Bremia lactucae. [Descriptions of Fungi and Bacteria].

1981 ◽  
Author(s):  
W. M. Morgan
Keyword(s):  
Geographical Distribution ◽  
Systemic Infection ◽  
Lower Surface ◽  
Globe Artichoke ◽  
Bremia Lactucae ◽  
Lettuce Plant ◽  
Mature Leaves ◽  
Secondary Infections ◽  
Important Means ◽  
Means Of Transmission

Abstract A description is provided for Bremia lactucae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: At least 230 species in the following genera of Compositae: Agoseris, Arctium, Carduus, Carthamus, Centaurea, Cichorium, Cineraria, Cirsium, Crepis, Cynara, Dendroseris, Dimorphotheca, Erechtites, Gaillardia, Gnaphalium, Helichrysum, Hemistepta, Hieracium, Hypochoeris, Jacobaea, Knightia, Lactuca, Lagoseris, Lapsana, Lappa, Leontodon, Mulgedium, Nabalus, Picris, Prenanthes, Rhodanthe, Saussurea, Senecio, Solidago, Sonchus, Taraxacum and Tragopogon. DISEASE: 'Downy mildew' of lettuce, globe artichoke, endive, chicory and many ornamental and wild species of Compositae. Infection can occur on any part of the lettuce plant (Lactuca sativa) except the capitulum (40: 197) and the fungus may colonize the plant systemically even as far as the roots (42: 429). In infected seedlings, the cotyledons stop growing, leading to stunting or death of the plant. Sporulation occurs on both sides of the cotyledon, which becomes chlorotic. As seedlings age, they become less susceptible, systemic infection becomes progressively less and fewer sporangiophores are produced (53, 3262). Newly formed true leaves are less susceptible than cotyledons (53, 3262). On mature leaves, profuse sporulation on the lower surface is sometimes preceded by a slight chlorosis; in widespread infections of wrapper leaves conidiophores are often the first sign of infection. On the upper surface chlorosis becomes severe and the lesion, bounded by the main veins, is frequently angular in appearance. Browning may occur later, probably due to secondary infections. On globe artichoke (Cynara scolymus) infection of the peduncle and basal bracts allows access to secondary infections (43, 3104). GEOGRAPHICAL DISTRIBUTION: World-wide except Antarctica and Arctic (CMI Map 86, ed. 3, 1969). TRANSMISSION: Sporulation is usually profuse and conidia are air-borne. Conidia from cultivated lettuce are viable for at least 60 days at low temperatures and high humidity (40: 197) and, where lettuce is grown throughout the year, conidia are the most important means of transmission of the disease. The fungus is probably also carried over from season to season by means of oospores in soil debris (51, 3663).

Pseudoperonospora humuli. [Descriptions of Fungi and Bacteria].

1983 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
Downy Mildew ◽  
Geographical Distribution ◽  
Systemic Infection ◽  
Humulus Lupulus ◽  
Convincing Evidence ◽  
Cone Production ◽  
Secondary Infections ◽  
Pseudoperonospora Humuli ◽  
Growing Crop ◽  
Curled Leaves

Abstract A description is provided for Pseudoperonospora humuli. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOST: Humulus lupulus. DISEASE: Downy mildew of hops. The first sign of infection, seen early in the year, is the development of spindly, stunted, shoots with pale, crowded and down-curled, leaves. These are known as 'primary basal spikes' and are shoots with a systemic infection developed from mycelium which has overwintered in the rootstock. The undersurfaces of the leaves of these shoots bear large crops of sporangia which in moist and humid conditions can soon spread the disease in the growing crop. Secondary infections may occur on leaves, growing tips, flowers and cones. On the leaves they are seen either as small discrete spots or larger, more angular, brown areas. The diseased shoots arising from secondary infections and depending upon the position of the infected bud are known as 'terminal' or 'lateral' spikes. They resemble basal spikes in appearance. Infection of the flowers can inhibit cone production. If cones do develop, and become infected, the brown spots and lesions of the fungus can make them unsaleable. GEOGRAPHICAL DISTRIBUTION: CMI Map No. 14, ed. 4, 1976, with the addition of Belorussia, Estonia, India, Kinghizia, Kazakhstan, Latvia, Lithuania, Moldavia, Ukraine and Uzebekistan. TRANSMISSION: Ware (1926) demonstrated the presence of mycelium in diseased rootstocks but its significance in the overwintering of the pathogen was not fully recognized until Coley Smith (1962) showed that the primary basal spikes which develop in spring originate from infected buds on the rootstocks. Oospores, which are often produced in abundance, were at one time thought to be responsible for infection of the shoots in spring but there is no convincing evidence to support this theory.

