Showing papers on "Leaf spot published in 2013"

Characterization of Species of Diaporthe from Wood Cankers of Grape in Eastern North American Vineyards.

Abstract: In eastern North America, Phomopsis cane and leaf spot, caused by Phomopsis viticola, is a foliar disease of grape but, in the Mediterranean climate of western North America, P. viticola is primarily associated with wood cankers, along with other Diaporthe spp. To determine the identity of wood-infecting Diaporthe spp. in eastern North America, 65 isolates were cultured from 190 wood-canker samples from 23 vineyards with a history of Phomopsis cane and leaf spot. Identification of 29 representative isolates was based initially on morphology, followed by phylogenetic analyses of DNA sequences of the ribosomal DNA internal transcribed spacer region, elongation factor subunit 1-α, and actin in comparison with those of type specimens. Three species were identified: P. viticola, P. fukushii, and Diaporthe eres. Inoculations onto woody stems of potted Vitis labruscana 'Concord' and V. vinifera 'Chardonnay' showed that D. eres and P. fukushii were pathogenic (mean lesion lengths of 7.4 and 7.1 mm, respectively, compared with 3.5 mm for noninoculated controls) but significantly less so than wood-canker and leaf-spot isolates of P. viticola (13.5 mm). All three species infected pruning wounds of Concord and Chardonnay in the field. Our finding of pathogenic, wood-infecting Diaporthe spp. in all 23 vineyards suggests a frequent co-occurrence of the foliar symptoms of Phomopsis cane and leaf spot and wood cankers, although the latter are not always due to P. viticola.

Evaluation of a Light-activated Nanoparticle Formulation of Titanium Dioxide with Zinc for Management of Bacterial Leaf Spot on Rosa ‘Noare’

Abstract: Bacterial leaf spot on roses caused by a Xanthomonas sp. is a new disease affecting commercial rose production with the potential to cause major economic losses. In the past few decades, antimicrobial photocatalyst technology has emerged from basic research and development to provide convenient formulations of titanium dioxide (TiO2) nanoparticles, which have the ability to destroy bacteria on surfaces in the presence of light. In this study, a TiO2 nanoparticle formulation containing zinc (TiO2/Zn) was tested for management of bacterial leaf spot on Rosa 'Noare'. TiO2/Zn caused significant reduction in the survival of Xanthomonas sp. strain Xr-1 on glass coverslips coated with the nanoparticles on exposure to light at 3 3 10 4 lux for 10 minutes. There was no reduction of bacterial viability in non-coated or non-illuminated controls. Field applications of TiO2/Zn at '500 to 800 ppm on Rosa 'Noare' significantly reduced bacterial spot severity compared with the untreated control. TiO2/Zn activity was better or on par with the ornamental industry standard for management of rose diseases.

Methods and Compositions for Gray Leaf Spot Resistance in Corn

Abstract: The present invention relates to the field of plant breeding. More specifically, the present invention includes a method of using haploid plants for genetic mapping of traits of interest such as disease resistance. Further, the invention includes a method for breeding corn plants containing quantitative trait loci (QTL) that are associated with resistance to Gray Leaf Spot, a fungal disease associated with Cercospora spp.

Cultivar-specific and ulvan-induced resistance of apple plants to Glomerella leaf spot are associated with enhanced activity of peroxidases

Abstract: Glomerella leaf spot (GLS) is an important disease of apple plants, and the use of the algal polysaccharide ulvan represents a new technology for its control. This study aimed to verify whether the defense mechanisms involved in cultivar-specific and ulvan-induced plant resistance to GLS are associated with changes in the activities of peroxidase and β-1,3-glucanase. Seedlings were first sprayed with ulvan or water and then inoculated with Colletotrichum gloeosporioides 6 days later. The disease severity was recorded daily on both young and old leaves up to 10 days after inoculation, and the enzyme activities were monitored from 24 to 72h after inoculation (HAI). Although the young leaves were more susceptible to GLS, ulvan reduced approximately 66% of the disease severity in both of the leaf age groups. Additionally, the cultivar-specific and ulvan-induced resistance was associated with enhanced peroxidase activity at 24 and 72 HAI, respectively. Both the resistant and susceptible seedlings exhibited similar glucanase activities.

