bluuebunny/crossref_metadata_2025 huggingface dataset:
Germinability of Venturia inaequalis Conidia Exposed to Sunlight
Authors: Aylor Donald E. , Sanogo Soumaila
Published: May 2007

Detached conidia of Venturia inaequalis were exposed simultaneously outdoors to direct sunlight or in an adjacent ventilated enclosure in darkness for periods ranging from 0.5 to 16.5 h. In addition, conidia were either exposed or not exposed to UV light (254 nm) from 1 to 64 min in the laboratory. After exposure, conidia were placed on water agar in closed petri dishes and allowed 24 h to germinate. Germinability of conidia in the laboratory was reduced up to 95% by doses of UV254 of 8.1 to 10.8 kJ m-2.Germinability of conidia in the field was reduced up to 95% by doses of UV-B of about 44 kJ m-2. A significant percentage of conidia survived radiation doses equivalent to 12 h in full sunlight.
Interaction of Four Antagonistic Fungi with Botrytis aclada in Dead Onion Leaves: A Comparative Microscopic and Ultrastructural Study
Authors: Köhl J. , Bélanger R. R. , Fokkema N. J.
Published: May 2007

The colonization of dead onion leaves by Botrytis aclada and the fungal antagonists Aureobasidium pullulans, Chaetomium globosum, Glio-cladium catenulatum, and Ulocladium atrum and the interactions between B. aclada and each of the four antagonists were studied at the microscopic and ultrastructural level. This approach was used in an attempt to understand the colonization pattern of these fungi and the nature of the biocontrol activity of the antagonists that have shown a potential to suppress spore production of Botrytis spp. on necrotic plant tissues. When applied alone, B. aclada and U. atrum were found throughout the leaf tissues in high densities after an incubation period of 6 days at 18°C in a moist chamber. C. globosum and G. catenulatum colonized only the outer portions of the leaf, whereas A. pullulans appeared to be concentrated in the leaf stomata. When pathogen and antagonists were applied together, ultrastructural observations revealed that cells of B. aclada were plasmolyzed in the presence of G. catenulatum, suggesting a reaction to antifungal molecules. Antibiosis also seemed to be involved, albeit to a lesser extent, in the antagonistic interactions between B. aclada and A. pullulans or C. globosum. No evidence of direct parasitism was recorded. On the other hand, U. atrum appeared to completely exclude B. aclada from dead onion tissues when both fungi competed for the substrate. Ultrastructural observations of the in vitro interaction between the two fungi did not reveal parasitism or antibiosis by either fungus. Based on previous records of its biocontrol potential and observations of its colonizing properties, it appears that U. atrum can compete for and utilize necrotic tissues rapidly and extensively, thus, excluding competitors without any other antagonistic action.
RAPD Analysis Provides Insight into the Biology and Epidemiology of Uncinula necator
Authors: Délye C. , Laigret F. , Corio-Costet M.-F.
Published: May 2007

Ninety isolates of grape powdery mildew (Uncinula necator) from Europe (sixty-two) and India (twenty-eight) were collected. Ten of the sixty-two European isolates originated from mycelium overwintering in dormant buds (“flagshoots”). Mating types were determined, and genetic variation was assessed by random amplified polymorphic DNA (RAPD). Forty-one European isolates, including all “flagshoot” isolates, were mating type +, and twenty-one were mating type -. All Indian isolates were mating type -. Phenetic analysis based on 414 amplicons revealed three main groups. Most European isolates (53) clustered together. Nine flagshoot isolates clustered in a second distinct group. These isolates, which coexisted with other isolates in the field, may represent a genetically isolated biotype of U. necator. Indian isolates clustered into two groups. The first group (15 isolates) was a subgroup of the group containing European nonflagshoot isolates. The second group (12 isolates) was distinct from the other groups. These two groups of Indian isolates may represent genetically isolated populations with different climatic tolerances. A polymerase chain reaction primer pair, derived from a RAPD fragment specific to the Indian isolates, proved to be suitable for field studies.
Clavibacter michiganensis subsp. Sepedonicus Elicits a Hypersensitive Response in Tobacco and Secretes Hypersensitive Response-Inducing Protein(s)
Authors: Nissinen R. , Lai F.-M. , Laine M. J. , Bauer P. J. , Reilley A. A. , Li X. , De Boer S. H. , Ishimaru C. A. , Metzler M. C.
Published: May 2007

Strains of Clavibacter michiganensis subsp. sepedonicus, causal agent of bacterial ring rot of potato, showed marked differences in virulence on host plants. When infiltrated into tobacco leaves, virulent strains caused a rapid localized necrotic response (within 24 to 48 h) characteristic of the hypersensitive response (HR), whereas nonpathogenic strains did not. Concentrated cell-free culture supernatants (CCS) from virulent strains caused a necrotic reaction on tobacco, whereas CCS from nonpathogenic strains did not. The necrosis-inducing activity was heat stable and protease sensitive. Inhibitors of eukaryotic metabolism suppressed the necrotic reaction of tobacco to CCS. No necrotic response was observed when host plants were infiltrated with either cells or CCS from virulent strains. HR-inducing protein(s) from a virulent strain separated from the majority of other proteins on DEAE cellulose at 250 to 300 mM NaCl. Ammonium sulfate-precipitated proteins from a virulent strain produced a necrotic reaction at a total protein concentration of 18 μg/ml, whereas those from a nonpathogenic strain did not, even at a concentration of 180 μg/ml. We conclude that virulent strains of C. michiganensis subsp. sepedonicus elicit a typical HR in tobacco and secrete proteinaceous elicitor(s) of the nonhost HR.
Populations of Nonpathogenic Fusarium oxysporum Associated with Roots of Four Plant Species Compared to Soilborne Populations
Authors: Edel V. , Steinberg C. , Gautheron N. , Alabouvette C.
Published: May 2007

