Showing papers on "Leaf spot published in 2007"

Molecular Characterization and Diagnosis of QoI Resistance in Cucumber and Eggplant Fungal Pathogens

Abstract: The molecular mechanism of QoI fungicide resistance was studied using isolates of cucumber Corynespora leaf spot fungus (Corynespora cassiicola) and the eggplant leaf mold (Mycovellosiella...

Transgenic Indian mustard (Brassica juncea) expressing tomato glucanase leads to arrested growth of Alternaria brassicae

Abstract: Brassica juncea is an important oilseed crop of the Indian sub-continent. Yield loss due to fungal disease alternaria leaf spot caused by Alternaria brassicae is a serious problem in cultivation of this crop. Nonavailability of resistance genes within crossable germplasms of Brassica necessitates use of genetic engineering strategies to develop genetic resistance against this pathogen. The pathogenesis related (PR) proteins are group of plant proteins that are toxic to invading fungal pathogens, but are present in plant in trace amount. Thus, overexpression of PR proteins leads to increased resistance to pathogenic fungi in several crops. The PR protein glucanase hydrolyzes a major cell-wall component, glucan, of pathogenic fungi and acts as a plant defense barrier. We report the expression of a class I basic glucanase gene, under the control of CaMV 35S promoter, in Indian mustard and its genetic resistance against alternaria leaf spot. Southern and Northern hybridization confirmed stable integration and expression of the glucanase gene in mustard transgenics. Several independent transgenics were screened in vitro and under poly house conditions for their resistance against Alternaria brassicae. In an in vitro antifungal assay, transgenics arrested hyphal growth of Alternaria brassicae by 15–54%. Under pathogen-challenged conditions in poly house, the transgenics showed restricted number, size and spread of lesions caused by Alternaria brassicae. Also, the onset of disease was delayed in transgenics compared to untransformed parent plants. The results demonstrate potentiality of a PR protein from a heterologous source in developing alternaria leaf spot resistance in Indian mustard.

Forest health condition in New South Wales, Australia, 1996-2005. I. Fungi recorded from eucalypt plantations during forest health surveys.

Abstract: Forests New SouthWales manages over 26 000 ha of young eucalypt (Eucalyptus and Corymbia) plantations, established since 1994. Forest health surveillance of these plantations was initiated in late 1995 to help protect this valuable and expanding resource. Fungi recorded during surveys from 1996 to 2005 are reported here. Over 50 species of fungi were identified, the majority being leaf spot fungi. The most commonly recorded were Quambalaria pitereka from leaves and shoots, Aulographina eucalypti, Kirramyces (=Phaeophleospora) epicoccoides and Mycosphaerella cryptica, all foliar fungi, and Botryosphaeria eucalypticola from both leaves and stems. Several species of fungi were recorded from many hosts, including A. eucalypti (18 hosts), M. cryptica (20 hosts), K. epicoccoides (14 hosts) and Botryosphaeria spp. (11 hosts). Others were restricted in their host range, such as Q. pitereka, Stigmina eucalypti, Kirramyces corymbiae prov. nom. and Lembosina corymbiae prov. nom., which were only found on species of Corymbia during these surveys. The published host range for several foliar fungi has been expanded from observations from these surveys, including for A. eucalypti, K. epicoccoides, M. cryptica, Mycosphaerella marksii, Mycosphaerella suberosa, Kirramyces eucalypti, Phaeothyriolum microthyrioides and S. eucalypti. Six new species of foliar fungi were identified during these surveys: Mycosphaerella tumulosa prov. nom., Mycosphaerella associata prov. nom., Mycosphaerella exentricum prov. nom., K. corymbiae, L. corymbiae and Lembosina eucalypticola prov. nom. Some foliar fungi were observed for the first time from New South Wales during these surveys, including M. marksii, M. suberosa, M. parva, Cryptosporiopsis eucalypti and Trimmatostroma excentricum. Tubercularia lateritia and Caliciopsis sp. spleomorpha, both stem fungi, are reported from eucalypts in New South Wales for the first time.