Characterisation and pathogenicity of Pestalotiopsis uvicola and Pestalotiopsis clavispora causing grey leaf spot of mango (Mangifera indica L.) in Italy

Abstract: During 2009 and 2010, twenty-one isolates of Pestalotiopsis spp. Associated with grey patches on the leaves, twigs, and panicles of mango were collected in six orchards located in Sicily (Italy). Morphological characteristics of colony (colour and mycelium appearance), and conidia (size, shape, septation, length and the number of apical and the basal appendages) as well as phylogenetic analysis of the Internal Transcribed Spacer (ITS) region (ITS1, 5.8S gene, and ITS2) of six representative isolates revealed the occurrence of P. uvicola and P. clavispora. The representative isolates of both species were pathogenic to the artificially inoculated detached mango leaves cv. Kensington Pride and showed significant variation in lesion size. This is the first report worldwide of P. uvicola and P. clavispora causing grey leaf spot of mango.

The First Report of Leaf Spots in Aloe vera Caused by Nigrospora oryzae in China

Abstract: Aloe vera L. var Chinese (Haw) Berg is a popular ornamental plant cultivated worldwide, whose extracts are used in cosmetics and medicine. Aloe plants are commonly affected by leaf spot disease caused by Alternaria alternata in Pakistan, India, and the United States (1). An outbreak of Alternaria leaf spot recently threatened aloe gel production and the value of ornamental commerce in Louisiana (1). During the summer of 2011, leaf spot symptoms were observed on A. vera plants growing in several greenhouses and ornamental gardens in Wuhan, Hubei Province, China. In two of the greenhouses, disease incidence reached 50 to 60%. The initial symptoms included chlorotic and brown spots that expanded to 2 to 4 mm in diameter and became darker with age. Lesions also developed on the tips of 30 to 50% of the leaves per plant. In severe infections, the lesions coalesced causing the entire leaf to become blighted and die. In September of 2012 and February of 2013, 10 symptomatic A. vera leaves were collected randomly from two greenhouses and gardens in Wuhan. A fungus was consistently recovered from approximately 80% of the tissue samples using conventional sterile protocols, and cultured on potato dextrose agar (PDA). The colonies were initially white, becoming grey to black, wool-like, and growing aerial mycelium covering the entire petri dish (9 cm in diameter) plate within 5 days when maintained in the dark at 25°C. The conidia were brown or black, spherical to subspherical, single celled (9 to 13 μm long × 11 to 15 μm wide), borne on hyaline vesicles at the tip of conidiophores. The conidiophores were short and rarely branched. These colonies were identified as Nigrospora oryzae based on the described morphological characteristics of N. oryzae (2). Genomic DNA was extracted from a representative isolate, LH-1, and the internal transcribed spacer region was amplified using primer pair ITS1/ITS4 (3). A 553-bp amplicon was obtained and sequenced. The resulting nucleotide sequence (GenBank Accession No. KC519728) had a high similarity of 99% to that of strain AHC-1 of N. oryzae (JQ864579). Pathogenicity tests for strain LH-1 were conducted in triplicate by placing agar pieces (5 mm in diameter) containing 5-day-old cultures on A. vera leaves. Four discs were placed on each punctured surface of each leaf. Noncolonized PDA agar pieces were inoculated as controls. Leaves were placed in moist chambers at 25°C with a 12-h photoperiod. After 3 days, the inoculated leaves showed symptoms similar to those observed in the greenhouses. N. oryzae was reisolated from these spots on the inoculated leaves. No visible symptoms developed on the control leaves. The pathogenicity tests were performed twice with the same results. Based on the results, N. oryzae was determined as a pathogen responsible for the leaf spots disease on A. vera. N. oryzae has been described as a leaf pathogen on fig (Ficus religiosa), cotton (Gossypium hirsutum) and Kentucky bluegrass (Poa pratensis) (4), and to our knowledge, this is the first report of N. oryae causing leaf spot disease on A. vera worldwide. References: (1) W. L. da Silva and R. Singh. Plant Dis. 86:1379, 2012. (2) M. B. Ellis. Dematiaceous Hyphomycetes, CAB, Kew, Surrey, England, 1971. (3) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990. (4) L. X. Zhang et al. Plant Dis. 96:1379, 2012.

