Showing papers on "Leaf spot published in 1986"

Corynespora leaf spot disease of rubber (Hevea brasiliensis) - a new record

Abstract: A severe spotting of leaves of rubber (Hevea brasiliensis Muell. — Arg.) followed by defoliation was observed for the first time in Sri Lanka in 1985 on clone RRIC 103, in a polybag nursery. Since then this disease has spread to seedling nurseries, susceptible clones in budwood nurseries, immature and mature plantations in all the rubber growing districts in Sri Lanka. At present, approxi­ mately 2400 and 1600 ha in the State and private sector, respectively, are affected. DISEASE SYMPTOMS The fungus affects the immature as well as mature leaves, the former being more susceptible. The symptoms first appear as greyish brown spots which enlarge into conspicuous circular or irregular lesions of varying sizes and shapes (Fig: 1). Severel spots may coalesce to produce extensive crisp brown areas on the leaf, some of which may become irregular papery lesions giving a scorched appearance (Fig 2).

Studies on inoculum sources of angular leaf spot of beans caused by Phaeoisariopsis griseola in Uganda

Abstract: Angular leaf spot of beans caused by Phaeoisariopsis griseola is a major problem on this crop in Eastern Africa. The sources of inoculum for this disease were investigated. The causal fungus was confirmed as seedborne in all the cultivars tested. The fungus caused seed discolouration but not all infected seeds were discoloured. Seed to seedling transmission was low. The fungus survived in infected crop debris for a maximum of nine and four to six months under indoor and outside conditions respectively. Under soil, the fungus survived for only two months. Infected offseason crops and volunteer plants were present at the time of planting the seasons’ crops and were an obvious source of the inoculum. It is concluded that the seed, crop debris, off‐season crops and volunteer plants are all possible sources of P. griseola infection under the local conditions.

Effects of Enhanced Ultraviolet-B Radiation on Yield, and Disease Incidence and Severity for Wheat Under Field Conditions

Abstract: The influence of enhanced UV-B radiation (280–320 nm) on wheat (Triticum aestivum cv. ‘Florida 301’) yield, and disease incidence and severity was investigated for two growing seasons under field conditions. Three levels of UV-B enhancement, simulating 8, 12, and 16% stratospheric ozone reduction, were employed during 1982, and two levels of UV-B radiation enhancement, simulating 12 and 16% ozone depletion, were used during 1983. At each level of UV-B enhancement during 1982, no significant direct effect upon yield was observed. However, in 1983, there was an indication that UV-B radiation was interacting with other parameters because there was a significant bimodal response on plant and seed dry weights. As determined by incidence survey, during 1982 the incidence of leaf rust (Puccinia recondita f. sp. tritici), leaf spot (Helminthosporium sativum), and glume blotch (Septoria nodorum) were not significantly affected by the enhanced levels of UV-B radiation. During 1983, specific small plots were used to test for leaf rust severity on a resistant and a susceptible cultivar. Leaf rust on the resistant cultivar ‘Florida 301’ decreased with plant age, but control and UV-treated plants were not different. With increased UV-B irradiation of the susceptible but tolerant cultivar ‘Red Hart’ severity increased with age, and all plots exposed to increased levels of UV-B radiation were significantly different from the control. However, these small plot tests did not allow us to determine if yield was influenced.

Lophiostoma mangrovis, a new marine ascomycete from the tropics

Abstract: Calpouzos, L., A. Santiago, T. Theis, and C. Colbert. 1959. Studies on the action of oils in the control of Mycosphaerella musicola on banana leaves. Phytopathology 49: 119-122. Klein, H. H. 1961. Effects of fungicides, oil, and fungicide-oil-water emulsions on development of Cercospora leaf spot on bananas in the field. Phy? topathology 51: 294-297. Kranz, J. 1975. Die Wirkung einiger Fungizide auf Mycosphaerella musicola Leach in laboratoriumsund Mikrofeldversuchen. Phytopathol. Z. 52: 5972. Medwid, R. D., and D. W. Grant. 1984. Germination of Rhizopus oligosporus sporangiospores. Appl. Environ. Microbiol. 48: 1067-1071. ont, W. 1960. Epidemiology and control of banana leaf spot (Mycosphaerella musicola Leach) in North Queensland. QueenslandJ. Agr. Sci. 17: 211-272.