Peronospora antirrhini. [Descriptions of Fungi and Bacteria].

1981 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
Downy Mildew ◽  
Geographical Distribution ◽  
Seed Transmission ◽  
Lower Surface ◽  
Flowering Plants ◽  
Antirrhinum Majus ◽  
High Humidity ◽  
Secondary Infections ◽  
Leaf Surfaces ◽  
Definite Proof

Abstract A description is provided for Peronospora antirrhini. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Antirrhinum majus, A. nuttallianum, Misopates orontium. DISEASE: Downy mildew of antirrhinum. This is mainly a disease of seedlings and young plants. The infection is systemic and affected plants appear stunted and pale yellowish-green. The leaves are curled inwards and droop down. Conidiophores develop on the lower surface forming a fine white to purple down. In heavy infections the down is found on both leaf surfaces and also on the stems. The growing point may be killed and then plants often break from the base and produce several new shoots. Conidia can cause secondary infections on the leaves of older plants especially in conditions of high humidity. These appear as pale yellowish spots. GEOGRAPHICAL DISTRIBUTION: Worldwide, see CMI Map No. 222 ed. 2, 1971. TRANSMISSION: Seed transmission by oospores was tentatively suggested by Yarwood (1947). Moore & Moore (1952) refer to circumstantial evidence but say there is no definite proof. Peronospora antirrhini is not recorded as a seed pathogen by Richardson (1979) but Neergaard (1977) points out that for seed-borne infection of a downy mildew to be effective all that is needed is a mere trace of the fungus on the seed. As Yarwood (1947) indicates, terminal infections of flowering plants could easily contaminate seed.

Peronospora arborescens. [Descriptions of Fungi and Bacteria].

1981 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
Geographical Distribution ◽  
Disease Transmission ◽  
Field Experiments ◽  
Indirect Evidence ◽  
Lower Surface ◽  
Diseased Plant ◽  
Infected Seed ◽  
Aerial Parts ◽  
Secondary Infections ◽  
One Year

Abstract A description is provided for Peronospora arborescens. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Papaver alpinum, P. dubium, P. caucasicum, P. nudicaule, P. rhoeas, P. somniferum, P. setigerum, Meconopsis spp. DISEASE: Downy mildew of the opium poppy, Papaver somniferum. Seedlings if attacked usually succumb. In older plants the infection may be systemic with all parts of the plant, including the growing point, affected. In Berkeley's original diagnosis of the pathogen on P. rhoeas he described infected plants as 'having a peculiar aspect by which they may be known at a distance'. The leaves appear greenish-yellow, thickened and deformed. Conidiophores develop as a greyish violet felt on the lower surface of the leaves and in severe attacks appear on the stems, buds and capsules. Local secondary infections also occur usually on the lower leaves and here the pathogen forms rather angular chlorotic blotches on the upper leaf surface. These are often associated with the larger veins. GEOGRAPHICAL DISTRIBUTION: Africa (Algeria, Egypt); Asia (Afghanistan, Azerbaijan (USSR), India, Iran, Japan, Turkey, Pakistan); Australasia (Australia); Europe (widespread); S. America (Argentina). TRANSMISSION: Authors agree that diseased plant debris remaining in the fields can infect a subsequent crop and that the practice of using this debris to manure the ground is to be deprecated. Opinions differ on the part that the oospores, which are formed in profusion in all aerial parts, play in this primary infection. Neither Behr (1956) nor Kothari & Prasad (1970) were able to germinate resting spores. Behr considered that they had no part in disease transmission. Kothari & Prasad (1970), however, in a series of field experiments obtained indirect evidence that oospores present in the soil could become infective one year after their formation. The role of infected seed in transmitting the disease is also disputed. Yossifovitch (1929) and Kothari & Prasad (1970) suggested that infected seed is not important while Behr (1956) showed that perennating mycelium was present in the seed from diseased crops. Alavi (1975), in experiments made over several years on farms in Iran, reported a high probability that the disease was transmitted by seeds.