Association of some plant defense enzyme activities with systemic resistance to early leaf blight and leaf spot induced in tomato plants by azoxystrobin and Pseudomonas fluorescens

Abstract: Azoxystrobin at three different concentrations, namely, 31.25, 62.50 and 125 g a.i. ha−1 mancozeb (1 kg ha−1) and Pseudomonas fluorescens (10 kg ha−1) were evaluated for their efficacy in inducing defense enzymes in tomato against Alternaria solani and Septoria lycopersici. The activity of defense enzymes peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia lyase (PAL), β-1, 3 glucanase, chitinase, catalase and defense-inducing chemicals (total phenols) was found to be increased in azoxystrobin and P. fluorescens-treated tomato plants. The activity of these defense enzymes and chemicals was higher in azoxystrobin (125 g a.i. ha−1) and P. fluorescens-treated tomato plants challenge inoculated with the pathogens compared to other treatments. Increased expression of specific isoforms of PO and PPO was also observed due to ISR induction.

Genetic Variability among Maize Cultivars Grown in Ekiti-State, Nigeria

Abstract: An appreciable level of variation within crop varieties is essential to initiate and sustain crop improvement using plant breeding methods. A field experiment was conducted with the aim of estimating variation among maize cultivars grown in Ekiti State. Twenty maize cultivars obtained from various locations within the state was evaluated between April to August 2005 at the Teaching and Research Farm, University of Ado-Ekiti. The twenty cultivars constituted the treatment, which was lied out in a Randomized Complete Block Design with three replicates. Result shows that there were significant (p<0.05) difference for in day to first silking and anthesis, days to 50% anthesis and silking, plant and ear heights, leaf blight and curvularia leaf spot and grain yield. Grain yield ranges from 3.02 t ha for Ijelu and 4.91 t ha for Ilupeju. Phenotypic and 11 genotypic variance was highest for plant and ear heights and least for the foliar disease rating and significant for all the traits except ear plant . Broad sense heritability estimates ranged from 0.16 for ear plant to 0.71 for 11 Curvularia leaf spot. Correlation coefficient was positive and significant between grain yield and both plant and ear heights, but negative with Curvularia leaf spot. These results are suggestive that the cultivars evaluated in this study are good candidates on which improvement activates can be initiated the incorporation of high grain yield traits would also have a long run advantage.

Nitrogen and Tillage Effects on Wheat Leaf Spot Diseases in the Northern Great Plains

Abstract: There is a need for management practices in cropping systems that can reduce the impact of plant diseases. Leaf spot diseases on wheat (Triticum aestivum L.) were evaluated for 11 yr to determine the influence of tillage, N fertilization, and cultivar on disease severity in a long-term cropping system project, which included two cropping systems {spring wheat (SWF)–fallow and annual cropping [spring wheat (SWA)–winter wheat (WWA)–sunflower (Helianthus annuus L.)]}. The major leaf spot diseases were tan spot and Stagonospora nodorum blotch. In low precipitation years, the impacts of management practices on leaf spot disease severity were minimal. No-till (NT) did not consistently increase the severity of leaf spot diseases. During the drier years, NT had the advantage of conserving soil water while not increasing the risk to leaf spot diseases. When N treatments influenced leaf spot disease severity, higher levels of disease severity were associated with the low-N fertilizer treatment compared with higher levels of N fertilization. When a tillage 3 N treatment interaction was significant, disease severity was higher with NT at the low N treatment, but at the high N treatment the differences among tillage treatments were greatly reduced or eliminated. This indicates an advantage of using adequate N fertilizer especially with NT under our environmental conditions. When differences in leaf spot diseases for cultivars were evident, Roughrider winter wheat had higher levels of disease severity compared with Norstar; however, the differences between the spring wheat cultivars Butte86 and Stoa were not consistent for both cropping systems. Producers should integrate a combination of management practices to develop a consistent long-term strategy for disease management suited to their production system and location.

