Water-soaked Spots Research Articles

Effect of Magnesium and Manganese Nutrition on Muskmelon Growth and Manganese Toxicity

Abstract Muskmelons (Cucumis melo L.) ‘Harvest Queen’ were grown in sand culture to evaluate the response to Mn toxicity as affected by solution concentration of Mn and Mg. Manganese toxicity symptoms were developed as water-soaked spots, necrotic spots, and necrotic lesions, which were most severe on the lower mature leaves. Leaves developed toxicity symptoms when they contained ≥900 μ-g·g-1 Mn. Increased levels of Mg in the nutrient solution alleviated symptoms of Mn toxicity, decreased Mn concentration in shoot and root tissues, and increased growth of muskmelon plants. The reduction in Mn toxicity was brought about by reduced root absorption of Mn at high Mg supply.

Pseudomonas ficuserectae sp. nov., the Causal Agent of Bacterial Leaf Spot of Ficus erecta Thunb.

Pseudomonas ficuserectae, a new nonfluorescent, phytopathogenic pseudomonad species, is described. This bacterium produces dark brown, water-soaked spots on the leaves and stems of Ficus erecta Thunb., resulting either in defoliation or shoot blight on severely infected plants. The colonies on nutrient agar plates are white, circular, and 3 to 4 mm in diameter after 6 days. P. ficuserectae is similar to Pseudomonas amygdali in many properties. The differences between these two species include size of colonies on agar plates, hydrolysis of Tween 80, production of H2S, utilization of ribose, raffinose, mannitol, sorbitol, and malonate, and pathogenicity. The deoxyribonucleic acid base composition of the type strain of P. ficuserectae, strain L7, is 59 mol% guanine plus cytosine. The specific epithet of this new species reflects the pathogenicity of the bacterium on F. erecta Thunb.

Erwinia mallotivora . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Erwinia mallotivora . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Mallotus japonicus ( Euphorbiaceae ). DISEASE: Bacterial leaf spot. The disease starts as water-soaked spots on the newly developing leaves in May and June. The spots tend to form close to the main veins. They enlarge and become angular as they are restricted by the veins, becoming dark brown, and often with a chlorotic halo about 1 mm wide. Spots may coalesce and kill the leaf, and shoot blight may also occur. Under humid conditions bacteria may exude on to the leaf surface. GEOGRAPHICAL DISTRIBUTION: Japan. TRANSMISSION: Unknown, but presumably rain splash plays a part at least in secondary spread.

Xanthomonas campestris pv. alfalfae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas campestris pv. alfalfae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Medicago sativa , which it infects naturally. A Romanian strain naturally infects Trifolium pratense . By artificial inoculation Melilotus indica, Pisum sativum and Trigonella foenum-graecum are readily infected. Other hosts by inoculation are: Lablab purpureus, Medicago truncatula, M. scutellata, Phaseolus vulgans, Trifolium incarnatum, Vicia benghalensis and Vigna mungo (all reported by Moffett & Irwin), Clitoria ternatea and Lupinus termis (48, 3266), and Glycine max, Medicago lupulina, Melilotus alba, M. officinalis, Trifolium pratense and Vicia sativa (all reported by Stuteville & Sorensen, 1966). DISEASE: Leaf spot of lucerne. Small water-soaked spots enlarge, become brown and may coalesce to form areas of dead, dry, papery tissue. Lesions may be interveinal, along the midribs, or at the margins of the leaflets. Stem lesions also occur (36: 650; Moffett & Irwin, 1975). These start as water-soaked circular spots about 2 mm diameter. They usually coalesce to form long lesions which may extend from one node to the next. The colour of these lesions becomes dark purplish, with a greenish-yellow central region and a greasy margin. When seedlings are attacked in damp conditions post-emergence damping off occurs (Stuteville & Sorensen, 1966). GEOGRAPHICAL DISTRIBUTION: Sudan (39: 3), India (Bombay State, 35: 287), Japan (51, 1579), USSR (Republic of Georgia, 53, 3747), Australia (Queensland, 55, 789), Romania (47, 1912), USA (Wisconsin, 14: 766; Kansas, 52, 3367; Iowa, 36: 650; probably Maryland, 57, 657), Nicaragua (42: 467). TRANSMISSION: By water-splash in the nursery and by wind-blown infested soil particles in the field (53, 2931). The pathogen survives in plant debris and soil from August to June in Kansas conditions, and in dry hay for many years (52, 3367).

