scholarly journals Relationship Between Flag Leaf Symptoms Caused by Xanthomonas translucens pv. translucens and Subsequent Seed Transmission in Wheat

Plant Disease ◽  
1998 ◽  
Vol 82 (12) ◽  
pp. 1341-1344 ◽  
Author(s):  
K. M. Tubajika ◽  
B. L. Tillman ◽  
J. S. Russin ◽  
C. A. Clark ◽  
S. A. Harrison
Keyword(s):  
Flag Leaf ◽  
Seedling Emergence ◽  
Subsequent Development ◽  
Seed Transmission ◽  
Threshold Level ◽  
Bacterial Leaf Streak ◽  
Flag Leaves ◽  
Disease Epidemiology ◽  
Growing Seasons ◽  
Xanthomonas Translucens

The relationship between foliar disease symptoms on parent plants, seed contamination by the causal bacterium (Xanthomonas translucens pv. translucens), and subsequent development of bacterial leaf streak in wheat was studied in microplots and in the laboratory to determine the role of seed transmission in disease epidemiology. Microplot experiments were carried out during the 1994-95 and 1995-96 growing seasons using seed harvested in Baton Rouge, Louisiana, in 1994 and 1995, respectively. Treatments were seed lots from plants with differing levels of bacterial leaf streak severity on the flag leaves of the parent tillers. X. translucens pv. translucens was detected in 1 to 20% of seed from susceptible cultivars Florida 304 and Savannah collected from plants with leaf streak symptoms. Correlations between seed contamination and disease on plants that developed from this seed were detected only when seed came from parent tillers that expressed flag leaf disease severity ≥15 to 20% in 1994-95 and ≥30 to 35% in 1995-96. However, symptoms of bacterial leaf streak on plants that developed from these seed were evident on only ≤3% of plants. Results suggest a possible threshold level for bacterial leaf streak on flag leaves that is necessary before X. translucens pv. translucens can be detected in seed. Seedling emergence in microplots correlated negatively with leaf streak severity on parent tiller flag leaves. Artificial infestation of seed with X. translucens pv. translucens also reduced seed germination, but this was more evident in Savannah than in Florida 304.

Direct seeding of PinusSylvestris using microsite preparation and invigorated seed lots of different quality: 2-year results

1994 ◽  
Vol 24 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Hans Winsa ◽  
Urban Bergsten
Keyword(s):  
Seed Quality ◽  
Seedling Survival ◽  
Seedling Emergence ◽  
Mineral Soil ◽  
Direct Seeding ◽  
Growing Seasons ◽  
Humus Layer ◽  
Negative Effect ◽  
Mean Germination Time ◽  
Better Than

Direct seeding of Pinussylvestris L. is a regeneration method, with potential for development considering scarification, microsite preparation, seed invigoration, and seed quality. Three seed lots of different quality concerning seed weight, germination percent, and mean germination time were used on two sites in northern Sweden. Microsite preparation, 2 cm deep pyramidal indentations, of the mineral soil improved seedling emergence on the two sites by 48 and 62%, respectively, compared with seeding without preparation other than removal of the humus layer. Microsite preparation in combination with invigorated seed, i.e., seed incubated at 30% moisture content for 7 days at 15 °C, resulted in seedling emergence of about 85% for the highest and about 50% for the lowest seed quality at both sites. Noninvigorated seed, seeded without microsite preparation, reached about 55% for the highest and 22% at one and 43% at the other for the lowest seed quality. Without microsite preparation there was no, or a negative, effect of seed invigoration on seedling emergence. Seedling survival after the first winter improved significantly with better seed quality. Survival averaged 92 and 72% at the two sites, with frost heaving causing most mortality. Seedlings from invigorated and redried seed survived better than seedlings from untreated seed. Seedlings from the best seed quality had higher values in seedling height, about 35%, shoot length, about 60%, and needle length, about 30%, after two growing seasons than seedlings from lower seed qualities. Invigoration and microsite preparation had no effect on measured growth characteristics.

