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Infection Levels (infection + level)

Distribution by Scientific Domains

Life Sciences	92%

Distribution within Life Sciences

Plant Science	41%
Plant Pathology	16%

Selected Abstracts

In vitro quantification of barley reaction to leaf stripe

PLANT BREEDING, Issue 5 2003
M. I. E. Arabi
Abstract An in vitro technique was used to quantify the infection level of leaf stripe in barley caused by Pyrenophora graminea. This pathogen penetrates rapidly through subcrown internodes during seed germination of susceptible cultivars. Quantification was based on the percentage of the pieces of subcrown internodes that produced fungal hyphae cultured on potato dextrose agar media. The disease severity was evaluated among five cultivars with different infection levels and numerical values for each cultivar were obtained. A significant correlation coefficient (r = 0.91, P < 0.02) was found among the in vitro and field assessments. In addition, the results were highly correlated (r = 0.94, P < 0.01) among the different in vitro experiments, indicating that this testing procedure is reliable. The method presented facilitates a rapid preselection under uniform conditions which is of importance from a breeder's point of view. Significant differences (P < 0.001) were found for the length of subcrown internodes between inoculated and non-inoculated plants with leaf stripe. Isolate SY3 was the most effective in reducing the subcrown internode length for all genotypes. [source]

In vitro quantification of the reaction of barley to common root rot

PLANT BREEDING, Issue 5 2001
M. I. Arabi
Abstract An in vitro technique was used to quantify the infection level of common root rot. This disease produces a brown to black discoloration of the subcrown internodes of barley. Quantification was based on the percentage of germinated infected pieces (1.5 mm) of subcrown internodes cultured on potato dextrose agar media. The disease severity was apparent among four different visually classified categories and numerical values for each category were applied. The results were highly correlated (r = 0.97, P < 0.01) among the different in vitro experiments, indicating that this testing procedure is repeatable. Highly significant differences (P < 0.001) were found for the length of first leaf and fresh weight between plants inoculated and uninoculated with common root rot. However, the effect of inoculation on fresh weight only differed significantly (P < 0.02) among the genotypes. [source]

Temperature mediates vector transmission efficiency: inoculum supply and plant infection dynamics

ANNALS OF APPLIED BIOLOGY, Issue 3 2009
M.P. Daugherty
Abstract Climate, particularly environmental temperature, frequently plays an important role in disease epidemiology. This study investigated the role of environmental temperature on transmission of the generalist plant pathogen Xylella fastidiosa by its leafhopper vectors. In this system temperature is known to influence both vector performance and feeding rate, yet the implications for pathogen transmission have not been documented. Experiments were conducted over a range of temperatures to document effects on transmission efficiency of the California native Graphocephala atropunctata (blue,green sharpshooter) and the invasive Homalodisca vitripennis (glassy-winged sharpshooter). Inoculation efficiency of H. vitripennis was positively related to temperature. Graphocephala atropunctata mortality and transmission responded non-linearly to temperature, with the highest rates of both at the highest temperature. The experiment also evaluated whether differences in inoculum supply contributed to plant infection level using quantitative PCR. Although total X. fastidiosa population within G. atropunctata was not related to plant infection, the number of infectious vectors was a strong predictor of plant infection level,suggesting that the number of inoculation events is important in the development of systemic infection of X. fastidiosa in grapevines. These results, along with existing evidence from the literature, point to wide-ranging impacts of climate on the epidemiology of X. fastidiosa diseases. [source]

Epidemiology of Plum pox virus strain M in Greece

EPPO BULLETIN, Issue 2 2006
C. Varveri
Plum pox virus has been endemic in Greece since 1967 causing important losses in apricot and to a lesser extent in peach crops. A survey undertaken in 1992 in public and private mother-tree plantations to estimate its incidence revealed that the virus was absent in isolated areas far from commercial stone-fruit crops. Virus titers decrease significantly during the hot months in the infected trees but re-increase in October,November permitting reliable detection. It is virulent M-type isolates which are effectively transmitted by aphids that are mostly recovered. Aphis gossypii and Hyalopterus pruni were the most abundant virus vectors captured during the small scale monitoring undertaken in apricot orchards in 1999 and 2000. Virus spread was monitored in two apricot orchards from 1996 to 2000 and analysed. Initial infections followed a completely random spatial pattern, while loose clusters appeared in succeeding years, to finally reach a uniform distribution representing high infection levels. The nearby ecological conditions greatly affected the rate of disease development. [source]