Pseudomonas cichorii . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Pseudomonas cichorii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Naturally infects the following: Araceae: Scindapsus sp. (46, 3116); Compositae: Chrysanthemum morifolium , Chrysanthemum sp. (40: 473; 51, 3694j), Cichorium intybus, C. endivia (5: 275; 42: 236), Gerbera jamesonii (53, 580), Lactuca sativa (50, 1025); Cruciferae: Brassica oleracea (cabbage and cauliflower: 35: 859; 51, 2027); Papaveraceae : Papaver rhoeas, P. orientale (50, 3853); Rubiaceae: Coffea arabica (55, 4727); Solanaceae : Lycopersicon escutentum (53, 4375), Nicotiana tabacum (40: 75), Solanum melongena (57, 5808); Umbelliferae: Apium graveolens (44, 2940). In addition to these natural hosts a large number of plants from various families have been successfully infected by artificial inoculation. DISEASE: Leaf spot symptoms start as small watersoaked spots, which enlarge and rapidly become dark brown to blackish. The disease is frequently systemic and produces a rot of the centre leaves in chicory, and long dark brown streaks on the stems of tomatoes. Vascular darkening is also seen in tomato (53, 4375). GEOGRAPHICAL DISTRIBUTION: The known distribution is widespread but rather scattered. It is probably present in many more countries than those reported, which include the following: Tanzania (as P. papaveris , 35: 188); India (58, 2991); Japan (57, 5808); Taiwan (14: 738); New Zealand (53, 4375); Bulgaria (45, 929); France (51, 2027); Germany (14: 418); Italy (50, 1025); England; USA (Montana, Illinois, Florida, Georgia, New York); Barbados; Brazil (40: 75). TRANSMISSION: Mainly by water splash. It is rapid under warm, wet conditions. Seed transmission occurs in lettuce (45, 929).

The fate of extracellular polysaccharide from Pseudomonas phaseolicola in leaves and leaf extracts from halo-blight susceptible and resistant bean plants ( Phaseofus vulgaris L.)

Purified extracellular polysaccharide (EPS) from Pseudomonas phaseolicola was infiltrated into the mesophyll of bush bean leaves ( Phaseolus vulgaris L.). The EPS disappeared from the intercellular spaces of the halo-blight resistant breeding line 02 12 h after infiltration. Simultaneously, the visible water-soaked spots had vanished. By contrast, the intercellular spaces of the halo-blight susceptible cultivar Red Kidney were still completely filled with EPS 3 days after infiltration, and the water-soaked leaf-areas persisted. The EPS formed a stable network in the intercellular spaces of Red Kidney, whereas small floccules were observed in the incompatible system. In vitro studies showed that the intercellular fluid (IF) from the trifoliates of breeding line 02 partially degraded the EPS, whereas IF from cultivar Red Kidney did not. EPS which had been incubated with IF from resistant leaves completely lost its capacity to induce persistent water-soaked spots. It is concluded, therefore, that the resistance of bean leaves towards persistent water-soaking caused by bacterial EPS was due to enzymatic degradation and inactivation of the introduced EPS.

Induction of water-soaking in plant leaves by extracellular polysaccharides from phytopathogenic pseudomonads and xanthomonads

Extracellular polysaccharides (EPS) were obtained and partially purified from culture filtrates of Pseudomonas glycinea, P. lachrymans, P. phaseolicola, P. pisi, Xanthomonas malvacearum and X. translucens f. sp cerealis. These preparations induced persistent water-soaked spots after infiltration into leaves of those plant species which were hosts of the respective EPS-producing bacteria. Treatment of non-host plants did not result in persistent water-soaking. EPS from P. fluorescens did not induce persistent water-soaked spots in any of the plants tested. Only the susceptible cultivars of a host, but not the resistant ones, were affected by the EPS of the corresponding bacterial species. Active EPS were also obtained from halo-blight-infected bean leaves.

A GENETICALLY-CONTROLLED NECROTIC SPOTTING OF CORN LEAVES

Corn plants of several cultivars were found in the field in 1972 and 1973 with a prominent pattern of small whitish necrotic spots on their leaves. No organisms could be isolated from the lesions. They start as water-soaked spots, and certain environmental conditions favor their appearance. The condition was shown to be seed-transmitted. Self-pollinating affected plants and cross-pollinations between affected and healthy plants resulted in genetically significant ratios of affected and healthy plants which supported the hypothesis that the condition is controlled by a single dominant gene. It very closely resembles a genetically-controlled necrotic leaf spotting produced by Neuffer and Calvert with a mutagen acting on pollen grains.

