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ABSTRACT: Flowering dogwood (Cornus florida L.) populations recently have experienced severe declines caused by dogwood anthracnose. Mortality has ranged from 48 to 98%, raising the concern that genetic diversity has been reduced significantly. Microsatellite data were used to evaluate the level and distribution of genetic variation throughout much of the native range of the tree. Genetic variation in areas affected by anthracnose was as high as or higher than areas without die-offs. We found evidence of four widespread, spatially contiguous genetic clusters. However, there was little relationship between geographic distance and genetic difference. These observations suggest that high dispersal rates and large effective population sizes have so far prevented rapid loss of genetic diversity. The effects of anthracnose on demography and community structure are likely to be far more consequential than short-term genetic effects.
Genetica 10/2010; 138(9-10):1047-57. · 2.15 Impact Factor
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ABSTRACT: Understanding the relative contribution of the different resistance components is necessary to develop selection schemes and accelerate resistant-cultivar development. This study was conducted to investigate spore germination, infection-structure formation, and fungal development of Erysiphe pulchra, the causal agent of powdery mildew, on leaf disks of six cultivars or lines of flowering dogwood (Cornus florida) with different levels of resistance. The cultivars and lines tested were grouped into the following three resistance categories: highly susceptible (‘Cherokee Daybreak’ and MW 94-60), moderately susceptible (‘Cherokee Princess’ and MW 95-25), and resistant (‘Cherokee Brave’ and ‘Karen’s Appalachian Blush’). Percentages of spore germination and secondary-appressoria formation were not significantly different among the cultivars and lines. Significantly less percent germinated conidia with branched hyphae were observed on resistant cultivars than on the moderately susceptible cultivar or line, which was less than on the highly susceptible cultivar or line. Infection efficiencies were significantly different among cultivars and lines in the three resistance categories, except that there were no differences between ‘Cherokee Princess’ and the resistant cultivars. Resistant cultivars supported shorter latent periods than moderately and highly susceptible cultivars or lines, but no differences in latent period were detected between the later two resistance categories. The recently released ‘Karen’s Appalachian Blush’ expressed higher levels of resistance to powdery mildew than did ‘Cherokee Brave’, as indicated by the longer latent period and reduced relative sporulation of the pathogen.
Canadian Journal of Plant Pathology 03/2010; March 2006(Vol. 28):71-76. · 0.88 Impact Factor
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ABSTRACT: Microsatellite discovery from genomic libraries is tedious because of the low number of clones that contain inserts and costly because of screening methodologies. A new procedure for screening clones for microsatellite DNA is described herein. Instead of colony hybridization, a polymerase chain reaction (PCR) with two vector standard primers and one synthesized repeat primer was used to directly screen colonies. PCR of colonies that produced a strong smear in gels contained the desired motif, whereas a single strong band indicated the lack of the desired motif. This simple screening method is a cost-effective way to identify microsatellite-containing colonies.
Molecular Ecology Notes 06/2007; 7(4):558 - 561. · 2.38 Impact Factor
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ABSTRACT: The anthracnose epidemic caused by exotic filamentous fungi of the genus Discula threatens the future of the prized flowering (Cornus florida L.) and Pacific (C. nuttalli Aud.) dogwoods in North America. A cross-section of fungi that cause anthracnose in broadleaf temperate trees was characterized using DNA amplification fingerprinting, sequence and secondary structure analysis of the internal transcribed spacers (ITS) of nuclear ribosomal DNA (rDNA), and compatibility of hyphal anastomosis. ITS-inferred phylogenies rejected the null hypothesis of only one fungal lineage, by defining four monophyletic and well differentiated groups, corresponding to Discula sp., D. quercina, D. umbrinella and D. destructiva, with the last two species sharing a common and recent ancestor. In turn, they showed that the dogwood pathogen, D. destructiva, did not evolve directly from an indigenous population related to Discula sp. In this study, rDNA spacers that are generally considered important for protein synthesis but are selectively neutral, appeared functionally constrained and subject to selective sequence diversification. Results confirmed the high variability of D. umbrinella and the remarkable homogeneity and exotic nature of D. destructiva at the genetic level, clarified the taxonomy and phylogeny of Discula, and provided clues as to the origin and diversification of dogwood anthracnose-causing fungi.