Endophytic foliar fungi in Betula spp. and their F1 hybrids

FOREST PATHOLOGY, Issue 4 2003
K. Saikkonen
Summary We examined foliar endophyte frequencies in two native (Betula pendula and Betula pubescens) and three exotic (Betula ermanii, Betula platyphylla and Betula resinifera) birch species and their hybrids in Punkaharju, Finland. The most frequently isolated endophytic fungi in the experimental trees were Fusicladium betulae and Gnomonia setacea making up 80,90% of all endophyte infections. Total endophyte infection levels varied from 0.5 colony forming units (CFU)/cm2 in B. platyphylla to 8.6 CFU/cm2 in B. pubescens that had highest total infection levels of both examined endophyte species. The resistance of hybrids was generally very close to the more resistant parent (the only exception being Fusicladium in B. platyphylla × B. pendula hybrid) supporting the hypothesis that the resistance of birch hybrids to these fungi is genetically based and caused by dominant inheritance of resistance traits. Résumé La fréquence d'endophytes foliaires a été étudiée chez deux espèces indigènes de bouleau (Betula pendula et Betula pubescens), trois espèces exotiques (Betula ermanii, Betula platyphylla et Betula resinifera) et leurs hybrides, à Punkaharju, Finlande. Les champignons endophytes les plus fréquemment isolés des arbres étudiés ont étéFusicladium betulae et Gnomonia setacea, qui constituent 80 à 90% de l'ensemble des infections endophytes. Les niveaux totaux d'infection endophyte varient de 0.5 CFU/cm2 chez B. platyphyllaà 8.6 CFU/cm2 chez B. pubescens, qui présente les plus forts niveaux d'infection pour chacune des deux espèces endophytes étudiées. La résistance des hybrides est généralement très proche de celle du parent le plus résistant (la seule exception étant Fusicladium chez l'hybride B. platyphylla × B. pendula), ce qui est conforme à l'hypothèse que la résistance des hybrides à ces champignons serait d'origine génétique, avec une héritabilité dominante de la résistance. Zusammenfassung Bei einheimischen (Betula pendula und Betula pubescens) und drei exotischen (Betula ermanii, Betula platyphylla und Betula resinifera) Birkenarten und ihren Hybriden wurde die Häufigkeit von Blattendophyten in Punkaharju, Finnland, untersucht. Die beiden häufigsten isolierten Pilze waren Fusicladium betulae und Gnomonia setacea. Diese umfassten 80,90% aller isolierten Endophyten. Die Anzahl der aus einem Quadratzentimeter isolierten koloniebildenden Einheiten (CFU/cm2) variierte von 0,5 bei B. platyphylla bis 8,6 CFU/cm2 bei B. pubescens. Letztere hatte die höchste Isolierhäufigkeit bei beiden untersuchten Endophytenarten. Das Resistenzverhalten der Hybriden war allgemein dem des resistenteren Elters sehr ähnlich (eine Ausnahme bildete Fusicladium bei B. platyphylla × B. pendula). Dies stützt die Hypothese, dass die Resistenz der Birkenhybriden gegenüber diesen Pilzen genetisch verankert ist und dominant vererbt wird. [source]

Occurrence and Distribution of Microdochium and Fusarium Species Isolated from Durum Wheat in Northern Tunisia and Detection of Mycotoxins in Naturally Infested Grain

