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SUMMARY New records are presented of bacterial diseases affecting the following weed plants: Heliotropium sudanicum, Rhynchosia memnonia, Vigna radiata, V. pubigera, Euphorbia acalyphoides and Phyllanthus niruri. Bacterial leaf blight of pigeon pea (Cajanus cajan) caused by Xanthomonas phaseoli f. cajani is reported for the first time from the Sudan. The causal bacteria, all of which belong to the genus Xanthomonas, are compared with related pathogens. The differences between these bacteria are considered of little diagnostic value. Pathogenically, they can be separated into three groups: (i) the Heliotropium pathogen; (ii) the bacteria affecting leguminous plants; and (iii) the bacteria affecting species of the family Euphorbiaceae. Because of the diversity in opinion on speciation in the genus Xanthomonas, two alternative proposals are put forward. In the first, Xanthomonas is considered a monotypic genus with X. campestris as the sole species. The pathogens reported in this work from previously unrecorded hosts, which proved to differ in pathogenicity from established ones, are considered to be new formae speciales. These are X. campestris f.sp. heliotropii from H. sudanicum, X. campestris f.sp. rhynchosiae from R. memnonia, X. campestris f.sp. vigna-radiatae from V. radiata, X. campestris f.sp. euphorbiae from E. acalyphoides and X. campestris f.sp. phyllanthii from P. niruri. The organism from V. pubigera is accordingly identified as X. campestris f.sp. vignicola. Other bacteria used for comparison are also reduced to ff.sp. of X. campestris. The other proposal is to lump together pathogens with overlapping host ranges in a single species that comprises a number of ff.sp. differing in pathogenicity. Thus the bacteria from leguminous plants are all considered to belong to X. phaseoli as previously suggested by Sabet. New ff.sp. are created for the pathogens from R. memnonia (X. phaseoli f.sp. rhynchosiae), and V. radiata (X. phaseoli f.sp. vigna-radiatae). The organism from V. pubigera is identified in this case as X. phaseoli f.sp. vignicola. The bacteria from members of the Euphorbiaceae are considered to belong to X. ricini on priority grounds. X. cassavae and X. poinsettiaecola which have been used for comparison are reduced to the ff.sp. X. ricini f.sp. cassavae and f.sp. poinsettiaecola respectively. Two new ff.sp. are created: for E. acalyphoides pathogen, X. ricini f.sp. euphorbiae and for P. niruri pathogen, X. ricini f.sp. phyllanthii. The creation of a new species (X. heliotropii sp.nov.) is proposed for the Heliotropium pathogen. The present study shows that many weed plants may be affected with new bacterial strains that can also infect cultivated crops.

The extracellular polysaccharide produced by Xanthomonas phaseoli has been purified and shown to be homogeneous by examination in the analytical ultra-centrifuge, by moving boundary electrophoresis, and by gradient precipitation with ethanol. Following hydrolysis the constituent sugars of the polysaccharide were isolated and positively identified as the crystalline derivatives of D-glucose and of D-mannose and as the crystalline lactone of D-glucuronic acid. The above hexoses were found to be present in the relative proportions of 1:1:1.The results of a preliminary investigation in which C14-labelled glucose was supplied to rapidly growing cells indicate that it is unlikely that a single six-carbon precursor is formed from which all three sugar components of the polysaccharide are synthesized directly.

Spontaneous mutations conferring resistance to the action of 500 to 2000 μg/ml streptomycin occur at an over-all rate of about 3 × 10−10per bacterium per generation in Xanthomonas phaseoli. Some mutants will not grow in the absence of streptomycin; others grow both in the presence and in the absence of the drug. In most cases resistance to high concentrations of streptomycin does not affect the virulence of this organism for bean plants.

The effects of introducing new varieties and bacterial strains upon the epidemiology, ecology, and control of Xanthomonas phaseoli and X. phaseoli var. fuscans in registered bean seed crops in southwestern Ontario between 1961 and 1968 are described. A new phage type of X. phaseoli, Ib, is reported. Problems related to plant introductions and the detection of seed-borne pathogens are discussed.

1. The utilizations of inorganic sulfur sources in seven strains of Xanthomonas oryzae and other five species belong to Xanthomonas were investigated.2. Although sulfur containing amino acids were required for the rapid growth of seven strains of Xanthomonas oryzae and Xanthomonas citri, it was observed that these bacteria utilize inorganic sulfate after prolonged latent period which may require for adaptive formation of the sulfate reducing enzyme system.3. No marked difference in pathogenicity has been observed when the cells prepared with either the complete medium or the synthetic basal medium containing sodium sulfate were inoculated to rice plant leaves.4. No direct relationship between the ability of utilizing inorganic sulfate, requirement of sulfur containing amino acids and pathogenicity and/or lysotype on bacteriophage was observed in seven strains of Xanthomonas oryzae.5. Xanthomonas malvacearum, Xanthomonas phaseoli, Xanthomonas pruni and Xanthomonas vesicatoria utilized extensively inorganic sulfate as a sole sulfur source.6. The utilization of inorganic sulfate in Xanthomonas citri, Xanthomonas oryzae and Xanthomonas pruni were promoted by the presence of nicotinic acid amide in the medium.