Long term losses caused by foliar diseases on growth and survival of Eucalyptus globulus in Uruguay

Abstract: Eucalyptus globulus is the most important forest species in Uruguay, with more than 250,000 ha of commercial plantations. Despite its high susceptibility to diseases, production losses caused by foliar diseases have not been properly quantified in this country. This study analyzes the effects of foliar damage on growth and survival using data from a progeny test of E. globulus naturally infected by Teratosphaeria leaf disease and eucalypt rust (Puccinia psidii). The severity of leaf spots and defoliation were quantified 8 months after planting and tree growth and mortality were evaluated 2, 4 and 6 years later. The trial had a high incidence of foliar damage, with a mean leaf spot severity of 28.7% and a mean defoliation of 37%. The greatest impact of foliar damage, both on growth rate and mortality, occurred in the first 2 years after damage was assessed. During this period, leaf spot severity less than 40% and defoliation below 50% did not affect growth, while survival was affected when leaf damage was 70% or greater. By the sixth year both stem growth and survival were affected by severe foliar damage (spotting or defoliation of 80% or more), with a loss of up to 25% in diameter and an accumulated mortality over 70%. It has been established for the first time that under the intensive Uruguayan productive conditions, E. globulus trees can tolerate a relatively high degree of leaf spotting or defoliation but severe foliar damage in the first months can cause considerable production losses, putting at risk the economical viability of this species.

Genetic variation of Alternaria brassicae (Berk.) Sacc., causal agent of dark leaf spot of cauliflower and mustard in India

Abstract: Cauliflower (Brassica oleracea L. var. botrytis) and mustard [Brassica juncea (L.) Czern] are important cruciferous crops facing serious yield and quality loss in India from dark leaf spot disease caused by Alternaria brassicae (Berk.) Sacc. Genetic variation among 32 pathogenic A. brassicae isolates from both crops was analyzed with random amplified polymorphic DNA and inter-simple sequence repeat primers in which the mean similarity coefficient was found to be 0.73 and 0.84, respectively. Further internal transcribed spacer analysis showed all isolates are 90–100 % similar to each other, indicating genetic similarity among different A. brassicae isolates that vary pathogenically.

Testing the ‘Hybrid Susceptibility’ and ‘Phenological Sink’ Hypotheses Using the P. balsamifera – P. deltoides Hybrid Zone and Septoria Leaf Spot [Septoria musiva]

Abstract: Hybrid genotypes that arise between plant species frequently have increased susceptibility to arthropod pests and fungal pathogens. This pattern has been attributed to the breakdown of plant defenses (‘Hybrid susceptibility’ hypothesis) and (or) to extended periods of susceptibility attributed to plant phenologies in zones of species overlap and (or) hybridization (‘phenological sink’ hypothesis). We examined these hypotheses by assessing the susceptibility of parental and hybrid Populus host genotypes to a leaf spot disease caused by the fungal pathogen Septoria musiva. For this purpose, 214 genotypes were obtained from morphologically pure zones of P. balsamifera and P. deltoides, and from an intervening zone of overlap and hybridization on the drainage of the Red Deer River, Alberta, Canada. Genotypes were identified as P. balsamifera, P. deltoides, or hybrid using a suite of 27 species-specific SNP markers. Initially the genetic structure of the hybrid zone was characterized with 27.7% of trees classified as admixed individuals. To test the hybrid susceptibility hypothesis, a subset of 52 genotypes was inoculated with four isolates of S. musiva. Levels of susceptibility were P. balsamifera > F1 hybrid > P. deltoides. A further 53 genotypes were grown in a common garden to assess the effect of genotype on variation in leaf phenology. Leaf phenology was more variable within the category of hybrid genotypes than within categories of either parental species. Leaf phenology was also more variable for the category of trees originating in the hybrid (P. balsamifera – P. deltoides [hybrid and parental genotypes combined]) zone than in adjacent pure zones of the parental species. The results from the inoculation experiment support the hybrid intermediacy hypothesis. The results from the common garden experiment support the ‘phenological sink’ hypothesis. These findings have greatly increased our understanding of the epidemiology and ecology of fungal pathogens in plant hybrid zones.