Screening of Asparagus species for resistance to Stemphylium leaf spot

Abstract: Fourteen taxa of the genus Asparagus were screened for their resistance to Stemphylium leaf spot under controlled conditions in growth chambers. The plants were inoculated with a conidial suspension of 2 isolates of Stemphylium sp. from asparagus. Disease assessment, based on percentage stem area necrotic, was made 13–17 days after inoculation. A. officinalis L. var. pseudoscaber (Grec.) Asch. & Graebn. and the 2 cultivars of A. officinalis L., Rutgers Beacon and Mary Washington, showed high levels of infection. Most other taxa showed low levels of infection. Seven of these were classed as highly resistant: A. asparagoides (L.) W.F. Wight, A. compactus Salter, A. densiflorus (Kunth) Jessop cv. Myers, A. densiflorus (Kunth) Jessop cv. Sprengeri, A. larcinus Burch., A. verticillatus L., and A. virgatus Bak. These species are considered to be potential sources of resistance for breeding commercial cultivars resistant to Stemphylium leaf spot.

Pathogenicity and epidemiology of Corynespora cassiicola in the Republic of Seychelles

Abstract: Corynespora cassiicola is reported in the Republic of Seychelles, where it causes a leaf spot disease of tomatoes, cucumbers and watermelons Isolates from tomatoes and cucumbers were cross pathogenic, but differences in symptoms indicated a degree of host specificity The fungus developed rapidly as a saprophyte and sporulated abundantly for at least 28 days on dead tomato leaves in the field Numbers of conidia increased with duration of wetting of the debris C cassiicola colonized and sporulated on papaya leaf debris Isolates from papaya leaf debris caused leaf lesions on tomato, cucumber and watermelon, but isolates pathogenic on papaya were not found C cassiicola is an aggressive facultative parasite that sporulates abundantly on plant debris Inoculum of C cassiicola from several sources can initiate disease cycles Consequently, sanitation as a control measure appears to be justified

Effects of host nutrition, leaf age, and preinoculation light levels on severity of leaf spot of dwarf schefflera caused by Pseudomonas cichorii

Abstract: ABSTRACT to runoff without wounding. Chase, A. R., and Jones, J. B. 1986. Effects of host nutrition, leaf age, and preinoculation light Effects of host nutritional level and levels on severity of leaf spot of dwarf schefflera caused by Pseudomonas cichorii. Plant Disease tissue age on disease expression. Rooted 70:561-563. cuttings were planted in 10-cm plastic pots with the potting medium described. The roles of preinoculation light level, nutrition, and age of tissue in susceptibility of Schefflera Ten plants each were fertilized with arboricola to bacterial leaf spot caused by Pseudomonas cichorii were tested. Lesion numbers and Osmocote 19-6-12 as a topdressing at 2,4, size were reduced significantly as fertilizer levels were increased up to 12 g/ 10-cm pot (about 6X 6×8, 10,or12 g/ 1 p ot The recommended rate). Lesion number and size decreased as leaf age increased from the top to the 6, 8, 10, or 12 g/10-cm pot. The bottom of the plant. These fertilizer levels did not affect plant height, color, number of leaves, or recommended rate is about 2 g/ 10-cm pot fresh weight of tops. Light intensities (125-800 gmol ms-') for plant production before (5). Plants were then grown in a inoculation did not affect the number of lesions that formed. glasshouse for 2 mo before inoculation. Plant height, number of leaves, and top

A comparative study of the pathogenicity and epidemiology of strains of Pseudomonas syringae pv. tabaci that cause wildfire and angular leaf spot diseases of tobacco in Zimbabwe

Abstract: The population dynamics of two strains of Pseudomonas syringae pv. tabaci that cause the foliar spot diseases of tobacco known as wildfire (WF) and angular leaf spot (ALS) were significantly different in leaves of a susceptible tobacco cultivar. After 48 h the population of WF strains changed abruptly from exponential growth to stationary phase, whereas there was a more gradual transition by the ALS strains. This resulted in smaller stationary-phase populations for WF than for ALS. The decline of the WF population started soon after the stationary phase was reached, whereas the ALS stationary phase was relatively stable. The strains reacted differently to climatic factors. On plants inoculated and exposed to the weather at weekly intervals, WF lesions grew faster when vapour pressure deficits, maximum temperatures and radiation were low. Multiple regression analysis showed that over 70% of the variation in WF infection was accounted for by variation in VPD, radiation and mean temperature. Variation in ALS infection was less easily explained in relation to the weather variables measured. Plant age and stalk position had a differential effect on the pathogenicity of the two strains. Lower leaves of young plants (42 days) were most susceptible to WF and top leaves of older plants (84 days) were most susceptible to angular leaf spot. Differences in pathogenicity and occurrence in the field suggest that pathovar status should be considered for the ALS pathogen of tobacco.