Xanthomonas phaseoli var. fuscans (Burkh.) Starr & Burkh. in naturally infected bean seeds stored at −20 to 35 °C retained its viability, virulence, and physiological properties for 3 years. Agar cultures of the pathogen maintained at −20 to 20 °C also retained their pathogenicity and physiological characters throughout the test period but showed less virulence than the seed-borne isolates by the end of 33 months. The viability of agar cultures held at 25, 30, and 35 °C was lost after 24, 18, and 9 months of storage, respectively.The effects of 24 carbon sources on the growth of the pathogen have been determined. The production of a brown diffusible pigment by the organism was influenced by temperature, aeration, and the carbon source. Sugar alcohols did not support good growth or inhibit pigment formation. Most carbohydrates, which supported good or fair growth of the organism, seemed to inhibit pigment production or its expression.

Techniques are described for lysing cells of the Gram-negative organism Xanthomonas phaseoli with lysozyme and with penicillin. In the presence of a supporting medium 'protoplasts' are formed which may be stabilized by the addition of magnesium ions at the appropriate time. The application of these methods to the preparation of cell-free extracts of this organism is discussed.

Intact cells and cell-free extracts of the phytopathogenic organism Xanthomonas phaseoli have been shown to contain flavoprotein and the respiratory carriers: cytochrome b1, cytochrome a1, and cytochrome a2. The reduced forms of these respiratory pigments are produced upon addition to a clear extract of substrate amounts of DPNH.The highly active DPNH oxidase system in extracts of this organism has been studied as to requirements for inorganic ions, optimum pH, product formation, distribution, and solubilization. Carbon monoxide inhibits the terminal oxidation system; this effect is reversed by bright light.An inhibitor study has shown members of the phenothiazine family of compounds to be most effective, followed by amytal, cyanide, BAL, atabrine, and pCMB. The most notable of the substances which did not inhibit were antimycin A, one of the quinoline-N-oxides, and azide.The possibility exists that H2O2may also be formed during the oxidation of DPNH although clear-cut evidence for its presence was difficult to obtain. X. phaseoli extracts do not contain a DPNH peroxidase. They exhibit, however, some DPNH – cytochrome c reductase activity which is believed to be quite independent of the DPNH oxidase system. The extracts are devoid of cytochrome c oxidase activity although they contain a respiratory system which readily oxidizes p-phenylenediamine.

In a medium containing bean, barley and wheat seed exudates,Xanthomonas phaseoli var.fuscans (Burk.) Starr et Burk. grew substantially better than in that containing root exudates of these plants. When the bacteria were cultivated in a medium containing root exudates of bean plants deprived of cotyledons after eleven days of growth, growth was slower than in the presence of root exudates of control plants. On the other hand, the growth was stimulated in a medium containing root exudates of bean plants deprived of leaves. It was found that seed exudates of these plants contained biologically active peptides stimulating the growth of the microorganism. These peptides were not found in root exudates. These findings suggest a relationship between the survival ofXanthomonas phaseoli var.fuscans in the rhizosphere of bean and the exudation of biologically active peptides originating from the stock substances of seeds and cotyledons.

(1) イネ白葉桔病菌およびインゲン葉焼病菌菌体より音波破砕法により電子伝達系標品を得,これをコハク酸ソーダまたはNADHで緩徐に還元することにより,各チトクローム成分の変化を記録した.この結果,従来報告されているとおり,前者ではチトクロームa1およびb1,後者でばa1, a2およびb1の存在をみとめた以外に,両者とも微量のc成分を併存するがわかった. (2) これらのことより,この菌のアンチマイシンA非感受性はb→c系の欠損よりもむしろこのb→c間に存在する因子の質的相違に帰因するものと考えられる. (3) 前記標品はNADHを電子供与体として結晶酵母チトクロームcを還元するこるができる. (4)以上の事実その他をもとにして,暫定的な両菌の電子伝達系のschemeが提出された.

Succinoxidase and succinic dehydrogenase were found in cell-free extracts of Xanthomonas phaseoli, obtained by sonic oscillation, and remained largely in the supernatant solution after ultracentrifugation. The effect of time of exposure of the cells to sonic oscillation on cell breakage was found to follow first order reaction kinetics, as was the "solubilization" of succinic dehydrogenase and succinoxidase. It appears that the two enzymatic activities are released from the cell in a particulate form which is further fragmented on continued treatment in the sonic oscillator.The clear supernatant solution obtained after ultracentrifugation of the cell-free extract was found to contain those members of the electron transport chain which had previously been found in the intact cell, namely, flavoprotein and cytochromes b1, a1, and a2. These substances could be reduced by the addition of succinate. Malonate prevented this reduction. The effects of various inhibitors on the succinoxidase system and on succinic dehydrogenase are presented and discussed in relation to the operation of the electron transport chain in the oxidation of succinate by this organism.