First report of leaf spot disease on oil palm caused by Pestalotiopsis theae in Thailand

Abstract: A leaf spot on oil palm, caused by Pestalotiopsis theae, was found in a plantation of Elaeis guineensis for the first time in the world in Chiang Mai Province, Thailand. The fungus was isolated from lesions on leaves, and its pathogenicity was confirmed. Pathogenicity tests showed that P. theae could infect E. guineensis, which developed the same symptoms after inoculation as those observed naturally in the field. The fungus was identified based on morphological characteristics and confirmed using comparisons of DNA sequences of internal transcribed spacer (ITS)1, ITS2 and 5.8S rDNA. This report is the first on oil palm leaf spot disease caused by P. theae.

First Report of Gray Leaf Spot of Maize Caused by Cercospora zeina in China.

Abstract: Gray leaf spot of maize (Zea mays L.) is an important foliar disease in many parts of China. The causal organism of gray leaf spot in China is generally regarded as Cercospora zeae-maydis (3). In October 2011, symptoms similar to gray leaf spot were observed on 77% of maize plants in 25 locations (about 3,000 ha.) of Yunnan Province, China, and the disease could cause yield losses of 35 to 50%. The symptoms of leaf spot were different from those caused by C. zeae-maydis. The lesions on leaves were oblong, pale gray to pale brown, 2 to 3 × 5 to 40 mm, and confined by leaf veins that eventually coalesced. To identify the pathogen, 75 leaf samples were collected from 25 fields (three leaf samples for each field) at the kernel maturity stage. Single, well-separated lesions were excised and surface-sterilized by placing them in 75% ethanol for 5 s, then disinfested in 2% sodium hypochlorite for 5 min and rinsed with sterilized water. The lesions were incubated on water agar (WA) at 24°C for 48 to 72 h to allow sporulation. Seventy-five single-conidial isolates were obtained and cultured as described in Crous (1). Morphology of the isolates was determined on plates containing maize leaf powder agar (MLPA). After 5 days, isolates produced pale brown mycelia that consisted of 3- to 4-μm-wide, septate, branched hyphae. Conidiophores were 5 to 7 × 55 to 100 μm, straight to slightly flexuous, and usually 1- to 5-septate. Conidia were average 7.5 × 68 μm, fusiform, apex subobtuse, base subtruncate, and 3- to 6-septate. These characteristics are similar to C. zeina (2). The internal transcribed spacer (ITS) region of rDNA was amplified from each of the 75 isolates using primers ITS1/ITS4 and sequenced. The same sequences were obtained and the sequence of isolate YNGLS was submitted to GenBank (Accession No. KC878692). BLAST analysis of the sequence showed 100% confirmation to C. zeina (DQ185081). Additionally, a PCR-based diagnostic test using species-specific primers (2) confirmed the identification of the 75 isolates as C. zeina. The pathogenicity of the isolates was tested on greenhouse grown maize variety Huidan 4. The test was performed on 40 plants and replicated three times. The plants were inoculated at the 10 leaf stage by injecting 2 ml of conidial suspensions (2,500 conidia ml-1) into leaf whorl using a hypodermic syringe, and control plants were injected with sterile water. Conidia were collected from 5-day-old cultures grown on MLPA and suspended in sterile water. Forty days after inoculation, all inoculated plants showed characteristic lesions on leaves, but control plants remained asymptomatic. C. zeina was reisolated from the lesions, and the identity of the reisolates was confirmed by the morphological and molecular characteristics as stated above. C. zeina was previously reported as the causal agent of maize gray leaf spot (2). To our knowledge, this is the first report of C. zeina causing gray leaf spot of maize in China. References: (1) P. W. Crous. Mycologia Memoir. 21:1, 1998. (2) P. W. Crous et al. Stud. Mycol. 55:189, 2006. (3) C. H. Lu et al. J. Southwest China Normal Univ. 37:51, 2012.

Detection of Pseudomonas Syringae pv. Lachrymans Associated with the Seeds of Cucurbits

Abstract: Seed-borne bacteria that impair germination and emergence of seedlings and reduce yield and quality of cucurbits are of major concerns for cucurbit production throughout the world. The present investigation has been carried out to detect bacteria from the seeds of eight cucurbits viz. cucumber, bottle gourd, wax gourd, sweet gourd, ridge gourd, bitter gourd, sponge gourd and snake gourd collected from the different shops of Mymensingh town during July to November 2011. Seed samples were tested to detect seed-borne bacteria by nutrient agar plate method, cassette holder and liquid assay method. Only one bacterium was isolated and identified through nutrient agar plate and liquid assay method. The bacterium was identified as Pseudomonas syringae based on creamy white color colonies on the nutrient agar plate. The Pathogenicity test revealed that the bacterium was able to cause leaf spot symptom on the seedlings of all cucurbits confirming that the bacterium was Pseudomonas syringae pv. lachrymans. Hypersensitive response (HR) test on tobacco leaves caused partial death of local cell of tissues (HR) within the infiltrated area of tobacco leaves (cv. Bankete -A1). Gram staining and KOH test indicated the bacterium was gram negative and it was not able to grow at temperature 37 0 C and