The effect of the plant on the diversity of soilborne populations of Fusarium oxysporum was assessed after successive cultures of flax, melon, tomato, and wheat in separate samples of the same soil. Forty soil-borne isolates of F. oxysporum and forty root-colonizing isolates of each plant species were sampled during the first (T0) and fourth (T1) cultures. The population structures were assessed by a genotypic method based on restriction fragment analysis of polymerase chain reaction-amplified ri-bosomal intergenic spacer (IGS) DNA. Sixteen IGS types were defined among the four hundred isolates analyzed. The distributions of soil isolates among IGS types were similar at both sampling times. The structure of F. oxysporum populations associated with the roots of flax or melon did not differ from the structure of soilborne populations. In contrast, the structure of F. oxysporum populations associated with roots of wheat or tomato differed from the structure of soilborne populations. High frequencies were found for IGS type 4 among wheat isolates at both T0 and T1 and for IGS type 11 among tomato isolates at T1. Moreover, a high level of genetic divergence was obtained between IGS types 4 and 11. Our results suggest that tomato and wheat have a selective effect on soilborne populations of F. oxysporum and that this effect seems to be plant specific.
Application of Amplified Restriction Fragment Length Polymorphism for Genetic Characterization ofColletotrichumPathogens of Alfalfa
Authors: O'Neill Nichole R. , van Berkum Peter , Lin Jhy-Jhu , Kuo Jonathan , Ude George N. , Kenworthy William , Saunders James A.
Published: May 2007

Amplified restriction fragment length polymorphism (AFLP) was used to assess the levels of genomic variations among species and isolates of the genus Colletotrichum. Our objective was to characterize at the molecular level two alfalfa pathogens, isolates Arl-NW and 57RR, which are unusually aggressive to anthracnose-resistant alfalfa cultivars and whose taxa has been uncertain based on morphological criteria. The fingerprint patterns obtained were complex but did enable us to place these two isolates within the species C. trifolii and C. gloeosporioides, respectively. The diversity detected with AFLP among and within Colletotrichum species from alfalfa and other crops corroborated their published taxonomy based on morphology, ribosomal DNA sequence, and random amplified polymorphic DNA analyses. Similarity matrices generated with three primer pairs were highly correlated and, thus, were combined to determine the similarity among the fungal species and isolates that were analyzed. Analysis of the data generated with each of the primer pairs individually and application of either distance or parsimony methods supported the placement of these two isolates. The parsimony method of data analysis was more confirmatory in the placement of Phoma medicaginis as an out-group than the distance method, using either simple matching or Jaccard's coefficients to generate the similarity matrices. Our conclusion is that the AFLP technique will be useful for identification of individual isolates within complex genera such as Colletotrichum because of its ability to generate large numbers of polymorphisms and the consistency of polymerase chain reaction amplification.
Molecular Mapping of Resistance to Blight in an Interspecific Cross in the Genus Castanea
Authors: Kubisiak T. L. , Hebard F. V. , Nelson C. D. , Zhang Jiansu , Bernatzky R. , Huang H. , Anagnostakis S. L. , Doudrick R. L.
Published: May 2007

A three-generation American chestnut × Chinese chestnut pedigree was used to construct a genetic linkage map for chestnut and to investigate the control of resistance to Endothia parasitica (chestnut blight fungus). DNA genotypes for 241 polymorphic markers (eight isozymes, 17 restriction fragment length polymorphisms [RFLPs], and 216 random amplified polymorphic DNAs [RAPDs]) were assayed on an F2 family consisting of 102 individuals. Of these markers, 196 were segregating as expected and, subsequently, used for primary linkage mapping. Two isozymes, 12 RFLPs, and 170 RAPDs were mapped to 12 linkage groups spanning a total genetic distance of 530.1 Kosambi centimorgans. F2 plants were evaluated for a response to E. parasitica infection by directly inoculating them with two unique fungal isolates and measuring canker expansion over a period of 3.5 months. Results were compared with the marker genotype data, thereby identifying genomic regions significantly associated with a resistance response. Single-marker or nonsimultaneous analyses of variance identified seven genomic regions that appear to have an effect on host response. Multiple-marker or simultaneous models suggest that three of these regions have a significant effect on host response, together explaining as much as 42.2% of the total variation for canker size. At each of the three putative resistance loci, alleles derived from the Chinese chestnut grandparent were associated with smaller canker size, or higher levels of resistance.
Variation in Pathogenicity and Genetic Structure in theEutypa lataPopulation of a Single Vineyard
Authors: Péros J-P. , Berger G. , Lahogue Florence
Published: May 2007