scholarly journals Molecular Typing Reveals High Genetic Diversity of Xanthomonas translucens Strains Infecting Small-Grain Cereals in Iran

2019 ◽  
Vol 85 (20) ◽  
Author(s):  
Moein Khojasteh ◽  
S. Mohsen Taghavi ◽  
Pejman Khodaygan ◽  
Habiballah Hamzehzarghani ◽  
Gongyou Chen ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Population Structure ◽  
Global Scale ◽  
Population Diversity ◽  
Bacterial Leaf Streak ◽  
High Genetic Diversity ◽  
Center Of Origin ◽  
Content Type ◽  
Xanthomonas Translucens ◽  
Insight Into

ABSTRACT This study provides a phylogeographic insight into the population diversity of Xanthomonas translucens strains causing bacterial leaf streak disease of small-grain cereals in Iran. Among the 65 bacterial strains isolated from wheat, barley, and gramineous weeds in eight Iranian provinces, multilocus sequence analysis and typing (MLSA and MLST) of four housekeeping genes (dnaK, fyuA, gyrB, and rpoD), identified 57 strains as X. translucens pv. undulosa, while eight strains were identified as X. translucens pv. translucens. Although the pathogenicity patterns on oat and ryegrass weed species varied among the strains, all X. translucens pv. undulosa strains were pathogenic on barley, Harding’s grass, rye (except for XtKm35) and wheat, and all X. translucens pv. translucens strains were pathogenic on barley and Harding’s grass, while none of the latter group was pathogenic on rye or wheat (except for XtKm18). MLST using the 65 strains isolated in Iran, as well as the sequences of the four genes from 112 strains of worldwide origin retrieved from the GenBank database, revealed higher genetic diversity (i.e., haplotype frequency, haplotype diversity, and percentage of polymorphic sites) among the Iranian population of X. translucens than among the North American strains of the pathogen. High genetic diversity of the BLS pathogen in Iran was in congruence with the fact that the Iranian Plateau is considered the center of origin of cultivated wheat. However, further studies using larger collections of strains are warranted to precisely elucidate the global population diversity and center of origin of the pathogen. IMPORTANCE Bacterial leaf streak (BLS) of small-grain cereals (i.e., wheat and barley) is one of the economically important diseases of gramineous crops worldwide. The disease occurs in many countries across the globe, with particular importance in regions characterized by high levels of precipitation. Two genetically distinct xanthomonads—namely, Xanthomonas translucens pv. undulosa and X. translucens pv. translucens—have been reported to cause BLS disease on small-grain cereals. As seed-borne pathogens, the causal agents are included in the A2 list of quarantine pathogens by the European and Mediterranean Plant Protection Organization (EPPO). Despite its global distribution and high economic importance, the population structure, genetic diversity, and phylogeography of X. translucens remain undetermined. This study, using MLSA and MLST, provides a global-scale phylogeography of X. translucens strains infecting small-grain cereals. Based on the diversity parameters, neutrality indices, and population structure, we observe higher genetic diversity of the BLS pathogen in Iran, which is geographically close to the center of origin of common wheat, than has so far been observed in other areas of the world, including North America. The results obtained in this study provide a novel insight into the genetic diversity and population structure of the BLS pathogen of small-grain cereals on a global scale.

scholarly journals Localized Genetic and Phenotypic Diversity of Xanthomonas translucens Associated With Bacterial Leaf Streak on Wheat and Barley in Minnesota

2020 ◽  
Vol 110 (2) ◽  
pp. 257-266
Author(s):  
Rebecca D. Curland ◽  
Liangliang Gao ◽  
Cory D. Hirsch ◽  
Carol A. Ishimaru
Keyword(s):  
Phenotypic Diversity ◽  
Housekeeping Genes ◽  
Field Trials ◽  
Bacterial Leaf Streak ◽  
Upper Midwest ◽  
Sequence Alignments ◽  
Xanthomonas Translucens ◽  
Population Structures ◽  
Pathogenic Diversity ◽  
Sequence Types