scholarly journals Host-Dependent Requirement for the Potato leafroll virus 17-kDa Protein in Virus Movement

2002 ◽  
Vol 15 (10) ◽  
pp. 1086-1094 ◽  
Author(s):  
Lawrence Lee ◽  
Peter Palukaitis ◽  
Stewart M. Gray
Keyword(s):  
Amino Acids ◽  
Solanum Tuberosum ◽  
Nicotiana Benthamiana ◽  
Systemic Infection ◽  
Potato Leafroll Virus ◽  
Virus Movement ◽  
Wild Type ◽  
Mature Leaves ◽  
Leafroll Virus ◽  
Virus Distribution

The requirement for the 17-kDa protein (P17) of Potato leafroll virus (PLRV) in virus movement was investigated in four plant species: potato (Solanum tuberosum), Physalis floridana, Nicotiana benthamiana, and N. clevelandii. Two PLRV P17 mutants were characterized, one that does not translate the P17 and another that expresses a P17 missing the first four amino acids. The P17 mutants were able to replicate and accumulate in agroinoculated leaves of potato and P. floridana, but they were unable to move into vascular tissues and initiate a systemic infection in these plants. In contrast, the P17 mutants were able to spread systemically from inoculated leaves in both Nicotiana spp., although the efficiency of infection was reduced relative to wild-type PLRV. Examination of virus distribution in N. benthamiana plants using tissue immunoblotting techniques revealed that the wild-type PLRV and P17 mutants followed a similar movement pathway out of the inoculated leaves. Virus first moved upward to the apical tissues and then downward. The P17 mutants, however, infected fewer phloem-associated cells, were slower than wild-type PLRV in moving out of the inoculated tissue and into apical tissues, and were unable to infect any mature leaves present on the plant at the time of inoculation.

Peronospora anemones. [Descriptions of Fungi and Bacteria].

1981 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
New Zealand ◽  
Botrytis Cinerea ◽  
Downy Mildew ◽  
Geographical Distribution ◽  
Primary Infection ◽  
Leaf Surface ◽  
Plant Debris ◽  
Lower Leaf Surface ◽  
Glass Slides ◽  
Secondary Infections

Abstract A description is provided for Peronospora anemones. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Anemone coronaria, A. globosa. DISEASE: Downy mildew of anemones. Infected leaves lose their natural bloom, appearing dull green, almost grey in colour and are often down curled giving the plant a rounded appearance. As the disease progresses, leaf colour may change to shades of pink or purple with necrotic areas appearing on the older leaves. Invasion by secondary organisms (e.g. Botrytis cinerea) is common, especially after frost or storm injury, and this accelerates plant death. In favourable conditions conidiophores develop forming a whitish-grey down on the lower leaf surface, on the bracts and, less frequently, on the petioles. It is not uncommon for affected plants to show little or no sporulation and in these cases the presence of extensive intercellular mycelium and, later in the season, oospores in petioles and peduncles helps diagnosis. GEOGRAPHICAL DISTRIBUTION: Australasia (New Zealand); Europe (England, Jersey, France, Italy, Netherlands). TRANSMISSION: Primary infection is caused by oospores in plant debris in the soil. Tramier (1963) was unable to germinate oospores and thus work out precise details of the conditions affecting their germination but he showed evidence that regular and prolonged rain encouraged germination. Conidia, which cause secondary infections, are dispersed by rain and during harvesting of the flowers. Wind is thought to be unimportant in their dissemination as shown by glass slides covered with vaseline and placed near an infected crop (Tramier, 1965).