Current Genetics 08/2001; 39(5-6):346-54. · 2.56 Impact Factor
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ABSTRACT: In a previous study, addition of Trichoderma harzianum Rifai isolate T-12 to a propagative medium resulted in improved performance of chrysanthemum cuttings. However, root and shoot growth of one cultivar, 'Dark Bronze Charm', were more responsive to a lower (5 g T-12/kg medium) than higher (25 g T-12/kg medium) rate of fungal propagules, suggesting potential phytotoxicity at higher concentrations. The objectives of this study were to investigate higher rates of T-12 medium amendment for phytotoxicity, and to examine an alternative method of delivering the fungus to the propagative medium in order to obtain a more uniform response from cuttings. Isolate T-12 was added to the propagative medium as either a powdered peat-bran amendment (0, 5, or 50 g T-12/kg medium) or as alginate prills (80 or 800 g T-12/kg medium). There were no differences among treatments on day seven, but by day 21, shoot fresh weight and heights were significantly greater for plants treated with prills at 800 g T-12/kg medium. Both prill treatments resulted in greater shoot height on day 14 and 21 than all other treatments, which were similar to controls. Amendment with T-12 powder at 50 g/kg increased root length, but 80 g/kg medium added as prills decreased root dry weight compared to the control. The highest rate of T-12 (800 g prills/kg medium) had no effect on root growth. This suggests that moderate, rather than high rates of T-12 are more effective in promoting rooting of unrooted chrysanthemum, and that there is a potential for phytotoxic effects on root growth with higher rates.
Canadian Journal of Microbiology 09/2000; 46(8):730-5. · 1.36 Impact Factor
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ABSTRACT: Isolates of Discula destructiva Redlin and an undescribed species of Discula, the filamentous fungi that cause anthracnose of flowering (Cornus florida L.) and Pacific (Cornus nuttalli Aud.) dogwoods, were analyzed for genetic variation by nucleic acid scanning with arbitrary mini-hairpin oligonucleotide primers. While the fungal population was highly homogeneous throughout the disease range in eastern and western North America, the generation of arbitrary signatures from amplification profiles (ASAP) distinguished isolates from the northeast, middle and southern Appalachian mountain range, and western United States and Canada. ASAP involves a dual-step arbitrary primer-based amplification procedure that generates a large number of informative allelic characters by amplification of monomorphic DNA fingerprints. ASAP analyses showed a fine fungal population structure consistent with the recent and separate introduction of the pathogen on the west and east coasts of North America.
FEMS Microbiology Letters 01/1997; 145(3):377-83. · 2.04 Impact Factor
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ABSTRACT: Microsatellite discovery from genomic libraries is tedious because of the low number of clones that contain inserts and costly because of screening methodologies. A new procedure for screening clones for microsatellite DNA is described herein. Instead of colony hybridization, a polymerase chain reaction (PCR) with two vector standard primers and one synthesized repeat primer was used to directly screen colonies. PCR of colonies that produced a strong smear in gels contained the desired motif, whereas a single strong band indicated the lack of the desired motif. This simple screening method is a cost-effective way to identify microsatellite-containing colonies.
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ABSTRACT: Sclerotinia homoeocarpa is the causal agent of dollar spot disease that reduces the uniformity and aesthetic value of golf putting greens. Fungicide-resistant isolates of S. homoeocarpa were collected from putting greens at 10 locations across Tennessee and northern Mississippi. Genetic diversity among the 60 isolates was investigated using vegetative compatibility, conserved gene sequences, and amplified fragment length polymorphism (AFLP). Six tester strains were paired with Tennessee and northern Mississippi isolates on potato dextrose agar. Some of the 60 isolates were delineated into vegetative compatibility groups, but fungicide resistance could not be associated with a particular vegetative compatibility group. Genetic similarities of isolates at the vegetative compatibility level could be attributed to founder effects. Sequencing the regions of CAD, EF1-α, β-tubulin, and internal transcribed spacers revealed 100% homology among isolates. Capillary gel electrophoresis and analysis of AFLP fragments indicated 86 to 100% similarity between the isolates. Vegetative compatibility and molecular data indicate that the populations of the pathogen are clonal. Isolates did not cluster according to fungicide resistance during unweighted pair group with arithmetic means analysis, but did appear to cluster according to vegetative compatibility group and location. Although associations could not be made between molecular markers and fungicide resistance, links between vegetative compatibility and AFLP markers may provide a foundation from which other studies could be performed.