Fifty-five isolates of Eutypa lata were collected in 1994 from a single vineyard, each from a different vine that showed either shoot and foliar symptoms of Eutypa dieback or only abnormalities during the period of 1990 to 1994. These isolates showed a large variation in pathogenicity after inoculation on cuttings in the greenhouse. Variability also was observed for cultural traits and radial growth rate on potato dextrose agar (PDA) medium, but no relation was found between these characteristics and pathogenicity. The isolates were paired on PDA medium, and a barrage reaction was observed for all pairings, indicating the isolates were vegetatively incompatible. Thirty-two random amplified polymorphic DNA (RAPD) markers were used to study the genetic relatedness of the isolates and the genetic structure of the population. Fifty-five different RAPD patterns were observed, confirming the genetic uniqueness of each isolate. Gametic disequilibrium values were calculated among all pairs of the 32 putative RAPD loci, and only one value was significant. Unweighted pair-group method with arithmetic averages analysis of distance data, as well as a heterogeneity statistic (Fst), did not indicate any population substructure. The results strongly suggest that isolates originated from a random-mating population and that the disease was propagated in this vineyard by ascospores produced from diverse outside sources. Southern hybridization performed for five markers indicated that the two-allele assumption made to interpret RAPD data may be violated for markers that are similar in size. However, the exclusion of such markers did not change the conclusions of the study.
Population Structure of Phytophthora cinnamomi in South Africa
Authors: Linde C. , Drenth A. , Kemp G. H. J. , Wingfield M. J. , von Broembsen S. L.
Published: May 2007

Phytophthora cinnamomi isolates collected from 1977 to 1986 and 1991 to 1993 in two regions in South Africa were analyzed using isozymes. A total of 135 isolates was analyzed for 14 enzymes representing 20 putative loci, of which four were polymorphic. This led to the identification of nine different multilocus isozyme genotypes. Both mating types of P. cinnamomi occurred commonly in the Cape region, whereas, predominantly, the A2 mating type occurred in the Mpumalanga region of South Africa. A2 mating type isolates could be resolved into seven multilocus isozyme genotypes, compared with only two multilocus isozyme genotypes for the A1 mating type isolates. Low levels of gene (0.115) and genotypic (2.4%) diversity and a low number of alleles per locus (1.43) were observed for the South African P. cinnamomi population. The genetic distance between the Cape and Mpumalanga P. cinnamomi populations was relatively low (Dm = 0.165), and no specific pattern in regional distribution of multilocus isozyme genotypes could be observed. The genetic distance between the “old” (isolated between 1977 and 1986) and “new” (isolated between 1991 and 1993) P. cinnamomi populations from the Cape was low (Dm = 0.164), indicating a stable population over time. Three of the nine multilocus isozyme genotypes were specific to the “old” population, and only one multilocus isozyme genotype was specific to the “new” population. Significant differences in allele frequencies, a high genetic distance (Dm = 0.581) between the Cape A1 and A2 mating type isolates, significant deviations from Hardy-Weinberg equilibrium, a low overall level of heterozygosity, and a high fixation index (0.71) all indicate that sexual reproduction occurs rarely, if at all, in the South African P. cinnamomi population.
Effect of Strawberry Density on the Spread of Anthracnose Caused by Colletotrichum acutatum
Authors: Madden L. V. , Boudreau M. A.
Published: May 2007

Spread of strawberry anthracnose, resulting from the rain splash dispersal of Colletotrichum acutatum conidia, was determined in field plots by assessing fruit disease incidence at a range of distances from an introduced point source of infected fruit with sporulating lesions. Four within-row plant densities were established in replicated plots in each of 2 years. A generalized linear model with a logit link function and binomial distribution for incidence was used to quantify the effects of distance and side of the row relative to the inoculum source, plant density treatment, and their interactions on disease incidence. At all assessment times, there was a significant (P ≤ 0.05) decline in incidence with increasing distance from the spore source. Moreover, row side had a significant effect, with the near side having higher incidence than the far side. Plant density treatment had a significant, but nonlinear, effect on incidence, with incidence generally declining with increasing density. Side of the row relative to the inoculum source and density treatment could affect the steepness of the disease gradient (slope) as well as the overall level of disease incidence, depending on the assessment time and year. The combined effects of plant density and row side on the height and steepness of the disease gradients could be measured using the predicted distance in which incidence equals 10% (d10). Estimated d10 generally increased in a nonlinear manner with decreasing plant density. Also, plant density had a significant negative effect on the proportion of incident rain that penetrated the canopy. In a separate study, plant density did not consistently affect infection of fruit that had been placed within the canopy immediately after being inoculated in the laboratory with a controlled inoculum density, indicating that conditions favoring infection were similar for the four densities. Thus, differences in mean disease incidence and disease gradients among the treatments were mostly due to differences in dispersal and not to other components of the disease cycle. As previously reported for controlled studies using a rain simulator, however, the effects of plant density on dispersal were complex, and increasing density did not universally lead to decreasing disease incidence.
Specific Detection of Clavibacter michiganensis subsp. sepedonicus by Amplification of Three Unique DNA Sequences Isolated by Subtraction Hybridization
Authors: Mills Dallice , Russell Brian W. , Hanus Janet Williams
Published: May 2007