Efeito da cercosporiose no rendimento de híbridos comerciais de milho

Abstract: Effect of Gray leaf spot on yield of Commercial Maize Hybrids With the objective of quantifying the effect of gray leaf spot (Cercospora zeae-maydis) on yield of 12 commercial maize hybrids and of correlating grain yield reduction with disease severity, two experiments were performed at two sowing dates (November 11 th and December 23 rd , 2005) in the experimental area of the Federal University of Lavras (UFLA), Lavras, MG, Brazil. Disease control in healthy plots of all hybrids was obtained through two applications of epoxiconazol + pyraclostrobin – 37.5 + 99.75 g i.a.ha -1 ) at a 15-day interval. In uncontrolled plots, epidemic development started from natural inoculum present in the area. Eight evaluations of disease severity based on visual symptoms were performed at seven-day intervals from the 60 th day after maize emergence, ranging from 1 (resistant) to 9 (susceptible). The area under the disease progress curve (AUDPC) was estimated and grain yield per plot was also obtained. Results of damage percentage and correlations between grain yield and damage percentage with the estimates of the AUDPC were supported by the data. Damage intensity varied according to sowing season and hybrid, with an average of 13.3%. Maize gray leaf spot reduces the corn grain yield, mainly in the late sowing season, and the use of resistant hybrids excludes the chemical control of the disease. Additional keywords: Zea mays, damage, disease evaluation, fungal disease.

Levels of variability in groundnut (Arachis hypogaea L.) to cercospora leaf spot disease implication for selection

Abstract: Groundnut (Arachis hypogaea L.) is an important crop both in subsistence and commercial agriculture in arid and semi-arid regions of the world. Leaf spot diseases caused by fungus have been a major destructive disease of groundnut and could cause a yield loss of up to 50 % or more. A two-year experiment was conducted during the cropping seasons of 2002 and 2003 at the Faculty of Agriculture Research Farm, University of Maiduguri, Nigeria. The objective of the study was to determine the reaction of different groundnut varieties to cercospora leaf spot disease to create basis for selection for cercospora leaf spot disease tolerance. The experiment consisted of twenty-four groundnut varieties, laid out in a randomized complete block design (RCBD) with three replications. The analysis of variance (ANOVA) indicated highly significant difference among the groundnut varieties in all the characters studied. The results indicated that ICGV-SM-93531, ICGV-IS-96802, ICGV-IS-96827 and ICGV-IS-96808 had the lowest cercospora leaf spot incidence. The variety ICGV-IS-96808 that produced the highest kernel yield also had the lowest days to 50% flowering and incidentally is among varieties that recorded the lowest leaf spot incidence. The study found tremendous level of variability existing among the groundnut varieties that is essential in crop improvement. This study recommends that development or selection of tolerant varieties to leaf spot should be based on their level of incidence. This will be the only effective measure in decreasing production costs and protect the environment from pollution. Potential therefore exist for selection among the groundnut varieties evaluated for cercospora leaf spot disease tolerance. There is however, a need to undertake further studies in order to determine the type and the number of genes controlling cercospora leaf spot disease tolerance in groundnuts for enhanced breeding strategies.

Epidemiology of cercospora leaf spot on sugar beet: modeling disease dynamics within and between individual plants.

Abstract: Disease dynamics of Cercospora leaf spot (CLS) of sugar beet was analyzed at two hierarchical scales: as vertical profiles within individual plants and in relation to disease on neighboring plants. The relative contribution of different leaf layers to increase in CLS was analyzed using a simple continuous-time model. The model was fitted to data from two field trials in the Netherlands: one in an area with a long history of CLS, the other in an area where CLS has only recently established; in each case these were unsprayed and twice-sprayed treatments. There were differences in the relative contribution of different leaf layers to disease increase on the target leaf layer according to the CLS history and whether the plants were sprayed or unsprayed. In both field trials, parameter estimates giving the relative contribution of the target leaf layer to disease increase at that leaf layer were higher than those for the lower leaf layer. On only a few occasions the contribution of an upper leaf layer to disease increase at the target leaf layer was significant. Thus, CLS increase at the target leaf layer was determined mainly by disease severity at that leaf layer and to a lesser extent by disease at the lower leaf layer. Our continuous-time model was also used to analyze CLS increase on an individual sugar beet plant in relation to its own and its neighbor's level of disease in field trials at five locations in the two CLS areas over two years. In all field trials, the contribution of the target plant itself to disease increase (auto-infection) was larger than that of its neighboring plants (allo-infection). The overall analysis in the two CLS areas also indicated a larger contribution of the target plant to its disease increase than of neighboring plants, and this pattern was also apparent in a pooled analysis across all sites. Thus, CLS increase on a sugar beet plant was mainly determined by the disease severity on that plant and to a lesser extent by its within-row neighboring plants.