JOURNAL OF PHYTOPATHOLOGY, Issue 9 2009
Lobna Gargouri Kammoun
Abstract An outbreak of Fusarium Head Blight of durum wheat occurred in 2004 being localized in sub-humid and higher semi-arid region of Northern Tunisia. A mycological survey carried out throughout these regions, revealed that 78% of the prospected fields were infested. Results of the morphological and molecular identification, showed that the most common species isolated from diseased wheat spikes was Microdochium nivale var. nivale (63.5%), followed by Fusarium culmorum (26%), F. pseudograminearum (9%) and F. avenaceum (1.5%). To evaluate mycotoxin content of naturally infected grain, the amounts of trichothecene mycotoxin deoxynivalenol (DON) in harvested grain from 45 fields were quantified by RIDASCREEN DON Enzyme Immunoassay Kit (ELISA). This study showed that the infection levels in freshly harvested grain were very low and the maximum deoxynivalenol (DON) level of the positive samples was 53 ppb. This is the first report on the natural occurrence of DON in naturally infected wheat grain sampled from Northern Tunisia. [source]

Salicylic acid confers resistance to a biotrophic rust pathogen, Puccinia substriata, in pearl millet (Pennisetum glaucum)

MOLECULAR PLANT PATHOLOGY, Issue 2 2009
BRIDGET G. CRAMPTON
SUMMARY Studies were undertaken to assess the induction of defence response pathways in pearl millet (Pennisetum glaucum) in response to infection with the leaf rust fungus Puccinia substriata. Pretreatment of pearl millet with salicylic acid (SA) conferred resistance to a virulent isolate of the rust fungus, whereas methyl jasmonate (MeJA) did not significantly reduce infection levels. These results suggest that the SA defence pathway is involved in rust resistance. In order to identify pearl millet genes that are specifically regulated in response to SA and not MeJA, and thus could play a role in resistance to P. substriata, gene expression profiling was performed. Substantial overlap in gene expression responses between the treatments was observed, with MeJA and SA treatments exhibiting 17% co-regulated transcripts. However, 34% of transcripts were differentially expressed in response to SA treatment, but not in response to MeJA treatment. SA-responsive transcripts represented genes involved in SA metabolism, defence response, signal transduction, protection from oxidative stress and photosynthesis. The expression profiles of pearl millet plants after treatment with SA or MeJA were more similar to one another than to the response during a compatible infection with P. substriata. However, some SA-responsive genes were repressed during P. substriata infection, indicating possible manipulation of host responses by the pathogen. [source]

Are endophytic fungi defensive plant mutualists?

OIKOS, Issue 1 2002
Stanley H. Faeth
Endophytic fungi, especially asexual, systemic endophytes in grasses, are generally viewed as plant mutualists, mainly through the action of mycotoxins, such as alkaloids in infected grasses, which protect the host plant from herbivores. Most of the evidence for the defensive mutualism concept is derived from studies of agronomic grass cultivars, which may be atypical of many endophyte-host interactions. I argue that endophytes in native plants, even asexual, seed-borne ones, rarely act as defensive mutualists. In contrast to domesticated grasses where infection frequencies of highly toxic plants often approach 100%, natural grass populations are usually mosaics of uninfected and infected plants. The latter, however, usually vary enormously in alkaloid levels, from none to levels that may affect herbivores. This variation may result from diverse endophyte and host genotypic combinations that are maintained by changing selective pressures, such as competition, herbivory and abiotic factors. Other processes, such as spatial structuring of host populations and endophytes that act as reproductive parasites of their hosts, may maintain infection levels of seed-borne endophytes in natural populations, without the endophyte acting as a mutualist. [source]

Expulsion of the gastrointestinal cestode, Hymenolepis diminuta by tolerant rats: evidence for mediation by a Th2 type immune enhanced goblet cell hyperplasia, increased mucin production and secretion

