Showing papers on "Leaf spot published in 1990"
TL;DR: Results of observation for three seasons in oilseed rape crops of the production and release of ascopores of Pyrenopeziza brassicae show that apothecia can continue to release ascospores for up to 3 weeks even when they are subjected to wet and dry cycles.
Abstract: The results of observation for three seasons in oilseed rape crops of the production and release of ascopores of Pyrenopeziza brassicae, the cause of light leaf spot disease of brassicas, are presented. Large apothecia (1–2 mm in diameter) take at least 3 weeks to develop on leaf petioles after infected leaves die, but small apothecia (50–200 um) may form on leaf lamellae after about 15 days. Apothecia were found on all 12 oilseed rape varieties examined. Spore trapping experiments in infected crops show that ascospore release is associated with rain, but most ascospores are released after rainfall when the crop debris bearing apothecia are wet. Ascospores can be released for up to 5 days after rain. Laboratory measurements show that apothecia can continue to release ascospores for up to 3 weeks even when they are subjected to wet and dry cycles. The consequences of the widespread occurrence of the sexual stage of P. brassicae are discussed and possible cycles of disease and spore production in oilseed crops are suggested.
59 citations
TL;DR: The ‘nurse-sucker’ technique was used to manage the cropping cycle and eliminate disease carry-over between crops, and a gradation of disease severities was maintained with eight fungicide treatments.
49 citations
01 Jan 1990
TL;DR: The most common and important foliar diseases of rice in the southern United States are sheath blight, blast, stem rot, brown leaf spot, narrow Brown leaf spot and leaf smut.
Abstract: The most common and important foliar diseases of rice in the southern United States are sheath blight, blast, stem rot, brown leaf spot, narrow brown leaf spot and leaf smut. Fungicides have been evaluated for more than 20 years for efficacy against these diseases at the Rice Research Station in Crowley, Louisiana, USA in small plot experiments. Five fungicides are presently registered for commercial use. The commercial fungicides benomyl, propiconazole, iprodione, copper plus sulfur, and thiabendazole have received registrations since 1976. Benomyl, propiconazole, and Iprodione have similar activity against sheath blight but thiabendazole and copper plus sulfur are not recommended because of poor performance. Benomyl also has activity against blast and narrow brown leaf spot. Propiconazole gives excellent control of narrow brown leaf spot and leaf smut. Iprodione suppresses the brown leaf spot disease. Several new fungicides which are narrow spectrum and specific for sheath blight control will soon be registered.
41 citations
TL;DR: It is suggested that the frequency of somaclonal variation is genetically determined and that screening for somac Lonal variation may be a feasible approach to obtaining leaf spot-resistant peach plants.
Abstract: A detached-leaf bioassay was used to evaluate peach (Prunus persica (L.) Batsch) regenerants derived from zygotic embryo callus cultures of cultivars Sunhigh (susceptible to leaf spot) and Redhaven (moderately resistant to leaf spot) for resistance to Xanthomonas campestris pv. pruni ((E.F. Sm.) Dews), the causal agent of bacterial leaf spot. Regenerants obtained from calli produced on two 'Sunhigh' embryos, #61 and #156, and on three 'Redhaven' embryos were evaluated. Sixty-four percent of the regenerants derived from 'Sunhigh' embryo #156 and 13% of the regenerants derived from 'Sunhigh' embryo #61 demonstrated significantly greater spot resistance than 'Sunhigh'. Regenerants with resistance greater than 'Redhaven' were also obtained from both 'Sunhigh' embryos. The frequency of variation in the 'Sunhigh' seedling population, with respect to the response to bacterial leaf spot, was not so great as that exhibited by the regenerants derived from 'Sunhigh' embryo #156. None of the 'Redhaven' seedlings or any of the regenerants derived from 'Redhaven' embryos were more resistant than 'Redhaven'. These studies suggest that the frequency of somaclonal variation is genetically determined and that screening for somaclonal variation may be a feasible approach to obtaining leaf spot-resistant peach plants.
39 citations
TL;DR: Regression of area under the disease progress curve data onto two models based on complete dominance indicated that dominance was important in inheritance of resistance to gray leaf spot.