Genetic variation of Prunus avium in susceptibility to cherry leaf spot (Blumeriella jaapii) in spatially heterogeneous infected seed orchards

Abstract: Cherry leaf spot (Blumeriella jaapii (Rehm) Arx.) is a very serious disease of wild cherry (Prunus avium L.), which produces premature leaf defoliation and vigor decrease. In two clonal seed orchards of P. avium naturally infected by B. jaapii, spatial heterogeneity and autocorrelation of neighbor damage caused by cherry leaf spot impeded proper analysis of the fungus incidence. The iterative spatial analysis (ISA), based on variography and kriging, was successfully used to eliminate the effect of this spatial heterogeneity in analysis of genetic variation in susceptibility to B. jaapii .S ig- nificant differences among P. avium clones were found, with moderate to high broad-sense heritability estimates. Genetic by environment interactions, although significant, were not quantitatively important. A strong relationship between leaf spot susceptibility and bud burst was found. However, other factors must be affecting the genetic variation in leaf spot susceptibility, as differences among clones remained highly significant when considering the bud burst as a covariate in the genetic model.

Crop Sequence Effects on Leaf Spot Diseases of No-Till Spring Wheat

Abstract: Crop sequence is an important management practice that may lower the risk for leaf spot diseases of spring wheat (Triticum aestivum L.). Field research was conducted near Mandan, ND, to determine the impact of crop sequences on leaf spot diseases of hard red spring wheat early in the growing season. Spring wheat was evaluated for disease severity following crop sequence combinations of 10 crops [buckwheat (Fagopyrum esculentum Moench), canola (Brassica napus L.), chickpea (Cicer arietinum L.), corn (Zea mays L.), dry pea (Pisum sativum L.), grain sorghum [Sorghum bicolor (L.) Moench], lentil (Lens culinaris Medik.), oil seed sunflower (Helianthus annuus L.), proso millet (Panicum miliaceum L.), and hard red spring wheat). Spring wheat leaves with distinct lesions were collected for determination of lesion number and percentage necrosis data, which were used to estimate leaf spot disease severity. Pyrenophora tritici-repentis (Died.) Drechs., the cause of tan spot, and Phaeosphaeria nodorum (E. Miiller) Hedjaroude, the cause of Stagonospora nodorum blotch, were the major leaf spot diseases and consistently present throughout the growing season. The frequency of isolation following alternative crops was generally lower compared with spring wheat following wheat. Leaf spot diseases on spring wheat were impacted by crop sequencing. Spring wheat following crop sequences with alternative crops for 1 or 2 yr had lower levels of disease severity compared with a continuous spring wheat treatment early in the growing season. Disease severity was apparently not related to the percentage of crop residue coverage on the soil surface associated with various crop sequence combinations. New alternative crops preceding spring wheat reduce levels of leaf spot diseases.

Assessment of major cassava diseases in Togo in relation to agronomic and environmental characteristics in a systems approach