Three single-copy, unique DNA fragments, designated Cms50, Cms72, and Cms85, were isolated from strain CS3 of Clavibacter michiganensis subsp. sepedonicus by subtraction hybridization using driver DNA from C. michiganensis subsp. insidiosus, C. michiganensis subsp. michiganensis, and Rhodococcus facians. Radio-labeled probes made of these fragments and used in Southern blot analysis revealed each to be absolutely specific to all North American C. michiganensis subsp. sepedonicus strains tested, including plasmidless and nonmucoid strains. The probes have no homology with genomic DNA from related C. michiganensis subspecies insidiosus, michiganensis, and tessellarius, nor with DNA from 11 additional bacterial species and three unidentified strains, some of which have been previously reported to display cross-reactivity with C. michiganensis subsp. sepedonicus-specific antisera. The three fragments shared no homology, and they appeared to be separated from each other by at least 20 kbp in the CS3 genome. Internal primer sets permitted amplification of each fragment by the polymerase chain reaction (PCR) only from C. michiganensis subsp. sepedonicus DNA. In a PCR-based sensitivity assay using a primer set that amplifies Cms85, the lowest level of detection of C. michiganensis subsp. sepedonicus was 100 CFU per milliliter when cells were added to potato core fluid. Erroneous results that may arise from PCR artifacts and mutational events are, therefore, minimized by the redundancy of the primer sets, and the products should be verifiable with unique capture probes in sequence-based detection systems.
Purification, Elicitor Activity, and Cell Wall Localization of a Glycoprotein from Phytophthora parasitica var. nicotianae, a Fungal Pathogen of Tobacco
Authors: Séjalon-Delmas N. , Mateos F. Villalba , Bottin A. , Rickauer M. , Dargent R. , Esquerré-Tugayé M. T.
Published: May 2007

A glycoprotein of 34 kDa (GP 34) was solubilized at acidic pH from the mycelium of Phytophthora parasitica var. nicotianae and was purified by ion exchange and gel permeation chromatography. Whole tobacco plants treated with GP 34 through their roots showed an enhanced lipoxygenase activity as well as hydroxyproline-rich glycoprotein accumulation, indicating that this molecule had elicitor properties. An antiserum raised against the pure glycoprotein allowed localization of GP 34 by immunogold-labeling on the cell surface of the mycelium when the fungus was grown in vitro. In the wall-less zoospores, GP 34 was limited to the flagellum surface. It was then abundantly synthesized at the onset of encystment. During infection of tobacco plants, labeling was very faint at early stages of colonization, particularly in the susceptible host cultivar. It appeared earlier in the resistant host cultivar and was restricted to the living fungus, declining with mycelium cell death.
Formation of Sclerotia and Aflatoxins in Developing Cotton Bolls Infected by the S Strain of Aspergillus flavus and Potential for Biocontrol with an Atoxigenic Strain
Authors: Garber R. K. , Cotty P. J.
Published: May 2007

Aspergillus flavus can be divided into the S and L strains on the basis of sclerotial morphology. On average, S strain isolates produce greater quantities of aflatoxins than do L strain isolates. Sclerotia of the S strain were observed in commercial seed cotton from western Arizona. Greenhouse tests were performed to better define sclerotial formation in developing bolls. Eight S strain isolates were inoculated into developing bolls via simulated pink bollworm exit holes. All eight isolates formed sclerotia on locule surfaces, and seven of eight isolates produced sclerotia within developing seed. Boll age at inoculation influences formation of sclerotia. More sclerotia formed within bolls that were less than 31 days old at inoculation than in bolls older than 30 days at inoculation. Frequent formation of sclerotia during boll infection may both favor S strain success within cotton fields and increase toxicity of A. flavus-infected cottonseed. Atoxigenic A. flavus L strain isolate AF36 reduced formation of both sclerotia and aflatoxin when coinoculated with S strain isolates. AF36 formed no sclerotia in developing bolls and was more effective at preventing S strain isolates than L strain isolates from contaminating developing cottonseed with aflatoxins. The use of atoxigenic L strain isolates to prevent contamination through competitive exclusion may be particularly effective where S strain isolates are common. In addition to aflatoxin reduction, competitive exclusion of S strain isolates by L strain isolates may result in reduced overwintering by S strain isolates and lower toxicity resulting from sclerotial metabolites.
Evidence for the Preemptive Nature of Tomato Race 3 ofXanthomonas campestrispv.vesicatoriain Florida
Authors: Jones J. B. , Bouzar H. , Somodi G. C. , Stall R. E. , Pernezny K. , El-Morsy G. , Scott J. W.
Published: May 2007

Until recently, tomato race 1 (T1) of Xanthomonas campestris pv. vesicatoria was the only race causing bacterial spot of tomato in Florida. In 1991, tomato race 3 (T3) was first identified in 3 of 13 tomato production fields surveyed. By 1994, T3 was observed in 21 of 28 fields and was the only race identified in 14 fields. In field studies, tomato genotypes with resistance to either T1 or T3 or susceptibility to both were co-inoculated with strains of both races. Lesions on 10 plants in each of three replications for each genotype were sampled three times during the experiment; bacterial isolations were made from each lesion, and tomato race identifications were made for each strain. At the third sampling date, T3 was isolated from 97% of the lesions on the susceptible genotype Walter and the T1-resistant genotype Hawaii 7998, while T3 was isolated from 23% of the lesions and T1 from the remaining 77% on the T3-resistant genotypes PI 128216 and PI 126932. In surface population studies done in growth rooms, suspensions of T1 and T3 were applied alone and in combination to the leaf surfaces of susceptible and resistant genotypes. T1 populations were reduced more than 10-fold when applied in combination with T3, compared with populations that developed when T1 was applied alone. T3 populations were not affected when applied in combination with a T1 strain. In greenhouse studies with the T3-resistant genotype Hawaii 7981, disease was significantly reduced in plants inoculated with T3 in combination with T1, compared with plants inoculated with T1 alone. These results clearly demonstrate the competitive nature of T3 in the presence of T1 and help explain the emergence of T3 as a prevalent race in Florida.
Pathogenicity of Four Blue-Stain Fungi Associated with Aggressive and Nonaggressive Bark Beetles
Authors: Krokene Paal , Solheim Halvor
Published: May 2007