Exposure of naturally infected and artificially inoculated seeds to radio-frequency (rf) electric waves of 59 to 64 Mc/sec was of varying effectiveness in eradicating internally borne fungi and bacteria. Diaporthe phaseolorum was eliminated from soybean seeds with little reduction in seed germination. Survival of Ascochyta pisi and A. pinodes (Mycosphaerella pinodes) in field pea seed was greatly reduced by similar treatment, but the fungi were not usually eradicated without appreciable reduction in germination. Germinability of pea seeds was unaffected by increasing the moisture content of the seed to 16% from 10.3%. The A. pinodes content of such seeds, however, was reduced by approximately 50%. Both seed and fungus were more susceptible to damage by rf treatment at the higher moisture level. Bean seed infected with Xanthomonas phaseoli var. fuscans and cabbage seed inoculated with X. campestris were killed by exposures which reduced but did not eradicate the bacteria. Colonies of both xanthomonads on nutrient agar media were destroyed by rf treatment.

Isolates of Xanthomonas phaseoli var. fuscans (Burkh.) Starr & Burkh. obtained from naturally infected bean (Phaseolus vulgaris L.) seeds stored at 10 C for 2–4 months were more virulent, as indicated by a stunting effect on Sanilac bean plants, than isolates obtained from seeds stored for 7–24 months. Neither the rate of growth of the organism nor its ability to produce a brown diffusible pigment was correlated with virulence. Growth rate and pigment production of all isolates in nutrient broth were similar and reached a maximum after 36 and 48 h respectively. In a medium containing inorganic salts and yeast extract, the growth rate of the organism was relatively slow and pigment development depended upon amendments added to the medium. Tyrosine enhanced, while glucose retarded, pigment production, but neither affected the growth of the pathogen adversely. The formation and color of the pigment in the media were not affected by pH values ranging from 5.5 to 9.0. The presence of living cells was essential for the continued production of the pigment. The melanoid nature of the pigment was demonstrated.

The bacterial leaf blights of dolichos bean (Dolichos lablab L.), soybean (Glycine soja Sieb. and Zucc.), catjang cowpea (Vigna unguiculata (L.) Walp.), lucerne (Medicago sativa L.) and three species of senna (Cassia L.) were investigated and found to be caused by Xanthomonas phaseoli (Smith) Dowson, X. phaseoli var. sojense (Hedges) Starr & Burkholder, X. vignicola Burkholder, X. alfalfae Riker, Jones & Davis and X. cassiae Kulkarni, Patel & Dhande, respectively. None of these diseases has been investigated before in the Sudan and the lucerne disease had not been previously reported from this country. A comparative study which included several strains of the above bacteria as well as X. phaseoli var. fuscans (Burkholder) Starr & Burkholder, X. cajani Kulkarni, Patel & Abhyankar, and X. tamarindi Patel, Bhatt & Kulkarni, showed that the organisms were indistinguishable by the usual bacteriological procedures and the minute differences in certain biochemical characters were considered of little or no diagnostic value. Cross-inoculations revealed that the host ranges of these pathogens, with the exception of X. cajani and X. tamarindi overlapped. The latter two organisms infected only their original hosts, viz. Cajanus cajan (L.) Millsp. and Tamarindus indica L., respectively. Where a particular host was infected by more than one pathogen, the symptoms and effects they produced on that host were similar in every respect except in the case of X. vignicola when infecting Phaseolus vulgaris L. and Dolichos lablab. In this exceptional case the mature spots were dry and white, not conforming to the usual russet or dark-brown, haloed spots produced by other bacteria. Infection in most cases first appeared as minute dark-green more or less watersoaked spots which generally developed on all parts of the plants including the stems, leaves and pods. The systematic position of the pathogens under investigation was reconsidered and for the reasons discussed below all the bacteria included in the study were reduced to special forms of X. phaseoli with the exception of X. phaseoli var. fuscans, the varietal rank of which has been maintained.

Cell-free extracts of Xanthomonas phaseoli (XP8) can convert ATP to hypoxanthine, the chief intermediates being ADP, AMP, IMP, and inosine. The following enzymes concerned in the breakdown of ATP are present: adenosine triphosphatase, myokinase, adenylic acid deaminase, a 5′-nucleotidase acting on IMP, and a nucleosidase which converts inosine to hypoxanthine. It is concluded that the conversion of ADP to AMP is, for the most part, carried out by the myokinase, the direct dephosphorylation of ADP being of questionable significance in these extracts.AMP is not dephosphorylated directly but is first deaminated to IMP. A method is presented which allows enzymatic deamination to be studied by manometric means. The deamination of AMP is found to explain the biphasic nature of the carbon dioxide output and uptake observed when hexokinase activity of extracts is measured by the manometric method.