First Report of Corynespora cassiicola-Incited Target Spot on Cotton in Alabama.

Abstract: Target spot symptoms were first observed on dryland and irrigated cotton (Gossypium hirsutum L.) statewide in Alabama in 2011. Leaf spots first appeared in the lower canopy and spread upward through the canopy toward the shoot tips. Individual leaf spots were roughly circular, formed concentric rings of alternating light and dark brown bands, and were up to 10 mm in diameter. Leaves with multiple lesions senesced prematurely. In 2012, target spot symptoms were observed as early as 68 days after planting in Tallapoosa County, Alabama. The possible combination of early disease onset and frequent showers/irrigation triggered rapid premature defoliation in some fields in excess of 75% in susceptible cultivars (Phytogen 499). Estimated yield losses in select cultivars (Deltapine 1050 and Phytogen 499) exceeded 336 kg/ha seed cotton. In 2012, symptomatic leaves were obtained from two separate locations in Alabama (Baldwin and Tallapoosa counties). The fungus was isolated from lesions by single spores plated on antibiotic V8 agar (1) and incubated at 21°C for 2 weeks under 12-h light cycles. Conidiophores arising from the gray, flocculose colonies were simple, erect, cylindrical, brown or olivaceous, unbranched, with two to seven septa. Conidia were borne singly, ranging from subhyaline to olivaceous, obclavate to cylindrical, straight to slightly curved, contained 4 to 15 pseudosepta, and were 50 to 209 μm long and 7 to 15 μm wide. These characteristics were consistent with the original description of Corynespora cassiicola on cotton (2). The internal transcribed spacer region (ITS) of two isolates, one representing each location, was amplified using primers 2234c and 3126t targeting a 550-bp region of the ITS1, 5.8S rRNA gene, and ITS2 (3). Sequences revealed 99% similarity to C. cassiicola in NCBI (Accession Nos. AY238606 and JQ717069). In greenhouse pathogenicity tests, 10 cotton seedlings (Phytogen 499) were inoculated by spraying a fungal suspension (2 × 104 spores/ml) of each of the two isolates prepared from 2-week-old cultures until runoff. Controls were inoculated with sterile water. Cotton seedlings were incubated in a moist chamber at 21°C for 72 h. All plants inoculated with the fungus developed leaf spot symptoms in 6 days. The fungus was reisolated from five inoculated plants. DNA was extracted from each isolate, amplified using primer pair 2234c/3126t, and sequenced. Sequences (550-bp) from all isolates shared 99% similarity to other C. cassiicola sequences in GenBank (Accession Nos. AY238606 and JQ717069). Nucleotide sequence data reported are available in GenBank under Accession Nos. KC544017 to 23. This pathogen has been reported previously to be economically important on a number of other hosts. To our knowledge, this is the first report of C. cassiicola on cotton in Alabama. Given the increasing prevalence of this disease in Alabama, its confirmation is a significant step toward developing management recommendations for growers. References: (1) L. J. Dixon et al. Phytopathology 99:1015, 2009. (2) J. P. Jones. Phytopathology 51:305, 1961. (3) J. Sequerra et al. Mycol. Res. 101:465, 1997.

