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Disease Complex (disease + complex)
Selected AbstractsDisease complex in coffee involving Meloidogyne arabicida and Fusarium oxysporumPLANT PATHOLOGY, Issue 3 2000B. Bertrand Coffee corky-root disease, also called corchosis, was first detected in 1974 in a small area of Costa Rica where the root-knot nematode Meloidogyne arabicida is the dominant species. An epidemiological study revealed a constant association between Meloidogyne spp. and Fusarium sp. in cases of corky root. No corky root appears to have been reported in association with Meloidogyne exigua, which is the prevalent root-knot nematode on coffee in Costa Rica. Fusarium spp. are often cited as components of disease complexes in association with nematodes. Combined inoculations using M. arabicida or M. exigua with Fusarium oxysporum under controlled conditions showed that only the combination with M. arabicida produced corky-root symptoms on Coffea arabica cvs Caturra or Catuai. Fusarium oxysporum alone was nonpathogenic. Meloidogyne exigua or M. arabicida alone caused galls and reduction in shoot height, but no corky-root symptoms. When cultivars susceptible and resistant to M. arabicida were studied under field conditions for 5 years, all the susceptible cultivars exhibited corky-root symptoms on 40,80% of their root systems. Cultivars that were resistant to M. arabicida but not to M. exigua showed no corky root. These observations lead to the conclusion that corky-root disease has a complex etiology, and emphasize the dominant role of M. arabicida as a predisposing agent to subsequent invasion by F. oxysporum. Consequently, genetic resistance to M. arabicida appears to provide an effective strategy against the disease. [source] Disease complexes involving plant parasitic nematodes and soilborne pathogensPLANT PATHOLOGY, Issue 6 2002M. A. Back This review discusses the mechanisms underlying synergistic interactions between phytophagous nematodes and soilborne pathogens, and identifies biotic and abiotic factors affecting these interactions. Approaches towards the resolution and management of nematode,pathogen complexes are considered and discussed. [source] An intranuclear bacilliform virus associated with near extirpation of Austropotamobius pallipes Lereboullet from the Nant watershed in Ardéche, FranceJOURNAL OF FISH DISEASES, Issue 9 2002B F Edgerton White-clawed crayfish, Austropotamobius pallipes, were endemic to the Nant watershed, Ardéche, France, until they were extirpated by epizootic mortality at the beginning of the twentieth century. A. pallipes were successfully reintroduced to the Nant watershed in the middle of the twentieth century. However, epizootic mortality was observed in the Nant watershed in the summer of 2000 during which time A. pallipes was extirpated from downstream regions. Dead and moribund crayfish were again detected in several episodes in summer 2001 and by October the range of A. pallipes was reduced to the headwaters of just one of the three streams in the watershed. Water quality for the watershed in summer 2001 was appropriate for crayfish habitation. Bacteriology and mycology on A. pallipes collected during several of the mortality episodes in 2001 failed to reveal a cause. However, histopathology revealed a high occurrence of intranuclear eosinophilic inclusions in hepatopancreatocytes of A. pallipes. The nuclei were hypertrophic and contained bacilliform virions consisting of a cylindrical nucleocapsid surrounded by a trilaminar envelope. Virions in section were approximately 63 × 258 nm and nucleocapsids were approximately 52 × 225 nm. It is unclear whether the intranuclear bacilliform virus was the cause of the mortality episodes or was a contributor to a disease complex involving one or several other undetected pathogens. [source] Incidence of Cotton Seedling Diseases Caused by Rhizoctonia solani and Thielaviopsis basicola in Relation to Previous Crop, Residue Management and Nutrients Availability in Soils in SW SpainJOURNAL OF PHYTOPATHOLOGY, Issue 11-12 2005A. Delgado Abstract Cotton seedling damping-off is considered a disease complex, in which several pathogens can be involved. In SW Spain, postemergence damping-off seems to be mainly associated with Rhizoctonia solani and Thielaviopsis basicola, posing a serious limitation for crop, especially in cold springs. Ninety-seven commercial plots, where postemergence damping-off of cotton seedlings was observed during previous years, were selected in April 2001. In each plot, plants were randomly sampled between cotyledon to three true-leaf stage and soil samples besides the plants were taken. Symptomatic plants were separated according to the main observable seedling disease symptom: black necrosis (black root rot), brown necrosis and other symptoms. Thielaviopsis basicola