Abstract: (...)Regression of area under the disease progress curve data onto two models based on complete dominance indicated that dominance was important. For the genotypes studied, a model more complex than simple additivity was required to fully explain inheritance of resistance to gray leaf spot; however, screening of inbreds prior to testing them for combining ability should be effective in eliminating those that are most susceptible
37 citations
TL;DR: Wild relatives of the authors' present crop plants, although agronomically undesirable, may have acquired many desirable stress-resistant characteristics as a result of their long exposure to nature’s stresses.
Abstract: Wild relatives of our present crop plants, although agronomically undesirable, may have acquired many desirable stress-resistant characteristics as a result of their long exposure to nature’s stresses. Early U.S. collection activities for wild forms ofBeta were conducted by George H. Coons (USDA-ARS) in 1925 and 1935. These collections were mainly wild forms of the sectionBeta, with major emphasis on leaf spot (Cercospora beticola) resistance. Little was done with this collection until 1976, when John McFarlane (USDA-ARS) transferred it to Salinas, California, to regenerate seed for preservation. Unfortunately, about half of the collection had lost germinability. Immunity to Rhizomania, a devastating root disease discovered in California in 1983, was discovered in several accessions of the Coons’ collection by E. D. Whitney. Interestingly, these same accessions subsequently have been found to exhibit Erwinia root rot resistance, sugar beet root maggot tolerance, and moderate leaf spot resistance. The value of wild germplasm is not always apparent immediately. Needs change and the value of wild germplasm may not be realized for years.
24 citations
TL;DR: Under high levels of disease, Tilt reduced the level of disease and significantly increased grain yield and the amount of large kernels in both wheat and barley and in barley, the increase in amount of seed in the larger size classes across all sites was correlated with reduction in net blotch severity.
Abstract: Field trials were conducted to determine the effect of foliar fungicides on grain yield, kernel size and seed size distribution in wheat and barley. Tilt (propiconazole) was applied at 125 g a.i. ha−1 between Zadoks growth stages 49 and 59. Following harvest, seed samples from treated and untreated plots were stratified into different size classes. In barley trials, net blotch was the most prevalent leaf disease while in wheat trials, tan spot, leaf rust and Septoria leaf spot were most prevalent. Under high levels of disease, Tilt reduced the level of disease and significantly increased grain yield and the amount of large kernels in both wheat and barley. Under low levels of disease, Tilt rarely increased grain yield, but frequently increased the amount of large kernels. In barley, the increase in amount of seed in the larger size classes across all sites was correlated (P < 0.05) with reduction in net blotch severity. No significant effect of Tilt on germination at 5 °C was observed for any of the wheat...
24 citations
TL;DR: A 10-parent diallel cross was performed using peanut lines susceptible and resistant to the three major foliar fungi to investigate the interrelationship of the multiple disease complex with host genes for resistance.
Abstract: Early leaf spot caused by Cercospora arachidicola, late leaf spot caused by Cercosporidium personatum, and rust caused by Puccinia arachidis are the three most important foliar fungal diseases of peanut (Arachis hypogaea) worldwide. A 10-parent diallel cross was performed using peanut lines susceptible and resistant to the three major foliar fungi. The objective was to investigate the interrelationship of the multiple disease complex with host genes for resistance. Parents and F 1 hybrid progeny were planted in the field in Thailand in 1985 (...)
22 citations
TL;DR: Leaf spot of tobacco caused by Rhizoctonia solani is reported for the first time from South Africa.
Abstract: Leaf spot of tobacco caused by Rhizoctonia solani is reported for the first time from South Africa. All the leaf spot isolates anastomosed with the AG-3 tester strain
22 citations
TL;DR: Preliminary testing of phosphonic acid for control of root and foliar diseases of stonefruit, apples and celery showed potential for control but was ineffective for peach brown rot, apple white root rot, and apple black spot.
Abstract: Following South African reports of the effectiveness of phosphonic acid for control of non-Oomycete diseases, preliminary testing of phosphonic acid was made for control of root and foliar diseases of stonefruit, apples and celery. Phosphonic acid showed potential for control of stonefruit Armillaria root rot (caused by Armillaria luteobuballna), apple white root rot (caused by Dematophora necatrix), and apple black spot (caused by Venturia inaequalis) but was ineffective for peach brown rot (caused by Monilinia fructicola) and celery leaf spot (caused by Septoria apiicola).