The bacterial leaf spot of alfalfa caused by Xanthomonas phaseoli f. sp. alfalfae was observed for the first time in Japan at the farm of National Institute of Animal Industry, in September 1962.Leaf spots are at first minute, round, watersoaked. Mature spots 2-3mm in diameter are pale yellow with a dark brown margin surrounded by a yellowish halo. The spots tend to coalesce along midrib and near the tip or the margin of the leaflets. Severely infected leaves often shed.The causal bacteria infected Phaseolus vulgaris by inoculation producing symptom similar to that produced by Xanthomonas phaseoli on the same host.The morphological, cultural and phsiological characters of the bacteria causing the disease were investigated, and hardly distinguishable from those described by Riker et al. (1935) and Sabet (1959).Therefore the causal bacteria were quite identical in all its characteristics with Xanthomonas phaseoli f. sp. alfalfae (Riker, Jones et Davis) Sabet.

Fuscous blight (Xanthomonas phaseoli var. fuscans), a new disease of field beans in Canada, was found to be present in a high proportion of bean seed samples from southwestern Ontario. Although symptoms of the disease are similar to those of common blight (Xanthomonas phaseoli), a greater intensity in color is apparent on infected seed and more hypertrophy, especially of nodal tissues, is caused by fuscous blight than by common blight. In epidemiological studies in the field, it was found that seed infection as low as 0.5% could cause a serious epiphytotic in the resulting crop. This points out the necessity of a zero tolerance for fuscous blight in valuable seed stocks. Furthermore the rapid phage plaque method can be used to determine zero tolerance. Garden varieties were generally more susceptible to the pathogen than field varieties. Great Northern showed the highest degree of resistance to the disease of all the varieties tested.An agar plating technique was developed whereby the organism can be isolated and identified in infected bean seed by the production of a brown diffusible pigment on nutrient agar. A bacteriophage spot test is also described which can also be used to identify the pathogen from infected bean seed. By means of phage typing, the relationship of X. phaseoli var. fuscans, X. phaseoli, and intermediate strains is shown.

Extracts of Xanthomonas phaseoli (XP8) degrade certain ribonucleosides readily by hydrolytic cleavage of the ribose moiety. Thus, uridine is converted to uracil and ribose, and cytidine to cytosine and ribose, with little deamination to uracil and ammonia taking place. Commercial adenosine is deaminated to inosine and ammonia without further significant cleavage. The data presented permit a choice to be made between the two theoretically possible pathways of guanosine degradation. With chromatographic evidence for xanthine but not for xanthosine and with spectrophotometric evidence for the intermediate formation of guanine, the mechanism of guanosine breakdown is described as being the result of hydrolytic cleavage to guanine and ribose followed by deamination to xanthine and ammonia.

Eight phage types of Xanthomonas phaseoli (E. F. Sm.) Dows. were identified by an experimental phage-typing system using four virulent phages and 310 isolates of this organism. The existence of phage subtypes was also demonstrated by the use of high-titer phage preparations. The phage subtypes could be located geographically. Correlation between strain virulence and phage subtype was demonstrated. Polyvirulent phage Pg 176 for X. phaseoli var. fuscans used in the typing system was partially characterized. The incidence and distribution of phages for strains of X. phaseoli and X. phaseoli var. fuscans in soil samples from southwestern Ontario from 1962 to 1965 were determined. The low ecological significance of soil-borne phage was demonstrated. Seventeen phages for X. phaseoli were isolated from 13 soil samples with the aid of enrichment, none without.

Ten bacteriophages for Xanthomonas phaseoli were characterized. On the basis of adsorption rates, latent period and burst size, plaque morphology, host range, efficiency of plating, ultrastructure, sensitivity to osmotic shock, streptomycin sensitivity, temperature effects on plating efficiency, and serology, the phages were separated into at least three groups. Some of the phages were infectious for Pseudomonas phaseolicola (four strains) and P. syringae (one strain) in a narrow temperature range. The taxonomic and ecological significance of this finding is discussed.

A species of Bacillus isolated from soil was found to elaborate an inducible, extracellular enzyme capable of degrading the polysaccharide of Xanthomonas phaseoli to low-molecular-weight oligosaccharides. The enzyme was characterized with respect to pH optimum, ion requirement, and stability. Examination of the polysaccharide degradation products revealed that the glucuronic acid moiety of the polysaccharide was altered to a Δ4,5unsaturated form as a result of enzyme action.