inoculum was estimated in soil samples. Soil samples were also analysed for nutrient availability (N, P, K, Ca, Mg, Fe, Cu, Mn and Zn). All the sampled plants showed some seedling disease symptom. Macroscopic symptoms can provide a reasonable distinction between these two major pathogens involved in seedling disease symptoms in the studied area: the percentage of T. basicola isolates (18%) from black necrosis symptomatic plants was significantly higher than that of R. solani (4.1%), whereas in brown necrosis symptomatic plants, the situation was reversed (10.7 vs. 12.8%). The percentage of plants with black necrosis symptoms was inversely related to the portion of plants with brown necrosis in each plot. The mean incidence of black necrosis was significantly lower in plots with residue incorporation (sugar beet as the preceding crop) than in plots without residue incorporation. No significant effect of preceding crop or residue management on brown necrosis incidence was observed. Incidence of black necrosis was negatively correlated with available N measured as NO3 -N when corn or sunflower were the preceding crop. The incidence of black necrosis was positively related to Fe availability in soil after cotton as preceding crop, whereas brown necrosis was negatively related to the availability of this micronutrient. [source] Genetic analysis of seedling resistance to Stagonospora nodorum blotch in selected tetraploid and hexaploid wheat genotypesPLANT BREEDING, Issue 2 2009P. K. Singh Abstract Stagonospora nodorum blotch (SNB), caused by Phaeosphaeria nodorum, is a major component of the leaf-spotting disease complex of wheat (Triticum aestivum L.) in the northern Great Plains of North America. This study was conducted, under controlled environmental conditions, to determine the inheritance of resistance to SNB in a diverse set of hexaploid and tetraploid wheat genotypes and to decipher the genic/allelic relationship among the resistance gene(s). Plants were inoculated at the two to three-leaf stages with a spore suspension of P. nodorum isolate Kelvington-SK and disease reaction was assessed 8 days after inoculation based on a lesion-type scale. Tests of the F1 and F2 generations and of F2 : 3 or F2 : 5 families indicated that a single recessive gene controlled resistance to SNB in both hexaploid and tetraploid resistance sources. Lack of segregation in intra-specific and inter-specific crosses between the hexaploid and the tetraploid resistant genotypes, indicated that these genetically diverse sources of resistance possess the same gene for resistance to SNB. Results of this study suggest that the wheat- P. nodorum interaction may follow the toxin model of the gene-for-gene hypothesis. [source] Molecular analysis of the major Phytophthora species on cocoaPLANT PATHOLOGY, Issue 2 2004A. A. Appiah The internally transcribed spacer (ITS) regions of the ribosomal RNA (rRNA) gene cluster of 161 isolates of Phytophthora species involved in pod rot, stem canker and leaf blight of cocoa were analysed to determine inter- and intraspecific variation in this disease complex. The species P. palmivora, P. megakarya, P. capsici, P. citrophthora and P. nicotianae could all be clearly distinguished by PCR amplification of the ITS region followed by restriction analysis with HaeIII, HinfI, PvuII and AluI. This method provided a relatively rapid identification procedure for these species, and was able to distinguish isolates that had previously been misidentified by morphological methods. Sequence analysis showed that the four main cocoa-associated species formed two distinct groups, one comprising P. capsici and P. citrophthora, and the other P. palmivora and P. megakarya. Detailed sequence analysis and comparison with published literature suggested that P. capsici isolates from cocoa may be closely related to P. tropicalis, a species recently described from Cyclamen and Dianthus. [source] Characterization of Ascochyta isolates and susceptibility of pea cultivars to the ascochyta disease complex in AlbertaPLANT PATHOLOGY, Issue 5 2000H. Wang The relative virulence of 109 Ascochyta isolates collected from pea fields in Alberta from 1996 to 1998 were evaluated on 10-day-old seedlings by the excised leaf-assay technique. Twenty-eight isolates were avirulent, while the others produced lesions of various sizes on pea leaves. DNA samples from 86 isolates were amplified by the RAPD technique using PCR with single primers. One dominant genotype of Ascochyta pisi was identified throughout Alberta, but variations in virulence were not clearly differentiated by the RAPD technique. Five Ascochyta isolates, four virulent and one avirulent, were used to assess the susceptibility of 20 field pea cultivars available in Alberta, including 13 yellow types and seven green types. Based on symptom development, the