18 citations
01 Jan 1990
TL;DR: Sixty-two cultivated and weed species in 16 botanical families were artificially inoculated or exposed to natural infection in greenhouse experiments and 27 species of Cucurbitaceae were found to be susceptible to a forma specialis of Alternaria alternata that attacks cucumber.
Abstract: Sixty-two cultivated and weed species in 16 botanical families were artificially inoculated or exposed to natural infection in greenhouse experiments. Of these, 27 species of Cucurbitaceae were found to be susceptible to a forma specialis of Alternaria alternata that attacks cucumber. To differentiate this A. alternata pathotype from others, it is proposed that it be designated Alternaria alternata f. sp. cucurbitae
TL;DR: The growth of Septoria apiicola was observed by SEM on excized celery leaves and on agar medium, and development of pycnidia was observed in detail in leaf tissue and on Agar.
TL;DR: The commonly cultivated groundnut varieties in the country are susceptible to early leaf spot, Cercospora arichidicola Hori, and rust, and fungicidal control is the short term remedy to this problem.
Abstract: The commonly cultivated groundnut varieties in the country are susceptible to early leaf spot (Cercospora arichidicola Hori), late leaf spot (Phaeoisariopsis personata Berk. & Curt. v. Arx.), and rust (Puccinia arachidis Speg.). Since the development of agronomically suitable disease resistant varieties will take considerable time, fungicidal control is the short term remedy to this problem
TL;DR: The fungus was pathogenic to many commonly grown cucumber cultivars in the Northeast, including Poinsett 76, Marketmore 76, Sweet-Slice, Dasher II, Pacer, and Raider.
Abstract: Ulocladium cucurbitae, a leaf spot pathogen of cucumber (Cucumis sativus), was recovered from commercial fields and breeding plots in two widely separated areas of New York. The fungus was pathogenic to many commonly grown cucumber cultivars in the Northeast, including Poinsett 76, Marketmore 76, Sweet-Slice, Dasher II, Pacer, and Raider. In addition, Alternaria alternata was recovered from all of the lesions examined. In pathogenicity tests, only U. cucurbitae produced symptoms identical to those observed in the field. A. alternata failed to infect cucumber directly (...)
TL;DR: Cercospora leaf spot infection predictions based upon weather data provide for effective timing of fungicide application in years of significant disease development and for avoidance of unnecessary use of fungicides when conditions are unfavorable for infection.
Abstract: Number of hours of leaf wetness on sugar beet foliage and average leaf surface temperature during the period of leaf wetness were determined by a leaf wetness sensor and an infrared thermometer (LWS/IRTI, respectively, connected to an automated weather station. Hours of relative humidity >90% and canopy air temperature were determined by a hygrothermograph (HYG). The two methods were com pared for determination of daily infection values (DIVs) judged favorable, marginal, or unfavorable for Cercospora leaf spot development during late July and August of 1986 and 1987. Low levels of leaf spot severity «1% of leaf area) adjacent to the weather station in 1986 fit favorably with infection predictions based on the LWSIIRT data. Leaf spot severity was <3% near the weather station in 1987 although favorable conditions for infection were indicated by both measuring systems. However, in an adjacent field sheltered on three sides, leaf spot severity developed to 50%. Fungicide application dates in 1986 based upon predictions by LWS/IRT data and first symptom appearance provided significantly (P=O.05) lower disease severity than a nontreated control in a plot area near the weather station. In 1987 one fungicide application following disease predictions based upon both the LWSIIRT and HYG systems provided control equal to three biweekly applications starting with first appearance of symptoms. Cercospora leaf spot infection predictions based upon weather data provide for effective timing of fungicide application in years of significant disease development and for avoidance of unnecessary use of fungicides when conditions are unfavorable for infection. IPublished as Paper No. 9202, Journal Series, Nebraska Agricultural Research Division. 59 July-December 1990 Fungicide Efficacy and Yield Response Additional
TL;DR: A new boll rot disease of cotton (Gossypium hirsutum L.) cv.
Abstract: A new boll rot disease of cotton (Gossypium hirsutum L.) cv. MCU 9 was observed in Tamil Nadu, India, in 1988. The causal organism was isolated in pure culture and identified asCorynespora cassiicola (Berk. & Curt.) Wei. The isolate, which on cotton is pathogenic only to bolls, is considered to be different from a strain ofC. Cassiicola known elsewhere causing leaf spot of cotton. The pathogenicity of this fungus on several other important crops was also tested. The fungus produced leaf spot and stem rot diseases on, respectively, eight and six host plants. Root rot, after inoculation, was observed only inVigna sinensis, Arachis hypogaea andSesamum indicium.