Etiology of phaeosphaeria leaf spot disease of maize

Abstract: Different fungal species and the bacterium Pantoea ananatis (Pa) have been reported as etiological agents of Phaeosphaeria leaf spot (PLS) disease. This work aimed at using molecular identification of the fungi and bacteria occurring in PLS and its etiology. Genomic DNAs from (i) pool of each of the four stages of PLS lesions; (ii) bacteria and fungi isolated from lesions of natural PLS (NPLS) and artificial injuries (AI); (iii) fungi isolated from lesions obtained from plants inoculated with Pa in greenhouse (GH) were used in PCR with universal primers for bacteria and fungal rRNA genes, and species-specific primers for Pa. Bacterial amplicons were observed at all stages of lesions and fungal amplicons in stages 3 and 4. Bacterial amplicons of pooled NPLS lesions were from Pa while fungal amplicons were from Phaeosphaeria sp. and Phoma sp. Bacteria from NPLS, GH and AI lesions were identified as Pa, Pa and Bacillus subtilis, respectively, while the fungi were Epicoccum nigrum, Leptosphaeria sacchari, Cochliobolus geniculatus, Pithomyces chartarum, Alternaria alternata, A. ricini, Gibberella intricans, G. fujikuroi, Phaeosphaeria sp., P. avenaria, Phoma sp., Phyllosticta sp., Sarocladium strictum, Glomerella graminicola, and Cochliobolus heterostrophus. Symptoms of PLS decreased by 90% with the use of oxytetracycline in foliar treatment of maize plants in the field, and its addition to culture medium completely inhibited the growth of Pa. The results strongly show that Pa is the causal agent of PLS disease and different species of opportunistic fungi appear late in the necrotic stages of lesions caused by Pa.

First report of Phoma betae on Aloe vera in India

Abstract: Leaf spot disease of A. vera was observed in nurseries of Gwalior city afterthe post-rainy season. As the disease progressed, the tip of the leaf shrank, then dried and eventually broke. The causal agent was identified as Phoma betae A.B. Frank. This is the first report of leaf spot disease on Aloe vera caused by P. betae in India.

Rapid and sensitive detection of Curvularia lunata associated with maize leaf spot based on its Clg2p gene using semi-nested PCR.

Abstract: UNLABELLED Curvularia lunata (Wakker) Boed, the causative agent of Curvularia leaf spot in maize, was determined according to conidiophore and conidium morphology in a previous study. In the current study, a sensitive polymerase chain reaction assay was developed for the detection of C. lunata. Two specific forward (ClgD1/ClgD2) and one reverse primers (ClgD3) were designed based on a Ras-related (Clg2p) gene. Eight C. lunata isolates that represent different virulent strains in maize, six other Curvularia spp., and 22 fungal plant pathogens were used to test the specificity of the primers. PCR amplification using ClgD1/ClgD3 as the first-round primers resulted in an 870-bp band from the C. lunata isolates. The detection sensitivity using ClgD1/ClgD3 was 100 pg of genomic DNA. In the second round of PCR, a 1 : 50 dilution of the first-round PCR products was used as a template with the ClgD2/ClgD3 primer pair, which increased the detection sensitivity to 1 fg. This semi-nested PCR procedure could also be used to detect C. lunata from infected maize leaves. The proposed PCR-based assay may be used for diagnosing and monitoring maize Curvularia leaf spot. SIGNIFICANCE AND IMPACT OF THE STUDY The semi-nested PCR assay may provide researchers and laboratory technologists a tool to rapidly detect C. lunata, which causes maize Curvularia leaf spot, compared with histological examination.

First report of bacterial blight of crucifers caused by Pseudomonas cannabina pv. alisalensis in Japan

Abstract: In October 2010, a bacterial disease produced flecks and spots on leaves of Chinese cabbage, cabbage and Japanese radish in Nagano Prefecture, Japan. The symptoms started on the abaxial surface of leaves as angular, water-soaked flecks of 1–2 mm in diameter with a yellow halo of 3–4 mm width. These flecks then became visible on both leaf surfaces, enlarged and coalesced into large blight lesions. The symptoms were similar to bacterial leaf spot caused by Pseudomonas syringae pv. maculicola. The bacterium isolated from leaf lesions formed a white colony and produced polysaccharides on YP agar. The isolates were identified as P. syringae group by LOPAT tests and the 16S rDNA sequence. Moreover, the results of pathogenicity on cruciferous plants, bacteriological characteristics, rep-PCR and the sequences of rpoD and gyrB showed that the isolates should be identified as P. cannabina pv. alisalensis (recently transferred from P. syringae pv. alisalensis). This is the first report of P. cannabina pv. alisalensis isolated from diseased crucifers in Japan.