Xanthomonas manihotis . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas manihotis . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Manihot esculenta . DISEASE: Cassava bacterial blight. The symptoms are unusually diverse, and include spotting, blight and wilt of leaves, wilt and dieback of stems, necrosis of vascular tissue of stems and roots, and exudation of bacterial ooze. The disease may begin with water-soaked angular leaf spots that enlarge and coalesce, forming necrotic areas and eventually causing the leaf to dry and fall. In moist conditions ooze is formed on the lesions. Infection may travel back to the petioles and stems, young stems being particularly susceptible. A progressive die-back may follow. The roots usually remain healthy in appearance, but in some susceptible varieties dry, rotted spots may develop around necrosed vascular strands (Lozano, 1975). When infected material is planted the first symptoms are wilting and dieback of the young shoots soon after emergence. GEOGRAPHICAL DISTRIBUTION: Argentina, Brazil, Colombia, Venezuela, Nicaragua, Nigeria, Ghana, Togo, Cameroon, Zaire, Uganda, Malawi, Madagascar, Mauritius, India, Malaysia, Indonesia, Taiwan. CMI Map 521, ed. 1, 1977. TRANSMISSION: The disease is spread in the field mainly by rain-splash. Dissemination is, therefore, mainly downwind (53, 3724). Insects may also transmit the disease, as does Pseudotheraptus devastans in Zaire (Maraite & Meyer, 1975). The disease overwinters and travels from one area to another in infected planting material. Infested tools may also spread disease, especially as harvesting is accompanied by much cutting (Lozano, 1975).

Xanthomonas pelargonii . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas pelargonii . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Pelargonium spp., also a number of Geranium spp. DISEASE: Bacterial stem rot and leaf spot. The leaf spot phase is characterized by irregular, small, brown, withered, initially water-soaked spots, bordered by a narrow greenish yellow zone, and exuding a small amount of bacterial slime. The stem rot phase gives a brownish black discoloration of the stem tissue and often wilting followed by angular necrosis of the leaves delimited by the main veins. These leaves die back to the stem, but remain attached until finally only the terminal leaves appear healthy. Pythium debaryanum causes very similar symptoms on Pelargonium stems. The fungus, however, produces a blackish-green to almost coal black rot, whereas the bacterium gives a brown to brownish-black rot. The fungal disease progresses much faster. Microscopical examinations reveal fungal mycelium. A Pseudomonas sp. has also been recorded as giving similar symptoms on Pelargonium (Baker, Ministry of Agriculture Technical Bulletin 25: 292, 1972). GEOGRAPHICAL DISTRIBUTION: Widespread in Europe and N. America, also reported from the Middle East and Australia (CMI Map 414, ed. 1, 1966). Additional occurrences include France (44, 3071), Netherlands (11, 767), Romania (46, 1409), Scotland (53, ld), Switzerland (55, 5239), Yugoslavia (54, 4405), Morocco (51, 3809), Iran (49, 910d) and Japan (46, 1947). TRANSMISSION: Under horticultural conditions the disease is spread mainly by operations concerned with vegetative propagation and, in particular, by diseased stock plants, which may appear healthy and by contaminated knives. Water splash dispersal also occurs (34, 369). Transmission by greenhouse whitefly, Trialeurodes vaporariorum , has also been demonstrated (41, 523; 42, 553).

Xanthomonas fragariae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas fragariae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Fragaria vesca , its crosses and cultivars. DISEASE: Angular leaf spot and vascular decline or collapse of strawberry. The leaf spot phase appears as minute water-soaked spots on the underside of leaves. They enlarge, coalesce, penetrate to the upper leaf surface and darken in colour, turning into large, irregular necrotic areas. Infection may closely follow the veins of leaves, especially when petioles are inoculated, but was not found within the vascular tissue under the conditions prevailing in Minnesota (Kennedy & King, 1962a). Dye & Wilkie (1973) reported that under New Zealand conditions stems, petioles, flowers and fruits are not infected. Systemic invasion has occurred in California (47, 862), probably under damp nursery conditions. The crowns become infected and vascular decline or complete collapse results. Most bacteria occur intercellularly in vascular tissue, forming pockets in the xylem and cambium that often rupture the tissues of the crown. Occasionally bacteria are found within the vessels of the xylem. GEOGRAPHICAL DISTRIBUTION: USA, Venezuela, Sicily, Australia, New Zealand (CMI Map 520, ed. 1, 1977). TRANSMISSION: Presumably by rain splash from infested leaf litter in the soil on to young healthy leaves. Wounds are not necessary for entry (Dye & Wilkie, 1973). The bacteria can survive the winter in leaf litter in the soil (41, 730) and for many years in dried leaf material, but do not live free in the soil. When systemic infection is present the bacteria are easily transmitted in planting material, which probably accounts for the widespread, extremely sporadic distribution. Determination of the presence of systemic infection can be very difficult which makes this phase of the disease particularly dangerous; it may well be a limiting factor in the establishment of a new variety (47, 862).