TL;DR: Pathogenicity and virulence of isolates were assessed by their ability to produce leaf spot, petiole blight and leaf chlorosis, and significant differences in the ability of isolate to produce symptom types were observed.
Abstract: Pathogenicity and virulence of isolates were assessed by their ability to produce leaf spot, petiole blight and leaf chlorosis. Significant differences in the ability of isolates to produce symptom types were observed. There was a significant relationship between the ability to produce leaf spot and petiole blight (r=0.33) but not between the ability to produce chlorosis and petiole blight (r=−0.12) or leaf spot (r=0.22)
TL;DR: This paper reviews the available literature on the pathogen Phaeoseptoria eucalypti with a view to establishing a base for future research in South Africa.
Abstract: SYNOPSIS Phaeoseptoria eucalypti is one of the more important leaf pathogens of Eucalyptus spp. in South Africa. It is capable of causing complete defoliation of an entire plantation and the death of seedlings. This paper reviews the available literature on the pathogen with a view to establishing a base for future research in South Africa.
Journal Article•
TL;DR: Heterosporium gracile, the anamorph of Mycosphaerella macrospora and causal agent of leaf blotch or leaf spot of Iris L. species and cultivars, is described and illustrated from nature and in vitro.
Abstract: The taxonomic status of the generic name Heterosporium Klotzsch is discussed and it is accepted as an entity separate from Cladosporium Link sensu stricto. Heterosporium gracile, the anamorph of Mycosphaerella macrospora and causal agent of leaf blotch or leaf spot of Iris L. species and cultivars, is described and illustrated from nature and in vitro.
TL;DR: The role of host-selective toxins and phytoalexins in host-parasite interaction was investigated from chemical as well as phytopathological point of view.
Abstract: Role of host-selective toxins and phytoalexins in host-parasite interaction was investigated from chemical as well as phytopathological point of view. As the results of phytopathological studies on host selection by Alternaria mali and A. kikuchiana, the causal agents of Alternaria leaf spot disease of apple and black spot disease of Japanese pear respectively, AM-toxin I, I1 and 111, and AK-toxin I and I1 were isolated as the primary determinants of these diseases , chemical structure of which were elucidated to be (la). (&I, (&I, (&) and (3) respectively, and the proposed structures were confirmed by total syntheses. The isolated crystalline AM- and AK-toxins showed not only extremely potent host-selective toxicity, but dilute solutions of these toxins also induced the same necrotic symptoms only on their host plant tissues as those observed on inoculation with the spores of the causal fungi. Structural features of the toxins that express the host selective toxicity were also analyzed using synthetic analogs of AM- and AK-toxins. On the other hand, in the course of the studies on the host-selection mechanism by obligate parasites, specific accumulation of the phytoalexins , avenalumin I, I1 a’nd 111, were confirmed in oat leaves infected with incompatible strains of crown rust fungus, Puccinia coronata f. sp. avenae and their structures were characterized as (@), (a) and (&I. These
01 Jan 1990
Journal Article•
TL;DR: The type and extent of microarthropod perithecial feeding occuning in the leaf litters are described and the possible role of Collembola and oribatid mites as probable main fungal feeders involved is investigated.
Abstract: Companion planting of the woody shrub autumn olive, Elaeagnus umbellata Thunb., with black walnut, Juglans nigra L., in plantations resulted in control of Mycosphaerella leaf spot (4, 5) and walnut anthracnose (3), important defoliating diseases of black walnut. One of the principal beneficial effects ofthe autumn olive was to reduce ascospore primary inoculum ofthe two disease causal agents, Mycosphaerella juglandis Kessler and Gnomonia leptostyla (Fr.) Ces. & de Not. in the spring. A major cause of the reduced ascospore production of M. juglandis and G. leptostyla was microarthropod feeding upon perithecia within infected fallen walnut leaves (4). The purpose of this study is (1) to describe the type and extent of microarthropod perithecial feeding occuning in the leaf litters and (2) investigate the possible role of Collembola and oribatid mites as probable main fungal feeders involved.