Extracts of the plant pathogenic organism Xanthomonas phaseoli contain both TPN- and DPN-linked glucose-6-phosphate dehydrogenases as well as a DPN-specific glyceraldehyde phosphate dehydrogenase. DPNH oxidase is very active and sensitive to high concentrations of cyanide. No evidence could be found for the presence of pyridine nucleotide transhydrogenase.Ribose-5-phosphate is metabolized via the pentose cycle; sedoheptulose phosphate is an intermediate and other criteria of the functioning of the pentose cycle are met when ribose-5-phosphate is the substrate. The same system also functions with 6-phosphogluconate as substrate but at a level which suggests that this pathway is not of great significance.The Entner–Doudoroff 6-phosphogluconate-splitting pathway is the major avenue of hexosephosphate utilization in cell-free extracts. Pyruvate formation and utilization are discussed in relation to function and cofactor requirements.While phosphoglucose isomerase, aldolase, triosephosphate isomerase, and the enzymes converting phosphoglyceraldehyde to pyruvate are present and enzymatically active, phosphofructokinase appears to be the "bottleneck" to glycolysis. On the other hand fructose-1,6-diphosphate is oxidized by both DPN- and TPN-linked pathways, the latter through the efficient functioning of a specific phosphatase which forms fructose-6-phosphate readily. Glycolysis is considered to play only a very minor role in these extracts.A new "hexose cycle" for the metabolism of hexosephosphate is proposed. It consists of oxidation through "Zwischenferment", followed by the Entner–Doudoroff splitting system and resynthesis of hexosemonophosphate through reversal of the aldolase reaction followed by specific carbon-1 phosphate hydrolysis of fructose-1,6-diphosphate. The cycle is shown to be metabolically feasible and thermodynamically likely. It is considered to be the pathway by which cells which tend not to utilize the pentose cycle or classical glycolysis, but have an active 6-phosphogluconate-splitting system, metabolize hexosephosphate. Pyruvate produced as a result of the operation of this system is then oxidized via the tricarboxylic acid cycle in glucose-grown cells.

Estudo sobre a presenca de bacterias associadas as sementes de feijao, na Paraiba, e sobre o metodo de hidrotermoterapia como tratamento alternativo. Sementes foram coletadas em dez municipios, e tradas a 40°C, 50°C. 60°C e 70°C, em intervalos de 10min em 10min, ate 60min. Um lote nao recebeu tratamento (testemunha absoluta). Com base nos resultados, concluiu-se que as sementes utilizadas pelos produtores no Estado, apresentam elevado nivel de infeccao por bactrias, e o tratamento por hidrotermoterapia nao foi eficiente no contrle das bacterias. Made available in DSpace on 2019-08-08T01:00:35Z (GMT). No. of bitstreams: 1 Id4451TsAlderi.pdf: 8019814 bytes, checksum: 76c8b9de22328e65b38c7b3db85244c8 (MD5) Previous issue date: 1987 Dissertação Mestrado.

A description is provided for Xanthomonas phaseoli var. fuscans . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Phaseolus vulgaris, P. lunatus and P. coccineus ; also on other leguminous hosts on inoculation (39: 3). DISEASE: Fuscous blight. On seeds, pods, leaves and stem. The symptoms of fuscous blight are very similar to common blight, X. phaseoli , with small water-soaked lesions on the leaves which develop into spots with dry, brown centres but X. phaseoli var. fuscans is stated to be more virulent on inoculation to bean and to produce a slight hypertrophy of the tissues about stem wounds. GEOGRAPHICAL DISTRIBUTION: Africa (Ethiopia, Sudan, Uganda): Australasia (New South Wales): Europe (Hungary, Switzerland, U.S.S.R., Yugoslavia); North America (Canada, U.S.A.); (CMI Map 402, 1965). TRANSMISSION: Seed-borne and by wind driven rain splash or wind blown soil in the field (31: 128). The pathogen can survive for long periods both in seed and on dead plant material.

THE bacterial pathogens of beans are widespread all over the world. In most cases four species of bacterium are the main causal organisms: Pseudomonas phaseolicola (Burkholder) Dowson, Xanthomonas phaseoli (E.F. Smith) Dowson, Corynebacterium flaccumfaciens (Hedges) Dowson, and Xanthomonas phaseoli var. fuscans (Burkholder) Starr et Burkholder. The symptoms, on the seed, of the diseases caused by these four bacteria are similar to such an extent that they can be identified only by means of laboratory methods. Katznelson et al. 1 succeeded in isolating the phages for P. phaseolicola and X. phaseoli. The Canadian authors worked out a rapid phage-count method using these two phages. By means of this procedure they were able to detect the halo-blight organism (P. phaseolicola) and the common blight bacterium (X. phaseoli) in beans. In order to apply this method for all the four important pathogens of beans, it was necessary to isolate also the phages for C. flaccumfaciens and X. phaseoli var. fuscans. This work, which was undertaken because C. flaccumfaciens and X. phaseoli var. fuscans are the major causative agents of bean diseases in Hungary, was recently carried out in our laboratory.