Peronospora hariotii. [Descriptions of Fungi and Bacteria].

1983 ◽  
Author(s):  
S. M. Francis
Keyword(s):  
Downy Mildew ◽  
Geographical Distribution ◽  
Weather Conditions ◽  
Lower Surface ◽  
Buddleja Davidii ◽  
Nursery Stock ◽  
Terminal Bud

Abstract A description is provided for Peronospora hariotii. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Buddleja davidii cv. White Profusion, B. globosa and cultivars, especially cv. Lemon Ball. DISEASE: Downy mildew of Buddleja. This is a disease of nursery stock and there are no reports of the fungus infecting mature plants. Young plants 1-2 ft. high bear conspicuous brown lesions on their leaves. These begin as a yellow area on the upper surface which soon turns brown and brittle. Leaves affected in this way usually drop off. The leading shoot and terminal bud may also die. The down, which develops on the lower surface of infected leaves, is pale to medium brown depending on age and weather conditions. GEOGRAPHICAL DISTRIBUTION: Europe (Britain, France). TRANSMISSION: Not known.

Xanthomonas cassavae. [Descriptions of Fungi and Bacteria].

2000 ◽  
Author(s):  
G. S. Saddler
Keyword(s):  
Geographical Distribution ◽  
Systemic Infection ◽  
Climatic Conditions ◽  
Euphorbia Pulcherrima ◽  
Disease Development ◽  
Long Distance ◽  
Green Point ◽  
Leaf Spots ◽  
Strong Winds ◽  
Dark Green

Abstract A description is provided for Xanthomonas cassavae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Manihot esculenta (Euphorbiaceae); by artificial inoculation: Euphorbia pulcherrima (Euphorbiaceae). DISEASE: Cassava leaf spot or bacterial necrosis. Angular leaf spots extend along veins but generally do not develop into blight. Spots age, turn dark brown and are surrounded by a yellow halo. Exudate is frequently produced. On stems, dark green point lesions develop slowly up to 1 cm diam. Lytic pockets generally develop under lesions in the cortex. Lateral extension can lead to girdling and tip dieback. Secondary colonization by Colletotrichum gloeosporioides[Glomerella cingulata] is frequently observed. Systemic infection and vascular browning are absent or very restricted. Entry into the host is through natural openings (stomata) or epidermal wounds, which can be caused (especially on the stem) by sand particles or small grains of gravel thrown up by the strong winds which precede the first rains. The optimum temperature for disease development is 25°C. Disease mainly occurs above altitudes of 800 m. There is evidence that disease severity is linked to poor plant nutrition. GEOGRAPHICAL DISTRIBUTION: AFRICA: Burundi, Congo Democratic Republic, Kenya, Malawi, Niger, Rwanda, Tanzania, Uganda, Zaire. SOUTH AMERICA: Colombia. TRANSMISSION: Long distance spread is restricted. Symptomless cuttings taken from diseased plants were unable to demonstrate propagation. Rapid disease development under favourable climatic conditions suggests a symptomless epiphytic phase on the host itself or on a plant other than cassava. In the field, dispersal is by wind and rain.

Urocystis cepulae. [Descriptions of Fungi and Bacteria].