Bacterial leaf streak (BLS) of wheat and barley has been a disease of increasing concern in the Upper Midwest over the past decade. In this study, intra- and interfield genetic and pathogenic diversity of bacteria causing BLS in Minnesota was evaluated. In 2015, 89 strains were isolated from 100 leaf samples collected from two wheat and two barley fields naturally infected with BLS. Virulence assays and multilocus sequence alignments of four housekeeping genes supported pathovar identifications. All wheat strains were pathogenic on wheat and barley and belonged to the same lineage as the Xanthomonas translucens pv. undulosa-type strain. All barley strains were pathogenic on barley but not on wheat. Three lineages of barley strains were detected. The frequency and number of sequence types of each pathovar varied within and between fields. A significant population variance was detected between populations of X. translucens pv. undulosa collected from different wheat fields. Population stratification of X. translucens pv. translucens was not detected. Significant differences in virulence were detected among three dominant sequence types of X. translucens pv. undulosa but not those of X. translucens pv. translucens. Field trials with wheat and barley plants inoculated with strains of known sequence type and virulence did not detect significant race structures within either pathovar. Knowledge of virulence, sequence types, and population structures of X. translucens on wheat and barley can support studies on plant–bacterial interactions and breeding for BLS disease resistance.

Subterranean clover mottle virus infection of subterranean clover: widespread occurrence in pastures and effects on productivity

1992 ◽  
Vol 43 (7) ◽  
pp. 1597 ◽  
Author(s):  
JM Wroth ◽  
RAC Jones
Keyword(s):  
Systemic Infection ◽  
Subterranean Clover ◽  
Trifolium Subterraneum ◽  
Seed Transmission ◽  
Dry Weight ◽  
Widespread Occurrence ◽  
Transmission Rates ◽  
Type Isolate ◽  
Growing Seasons ◽  
South West

In 1989 and 1990, infection with subterranean clover mottle sobemovirus (SCMV) was widespread in subterranean clover ( Trifolium subterraneum L.) pastures in the south-west of Western Australia. The virus was detected in 61% of the pastures sampled and incidences of infection ranged from 1 to 50%. The virus was more common in old pastures than in pastures resown with newer cultivars during the preceeding 5 year period. When 12 isolates of SCMV were inoculated to subterranean clover plants grown in the glasshouse, symptoms varied from mild to severe. SCMV isolates P23 and F4 decreased the herbage dry weight of cw. Daliak and Woogenellup grown in plots as spaced plants by 81-88% while the Type isolate caused losses of 92%. By contrast, losses were 37-49% with cv. Karridale, a cultivar in which systemic infection was either delayed or prevented during winter. Infection decreased seed yield by c. 90% in cvv. Karridale and Woogenellup with all three isolates; seed weight was decreased 21-55%. A small proportion of cv. Woogenellup transplants outgrew the infection in new shoots during late spring to produce abundant healthy foliage. SCMV seed transmission rates in seed collected from infected transplants of cv. Woogenellup were 0.06, 0.07 and 0.43% for the Type, P23 and F4 isolates respectively. It was concluded that SCMV was present in most pastures, but at low incidences, and that it persists in them from year to year. Extended growing seasons and hard grazing are likely to increase its incidence.

Adaptations of plants to burial in coastal sand dunes

1998 ◽  
Vol 76 (5) ◽  
pp. 713-738 ◽  
Author(s):  
M A Maun
Keyword(s):  
Sand Dune ◽  
Sand Dunes ◽  
Seedling Emergence ◽  
Soil Surface ◽  
Threshold Level ◽  
Coastal Sand Dune ◽  
Bare Area ◽  
Plant Vigour ◽  
Storage Organs ◽  
Coastal Sand