Abstract: A cassava disease survey was conducted in four agroecological zones of Togo. High incidences of cassava bacterial blight, cassava mosaic disease and cercosporioses were observed across ecozones, while anthracnose disease was rare. Bacterial blight field incidences of 90.5% in the dry savanna zone, 70% in the forest savanna transition zone, 64% in the wet savanna zone and 52.6% in the forest zone, were recorded, with plant incidences ranging from 27.4% in the forest zone to 72.7% in the dry savanna zone. Mosaic disease field incidences were nearly 100% in all the ecozones and high plant incidences up to 86.9% were found. Cercospora leaf diseases – brown leaf spot, blight leaf spot and white leaf spot - occurred in all the ecozones with incidences ranging from 68 to 100%. Negative correlations between bacterial blight and mosaic disease, and between mosaic disease and white leaf spot were found, while brown leaf spot and blight leaf spot, brown leaf spot and white leaf spot, and blight leaf spot and white leaf spot were positively correlated. Field incidence of bacterial blight was positively correlated with plant age, ecozones - higher severity in dryer ecozones (P < 0.01), and weed density (P < 0.05). Further significant, but negative correlations occurred between bacterial blight and cercospora brown leaf spot on the other hand and vegetation type in the surroundings field (number of trees) (P < 0.05).Cercospora brown leaf spot was also significantly negatively associated with the number of crops in a field (intercropping) (P < 0.05), and Cercospora white leaf spot with sandy soils (P < 0.01). Results indicate that agroecological factors such as ecozone, plant age, weed density, vegetation type, intercropping and soil type and moisture influence disease occurrence and should be considered when developing integrated control measures. Key words: Blight leaf spot, brown leaf spot, cassava bacterial blight, cassava mosaic disease, white leaf spot, Cercospora henningsii, Cercospora caribaea, Cercospora vicosae, Colletotrichum gloeosporioides f. sp. manihotis, Manihot esculenta, Xanthomonas axonopodis pv. manihotis.

Relating plant and pathogen development to optimise fungicide control of phoma stem canker (Leptosphaeria maculans) on winter oilseed rape (Brassica napus)

Abstract: In winter oilseed rape experiments at Rothamsted in 2000/01 to 2002/03 growing seasons, the severity of phoma stem canker epidemics in summer depended on the timing of phoma leaf spot epidemics in the previous autumn, and hence on the timing of Leptosphaeria maculans ascospore release. The first major release of L. maculans ascospores was earlier in 2000 (26 September) and 2001 (18 September) than in 2002 (21 October). Consequently, the autumn phoma leaf spot epidemic was also earlier in 2000 and 2001 than in 2002. The resulting stem canker epidemics were severe by harvest (July) in 2001 and 2002 but not in 2003. No correlation was found between the severity or duration of phoma leaf spotting (lesion days or lesion °C-days) and the subsequent severity of phoma stem canker epidemics. Rates of leaf production and loss were similar in the three growing seasons. Out of ca. 25 leaves produced on plants during each season, leaf numbers 10–14 generally remained on plants for the longest. Treatment with flusilazole + carbendazim in autumn decreased the severity of phoma leaf spotting for several weeks after treatment, decreased the severity of stem canker the following summer and increased yield significantly in 2001 and 2002 but not in 2003. The most effective timings for flusilazole + carbendazim application were when leaves 7–11 were present on most plants and at least 10% of plants were affected by phoma leaf spot. Two half-dose applications of fungicide reduced phoma stem canker and increased yield more than a single full dose application when phoma leaf spot epidemics were early (<800 °C-days after sowing).

Characterization of early leaf spot suppression by strip tillage in peanut.

Abstract: Epidemics of early leaf spot of peanut (Arachis hypogaea), caused by Cercospora arachidicola, are less severe in strip-tilled than conventionally tilled fields. Experiments were carried out to characterize the effect of strip tillage on early leaf spot epidemics and identify the primary target of suppression using a comparative epidemiology approach. Leaf spot intensity was assessed weekly as percent incidence or with the Florida 1-to-10 severity scale in peanut plots that were conventionally or strip tilled. The logistic model, fit to disease progress data, was used to estimate initial disease (y0) and epidemic rate (r) parameters. Environmental variables, inoculum abundance, and field host resistance were assessed independently. For experiments combined, estimated y0 was less in strip-tilled than conventionally tilled plots, and r was comparable. The epidemic was delayed in strip-tilled plots by an average of 5.7 and 11.7 days based on incidence and severity, respectively. Tillage did not consi...

Genetic Diversity of Lettuce for Resistance to Bacterial Leaf Spot Caused by Xanthomonas campestris pv. vitians

Abstract: Lettuce plants were artificially inoculated with three isolates of Xanthomonas campestris pv. vitians in field and greenhouse evaluations for genetic variation in resistance to bacterial l...