1971 ◽  
Author(s):  
J. L. Mulder
Keyword(s):  
Geographical Distribution ◽  
Allium Cepa ◽  
Cotyledon Stage ◽  
Indefinite Number ◽  
Secondary Infections ◽  
Western Asia

Abstract A description is provided for Urocystis cepulae. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On species of Allium, including A. cepa, A. porrum, A. sativum and A. vineale. DISEASE: Smut of onion (Allium cepa). The infection on other species of Allium is much less serious. Symptoms are first seen at the cotyledon stage when a dark, thickened area appears which, when large, may cause a downward curvature. As growth occurs the lesions, which break open to reveal the dark spore masses, form at the base of the leaves. Most plants are killed in 3-4 weeks but if they survive the leaves become short, brittle, distorted and may bear lesions throughout their length. Spores develop on the bulb which may be undersize and, although it does not rot in storage, resistance to secondary infections from other pathogens is low. GEOGRAPHICAL DISTRIBUTION: Widespread in Europe, western Asia, north and central N. America; also Australia, Chile, Egypt, Japan, Korea, Morocco and Peru (CMI Map 12, ed. 3, 1965). Records not yet mapped are: Finland, Iraq, Mexico, Norway, Philippines, Thailand and India where measures for eradication were taken (39: 526; 43, 1490). TRANSMISSION: It has not been definitely established whether the pathogen is seed-borne and this is not considered to be important. Sets and transplants form the main manner of spread and U. cepulae persists in the soil as dormant spores for an indefinite number of years (45, 1600).

Pseudoperonospora cubensis. [Descriptions of Fungi and Bacteria].

1975 ◽  
Author(s):  
J. Palti
Keyword(s):  
Downy Mildew ◽  
Geographical Distribution ◽  
Lower Surface ◽  
Pseudoperonospora Cubensis ◽  
Bright Yellow ◽  
Arid Conditions ◽  
Winter Crops ◽  
Cultivated Species ◽  
China And Japan ◽  
Semi Arid

Abstract A description is provided for Pseudoperonospora cubensis. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Chiefly of cultivated species of Cucumis (cucumber, melon), Cucurbita (squash, marrow, pumpkin) and Citrullus (watermelon). Less frequent on approximately 40 wild and cultivated species of 18 other genera (e.g. Benincasa, Lagenaria, Luffa, Momordica, Trichosanthes). DISEASE: Causes downy mildew of Cucurbitaceae. Infection normally confined to bright yellow spots on upper surface of leaves, with light spots covered by greyish-black down on their lower surface, spots become necrotic and turn brown from their centre outwards. On cucumbers the spots are angular, clearly limited by leaf veins, but on melons and most other hosts vein delimination is not so clear. Cotyledons sometimes affected, but very young true leaves are not. Strongest development on leaves 5-15 days after their formation. Affected leaves dry up, do not shed. Flower parts are rarely affected and fruit and seeds never affected. GEOGRAPHICAL DISTRIBUTION: Widely distributed especially on cucumbers and melons in warm and humid zones (CMI Map 285. ed. 3. 1969). TRANSMISSION: All year round transmission in warm and humid climates from older to younger crops, under semi-arid conditions from irrigated summer crops to winter crops grown under cover and then to spring crops. Summer invasions from countries wilh mild winters to those with cooler winters is likely. Overwintering by oospores held to be possible in China and Japan.

Phragmidium rubi-idaei. [Descriptions of Fungi and Bacteria].

1969 ◽  
Author(s):  
G. F. Laundon
Keyword(s):  
New Zealand ◽  
North America ◽  
Geographical Distribution ◽  
Yellow Rust ◽  
Lower Surface ◽  
Early Spring ◽  
Rubus Idaeus ◽  
Leaf Surfaces

Abstract A description is provided for Phragmidium rubi-idaei. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Rubus idaeus (raspberry) and a few wild Rubus species. DISEASE: Cane rust or western yellow rust of raspberry, infecting canes, leaves, petioles and fruiting laterals. GEOGRAPHICAL DISTRIBUTION: Widespread throughout temperate areas in North America, Europe, U.S.S.R. and Japan. Also in Australia and New Zealand. TRANSMISSION: By wind-blown spores. Basidiospores arise from teliospores on dead leaves on the ground in early spring and infect through both leaf surfaces; aeciospores and urediospores apparently infect only through the lower surface (Zeller & Lund, 1934).

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