yellow-type cultivars Swing, Eiffel and Delta, and the green-type cultivar Orb, were the most susceptible. Of yellow-type cultivars, Voyageur, Carneval and Montana were most resistant to Ascochyta infection. [source] Bruch's membrane and the vascular intima: is there a common basis for age-related changes and disease?CLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 5 2005Sobha Sivaprasad FRCS Abstract Several clinical and epidemiological studies have concurrently illuminated established cardiovascular risk factors in age-related macular degeneration (AMD), raising the possibility that cardiovascular disease and AMD may share a similar pathogenic process. The vascular intima and the Bruch's membrane share several age-related changes and are the seat of many common molecules. Diseases of these structures may represent parallel responses to the tissue injury induced by multiple intercalated factors such as genetic variations, oxidative stress, inappropriately directed immune response or inflammatory disease complex. However, there are marked differences in the age-related changes in these two structures. The strategic location of the Bruch's membrane between the retinal pigment epithelium and the choriocapillaris can at least partially explain the differential susceptibility of AMD to cardiovascular risk factors. Unlike the vascular wall that is exposed to changes from the endothelium, the Bruch's membrane is subject to changes from both the endothelium (choriocapillaris) and epithelium (retinal pigment epithelium). Moreover, although both the vascular wall and Bruch's membrane become lipid laden with age, the lipid composition is characteristically different. This review examines the morphological and biochemical alterations in the senescent Bruch's membrane and its analogy to the vascular wall to evaluate the concurrence of atherosclerosis and AMD. [source] Advances in insect biotechnology for human welfareENTOMOLOGICAL RESEARCH, Issue 2008Thomas A. MILLER Abstract Biotechnology is the latest scientific breakthrough in the history of agriculture. Yet despite the promise of developing new tools for pest and disease control, transgenic organisms have encountered a mixed reception by the lay and scientific public alike. Yields are unable to keep pace with rising costs resulting in a decline in traditional farming. Switching to a new organic growing paradigm is occurring in Korea and the United States today. These new approaches ignore traditional tools that were responsible for the increased yields that support the current affluence and allowed us to protect crops while buying time to find more ecologically-friendly methods. The perception that we understand crop diseases and pests is false and those making this assumption risk destabilizing global food production. There are new pests and diseases that are very difficult to control without these traditional non-organic methods. Invasive species continue to arrive at high rates adding to the burden of farming. Global climate change is already causing changes in the pest and disease complexes and is forcing the entomologist and plant pathologist to make drastic changes to adjust to them. [source] Disease complex in coffee involving Meloidogyne arabicida and Fusarium oxysporumPLANT PATHOLOGY, Issue 3 2000B. Bertrand Coffee corky-root disease, also called corchosis, was first detected in 1974 in a small area of Costa Rica where the root-knot nematode Meloidogyne arabicida is the dominant species. An epidemiological study revealed a constant association between Meloidogyne spp. and Fusarium sp. in cases of corky root. No corky root appears to have been reported in association with Meloidogyne exigua, which is the prevalent root-knot nematode on coffee in Costa Rica. Fusarium spp. are often cited as components of disease complexes in association with nematodes. Combined inoculations using M. arabicida or M. exigua with Fusarium oxysporum under controlled conditions showed that only the combination with M. arabicida produced corky-root symptoms on Coffea arabica cvs Caturra or Catuai. Fusarium oxysporum alone was nonpathogenic. Meloidogyne exigua or M. arabicida alone caused galls and reduction in shoot height, but no corky-root symptoms. When cultivars susceptible and resistant to M. arabicida were studied under field conditions for 5 years, all the susceptible cultivars exhibited corky-root symptoms on 40,80% of their root systems. Cultivars that were resistant to M. arabicida but not to M. exigua showed no corky root. These observations lead to the conclusion that corky-root disease has a complex etiology, and emphasize the dominant role of M. arabicida as a predisposing agent to subsequent invasion by F. oxysporum. Consequently, genetic resistance to M. arabicida appears to provide an effective strategy against the disease. [source] |