One of the most obvious features on the foredunes and strands of coasts and lakes is recurrent burial in sand. Burial levels vary in different coastal sand dune systems and influence the physical and biotic microenvironment of the plant and soil. Foredune plants along coasts possess numerous adaptations to withstand burial. Studies show that below a certain threshold level of burial, the growth of all foredune plant species is stimulated probably because of multiple factors, namely improved soil resources, increase in soil volume, reactive plant growth, and enhanced mycorrhizal activity. However, as the level of burial increases, the positive response starts to decline until it becomes a negative value. For example, burial may reduce seed germination, seedling emergence, survival, and growth of seedlings and adult plants. At the community level, burial acts as a filter and selectively eliminates susceptible species, reduces the relative abundance of less tolerant species, and increases the abundance of tolerant and sand-dependent species. However, if sand deposition continues unabated, even the sand-dependent species are eliminated and a bare area is created. The emergence of a plant from a burial deposit primarily depends on the energy reserves in its storage organs and the speed, depth, and frequency of burial. Upon burial the plants shift resources from the belowground to the aboveground parts. Different plants show varied morphological responses to sand accretion. For example, the culms of grasses emerge by an increase in the number of nodes per culm and the elongation of internodes. Similarly, the emergent trunks and woody branches of tolerant trees and shrubs produce new buds and suckers at a higher level on the stem. In response to burial, the coastal sand dune species produce shootborne roots close to the new soil surface probably because of decreased oxygen levels.Key words: sand accretion, adaptations to burial, zonation of vegetation, burial of seeds, plant vigour, impact on communities, modes of emergence.

scholarly journals Agronomic Factors Associated with Bacterial Leaf Streak Development Caused by Xanthomonas vasicola pv. vasculorum in Corn

2020 ◽  
Vol 110 (6) ◽  
pp. 1132-1138 ◽  
Author(s):  
T. Hartman ◽  
J. Harbour ◽  
B. Tharnish ◽  
J. Van Meter ◽  
T. A. Jackson-Ziems
Keyword(s):  
Crop Rotation ◽  
Regression Tree ◽  
Classification And Regression Tree ◽  
Bacterial Leaf Streak ◽  
Leaf Sample ◽  
Planting Dates ◽  
Corn Production ◽  
Growing Seasons ◽  
Production Practices ◽  
Survey Responses

In 2016, the bacterium Xanthomonas vasicola pv. vasculorum was reported causing bacterial leaf streak on Nebraska corn. Prior to this report, the pathogen was reported on corn only in South Africa. Hence, there was a lack of information about the effects of corn production practices on bacterial leaf streak development. A survey of growers, crop consultants, extension agents, and others in the field of agriculture was initiated during the 2016 and 2017 corn growing seasons to examine agronomic factors that may affect the disease. Survey respondents were asked to submit a symptomatic leaf sample for pathogen confirmation via polymerase chain reaction, along with a completed survey on corn production practices. Analyses of 325 survey responses via random forest analysis indicated that irrigation, planting date, and crop rotation were the three most important predictors of corn samples testing positive for X. vasicola pv. vasculorum. According to a classification and regression tree analysis, irrigation use, the V7-R2 range of crop stages, multiple years of corn in a crop rotation or a corn-sorghum rotation, and planting dates after 2 May, were most closely associated with corn samples testing positive for X. vasicola pv. vasculorum. χ2 tests of independence indicated that applications of nitrogen fertilizer and glyphosate herbicide use may also be related to bacterial leaf streak development.

Population regulation in ticks: the role of acquired resistance in natural and unnatural hosts

Parasitology ◽  
1979 ◽  
Vol 79 (1) ◽  
pp. 141-156 ◽  
Author(s):  
Sarah E. Randolph
Keyword(s):  
Population Regulation ◽  
Acquired Resistance ◽  
Subsequent Development ◽  
Immunological Response ◽  
Threshold Level ◽  
Tick Population ◽  
Dependent Manner ◽  
Laboratory Mice ◽  
Natural Hosts ◽  
Host Parasite

SUMMARYAttachment, engorgement and subsequent development of successive infestations of Ixodes trianguliceps larvae and nymphs on natural hosts, Apodemus sylvaticus, and unnatural hosts, laboratory mice, are compared. In laboratory mice, primary infestations above a threshold level of about 10 ticks elicit an immunological response which reduces, in a density-dependent manner, the rate of successful tick engorgement during subsequent infestations. In contrast, in A. sylvaticus successive infestations of larvae result in unchanged or slightly improved survival through to nymphs. The relevance of these results to the concept of host-parasite co-evolution and to tick population regulation is discussed.