The pathogenicity of two isolates of each of four bark beetle-associated blue-stain fungi was evaluated after mass inoculation of about 40-year-old Norway spruce trees (Picea abies). Trees were inoculated with a different isolate of each fungus in 1995 and 1996 at a density of 400 inoculations per m2 in a 1.2-m-wide band on the lower bole (about 270 inoculations per tree). Trees were felled 15 weeks after inoculation. In 1995, Ceratocystis polonica was the only fungus that had stained the sapwood (56.3% of cross-sectional sapwood area). It induced five times longer phloem necroses, 21 times more dead cambium, and 11 times more dead phloem than any other fungus. In 1996, C. polonica induced less extensive host symptoms and an unidentified Ambrosiella sp. induced comparable symptoms to C. polonica in the phloem and cambium. No trees showed any foliar symptoms 15 weeks after inoculation, but six out of eight trees inoculated with C. polonica in 1995 had only 0 to 25% functional sapwood and probably would have died if felling had been delayed. This study confirms that C. polonica, an associate of the aggressive bark beetle Ips typographus, is pathogenic to Norway spruce. The pathogenicity of the Ambrosiella sp., which is associated with a nonaggressive bark beetle, seems moderate and varies between isolates. The two remaining fungi included in this study (Ophiostoma piceae and a dark fungus with sterile mycelium), which are associated with nonaggressive bark beetles, were nonpathogenic in both experiments. These results are consistent with the hypothesis that aggressive bark beetle species vector virulent fungi that may help them kill trees, but the results also show that some nonaggressive bark beetles may vector phytopathogenic fungi.
Determinants of Density- and Frequency-Dependent Fitness in Competing Plant Pathogens
Authors: Newton M. R. , Kinkel L. L. , Leonard K. J.
Published: May 2007

Using mathematical models, we investigated how infection and sporulation characteristics of competing plant pathogens determine the density and frequency dependence of relative fitness. Two models, one for the infection stage and one for the sporulation stage of a pathogen's life cycle, describe reproductive output of pathogen strains in mixture as a function of the strains' population densities. Model parameters include infection and sporulation efficiencies, carrying capacities on leaves for sporulating lesions and spore production, and coefficients of interstrain competitive effects in both life cycle stages. Although the models were originally developed for rust fungi, they are generally applicable to any organism with distinct colonization (e.g., infection) and propagative (e.g., sporulation) life cycle stages. In this work, paired hypothetical strains were assigned equal baseline parameter values. Parameters were then altered one at a time for one or both strains, and relative fitness was calculated over a range of densities and strain frequencies. Except for infection efficiency, the fitness benefit conferred by an advantage in a single parameter was always density dependent. Relative fitness was frequency dependent whenever inter- and intrastrain competitive effects were not equal. These results suggest that the fitness of pathogens in nature is rarely fixed, but, rather, may typically be highly dependent on the densities and frequencies of all coexisting strains in a habitat.
Effects of Crop Rotation and Irrigation on Verticillium dahliae Microsclerotia in Soil and Wilt in Cauliflower
Authors: Xiao C. L. , Subbarao K. V. , Schulbach K. F. , Koike S. T.
Published: May 2007

Experiments were conducted in field plots to evaluate the effects of broccoli residue on population dynamics of Verticillium dahliae in soil and on Verticillium wilt development on cauliflower under furrow and subsurface-drip irrigation and three irrigation regimes in 1994 and 1995. Treatments were a factorial combination of three main plots (broccoli crop grown, harvested, and residue incorporated in V.dahliae-infested plots; no broccoli crop or residue in infested plots; and fumigated control plots), two subplots (furrow and subsurface-drip irrigation), and three sub-subplots (deficit, moderate, and excessive irrigation regimes) arranged in a split-split-plot design with three replications. Soil samples collected at various times were assayed for V. dahliae propagules using the modified Anderson sampler technique. Incidence and severity of Verticillium wilt on cauliflower were assessed at 7- to 10-day intervals beginning a month after cauliflower transplanting and continuing until harvest. Number of propagules in all broccoli plots declined significantly (P < 0.05) after residue incorporation and continued to decline throughout the cauliflower season. The overall reduction in the number of propagules after two broccoli crops was approximately 94%, in contrast to the fivefold increase in the number of propagules in infested main plots without broccoli after two cauliflower crops. Disease incidence and severity were both reduced approximately 50% (P < 0.05) in broccoli treatments compared with no broccoli treatments. Differences between furrow and subsurface-drip irrigation were not significant, but incidence and severity were significantly (P < 0.05) lower in the deficit irrigation regime compared with the other two regimes. Abundance of microsclerotia of V. dahliae on cauliflower roots about 8 weeks after cauliflower harvest was significantly (P < 0.05) lower in treatments with broccoli compared with treatments without broccoli. Rotating broccoli with cauliflower and incorporating broccoli residues into the soils is a novel means of managing Verticillium wilt on cauliflower and perhaps on other susceptible crops. This practice would be successful regardless of the irrigation methods or regimes followed on the susceptible crops.
Allocation of Resources: Sources of Variation in Fusarium Head Blight Screening Nurseries
Authors: Campbell K. A. G. , Lipps P. E.
Published: May 2007