Yellow leaf spot of cashew: A case of molybdenum deficiency*

Abstract: The occurrence of yellow leaf spot, an enigmatic disorder in cashew, (Anacardium occidentale L.) was found to be associated with low soil pH (4.5–5.0). The affected leaves were deficient in molybdenum and had excessive amounts of manganese. Besides, the spotted leaves typically had lower levels of Kjeldahl nitrogen.

Plant microbiocidal compound and method.

Abstract: A microbiocidal method and organo-silicon compound for plants The microbiocidal organo-silicon compound can be mixed with water and applied to a plant to kill or inhibit a wide variety of micro-organisms The plant microbiocidal compound and method is highly effective in controlling a wide variety of pathogenic micro-organisms including the citrus canker bacterium Xanthomonas campestris and ice nucleation bacteria such as Pseudomonas syringae and Erwinia herbicola In addition, the plant microbiocidal compound is also effective against fungi such as peanut leaf spot fungus (Cercospora arachidicola)

Zonate Leaf Spot of Mulberry, with Special Reference to the Life-Cycle and Taxonomy of Causal Fungus Gonatophragmium mori

Abstract: The zonate leaf spot fungus newly found on mulberry, Morus alba, in Japan since 1978 was identified as Gonatophragmium mori (Sawada) Deighton (=Spondylocladium mori Sawada). Many new host plants, being 28 species belonging to 24 genera of 16 families, were recorded through the field surveys around mulberry plantations. In the overwintering experiments with naturally or artificially infected leaves on Morus, Vitis and Broussonetia, development of teleomorph, the perfect state was confirmed. Ascospores serve as the primary infection source in early summer. From the pathogenicity to Morus and Vitis with ascospores and conidia, and the identity of morphological characteristics of perithecial and anamorph, conidial states, the causal fungus was re-classified as Acrospermum viticola Ikata apud Ikata and Hitomi (1931) having the conidial state, Gonatophragmium mori (Sawada) Deighton (1969).

Survey and Screening of Benomyl Resistant Strains of Cercospora beticola in Minnesota and North Dakota

Abstract: INTRODUCTION The incidence and severity of Cercospora leaf spot of sugar beet (Beta vulgari 5 L.), caused by Cercospora bet i­ cola Sacc, has increased in Minnesota and North Dakota during the last 3 years (2). The occurrence of benomyl­ resistant strains of C. beticola has been reported from Texas (7) , Arizona (6), southern Minnesota (1,5) and Greece (4). Benomyl-resistant strains of C. beticola have been shown to be cross-resistant to the related fungicides thiophanate and thiabendazole (3). The purposes of this investigation were to determine the geographical distribu­ tion of benomyl-resistant strains of C. beticola, and to develop an accurate and efficient bioassay for benomyl re­ sistance. MATERIALS AND METHODS Fungicide resistance screening. Sugar beet leaves were collected weekly from early August through late Sep­ tember 1984 from 50 fields located throughout the Minne­ sota and North Dakota sugar beet production areas. Sample size for each field was 10 55, with an average of 18 leaves (1 leaf/plant). Leaves were collected from sites 16 24 ha in size. Sugar beet leaves collected" from survey fields were immediately placed in 3.8 plastic bags and temporarily stored in portable ice chests, until placed in an incubator at 4 °C . To indentify benomyl-resistant strains of C. beticol a ,

Chemical Control of Cercospora Leaf Spot of Green Gram

Abstract: Efficacy of certain fungicides for the control of leaf spot disease of green gram incited by Cercospora canescens was evaluated in field during the 1982–83 and 1983–84 kharif seasons at Regional Research Station, Keonjhar, Orissa. Carbendazim at 0.05% was found most effec-tive in controlling the disease with the lowest disease index (24.3%) and the highest disease control (65.0%). This treatment resulted in the highest grain yield of 8.9 and 8.0 q/ha in the first and second year, respectively as against 4.4 and 3.9 q/ha in the check.