Cell-free extracts of Xanthomonas phaseoli contain the individual enzymes of the tricarboxylic acid cycle, and it is suggested that this is the main pathway for the terminal oxidation of carbohydrate in this organism. X. phaseoli can grow on a medium containing acetate as the sole source of carbon. Cell-free extracts of such acetate-grown organisms contain the enzymes of the glyoxylate cycle, and it is concluded that the operation of this cycle permits the initial stages of synthesis of complex cell material from acetate at a rate sufficiently high to account for the observed rate of growth on the acetate medium. The two enzymes required to modify a tricarboxylic acid cycle into a glyoxylate cycle are present in very small amounts (malate synthetase) or absent entirely (isocitritase) in extracts of glucose-grown X. phaseoli.

A description is provided for Xanthomonas phaseoli . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Phaseolus vulgaris and other species of Phaseolus and Lablab niger [Lablab purpureus] . DISEASE: Common blight. A disease affecting leaves, stems, seed and pods, mainly confined to the parenchyma but which may invade the vascular system and cause a wilt. Symptoms are very similar to halo blight and the two diseases often occur together. An association with common bean mosaic virus is also found. The leaf symptoms are enhanced synergistically in mixed infections (38: 437; 24: 47), but after serial passage the virus becomes dominant. GEOGRAPHICAL DISTRIBUTION: As with Pseudomonas phascolicola , the pathogen is probably found in most countries where beans are grown (CMI Map 441, 1965). TRANSMISSION: The pathogen is seed-borne and is harboured beneath the seed coat where it may remain viable for several years. Dissemination in the field is by wind-driven rain, insects, infected plant debris or wind blown soil (37: 128). The pathogen enters through the stomata or wounds Overhead sprinkler irrigation may be a means of spread, but not furrow irrigation (34: 339). Unlike the halo blight pathogen, X. phaseoli can overwinter on infected stems and leaves, and be perpetuated on hosts other than species of Phaseolus . Soaking bean seeds in suspensions of the root nodule bacterium for inoculation purposes may inadvertently result in a great increase in infection where the original incidence was slight.

Transcription activator-like effectors (TALEs) play a significant role for pathogenesis in several xanthomonad pathosystems. Xanthomonas phaseoli pv. manihotis (Xpm), the causal agent of Cassava Bacterial Blight (CBB), uses TALEs to manipulate host metabolism. Information about Xpm TALEs and their target genes in cassava is scarce, but has been growing in the last few years. We aimed to characterize the TALE diversity in Colombian strains of Xpm and to screen for TALE-targeted gene candidates. We selected eighteen Xpm strains based on neutral genetic diversity at a country scale to depict the TALE diversity among isolates from cassava productive regions. RFLP analysis showed that Xpm strains carry TALomes with a bimodal size distribution, and affinity-based clustering of the sequenced TALEs condensed this variability mainly into five clusters. We report on the identification of 13 novel variants of TALEs in Xpm, as well as a functional variant with 22 repeats that activates the susceptibility gene MeSWEET10a, a previously reported target of TAL20Xam668. Transcriptomics and EBE prediction analyses resulted in the selection of several TALE-targeted candidate genes and two potential cases of functional convergence. This study provides new bases for assessing novel potential TALE targets in the Xpm–cassava interaction, which could be important factors that define the fate of the infection.

Background: Xanthomonas citri pv. fuscans (Xcf) and Xanthomonas phaseoli pv. phaseoli (Xpp) are the causal agents of common bacterial blight of bean (CBB), an important disease worldwide that remains difficult to control. These pathogens belong to distinct species within the Xanthomonas genus and have undergone a dynamic evolutionary history including the horizontal transfer of genes encoding factors probably involved in adaptation to and pathogenicity on common bean. Seed transmission is a key point of the CBB disease cycle, favouring both vertical transmission of the pathogen and worldwide distribution of the disease through global seed trade. Taxonomy: Kingdom: Bacteria; phylum: Proteobacteria; class: Gammaproteobacteria; order: Lysobacterales (also known as Xanthomonadales); family: Lysobacteraceae (also known as Xanthomonadaceae); genus: Xanthomonas; species: X. citri pv. fuscans and X. phaseoli pv. phaseoli (Xcf‐Xpp). Host range: The main host of Xcf‐Xpp is the common bean (Phaseolus vulgaris). Lima bean (Phaseolus lunatus) and members of the Vigna genus (Vigna aconitifolia, Vigna angularis, Vigna mungo, Vigna radiata, and Vigna umbellata) are also natural hosts of Xcf‐Xpp. Natural occurrence of Xcf‐Xpp has been reported for a handful of other legumes such as Calopogonium sp., Pueraria sp., pea (Pisum sativum), Lablab purpureus, Macroptilium lathyroides, and Strophostyles helvola. There are conflicting reports concerning the natural occurrence of CBB agents on tepary bean (Phaseolus acutifolius) and cowpea (Vigna unguiculata subsp. unguiculata). Symptoms: CBB symptoms occur on all aerial parts of beans, that is, seedlings, leaves, stems, pods, and seeds. Symptoms initially appear as water‐soaked spots evolving into necrosis on leaves, pustules on pods, and cankers on twigs. In severe infections, defoliation and wilting may occur. Distribution: CBB is distributed worldwide, meaning that it is frequently encountered in most places where bean is cultivated in the Americas, Asia, Africa, and Oceania, except for arid tropical areas. Xcf‐Xpp are regulated nonquarantine pathogens in Europe and are listed in the A2 list by the European and Mediterranean Plant Protection Organization (EPPO). Genome: The genome consists of a single circular chromosome plus one to four extrachromosomal plasmids of various sizes, for a total mean size of 5.27 Mb with 64.7% GC content and an average predicted number of 4,181 coding sequences. Disease control: Management of CBB is based on integrated approaches that comprise measures aimed at avoiding Xcf‐Xpp introduction through infected seeds, cultural practices to limit Xcf‐Xpp survival between host crops, whenever possible the use of tolerant or resistant bean genotypes, and chemical treatments, mainly restricted to copper compounds. The use of pathogen‐free seeds is essential in an effective management strategy and requires appropriate sampling, detection, and identification methods. Useful websites: https://gd.eppo.int/taxon/XANTPH, https://gd.eppo.int/taxon/XANTFF, and http://www.cost.eu/COST_Actions/ca/CA16107.