Registration of ‘DP-1’ Peanut

Abstract: The peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) cultivar DP-1 (Reg. No. CV-103, PI 633047) was developed by the University of Florida, Florida Agricultural Experiment Station and approved for release in 2002. Tested under the experimental designation UF97318, DP-1 has runner market-type seed and pod size with a runner growth habit. Under irrigation, it matures about 150 d after planting, which places it in the category of late relative maturity. Release of DP-1 was based on its resistance to spotted wilt caused by tomato spotted wilt tospovirus, white mold caused by Sclerotium rolfsii Sacc., and late leaf spot caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton, as well as competitive pod yield and grade characteristics.

First Report of Gray Leaf Spot of Mango (Mangifera indica) Caused by Pestalotiopsis mangiferae in Taiwan.

Abstract: Mango (Mangifera indica L.; family Anacardiaceae) is one of the world's most important fruit crops and is widely grown in tropical and subtropical regions. Since 2001, a leaf spot disease was found in mango orchards of Taiwan. Now, the disease was observed throughout (approximately 21,000 ha) Taiwan in moderate to severe form, thus affecting the general health of mango trees and orchards. Initial symptoms were small, yellow-to-brown spots on leaves. Later, the irregularly shaped spots, ranging from a few millimeters to a few centimeters in diameter, turned white to gray and coalesced to form larger gray patches. Lesions had slightly raised dark margins. On mature lesions, numerous black acervuli, measuring 290 to 328 μm in diameter, developed on the gray necrotic areas. Single conidial isolates of the fungus were identified morphologically as Pestalotiopsis mangiferae (Henn.) Steyaert (2,3) and were consistently isolated from the diseased mango leaves on acidified (0.06% lactic acid) potato dextrose agar (PDA) medium incubated at 25 ± 1°C. Initially, the fungus grew (3 mm per day) on PDA as a white, chalky colony that subsequently turned gray after 2 weeks. Acervuli developed in culture after continuous exposure to light for 9 to 12 days at 20 to 30°C. Abundant conidia oozed from the acervulus as a creamy mass. The conidia (17.6 to 25.4 μm long and 4.8 to 7.1 μm wide) were fusiform and usually straight to slightly curved with four septa. Three median cells were olivaceous and larger than the hyaline apical and basal cells. The apical cells bore three (rarely four) cylindrical appendages. Pathogenicity tests were conducted with either 3-day-old mycelial discs or conidial suspension (105 conidia per ml) obtained from 8- to 10-day-old cultures. Four leaves on each of 10 trees were inoculated. Before inoculation, the leaves were washed with a mild detergent, rinsed with tap water, and then surface sterilized with 70% ethanol. Leaves were wounded with a needle and exposed to either a 5-mm mycelial disc or 0.2 ml of the spore suspension. The inoculated areas were wrapped with cotton pads saturated with sterile water and the leaves were covered with polyethylene bags for 3 days to maintain high relative humidity. Wounded leaves inoculated with PDA discs alone served as controls. The symptoms described above were observed on all inoculated leaves, whereas uninoculated leaves remained completely free from symptoms. Reisolation from the inoculated leaves consistently yielded P. mangiferae, thus fulfilling Koch's postulates. Gray leaf spot is a common disease of mangos in the tropics and is widely distributed in Africa and Asia (1-3); however, to our knowledge, this is the first report of gray leaf spot disease affecting mango in Taiwan. References: (1) T. K. Lim and K. C. Khoo. Diseases and Disorders of Mango in Malaysia. Tropical Press. Malaysia, 1985. (2) J. E. M. Mordue. No. 676 in: CMI Descriptions of Pathogenic Fungi and Bacteria. Surrey, England, 1980. (3) R. C. Ploetz et al. Compendium of Tropical Fruit Diseases. The American Phytopathological Society. St. Paul, MN, 1994.

Gene action determining Phaeosphaeria leaf spot disease resistance in experimental maize hybrids

Abstract: Phaeosphaeria leaf spot (Phaeosphaeria maydis Henn.) has the potential to cause substantial yield losses in maize. Maize is grown by small-scale farmers without fungicides; hence there is need to breed for resistance in regionally adapted germplasm. Little information about the gene action determining Phaeosphaeria leaf spot disease (PLS) resistance in African maize germplasm is currently available. This study was therefore conducted to determine the gene action controlling resistance to PLS in African maize germplasm. Seventy-two experimental hybrids were generated in eight sets according to a North Carolina Design II mating scheme. Experimental and check hybrids were evaluated in an 8 × 8 simple lattice design during the 2003/4 season, and in an 8 × 10 α-lattice design, with two replications, during the 2004/5 seasons at the Cedara and Rattray Arnold Research Stations, in South Africa and Zimbabwe, respectively. There was significant variation among hybrids for resistance. General combining ability (GCA...