Alternaria alternata causes leaf spot and fruit rot on loquat (Eriobotrya japonica) in Greece

Abstract: In 2011, a leaf spot and fruit rot disease was observed on loquat trees (Eriobotrya japonica) in Thessaloniki, Greece. The pathogen was identified as Alternaria alternata (Fr.) Keissl. on the basis of morphology and ITS sequencing. A pathogenicity test was performed and Koch’s postulates were confirmed by re-isolation of the fungus A. alternata from artificially inoculated leaves and fruits. This is the first report of A. alternata as the cause of leaf spots and fruit rot on loquat in Greece.

Exserohilum rostratum causing sugarcane leaf spot in Iran

Abstract: A new sugarcane leaf spot disease caused by Exserohilum rostratum was found in Ahvaz, southwestern Iran during a series of surveys on fungal species causing sugarcane leaf diseases in 2011. Three single spore derived isolates were obtained from diseased sugarcane leaves and the pathogenicity of each isolate to sugarcane plants was confirmed by inoculation tests based on Koch’s postulates. The isolates were identified as members of E. rostratum based on their morphological characters as well as rDNA-ITS (internal transcribed spacer) sequences. This is the first report of leaf blight caused by E. rostratum on S. officinarum in Iran.

Effect of Certain Micronutrients on Some Agronomic Characters, Chemical Constituents and Alternaria Leaf Spot Disease of Faba Bean

Abstract: To study the effects of foliar application with micronutrients on yield and yield components of faba bean (c.v. Misr 1), an experimental research was conducted in complete randomized block design by three replications during the two growing seasons of 2009/2010 and 2010/2011 in Etay El-Baroud Agricultural Research Station, El-Behera Governorate. Results shwoed that, spraying with Fe+Zn+Mn increased plant height, number of pods/plant, number of seeds/pod, number of seeds/plant, 100 seed weight and seed yield /faddan in the combined data. Also, chemical constituent, chlorophyll A, chlorophyll B, reducing sugars and the non reducing sugars significantly increased in all treatments spray with micronutrients compared with non-treated (control). Meanwhile, Altermaria leaf spot incidence on treated plants significantly decreased 18.2% 60.5% compared with non-treated control plants.

First Report of QoI Insensitive Cercospora beticola on Sugar Beet in Ontario, Canada.

Abstract: Cercospora beticola Sacc. causes Cercospora leaf spot (CLS) of sugar beet (Beta vulgaris L.) and is the most destructive foliar disease of sugar beet worldwide (1). The QoI fungicide pyraclostrobin has been an important management tool for CLS in Canada since 2003. Beginning in 2010, some growers reported poor disease control after applying pyraclostrobin. Leaf disk samples with CLS lesions were collected in September 2012 from 16 commercial fields located in Kent and Lambton Counties, Ontario, Canada. These counties (ca. 300,000 ha) encompass the major commercial sugar beet production area in Ontario (ca. 3,925 ha). CLS severity ranged from low to severe among the sampling sites. Leaf discs with a single leaf spot were cut from leaves using a hole punch. Spots were up to 5 mm in diameter with tan, light brown, or sometimes gray centers. DNA was extracted from leaf discs using a Qiagen DNeasy Plant Mini Kit (Germantown, MD) according to the manufacturer's instructions. PCR was used to amplify a fragment of the C. beticola cytochrome b (CYTB) gene (4). Pure cultures were obtained by placing plant tissue in a moist chamber and transferring single spores to V8 juice agar. PCR products were sequenced for 32 samples at the Genomics Technology Support Facility (Michigan State University, East Lansing, MI) and 25 were confirmed to have 100% identity with the sequence of QoI-resistant C. beticola from Michigan (2) and to QoI-resistant isolates from GenBank (Accession Nos. JQ619933 and JQ360628). The remaining seven had 100% identity with a sensitive isolate (EF176921.1). Each resistant isolate contained a change in codon 143 that is predicted to lead to a substitution of G143A in the cytochrome b gene. This G143A mutation has been associated with QoI resistance in a number of fungi (3). To confirm the result, a conidium germination bioassay was carried out using nine isolates with the G143A mutation on sugar beet leaf agar covered with water agar amended with pyraclostrobin at concentrations ranging from 0 to 54.3 μg/ml and distributed on a spiral gradient using an Eddyjet II spiral plater. The medium was supplemented with salicylhydroxamic acid (SHAM) to block the alternate oxidation pathway. Following incubation at 25°C for 2 days, the distance between the center of the plate at which conidial germination was 50% of the maximum observed growth (EC) and the point at which conidial germination terminated were measured (TEC). The EC50 values were determined from the SGE software for each isolate by entering the EC and TEC values, respectively. The estimated EC50 for a representative wild type (sensitive) isolate was 0.03 μg/ml, while the value for the resistant isolate could not be calculated because it was greater than the highest concentration tested (54.3 μg/ml). Additionally, in the controls with no SHAM or fungicide, the resistant isolate showed a consistent reduced germination rate compared to the sensitive isolate (30.0% and 93.5% germination, respectively). Confirmation of fungicide insensitivity will require a re-evaluation of current management practices in Ontario to minimize economic losses due to CLS. References: (1) B. J. Jacobsen and G. D. Franc. Compendium of Beet Diseases and Pests, 2nd ed, APS Press, St. Paul, MN, 2009. (2) W. Kirk et al. New Dis. Rep. 26:3, 2012. (3) Z. Ma and T. J. Michailides. Crop Prot. 24:853, 2005. (4) A. Malandrakis et al. Pestic. Biochem. Physiol. 100:87092, 2011.

