferin addition to ozone treatment, raised the levels of both stilbenes even more. Exposing berries to ozone was almost as effective as SO₂fumigation for the control of storage decay caused byR. stoloniferand no deleterious effects were observed on the appearance of the grape cluster. Ozone treatments can therefore be considered as a possible substitute for SO₂fumigation for the control of post-harvest fungal decay.     

Identification of a tractable model system and oxalic acid-dependent symptom development of the dollar spot pathogen Clarireedia jacksonii

Clarireedia jacksonii causes dollar spot disease of cool-season turfgrasses in the United States and produces the phytotoxin oxalic acid. The role of oxalic acid in host–pathogen interactions of C. jacksonii is unknown and there are multiple challenges to studying these interactions in natural turfgrass hosts. Consequently, identification of model plants to study C. jacksonii–host interactions and the role of oxalic acid in pathogenesis is necessary. Controlled environment inoculation assays were used to evaluate pathogenesis of C. jacksonii in various model plants and investigate the role of oxalic acid in symptom development. Observations at microscopic and macroscopic levels demonstrated that infection progressed similarly in all monocots tested (creeping bentgrass, wheat, barley, rice, Brachypodium distachyon) but not in the dicot Arabidopsis thaliana. Plant oxalic acid content increased from near zero to around 0.2–0.4 mM following inoculation with C. jacksonii in creeping bentgrass, barley, and wheat. Conversely, oxalic acid content remained near zero in A. thaliana and was not well correlated with inoculation in rice and B. distachyon, both of which had higher endogenous oxalic acid levels than other monocots. Time-course oxalic acid quantification experiments with creeping bentgrass and B. distachyon further supported a link between symptom development and in planta oxalic acid content and identified 48 hr postinoculation as a critical time-point for investigating the role of oxalic acid in C. jacksonii pathogenesis. These studies demonstrate that various monocots can serve as tractable model systems for studying C. jacksonii–host interactions and that increases in oxalic acid content are associated with C. jacksonii symptom development.     

Mating type gene MAT1-2-1 is common among Japanese isolates of Verticillium dahliae

Mating type genes of Verticillium dahliae, a wilt pathogen affecting many plant species, were identified to examine sexual recombination between Japanese pathotypes. We amplified a DNA sequence encoding high mobility group (HMG) box from V. dahliae using PCR. A cloned genomic DNA fragment included a sequence homologous to MAT1-2-1 gene. Despite that sequence's presence in all V. dahliae isolates we used, MAT1-1-1 (an opposite mating type gene) was never amplified. We concluded that V. dahliae is potentially heterothallic. Furthermore, sexual bias practically obviates sexual recombination between Japanese pathotypes. This report describes, for the first time, a mating type gene of phytopathogenic Verticillium.     

水稻白叶枯病菌酸性还原酮加双氧酶的鉴定分析

 酸性还原酮加双氧酶(ARD)催化很多原核和真核生物中的甲硫氨酸急救途径(MSP)倒数第二步。本研究鉴定了水稻白叶枯病菌Xanthomonas oryzae pv. oryzae (Xoo)中的酸性还原酮加双氧酶, 命名为xard。Xoo 菌株PXO99^A、MAFF311018和KACC10331中的xard核苷酸序列完全相同。xard基因突变菌株在甲硫基腺苷(MTA)为唯一硫源时不能正常生长。这一结果证明Xard在MSP中起作用。xard突变体和野生型菌株PXO99^A 接种水稻IR24后病斑长度数据表明该基因突变对Xoo在水稻上的毒性没有影响。