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ABSTRACT: Agar is a commonly used gelling agent and a raw material used in other gelling agents. The effects of five gelling agents and potato dextrose agar on urediniospore germination, and changes in percent urediniospore germination and germ-tube elongation in Puccinia hemerocallidis over time were investigated in vitro. Percent urediniospore germination differed significantly between the tested gelling agents. Urediniospores germinated well on Gelrite, agarose, Phytagar, and Oxoid No. 3 agar in decreasing order, and percent urediniospore germination was negatively correlated with the concentration of gelling agent. Urediniospores germinated poorly on the substrates containing more than 0.5% Bacto Agar. The concentration of Bacto Agar that caused 50% inhibition of urediniospore germination was 18.2 µg/mL in 1% agarose substrate. However, there were no significant differences in germ-tube elongation between the concentrations of Bacto Agar water extract tested. Unidentified inhibitory compounds from Bacto Agar water extract were adsorbed on a C18 column and the effluent water did not affect spore germination. However, the methanol-eluted solution from the C18 column completely inhibited urediniospore germination when the solution was evaporated and reconstituted with water. Changes in percent urediniospore germination and germ-tube length on 1% agarose water substrate over time fitted well with negative exponential models. The time to the half-asymptote of percent urediniospore germination and germ-tube length was 1.4 and 6.0 h, respectively, and the time to 95% of the asymptote was 6.1 and 30.9 h for spore germination and germ-tube elongation, respectively.
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ABSTRACT: Additional index words. arbitrary signatures from amplifi cation profi les (ASAP), Cornus kousa, cultivar identifi cation, DNA profi ling, DNA amplifi cation fi ngerprinting (DAF), fl owering dogwood Abstract. Cornus kousa Hance (korean or kousa dogwood) cultivars are increasingly used as landscape plants because they lack the disease and insect problems typically associ- ated with the native C. fl orida L. (fl owering dogwood). A number of red-bracted kousa dogwood cultivars are now available and several are phenotypically indistinguishable from one another. Plants of six cultivars obtained from three nurseries were characterized genetically using deoxyribonucleic acid (DNA) amplifi cation fi ngerprinting (DAF) and arbitrary signatures from amplifi cation profi les (ASAP). DAF profi les of three red-bracted cultivars—'Rosabella', ' Satomi' and 'Heart Throb'—were nearly identical. ASAP also failed to clearly differentiate these cultivars and indicated consistent genetic similarities. In contrast, another red-bracted cultivar 'Christian Prince' and two white-bracted cul- tivars—'Little Beauty' and 'Samaritan'—were identifi ed and separated from all other cultivars by both DAF and ASAP techniques. Cornus kousa Hance (korean, chinese, or kousa dogwood) cultivars are becoming more popular as landscape plants because they are generally resistant to many diseases (e.g., powdery mildew and dogwood anthracnose) that plague C. fl orida L. (fl owering dogwood) (Hagan, et al., 1998; Ranney et al., 1995). The number of introduced kousa dogwood cultivars has increased dramatically in the last two de- cades (Dirr, 1998). These plants, which bloom ≈1 month after fl owering dogwood, are now available with either white, cream, pink, or red bracts. However, with rapid introduc- tion of similar types of pink and red kousa dogwoods, there is an increased potential for mistakes in the trade, ranging from mislabeling and multiple release to misappropriation and misrepresentation. A variety of red-bracted kousa dogwoods can be purchased through wholesale or retail nurseries. Although some of these cultivars are distinctive (i.e., variegated leaves), others appear quite similar or nearly identical. For example, 'Satomi' (synonym 'Miss Satomi') and 'Rosabella' have medium rose-pink bracts in cooler climates (blotchy pink in warmer) and share many vegetative characteristics and are considered to be the same cultivar (Dirr, 1998). 'Heart Throb' ('Schmred') has similar shoot attributes but has deep-red bracts and several Tennessee nurserymen have commented on the vegetative and reproductive similarities between 'Satomi' and 'Heart Throb' (Don Shadow, Shadow Nursery Inc., Winchester,