Severe epidemics of Fusarium head blight (FHB) caused by Fusarium graminearum, group II (teleomorph: Gibberella zeae) have been occurring on wheat crops in the northcentral United States and southern Canada. Evaluation of resistance to FHB is difficul, because resistance is partial and infection depends upon host plant maturity. Variance component analysis was conducted to determine how best to allocate resources among environments, replications, and subsamples (heads per plot) in FHB screening nurseries. Advanced breeding lines from the Ohio State University wheat-breeding program were evaluated in screening nurseries from 1995 to 1997. Nurseries were artificially inoculated and sprinkler-irrigated to induce FHB epidemics. Over 80% of the variation within an environment resulted from variation associated with subsampling individual heads within plots. The second greatest source of variation was due to genotype by replication interactions. Host plant maturity influenced disease ratings in 1997. The repeatability of genotype means was approximately 50% within environments. The greatest reduction in genotype standard errors was obtained through additional environments, and then replications. Because the cost of an additional environment was estimated at five times the cost of an additional replication, the most cost-effective improvement in precision was obtained through the addition of replications. Advanced breeding lines should be evaluated in at least four replications per environment. Segregating populations will require more replications.
Occurrence of Indole-3-Acetic Acid-Producing Bacteria on Pear Trees and Their Association with Fruit Russet
Authors: Lindow Steven E. , Desurmont Caroline , Elkins Rachel , McGourty Glenn , Clark Ellen , Brandl Maria T.
Published: May 2007

A relatively high percentage of epiphytic bacteria on pear leaf and fruit surfaces had the ability to produce indole-3-acetic acid (IAA) in culture media supplemented with tryptophan. While over 50% of the strains produced at least small amounts of IAA in culture, about 25% of the strains exhibited high IAA production as evidenced by both colorimetric and high-performance liquid chromatography analysis of culture supernatants. A majority of the strains that produced high amounts of IAA were identified as Erwinia herbicola (Pantoea agglomerans), while some strains of Pseudomonas syringae, Pseudomonas viridiflava, Pseudomonas fluorescens, Pseudomonas putida, and Rahnella aquaticus that produced high amounts of IAA also were found on pear. Fruit russeting was significantly increased in 39 out of 46 trials over an 8-year period in which IAA-producing bacteria were applied to trees compared with control trees. A linear relationship was observed between fruit russet severity and the logarithm of the population size of different IAA-producing bacteria on trees in the 30 days after inoculation, when normalized for the amount of IAA produced by each strain in culture. On average, the severity of fruit russet was only about 77% that on control trees when trees were treated at the time of bloom with Pseudomonas fluorescens strain A506, which does not produce IAA. Both total bacterial populations on pear in the 30-day period following full bloom and fruit russet severity varied greatly from year to year and in different commercial orchards over a 10-year period. There was a strong linear correlation between the logarithm of total bacterial population sizes and fruit russet severity.
Maturation and Seasonal Discharge Pattern of Ascospores of Anisogramma anomala
Authors: Pinkerton J. N. , Johnson K. B. , Stone J. K. , Ivors K. L.
Published: May 2007

Maturation and release of ascospores of Anisogramma anomala were monitored over a 6-year period (1988 to 1995) in European hazelnut orchards located in western Oregon. Perithecia of A. anomala were dissected from stromata collected monthly from September to May to determine spore maturation. Spore maturation began in late summer; by January, >90% of the spores were morphologically mature. Similarly, both the number of mature ascospores per perithecium and the proportion of ascospores that germinated increased through autumn. After January, the number of spores per perithecium declined until May, when few viable spores remained. Each of the 6 years, rain catch-type spore traps were placed under cankers in diseased trees from 15 September to 30 June. Based on spore collection periods of 1 to 4 weeks, three patterns for the seasonal release of A. anomala ascospores were observed: in the 1988-1989 season, >80% of the seasonal ascospore release occurred between September and January; in the 1989-1990 season, 32 to 42% of the seasonal ascospore release occurred after mid-April; and in the other 4 years, monthly releases of ascospores were relatively uniform over the 9-month seasonal period. Timing and amount of precipitation were the most important variables accounting for the differences among the yearly patterns of ascospore release. Over all years and sites, the cumulative proportion of total ascospores collected in each orchard was highly correlated (R2 = 0.90) with cumulative precipitation. This relationship was confirmed in mist chamber experiments. A regression model was developed relating cumulative ascospore release to cumulative hours of precipitation. The model provides an estimate of the proportion of ascospores remaining to be released after budbreak, which coincides with the period of highest susceptibility to infection.
Diversity Within Streptomyces ipomoeae Based on Inhibitory Interactions, rep-PCR, and Plasmid Profiles
Authors: Clark C. A. , Chen C. , Ward-Rainey N. , Pettis G. S.
Published: May 2007