scholarly journals Involvement of Beet western yellows virus, Cauliflower mosaic virus, and Turnip mosaic virus in Internal Disorders of Stored White Cabbage

2002 ◽  
Vol 92 (8) ◽  
pp. 816-826 ◽  
Author(s):  
P. J. Hunter ◽  
J. E. Jones ◽  
J. A. Walsh
Keyword(s):  
Mosaic Virus ◽  
Leaf Tissue ◽  
Subsequent Development ◽  
Turnip Mosaic Virus ◽  
Cauliflower Mosaic Virus ◽  
Beet Western Yellows Virus ◽  
Growing Seasons ◽  
White Cabbage ◽  
Necrotic Spots ◽  
Internal Necrosis

Experiments over two growing seasons clearly showed that Turnip mosaic virus (TuMV) infection was associated with internal necrosis (sunken necrotic spots 5 to 10 mm in diameter) and Beet western yellows virus (BWYV) infection was associated with collapse of leaf tissue at the margins (tipburn) in heads of stored white cabbage (Brassica oleracea var. capitata). Virtually no tipburn was seen in cv. Polinius, whereas cv. Impala was affected severely. Internal necrotic spots were seen in both cultivars. BWYV appeared to interact with TuMV. Plants infected with both viruses showed a lower incidence of external symptoms and had less internal necrosis than plants infected with TuMV alone. Cauliflower mosaic virus (CaMV) did not induce significant amounts of internal necrosis or tipburn, but did, in most cases, exacerbate symptoms caused by TuMV and BWYV. BWYV-induced tipburn worsened significantly during storage. Post-transplanting inoculation with TuMV induced more internal necrosis than pre-transplant inoculation. There was a significant association between detection of TuMV just prior to harvest and subsequent development of internal necrotic spots. Individually, all three viruses significantly reduced the yield of cv. Polinius, whereas only BWYV and CaMV treatments reduced the yield of cv. Impala.

scholarly journals Enhancing Seed Yield of Hybrid Rice by Maintaining Row Ratio and Dosages of Gibberellic Acid

2017 ◽  
Vol 50 (1) ◽  
pp. 31-45
Author(s):  
M. Abo-Youssef ◽  
A. El Sabagh ◽  
G. Abo-Gendy ◽  
A. Mohamed
Keyword(s):  
Gibberellic Acid ◽  
Seed Yield ◽  
Seed Set ◽  
Hybrid Rice ◽  
Flag Leaf ◽  
Hybrid Seed Production ◽  
Panicle Length ◽  
Growing Seasons ◽  
Main Plot ◽  
Panicle Weight

Abstract The purpose of this study was to identify the optimum levels of gibberellic acid and suitable row ratio for maximization the seed yield of hybrid rice. An experiment was conducted at the experimental farm of Rice Research and Training Center, Egypt, during 2013 and 2014 growing seasons. The material under this study included the parental lines of IR69625A (Female lines) and Giza 179 R (Restorer line) to produce F0 hybrid seeds. A split-plot design with three replications was used. The main plot was row ratio (2R:8A, 2R:10A and 2R:12A) and sub plots was the doses of gibberellic acid (g/ha) (control, 300, 350, 400). The results indicated that, Application of GA3 and row ratio had significant effect on different traits of seed yield and hybrid seed production. The highest values of flag leaf area, panicle length, seed set, panicle weight, panicle exsertion and seed yield were acheived by using 2R: 8A row ratio and was observed the lowest values were obtained at the 2:12 row ratio. Acoording to gibberellic acid application, the highest values for panicle length (cm), seed set (%), panicle weight (g), panicle exertion (%), harvest index and seed yield were recorded by using 400 g /ha gibberellic acid. Accordingly, the highest net economic return from seed yield was obtained with the treatment combination of 400 g/ha GA3 x 2:8 (R: A) row ratio.

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