Mycosphaerella macrospora . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Mycosphaerella macrospora . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Iris, Glodiolus ; also recorded from Narcissus, Freesia and Hemerocallis . DISEASE: Leaf spot or blotch of iris. Initially, symptoms appear as small water-soaked spots soon turning brown and enlarging to produce oval lesions with a greyish centre and dark brown margin. These become irregular and coalesce and may destroy much of the leaf tissue. The disease is most serious after flowering and on the distal portions of leaves. GEOGRAPHICAL DISTRIBUTION: Europe, North America, South Africa, Australia and Middle East. TRANSMISSION: Conidia are dispersed by wind and rain. Overwintering infected leaf debris is an important source of spring inoculum. The perfect state appears to be uncommon.

Xanthomonas ricini . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Xanthomonas ricini . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Ricinus communis . DISEASE: Normally a leaf spot disease in which the bacteria are confined to the parenchymatous tissues. The tiny, dark green, water-soaked spots expand and become brownish, angular and necrotic. They may coalesce to form larger necrotic areas and badly infected leaves become chlorotic and may drop. Occasionally petioles and succulent branches have minute oval or linear spots. Sabet (40, 334) obtained atypical symptoms from inoculation of buds. When the leaves opened, the main veins became infected and tissues dependent on infected veins became yellow and flaccid and finally withered. GEOGRAPHICAL DISTRIBUTION: Scattered, more or las world-wide (CMI Map 394, ed. 1, 1962). Extra references include Hong Kong (43, 345), Poland (48, 554b), Zambia and confirmation of Kenya. TRANSMISSION: Probably in wind and rain; it is rapid in wet weather. One report suggests that it is also seedborne (33, 181).

Asperisporium caricae . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Asperisporium caricae . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Carica papaya . DISEASE: Black spot, blight or 'rust' of papaw ( Carica papaya ). Water-soaked spots on mature leaves become necrotic, usually circular and up to 4 mm diam., the dark conidia! masses being conspicuous on the under surface. Abundant spotting causes defoliation and over 50% leaf fall can occur. Similar spots form on the fruit; they cause shallow lesions and no decay. Young leaves are not attacked. GEOGRAPHICAL DISTRIBUTION: Restricted to Central and S. America, West Indies and USA (Florida, Texas) (CMI Map 488, ed. 1, 1972). TRANSMISSION: Presumably air dispersed but no experimental work has been reported and there is no confirmation of an early suggestion of seed transmission (4: 682).

Cladosporium cucumerinum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Cladosporium cucumerinum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Cucumis sativus, Cucumis melo, Cucurbita pepo . DISEASE: Scab of Cucurbits, especially cucumber ( Cucumis sativus ), muskmelon and cantaloupe ( C. melo ), and pumpkin, squash and marrow ( Cucurbita pepo ). Symptoms are most severe on the young fruit where deeply sunken lesions are formed, up to 1 cm diam. and with a gummy exudate. On older fruit infection is restricted by the host reaction and results in the formation of brown, cork-like scabs. Foliage infection (necrotic, water-soaked spots sometimes with a gummy exudate) is not very destructive. Sporulation on the leaf tends to be sparse. At favourable temperature the apical shoots of young plants are killed back. GEOGRAPHICAL DISTRIBUTION: Widespread in N. America and Europe; also in parts of Africa, S. and E. Asia, Panama and Trinidad. The disease has not been reported from Australasia or S. America (CMI Map 310, ed. 2, 1968). Additional records not mapped are Israel and Lebanon. TRANSMISSION: Probably by air dispersed conidia, and the pathogen survives between crops on host debris. Although seed treatment has been recommended (34: 341; 44, 311) C. cucumerinum is probably rarely seed-borne (47, 3058).