PARASITE IMMUNOLOGY, Issue 1 2007
R. A. WEBB
SUMMARY The processes underlying expulsion of Hymenolepis diminuta in rats are not known. Expression levels of mRNAs of several cytokines revealed a Th2 response that differed between worm infection levels. IL-4 protein levels decreased while IL-13 levels increased in a 50-worm infection by 30 dpi; the converse was seen with a five-worm infection. A negative correlation was found between IL-4 or IL-13 mRNA expression and worm biomass, between IL-13 protein levels and worm number or worm biomass, and between IL-4 protein levels and worm biomass in 50-worm infections. A negative correlation between IL-4 mRNA or protein expression and worm biomass was observed with five-worm infections. A strong correlation between Muc2 mRNA expression and decreased worm number or biomass in a 50-worm infection was observed. Muc2 protein, goblet cell numbers and mucin decreased in a 50-worm infection by 20 days post-infection. These changes were not seen with five-worm infections where worms are not expelled. The data show that rats infected with 50 H. diminuta mount a Th2 response leading to high levels of IL-13, increased goblet cell numbers and increased mucin2 production and release. The mucus traps the worms, which are progressively expelled from the small intestine. [source]

In vitro quantification of barley reaction to leaf stripe

Vectoring of Pepino mosaic virus by bumble-bees in tomato greenhouses

ANNALS OF APPLIED BIOLOGY, Issue 2 2008
J.L. Shipp
Abstract Pepino mosaic virus (PepMV) has become an important viral disease of greenhouse tomatoes worldwide. The ability of bumble-bees (Bombus impatiens), used for pollination, to acquire and transmit PepMV was investigated, and the prevalence of PepMV in plants and bumble-bees in commercial tomato greenhouses was determined. PepMV infection in plants was determined using enzyme-linked immunosorbent assay, while in bumble-bees direct real-time PCR was used. In the first experiment, the bumble-bees were exposed for 14 days to PepMV-infected plants. After 14 days, almost all bumble-bees were PepMV positive both in the hive (78.5 ± 17.5%) and in the flowers (96.3 ± 3.6%). In the second experiment, bumble-bees were released into a greenhouse with both PepMV-infected source plants and healthy non-infected target plants for 14 days. At the end of the experiment, 61.0 ± 19.5% of the bees collected from the hive and 83.3 ± 16.7% of the bees sampled from the flowers were PepMV positive. Bumble-bees transmitted PepMV from the infected to the healthy non-infected tomato plants. Two weeks after bumble-bee release, the virus was detected in leaf, fruit and flower samples of formerly healthy plants. After 6 weeks, the percentage of PepMV positive samples from the target plants increased to 52.8 ± 2.8% of the leaves and 80.6 ± 8.4% of the fruits. In the control greenhouse without bumble-bees, the target plants did not become infected. Based on the infection levels in flowers, fruits and leaves, the PepMV infection occurred possibly first in the pollinated flowers, and then spread from the fruit that developed from the flowers to other parts of the plant. In commercial greenhouses where PepMV was present, 92,100% of the plants and 88,100% of the bumble-bees were PepMV positive. No infected plant samples were found in the control commercial greenhouse, but a small number of bumble-bees (10%) tested PepMV positive. [source]

Temporal patterns of geographic parthenogenesis in a freshwater snail

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2007
FRIDA BEN-AMI
Geographic parthenogenesis describes the observation that parthenogenetic organisms tend to occupy environments different from those of their close, sexually reproducing relatives. These environments are often described as extreme or disturbed habitats. We examined whether patterns of geographical parthenogenesis persist over time, by conducting a 3-year life-history survey and comparing two very proximate habitats of the freshwater snail Melanoides tuberculata: Nahal Arugot, a desert stream naturally disturbed by flash floods, and Or Ilan, a stable freshwater pond. Both sites occur in a xeric environment and are subject to otherwise similar biotic (e.g. parasites, predators) and climatic conditions. In the stable habitat, male frequencies and snail densities were significantly higher than in the disturbed one, whereas infection levels, mean embryo counts, and water temperatures were similar at both sites. Additionally, male frequencies declined after density decreased, thereby providing evidence for geographical parthenogenesis via reproductive assurance. Infection prevalence was very low regardless of reproduction mode. Although further genetic work is required, the apparent metapopulation structure of M. tuberculata in the Judean desert may be suitable for evaluating other possible explanations of geographical parthenogenesis. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 711,718. [source]