First Occurrence of Calonectria Leaf Spot on Mexican Blue Palm in Italy.

Abstract: In April 2006, a new leaf disease occurred in a private garden in eastern Sicily (Italy) on young, 2-year-old seedlings of Mexican blue palm, Brahea armata S. Watson, in the Arecaceae. Symptoms were detected on 80% of seedlings. The leaves had minute, brown spots that enlarged into dark brown, circular or elliptical lesions, 3 to 6 mm in diameter, and with a necrotic, gray center. The lesions sometimes were surrounded by a chlorotic halo, and older leaves had larger chlorotic areas between spots. Conidia, conidiophores, and terminal vesicles were examined from diseased leaves. A Cylindrocladium sp. was consistently isolated from leaf lesions on Oxoid (Basingstoke, Hampshire, England) potato-dextrose agar after surface disinfestations with 0.8% NaOCl. Cylindrocladium isolates were cultured on carnation leaf agar (CLA) using single hyphal tips. Five isolates were established and identified as Calonectria pauciramosa C.L. Schoch & Crous based on obpyriform to broadly ellipsoidal terminal vesicles, conidiophore branching pattern, conidia size (52 × 4.6 μm), perithecium morphology, and ascopores size (36 × 6.8 μm). Perithecia were obtained with C. pauciramosa tester strains from Italy (G87 and G128) and South Africa (U 971 and U 1670) (2,3) that confirmed both mating types to be present. Further confirmation was obtained by internal transcribed spacer (ITS) analysis. The sequence of rDNA ITS1-5.8 S-ITS2 regions, obtained after amplification with primer ITS1 and ITS4, revealed that the Brahea isolates showed total homology with the sequence of the C. pauciramosa (STE-U 971 from soil) (= Cylindrocladium pauciramosum) available in GenBank. Isolate CBS 120619 from Mexican blue palm was deposited at Centraalbureau voor Schimmelcultures. Spray inoculations of 10 2-year-old Mexican blue palm seedlings were performed with a spore suspension of the fungus adjusted to 105 conidia per ml obtained from 14-day-old single-spore colonies on CLA at 24°C under cool white fluorescent irradiation on a 12-h light/dark regimen. In addition, the following species were similarly inoculated using 10 1-year-old plants: Arecastrum romanzoffianum (Cham.) Becc., B. edulis H. Wendl. ex S. Watson, Chamaerops humilis L., Howea forsteriana Becc., Phoenix canariensis Hort. ex Chabaud., Trachycarpus fortunei (Hook.) H. Wendl., and Ravenea rivularis Jumelle & Perrier. Inoculated, and 10 control plants were placed in separate plastic bags in a growth chamber at 25 ± 1°C. After 7 to 10 days, foliar symptoms including flecks and spots developed on both species of Brahea and on Chamaerops humilis, and on these hosts, pathogenicity tests were repeated. Other palm species and control plants remained healthy. C. pauciramosa was consistently reisolated from inoculated plants on the basis of vesicle shape and conidia sizes of the anamorph. Cylindrocladium candelabrum, Cylindrocladium colhounii, Cylindrocladium floridanum, Cylindrocladium parasiticum, Cylindrocladium pteridis, Cylindrocladium scoparium, and Cylindrocladium theae have been reported as leaf spots pathogens of Arecaceae (1). To our knowledge, this is the first occurrence of C. pauciramosa on Mexican blue palm and the first report of the pathogen on Arecaceae. References: (1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul MN, 2002. (2) P. W. Crous et al. Stud. Mycol. 50:415, 2004. (3) G. Polizzi and P. W. Crous Eur. J. Plant Pathol. 105:407, 1999.