Ecologic and Taxonomic Studies on Pythium as Pathogenic Soil Fungi

Amakuri squash seedlings were cultivated in Hoagland solution in plant growth chamber, and water-soaked spots and spreading lesions were described on Pythium-infected hypocotyls when the seedlings were pre-treated with sodium diethyldithiocarbamate (NaDEDC) in relation to increase in host susceptibility. A slight abnormal elongation of the growth of the seedlings was found both in plant growth chamber and in water culture. Browning spots were formed in both soil and solution-grown seedlings after inoculation. The nutrient solution did not give any effect on the mycelial growth of the pathogen. The cell sap expressed from hypocotyls treated with NaDEDC did neither stimulate nor inhibit the fungal growth. Water-soaked lesions were found without any phytotoxicity when pre-treated with ether for 20-120 seconds. Only NaDEDC and sodium fluoride were considered good among the metabolic inhibitors used which induced water-soaked lesions because of the absence of phytotoxicity and stimulative effects on the fungal growth. Cuttings of the seedling which were supplied with the NaDEDC through their cut ends did not exhibit browning spots but rather formed water-soaked lesions. The water culture was more desirable method with NaDEDC than the injection in obtaining plant materials with water-soaked lesions.

Alternaria longipes . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Alternaria longipes . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Nicotiana tabacum . DISEASE: Brown spot of tobacco. Symptoms first occur on the lower leaves as small, water-soaked spots, becoming brown, orbicular, zonate, up to 3 cm diam., with the centre becoming lighter lesion is surrounded by a yellow halo, which is absent from spots formed on seedlings. Severe spotting leads to general leaf necrosis and death. The spotting is liable to extend during curing. Symptoms are much less conspicuous on young leaves. Necrotic lesions (halo absent) also occur on petioles, seed capsules and stems, in the later forming dark brown elongated longitudinal depressions. GEOGRAPHICAL DISTRIBUTION: Widespread, see CMI Map 63, ed. TRANSMISSION: Air-dispersed conidia are more abundant on dry sunny days but spread by splash droplets probably occurs also. The pathogen is harboured in host debris and is also possibly seedborne.

Pseudomonas striafaciens . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Pseudomonas striafaciens . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Avena sativa, A. byzantina and Hordeum vulgare are also susceptible (Elliott, 1951). Tessi (1953) showed that Briza maxima, Bromus catharticus, B. hordeaceans and B. rubens are all slightly susceptible to artificial inoculation. DISEASE: Bacterial stripe blight of oats. Lesions appear mainly on the leaves as sunken, water-soaked spots, which grow or coalesce forming long water-soaked stripes. Bacterial exudate is often seen, especially under humid conditions. Older lesions become a translucent brownish colour. Sheaths, culms, pedicels and glumes are sometimes affected. GEOGRAPHICAL DISTRIBUTION: N. America, Argentine, U.S.S.R. Australia (CMI Map 363, 1959) and Japan (47, 2693). TRANSMISSION: As for P. coronafaciens .

Pseudomonas lachrymans . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Pseudomonas lachrymans . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Cucumis sativus and C. anguria . It may also attack C. melo var. inodorus (26: 140) and some other cucurbits. Elliott (31: 105) lists 10 hosts, all in the Cucurbitaceae . DISEASE: Angular leaf spot of cucumber. Small water-soaked spots appear on the leaves, petioles, stems, and fruits. On leaves they enlarge and become angular as they are delimited by veins They become tan to brown and the necrotic centres may fall out. On petioles, stems, and fruit spots develop white crusty bactenal exudate. A fruit rot develops if the bacteria penetrate deeply. GEOGRAPHICAL DISTRIBUTION: North and parts of Central America, most of Europe, U.S.S.R., China, Japan, W. Australia, Israel, southern Africa. (CMI Map 355, ed. 2, 1964). TRANSMISSION: The pathogen is seed-borne and infects the cotyledons dunng germination. It can overwinter on infected crop residue in the soil and has been found viable in dry leaf matenal after two and a half years (36: 677). The bacteria are carried from plant to plant within a crop by rain splash and probably by insects (Carsner, 1918; 31: 272). Workers can also spread the disease, particularly when foliage is wet with rain or dew (35: 810).

STUDIES IN THE BACTERIAL DISEASES OF SUDAN CROPS: III. ON THE OCCURRENCE, HOST RANGE AND TAXONOMY OF THE BACTERIA CAUSING LEAF BLIGHT DISEASES OF CERTAIN LEGUMINOUS PLANTS

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.