Streptomyces soil rot is a destructive disease of sweetpotato (Ipomoea batatas) that causes yield loss resulting from decay of the feeder root system and reduced quality due to the presence of necrotic lesions on the storage roots. It is managed by the use of resistant cultivars, but variability of the pathogen has not been previously assessed. This study compared 36 strains of the pathogen Streptomyces ipomoeae from different locations in the United States and Japan. The strains could be separated into three groups on the basis of their ability to inhibit the growth of one another in in vitro assays. Although some strains contained plasmids of approximately 18, 42, or 270 kb in size, plasmid profiles did not correspond to inhibition grouping. Fingerprinting by repetitive element-based polymerase chain reaction (rep-PCR) using outwardly facing primers for the BOX, enterobacterial repetitive intergenic consensus (ERIC), and repetitive extragenic palindromic (REP) sequences indicated relatively high genomic homogeneity within S. ipomoeae. However, cluster analysis of similarity coefficients among strains using rep-PCR data revealed clusters that correlated with the inhibition grouping. The neotype strain of S. ipomoeae had lower similarity values by rep-PCR than any of the other strains and could not be grouped by inhibitory interactions.
Effects of Host Resistance, Temperature, Leaf Wetness, and Leaf Age on Infection and Lesion Development of Pecan Scab
Authors: Turechek W. W. , Stevenson K. L.
Published: May 2007

The effects of partial host resistance, temperature, leaf wetness duration, and leaf age on infection and lesion development of pecan scab were evaluated. Trees of cultivars Wichita (susceptible) and Sumner (resistant) were inoculated with conidia of Cladosporium caryigenum and placed in mist chambers set at 15, 25, or 35°C. The trees were removed from the chambers after 3, 6, 12, 24, 36, or 48 h of leaf wetness and placed in a greenhouse to allow disease development. After 8 to 16 days, disease began to develop on both ‘Wichita’ and ‘Sumner’. Logistic regression analysis showed that the probability of a leaf becoming infected was greatest for ‘Wichita’ it decreased with increasing leaf age and temperature and increased with increasing leaf wetness. Leaves on ‘Wichita ’ were susceptible to infection between 2 and 23 days after budbreak, while leaves on ‘Sumner’ were susceptible to infection from 2 to 18 days after budbreak. Infection frequency, lesion size, and conidia production decreased proportionately with increasing leaf age. The magnitude of this effect was greatest on ‘Sumner’. Conidia production was positively correlated with lesion size, and both were positively correlated with infection frequency on both cultivars.
Effect of Sowing Date, Host Cultivar, and Race of Fusarium oxysporum f. sp. ciceris on Development of Fusarium Wilt of Chickpea
Authors: Navas-Cortés Juan A. , Hau Bernhard , Jiménez-Díaz Rafael M.
Published: May 2007

Microplots experiments were carried out at Córdoba, southern Spain, from 1986 to 1989 to determine the effects of sowing date in the management of Fusarium wilt of chickpea as influenced by virulence of the pathogen race and by cultivar susceptibility. A total of 108 epidemics of the disease were described, analyzed, and compared to assess the degree of disease control. The epidemics were characterized by five curve elements: final disease intensity index (DII), standardized area under DII progress curve, time to epidemic onset, time to inflection point (tip), and the DII value at tip, the last two parameters being estimates from the Richards function adjusted by nonlinear regression analysis. The structure of Fusarium wilt epidemics was examined by conducting multivariate principal components and cluster analyses. From these analyses, three factors accounting for 98 to 99% of the total variance characterized the DII progress curves and provided plausible epidemiological interpretations. The first factor included the tip and the time to disease onset and can be interpreted as a positional factor over time. This factor accounted for the largest proportion of the total variance and may, therefore, be considered as the main factor for analysis of Fusarium wilt epidemics. The second factor concerns the standardized area under DII progress curves and the final DII of the epidemics. The third factor identified the uniqueness of the estimated value for the point of inflection of the DII progress curve over time. Our results indicate that for each year of experiment epidemic development was related mainly to the date of sowing. Thus, for chickpea crops in southern Spain, advancing the sowing date from early spring to early winter can slow down the development of Fusarium wilt epidemics, delay the epidemic onset, and minimize the final amount of disease. However, the net effect of this disease management practice may also be influenced, though to a lesser extent, by the susceptibility of the chickpea cultivar and the virulence and inoculum density of the Fusarium oxysporum f. sp. ciceris race.
Pathogenicity of Aster Yellows Phytoplasma and Spiroplasma citri on Periwinkle
Authors: Chang Chung-Jan
Published: May 2007

