Showing papers on "Leaf spot published in 1974"

Pseudomonas cichorii causing tomato and celery diseases in New Zealand.

Abstract: A disease of tomato, not previously described, was found to be caused by Pseudomonas cichorii (Swingle 1925) Stapp 1928. This appears to be a new natural host for Ps. cichorii. In addition this organism has been found causing a leaf spot in celery in New Zealand. These are new disease records for this country. Symptoms of the diseases are described and identification procedures given.

Rice Diseases in Nigeria

Abstract: The two major fungal diseases of rice in Nigeria are rice blast (Pyricularia oryzae Cav.) and brown spot (Cochliobolus miyabeanus (Ito and Kuribayashi) Dreschler ex Dastur). The loss in grain yield attributable to these diseases ranges from 11.5–39.6% and 12–43% respectively, Mancozeb, blasticidin-S, fentin hydroxide, benomyl and edifenphos as foliar sprays effectively control rice blast in the laboratory and field. Brown spot is controlled by spraying with thiram, mancozeb or blasticidin-S. A more useful approach to the control of these diseases being adopted in Nigeria is the search for horizontally resistant varieties. Other fungal diseases of rice in Nigeria are the green smut (Ustilaginoidea virens (Cooke) Tak.), basal sheath rot (Rhizoctonia solani Kuhn), sheath blight (Corticium sasakii (Shirai), Matsumoto.), leaf scald (Rhynchosporium oryzae Hashioka and Yokogi), narrow brown leaf spot (Cercospora oryzae Miyake) and bakanae disease, a foot rot caused by Fusarium moniliforme Sheldon. Two s...

Mode of Survival of Isariopsis Griseola Sacc. the Causal Agent of Angular Leaf Spot of Beans

Abstract: Under the conditions at Solan Isariopsis griseola mainly over winters on host debris through stromata. The disease was also found to be seed borne and this formed one of the primary sources of inoculum to new localities. The actual seat of infection on the seeds was found to be hilum cavity where profuse mycelial growth comprising of conidiophores and conidia was observed. The macrosclereids were not infected. The fungus was isolated from seeds extracted from diseased pods of different varieties.

Possible rôle of sugars in restriction of lesion development in finger millet leaves infected with Helminthosporium tetramera

Abstract: Helminthosporium tetramera causes a leaf spot disease of finger millet. Small irregular brown spots appear within 3 days after inoculation but further lesion enlargement is restricted. Total soluble sugars, particularly glucose, fructose and sucrose accumulated in the infected leaves, but starch concentrations were reduced. The rate of photosynthesis was lower in infected than in healthy leaves. β-Amylase activity increased while starch phosphorylase activity decreased as a result of infection. The pathogen produced β-amylase and an inhibitor of phosphorylase in vitro . A possible relationship between sugar concentrations and lesion size was found. Increased sugar concentrations, induced by growth in continuous light or by glucose sprays, resulted in low levels of disease. Relatively severe infections developed on leaves with low sugar levels achieved by growing plants in soil with excessive nitrogen, or in the dark. H. tetramera produced pectic and cellulolytic enzymes in vitro , but production of these enzymes was inhibited by addition of glucose to the medium. It is suggested that the increased sugar concentrations in diseased leaves, by inhibiting production of enzymes which degrade cell walls, have at least a partial effect in limiting lesion size.

Necrotic Leaf Spot, A New Virus Disease of Eggplant Caused by Broad Bean Wilt Virus

Abstract: A virus disease of eggplant was found in the vicinity of Tokyo during 1971-1972. Young leaves of the diseased plants showed necrotic spots, sometimes followed by twisting or crinkling of the leaves and dwarfing of whole plant. Some experiments were made to identify the causal virus.The disease was easily transmitted by sap inoculation. Out of 38 species of plants among 15 families, 24 species among 10 families were proved to be susceptible to the causal virus. The virus was also transmitted by the green peach aphid, Myzus persicae (Sulz.).The virus in infective sap was inactivated in 10 minutes at 60-70C, and in 4-6 days at room temperature. Its dilution end point lied between 1:10, 000 and 1:100, 000.Spherical virus particles of about 25nm in diameter were detected in the diseased eggplant leaves under the electron microscope by the direct negative staining method. The same virus particles were also detected in leaves of mechanically inoculated plants.The diseased spinach leaves were ground in phosphate buffer (0.2M, pH 7.6), and then the virus in the extract was partially purified by differential centrifugation followed by sucrose density gradient centrifugation. The finally obtained virus preparation contained a large number of spherical virus particles of about 25nm in diameter. Size and shape of these particles were quite uniform. The preparation showed a high infectivity to Chenopodium amaranticolor.Electron microscopy of the diseased eggplant leaves showed that the virus particles distributed as individuals or as amorphous, sometimes crystalline, aggregates in vacuole and cytoplasm. They were found in epidermal, mesophyll, and also phloem parenchyma cells. Sometimes a chain-like array of the virus particles was observed in plasmodesmata connecting two neighbouring cells. Necrosis and abnormal development of vesicular bodies were common in cells of the diseased tissues.From these results it is evident that the causal virus is broad bean wilt. Broad bean wilt virus has not been reported to occur on eggplant. Thus we propose to name the disease “necrotic leaf spot of eggplant”.

Effect of infection byColletotrichum capsici and toxin treatment on the permeability changes of turmeric leaves

Abstract: A toxin produced byColletotrichum capsici, pathogen of turmeric leaf spot disease has been found to alter the cell permeability of turmeric leaf tissue even at very low concentrations. This led to leaching of large quantities of water soluble constituents. The possibility of the involvement of a toxin in the pathogenesis is discussed.