Controle genético da resistência à mancha-de-Phaeosphaeria em milho

Abstract: The Phaeosphaeria leaf spot, of ample occurrence in Brazil, has been causing an expressive reduction in the corn yield in the country. Thus, the development of resistant hybrids to this disease is one of the main objectives of corn breeding programs. Information about the genetic control of resistance to the disease is necessary so that the programs can be efficient. The main goal of this study was to determine the genetic control of resistance to the Phaeosphaeria leaf spot in maize through the assessment of the generation means from two crossing between a resistant inbred line (DAS95 or DAS72) with a susceptible line (DAS21) under natural infection conditions of the disease. The experiment was carried out in Indianopolis (MG) in two sowen dates, October and November, 2000. The randomized blocks design with three repetitions was utilized. The evaluation to resistance was performed thirty days after the flowering using a diagrammatic scale of percentage of the total foliar tissue of the plant affected by the disease. Disease severity means of parental lines and generations F1, F2, RCP1 and RCP2 were analysed according to the model by MATHER & JINKS (1971). Genetic variation due to additive effects varied from 73% to 84% whilst dominant effects ranged from 13% to 23%. In both studied population, the predominance of gene additive over dominant effects was evidented. The inheritance values were high, varying from 61% to 88%. These results indicate favourable conditions to develop new resistance lines to Phaeosphaeria leaf spot with the studied populations.

Estudos histopatológicos de Colletotrichum spp. em plântulas de cafeeiro

Abstract: The objective of this work was to follow the process of infection, colonization and reproduction of different isolates of Colletotrichum spp. in coffee plantlets, obtained by embryo culture, using scanning electron microscopy. The embryo explants were obtained from coffee seeds cv. Rubi. Plants produced in vitro were inoculated with 5µL of a 106 conidia.mL-1 spore suspension, on the hypocotyl region and leaves, wounding with an entomological needle. Isolates of Colletotrichum gloesporioides were obtained from stem (IS) and leaves (IL) from plants with symptoms of greasy leaf spot, and from mangos with symptoms of anthracnose (IM). Isolates of Colletotrichum dematium were obtained from healthy coffee plants. Three hours after inoculation (h.a.i.), leaves and hypocotyl fragments were transferred to 1.5mL-microtubes containing modified Karnovsky's fixative solution. Further samples were collected at 3, 5, 12, 16, 24, 48, 72, 96, 114 and 144 h.a.i. Conidia of all isolates adhered more frequently in the depressions of hypocotyls and guard-cells, forming a septum 5 h.a.i. Germ tubes were observed 12 h.a.i. starting from the extremities as well as laterally in the conidia. Appressoria were produced by C. dematium (globoses, trilobullated and foot and comma-shaped), and C. gloeosporioides, respectively globoses, 24 h.a.i. C. gloeosporioides (IH and IF) produced conidiogenic cells 48 h.a.i. Acervuli were produced 72 h.a.i. by C. gloeosporioides (IH), 96 h.a.i. by C. dematium. C. gloeosporioides isolated from mango colonized coffee plant tissues, producing conidiogenic cells without production of acervuli. The most aggressive isolates were IS and IL.

Angular Leaf Spot of Cucumber Caused by Pseudomonas syringae pv. lachrymans in Kurdistan.

Abstract: During the spring of 2004 and 2005, angular leaf spot was observed on cucumber (Cucumis sativus L.) in some areas of Kurdistan Province in Iran for the first time. Disease incidence in affected fields was approximately 100%. Symptoms were initially small, round or irregular, water-soaked spots on leaves ranging from 3 to 5 mm in diameter. These spots were limited by the leaf veins that gave them an angular appearance. Under humid conditions, tiny, white exudates formed on the undersides of the leaves and severely infected leaves turned yellow. A fluorescent pseudomonad was consistently isolated from lesions on King's medium B and characterized. Twelve strains were selected from Marivan, Dehgolan and Kamyaran in western Iran. When compared with previously identified strains, (1,2) on the basis of phenotypic, biochemical, and physiological properties, isolates were identified as Pseudomonas syringae pv. lachrymans. This was confirmed with data from whole-cell protein pattern analysis, which indicated that t...