Xanthomonas phaseoli pv. manihotis (Xpm) and X. cassavae (Xc) are two bacterial pathogens attacking cassava. Cassava bacterial blight (CBB) is a systemic disease caused by Xpm, which might have dramatic effects on plant growth and crop production. Cassava bacterial necrosis is a nonvascular disease caused by Xc with foliar symptoms similar to CBB, but its impacts on the plant vigour and the crop are limited. In this review, we describe the epidemiology and ecology of the two pathogens, the impacts and management of the diseases, and the main research achievements for each pathosystem. Because Xc data are sparse, our main focus is on Xpm and CBB.

Cassava bacterial blight (CBB), which is a vascular disease caused by Xanthomonas phaseoli pv. manihotis (Xpm), previously known as Xanthomonas axonopodis pv. manihotis, poses a major threat to cassava (Manihot esculenta) production worldwide. Typical symptoms include angular leaf lesions, blight, wilting, stem exudates, and stem cankers. Stem cuttings are used to propagate cassava and play a crucial role in Xpm dissemination. In line with a growing interest of smallholder farmers for cassava in West Africa, recent surveys revealed the occurrence of CBB in Burkina Faso (Wonni et al. 2015) and Ivory Coast (Kone et al. 2015). In Mali, which shares borders with these two countries, CBB was reported in the early 1980s, but the available information is quite limited: there is no description of symptoms nor of the causal agent, and no strain of the pathogen has been isolated (CABI 2018). To fill this gap, cassava fields were surveyed in the regions of Segou (site of Bla) and Bamako (sites of Sotuba and Samanko) from December 2015 to January 2016. Approximately 80 leaves exhibiting typical angular translucent spots were collected at the three sites and processed for bacterial isolation. White Xanthomonas-like colonies were isolated from ground diseased leaf tissues 48 h after incubation at 28°C on LPGA medium (yeast, 5 g; peptone, 5 g; glucose, 5 g; Bacto agar, 15 g; distilled water, 1 liter). Fifty candidate Xpm strains were then tested using a diagnostic multiplex PCR (Bernal-Galeano et al. 2018) using the Xpm reference type strain CFBP 7661 as a positive control. The two bands expected for Xpm were obtained for 40 candidate strains, as well as for CFBP 7661. Xpm strains CIX2484, CIX2492, CIX2502, CIX2504, CIX2497, and CIX2498 were further analyzed by sequencing of the housekeeping gene gyrB, resulting into 98 to 100% identity with the gyrB sequence of 66 Xpm strains available at NCBI, including the type strain CFBP 7661. Pathogenicity tests were performed on 4-week-old cassava plants of the MCOL1522 cultivar. CIX2484, CIX2492, CIX2502, CIX2504, CIX2497, and CIX2498 strains were grown overnight in LPGA medium and resuspended in sterile water at 1 × 10⁸ CFU/ml. Bacterial suspensions were inoculated into cassava leaves and stems as previously described (Wonni et al. 2015), whereas sterile water and Xpm strain CFBP 7661 were used as negative and positive controls, respectively. After 7 days of incubation under greenhouse conditions (28°C, 70% relative humidity, and a photoperiod of 12 h), cassava leaves developed typical CBB water-soaked lesions. Wilted leaves and stem exudates were also visible 30 days after stem inoculation, with symptoms being reminiscent of those typically seen in the field. By contrast, plants inoculated with water remained symptomless. White colonies with a typical Xanthomonas-like morphology were next reisolated from diseased leaves and confirmed as Xpm using the diagnostic PCR assay, thus fulfilling Koch’s postulates. Strains CIX2484, CIX2492, and CIX2504 were deposited in the French Collection for Plant-Associated Bacteria (CIRM-CFBP). Information on Xpm strains as well as gyrB sequences is available through CIRM-CFBP: https://www6.inra.fr/cirm_eng/CFBP-Plant-Associated-Bacteria. To our knowledge, this is the first report of CBB in Mali supported by molecular diagnostic methods. Given the growing importance of cassava for human consumption, CBB could represent a major threat in Mali, as well as in neighboring countries. Further surveys at the national level will help to evaluate the prevalence of CBB in Mali and help orientate adapted control strategies.