Using Murashige and Skoog (MS) as a basal medium, the effects of varying levels and combinations of plant growth regulators required for shoot tip and root proliferation in healthy and aster yellows phytoplasma (AYP)- and Spiroplasma citri-infected periwinkle (Catharanthus roseus) shoots were studied. Number of shoots and fresh and dry mass of healthy and AYP-infected shoots increased when benzyladenine (BA) concentrations were increased from 0.5 to 4 mg/liter. The maximum number of shoots for both healthy and AYP-infected plants was obtained when grown in MS medium supplemented with BA at 4 mg/liter and indole-3-acetic acid (IAA) at 0.5 mg/liter. S. citri-infected shoots proliferated the most when grown in MS medium containing BA at 2 mg/liter and IAA at 0.5 mg/liter. The best medium for root production in healthy periwinkle shoots contained α-naphthaleneacetic acid (NAA) at 0.5 mg/liter, whereas the best medium for AYP-infected shoots contained indole-3-butyric acid (IBA) at 2.5 mg/liter, both in combination with kinetin at 0.1 mg/liter. S. citri-infected shoots had the best root growth when grown in medium supplemented with IBA at 5.0 mg/liter and kinetin at 0.1 mg/liter. The concentration of cytokinin and auxin needed for maximum shoot proliferation differed between AYP- and S. citri-infected shoot tips, strongly indicating that the two mollicutes may cause different changes in endogenous cytokinin and auxin levels. The concentrations of NAA and IBA needed for root growth of S. citri-infected shoots were two- to fivefold higher than the concentrations needed for healthy and AYP-infected shoots, clearly demonstrating that S. citri infection caused a shortage of auxins that resulted in retardation of secondary root growth. Chlorophyll content was markedly reduced in periwinkles infected with AYP or S. citri compared with chlorophyll in healthy periwinkles. AYP caused a decrease in carotenoid in leaves 6 weeks after graft-inoculation, but carotenoid content was unchanged in S. citri-infected leaves throughout the test period. Anthocyanin content in periwinkles infected with AYP decreased significantly by 4 weeks postinoculation, whereas anthocyanin content in periwinkles infected with S. citri increased. Anthocyanin content in leaf tissues, however, was reduced as a result of AYP and S. citri infection. Pigment changes induced by AYP and S. citri, whether similar or different compared with those of healthy periwinkle shoots, provide important information for interpreting pathogenesis when linked with plant growth regulators.
Association of Mmd1, a Major Gene for Resistance to Melampsora medusae f. sp. deltoidae, with Quantitative Traits in Poplar Rust
Authors: Newcombe G.
Published: May 2007

A single gene, Mmd1, which conditions resistance and a necrotic flecking response to a monouredinial isolate of Melampsora medusae f. sp. deltoidae and is presumed to possess the corresponding avirulence gene, was previously shown to segregate 3:1 (resistant to susceptible) in an interspecific hybrid poplar F2 progeny. Some inoculated clones of the resistant phenotypic class of this progeny were completely resistant and bore no uredinia, but most bore some sporulating uredinia with accompanying necrotic flecking. The dominant allele at the Mmd1 locus in these incompletely resistant clones was significantly associated with reduced uredinial density and diameter and longer latent period in a growth-room assay and with reduced disease incidence and infection efficiency and longer latent period in a leaf-disk assay. However, high clone-mean heritabilities within the susceptible phenotypic class indicated that genes other than Mmd1 also contribute to control of quantitative traits. Leaf age had a significant effect on uredinial density and latent period but not on uredinial diameter in the growth-room assay. All quantitative traits were intercorrelated to varying extents. A principal components analysis (PCA) demonstrated that uncorrelated components associated with uredinial diameter and uredinial density explained two-thirds of the total variation. Since uredinial diameter (PC1) and necrotic flecking are the visual components of an infection-type rating scale, genetic analyses of poplar rust should be based on infection type. Mmd1 is a major gene for resistance associated with a significant effect on all quantitative traits measured. Gene complexes in domesticated, agricultural rust pathosystems known to provide durable resistance consist of similar “pivotal” major genes and inferred ancillary genes or quantitative trait loci.
Dispersal of Formulations of Fusarium oxysporum f. sp. erythroxyli and F. oxysporum f. sp. melonis by Ants
Authors: Gracia-Garza J. A. , Fravel D. R. , Bailey B. A. , Hebbar P. K.
Published: May 2007

A natural epidemic of Fusarium wilt on coca (Erythroxylum coca) in Peru prompted the suggestion of possibly using the pathogen Fusarium oxysporum f. sp. erythroxyli as a mycoherbicide against this narcotic plant. During field trials conducted in Kauai, HI, to test the pathogenicity of the coca wilt pathogen, ants were observed removing formulations from test plots. While removal of formulations by ants was considered detrimental with respect to conducting field tests, ant removal was considered potentially beneficial in disseminating the mycoherbicide. Thus, research was initiated to assess the ability of formulation additives to alter the preference of ants for the formulated mycoherbicide. In Hawaii, preference of indigenous ants for removing formulations was tested using three different food bases (rice, rice plus canola oil, and wheat flour [gluten]). Similar tests were conducted at Beltsville, MD, using F. oxysporum f. sp. melonis, in which the formulation based on wheat flour was replaced by a formulation based on canola meal. Formulations based on wheat were preferred by ants in both locations; up to 90% of the wheat plus rice flour granules (C-6) and the wheat gluten plus kaolin granules (pesta) were removed within 24 h, while only 20% of those containing rice without oils were taken. However, when either canola, sunflower (Maryland only), or olive oil was added to the rice formulation, up to 90% of the granules were taken. The formulation based on canola meal was less attractive to ants, as only 65% of the granules were removed within a period of 24 h. Ants showed no preference with respect to presence or absence of fungal biomass. To alter the attractiveness of the C-6 formulation to ants, C-6 was amended with three natural products. Canna and tansy leaves were added to C-6 at a ratio of 1:5 (wt/wt), while chili powder was added at 1:25 or 1:2.5 (wt/wt). Canna, tansy, and the higher rate of chili powder significantly reduced the number of C-6 granules removed by ants. Canna and tansy leaves affected neither germination nor sporulation of the mycoherbicide, while the high concentration of chili powder reduced viability of propagules in the formulation. More F. oxysporum f. sp. erythroxyli-type colonies were recovered from inside ant nests (9 cm depth) than from nest surfaces, indicating that ants may distribute the mycoherbicide in the soil profile. Ants passively carried propagules of F. oxysporum f. sp. erythroxyli outside their bodies, as well as either very closely adhering to the outside or within their bodies.