Journal Article•
TL;DR: Seven fungicides, namely, ernisan-S, bavistin, captaf, cuman-L, difolatan, dithane M-45 and dithanes Z-78 were tested under field conditions for suggesting economically viable control measures acceptable to farmers.
Abstract: Leaf spot caused by Alternaria brassicae inflicts severe damage to cauliflower right. from germination till harvest and also in storage and transit. The pathogen produces various types of symptoms like damping-off, seedling blight, stump rot, leaf spot, leaf blight and curd rot. Seven fungicides, namely, ernisan-S, bavistin, captaf, cuman-L, difolatan, dithane M-45 and dithane Z-78 were tested under field conditions for suggesting economically viable control measures acceptable to farmers. Three sprays with difolatan (0.2 per cent) distinctly scored over other fungicides, both in terms of additional crop yield (137.03 q/ha) and net profit (Rs. 9554.47/ha) with a benefit-cost ratio of 13 : 2.
Journal Article•
TL;DR: The degree of leaf injury due to rapid fall of leaf temperature was influenced by temperature conditions during plant growth and pre-treatment, and Electrolyte leakage from old leaves was greater than that from young leaves.
Abstract: This study was carried out to clarify the relation between occurrence of leaf injury, so-called “leaf spot”, and amount of electrolytes leaked from leaf tissue of Saintpaulia ionantha Wendl cv. Beth Elen. Leaves were dipped in water at a temperature lower than leaf (rapid fall of leaf temperature) for the development of leaf spot, and the leakage of electrolytes from leaf discs to water at different temperatures was determined.1. Leaves were dipped in water at 40, 45 and 50°C for 60sec, followed by a dipping in water at 25°C for 60sec. The degree of leaf injury increased with the increasing differences between water and leaf temperatures.2. The degree of leaf injury due to rapid fall of leaf temperature was influenced by temperature conditions during plant growth and pre-treatment.3. Electrolyte leakage from leaf discs was minimum by soaking in 20-25°C water and increased above and below these temperatures. In this case, the amount of leakage in darkness was larger than that in exposure to light.4. Exposure of leaf discs to a rapid fall of leaf temperature considerably increased the amounts of K+ and Mg++ leakage.5. Leaf discs were divided transversely into two portions, adaxial and abaxial, and they were exposed to rapid fall of leaf temperature. The adaxial half containing palisade tissue had a greater amount of K+ leakage than the abaxial half.6. Shrinkage of palisade cells was microscopically observed in injured leaf portions one day after rapid fall of leaf temperature, and then breakdown of chloroplasts was observed.7. Electrolyte leakage from old leaves was greater than that from young leaves.8. Exposure of leaves to high light intensity before rapid fall of leaf temperature increased leaf injury and electrolyte leakage.
01 Jan 1990
TL;DR: Results from exeperiments at the international crop research institute for the semi-arid tropics (ICRISAT) center are used as a propose a simpple model to describe the effects of temperature and leaf wetness on infection of groundnut.
Abstract: The literature of effect of weather on infection of groundnut (Arachis hypogaea L.) by late leaf sopt (phaeoisatiopsis personata) is examined. In addition, results from exeperiments at the international crop research institute for the semi-arid tropics (ICRISAT) center are used as a propose a simpple model to describe the effects of temperature and leaf wetness on infection.
TL;DR: It was concluded that resistance to three isolates of Pseudomonas syringae pv.
Abstract: The genetics of resistance to angular leaf spot caused by Pseudomonas syringae pv. tabaci in Nicotiana tabacum cultivars Burley 21 and Kentucky 14 was investigated by studying disease reactions to three isolates of parental, F1, F2 and backcross generations derived from crosses between the resistant cultivars and the susceptible cultivar Judy's Pride. Studies were conducted in the greenhouse and in field plant beds. Chi-square values were computed to determine whether the observed ratios for disease reactions deviated from expected Mendelian ratios for a single, dominant gene controlling resistance to angular leaf spot in tobacco. Based on the resistance of the F1 and the backcross generation to the resistant parent (BC-R), a 3 resistant: 1 susceptible segregation ratio in the F2, and a 1 resistant: 1 susceptible segregation ratio in the backcross generation to the susceptible parent (BC-S), it was concluded that resistance to three isolates of Pseudomonas syringae pv. tabaci is governed by a single, dominant gene.