Background Common bacterial blight (CBB) caused by Xanthomonas phaseoli pv. phaseoli and Xanthomonas citri pv. fuscans is one of the major threats to common bean crops (Phaseolus vulgaris L.). Resistance to CBB is particularly complex as 26 quantitative resistance loci to CBB have been described so far. To date, transcriptomic studies after CBB infection have been very scarce and the molecular mechanisms underlying susceptibility or resistance are largely unknown. Results We sequenced and annotated the genomes of two common bean genotypes being either resistant (BAT93) or susceptible (JaloEEP558) to CBB. Reciprocal BLASTp analysis led to a list of 20,787 homologs between these genotypes and the common bean reference genome (G19833), which provides a solid dataset for further comparative analyses. RNA-Seq after inoculation with X. phaseoli pv. phaseoli showed that the susceptible genotype initiated a more intense and diverse biological response than the resistant genotype. Resistance was linked to upregulation of the salicylic acid pathway and downregulation of photosynthesis and sugar metabolism, while susceptibility was linked to downregulation of resistance genes and upregulation of the ethylene pathway and of genes involved in cell wall modification. Conclusions This study helps better understanding the mechanisms occurring during the early colonization phase of common bean by Xanthomonas and unveils new actors potentially important for resistance and susceptibility to CBB. We discuss the potential link between the pathways induced during bean colonization and genes induced by transcription activator-like effectors (TALEs), as illustrated in other Xanthomonas pathovars.

IT has been suggested1 that bacterial cells which do not utilize classical glycolysis or the pentose cycle to any significant extent, but which contain a highly active system for splitting 6-phosphogluconate, resynthesize hexose phosphate from triose phosphate via a hexose cycle. This suggestion was based, in part, on the discovery in extracts of such cells (for example, the phytopathogenic organism Xanthomonas phaseoli) of a highly active fructose-1,6-diphosphatase which was shown to remove preferentially the C-1 phosphate grouping at near neutral and alkaline pH values.

Survival of Pseudomonas phaseolicola and Xanthomonas phaseoli in soil between successive bean crops was studied in a field situation at Bairnsdale. P. phaseolicola and X. phaseoli survived on nylon netting for maximum periods of 6 and 3 weeks, respectively, on the soil surface, and for 6 and 2 weeks when buried. On infected leaf, stem and pod tissue P. phaseolicola survived for 20 weeks on the soil surface and for 11 weeks when buried; X. phaseoli survived up to 11 weeks on the soil surface and for 3 weeks when buried. In heavily infected bean plots neither pathogen was carried over from one growing season to the next. It is concluded that infected bean debris in the soil from the previous growing season is not a source of common and halo blight infection in East Gippsland.

WELLER, D. M., and A. W.. SAETTLER. 1978. Rifampin-resistant Xanthomonas phaseoli \ar. hiiscans and Xanthomonas phaseoli: Tools for field study of bean blight bacteria. Phytopathology 68: 778-781. Rifampin-resistant mutants of Xanthomonas phaseoli rifampin-resistance marker permitted selective isolation of (Xp) and X. phaseoli var. fuscans (Xpf) were screened for RIO and Ra from field-grown inoculated bean leaves; growth. similarity to wild-type isolates and their utility as tools for of all phyllosphere bacteria was inhibited on media with field study of bean blight bacteria. A mutant (R I0) isolate of rifampin (50 uig/ ml). Addition of cycloheximide at 25 Ag/ ml Xpf and one (Ra) of Xp were similar to wild types in reduced growth of resident yeasts and fungi. The rifampin numerous bacteriological tests, grew at rates identical to, and resistance marker was stable when the bacteria were grown in were as virulent as the wild types in bean leaves. The doubling culture or beans; no reversions to rifampin sensitivity have time for R 10 and Ra was about 11% longer than that for the been detected. wild types in buffered yeast-extract liquid medium. The

In order to assess the effects of air pollution on plant disease development, the authors investigated the effects of SO/sub 2/ on lesion development by two bacterial pathogens. Maize or soybean plants were exposed to sulfur dioxide (SO/sub 2/) at 524 ..mu..g m/sup -3/ or 262 ..mu..g m/sup -3/ before, after or before and after inoculation with Corynebacterium nebraskense or Xanthomonas phaseoli var. sojensis, respectively. Lesion development was inhibited in both cases, regardless of when the exposures occurred. The time of exposure, however, altered the subsequent effect on lesion size. Dry weight and sulfur content of host tissue were not altered by the joint effects of the pollutant and the pathogens.