A Novel Screening Method for Evaluation of Lettuce Germplasm for Bacterial Leaf Spot Resistance

Abstract: Bacterial leaf spot of lettuce, caused by Xanthomonas campestris pv. vitians ,i s a devastating disease of lettuce worldwide. Because there are no chemicals available for effective control of the disease, host-plant resistance is highly desirable to protect lettuce production. A new method for fast screening and accurate identification of bacterial leaf spot (BLS)-resistant lettuce has been developed in our laboratory. A total of 79 lettuce genotypes (69 germplasm lines and 10 adapted cultivars) were evaluated with this technique for response to X. c. vitians. Disease incidences ranged from 92% to 100% and disease severities were between 1.6 and 3.6 on the 0 to 4 scale. No highly resistant genotypes were identified. However, 12 genotypes did not significantly differ for disease severities from the moderately resistant 'Little Gem' lettuce that was used as a resistant control. Comparison of disease severities of 10 commercial cultivars and three moderately resistant germplasm lines tested at the seedling stage and adult stage showed a high positive correlation (r = 0.87, P < 0.0001) between tests. The new screening method shouldbeusefulinbreedingprograms,inwhichgreatnumbersofplantsneedtobetested during germplasm evaluation, and for single plant selection as well as other studies. The identification of new sources of moderate resistance in this study could facilitate development of cultivars with a higher level of resistance through the gene pyramiding approach.

Stemphylium Leaf Spot of Parsley in California Caused by Stemphylium vesicarium.

Abstract: From 2009 through 2011, a previously undescribed disease occurred on commercial parsley in coastal (Ventura County) California. Symptoms of the disease consisted of circular to oval, tan to brown leaf spots and resulted in loss of crop quality and, hence, reduced yields. A fungus was consistently isolated from symptomatic parsley. Morphological and molecular data identified the fungus as Stemphylium vesicarium. When inoculated onto parsley leaves, the isolates caused symptoms that were identical to those seen in the field; the same fungus was recovered from test plants, thus completing Koch's postulates. Additional inoculation experiments demonstrated that 10 of 11 tested flat leaf and curly parsley cultivars were susceptible. The parsley isolates also caused small leaf spots on other Apiaceae family plants (carrot and celery) but not on leek, onion, spinach, and tomato. Isolates caused brown lesions to form when inoculated onto pear fruit but only when the fruit tissue was wounded. Using a freeze-blotter seedborne pathogen assay, parsley seed was found to have a low incidence (0.25%) of S. vesicarium. When inoculated onto parsley leaves, three of four isolates from seed caused the same leaf spot disease. This is the first documentation of a foliar parsley disease caused by S. vesicarium. The occurrence of S. vesicarium on parsley seed indicates that infested seed may be one source of initial inoculum. Based on the negative results in the host range experiments, it appears that this parsley pathogen differs from the S. vesicarium that causes disease on leek, garlic, onion, and pear fruit.

Calonectria pseudonaviculata can cause leaf spot and stem blight of Pachysandra procumbens.

Abstract: The authors' objective in this study was to determine the susceptibility of P. procumbens to C. pseudonaviculata. This is the first report of C. pseudonaviculatum causing a leaf spot and stem lesio...