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Stem Base (stem + base)

Distribution by Scientific Domains

Life Sciences	66%
Earth and Environmental Science	33%

Selected Abstracts

Associations among symptoms of dieback in even-aged stands of ash (Fraxinus excelsior L.)

FOREST PATHOLOGY, Issue 1 2010
J. P. Skovsgaard
Summary The objective of this study was to establish statistically based associations among macroscopic symptoms of crown dieback, cankers due to Chalara fraxinea, and symptoms caused by other pathogens and pests on Fraxinus excelsior. A total of 454 trees were observed in two plots of a 15-year-old experimental stand. The symptoms included: (i) overall extent of crown dieback; (ii) dieback of upper parts of the crown; (iii) canker in upper parts of the crown; (iv) wilting foliage; (v) cankers and bark proliferations at the lower part of the stem; and (vi) discolouration at stump or stem base. The analysis suggested that the observed symptoms of crown dieback are caused by a primary disease. The macroscopic symptoms attributed to dieback and canker in the crown were strongly associated. Moreover, the disease was associated with symptoms of Armillaria gallica, but no associations were found for symptoms of Neonectria galligena, Pseudomonas syringae subsp. savastanoi pv. fraxini, Hylesinus fraxini or H. varius when considered collectively. Dieback was more frequent on trees of average or below-average size, suggesting that individual tree resistance decreased with decreasing growth potential or tree vigour. The extent of canker in the crown depended on site conditions and possibly on silvicultural practices. The development of phytosanitary prescriptions for silviculture should primarily be targeted towards young stands as these represent the most critical phases of stand development. [source]

Interactions between the stem-mining weevils Ceutorhynchus napi Gyll. and Ceutorhynchus pallidactylus (Marsh.) (Coleoptera: Curculionidae) in oilseed rape

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2004
Georg Dechert
Abstract 1,The rape stem weevil Ceutorhynchus napi Gyll. and the cabbage stem weevil Ceutorhynchus pallidactylus (Marsh.) share the same habitat and food resource within the stems of oilseed rape, Brassica napus L. var. oleifera. Interactions occurring between these two sympatric species on this host were studied under both field and laboratory conditions. 2,The oviposition preference of C. pallidactylus and the within-plant distribution of eggs and larvae were examined in field plots of oilseed rape. Female C. pallidactylus tended to lay their eggs in plants already infested by eggs and larvae of C. napi rather than in uninfested plants. The within-plant distribution of the egg batches of C. pallidactylus did not differ significantly between uninfested plants and those preinfested by C. napi. Ovipositing females of C. napi and C. pallidactylus generally showed a significant preference for plants with larger stem diameter. 3,Laboratory choice tests provided further evidence for the oviposition preference of C. pallidactylus. Females laid significantly more eggs in leaves of plants that had been previously infested by C. napi than in leaves of previously uninfested plants. 4,Larvae of C. pallidactylus showed a significant shift of their feeding niche towards the stem base when feeding in individual plants attacked by both species. This possibly indicates ressource partitioning between C. pallidactylus and C. napi. The within-plant distribution of C. napi larvae was not affected by the simultaneous attack of C. pallidactylus. 5,The size of the head capsule of full-grown larvae of C. napi and C. pallidactylus was not significantly correlated with the diameter of the stem of their host plant or with the number of conspecific larvae within individual plants. [source]

Quantification of soil structural changes induced by cereal anchorage failure: Image analysis of thin sections

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2007
Sacha J. Mooney
Abstract Cereal anchorage failure, or lodging, is the permanent displacement of a crop from the vertical and results in significant annual yield losses globally. Several factors have been identified as contributors to this phenomenon but the precise mechanisms of failure are still largely unknown because of difficulties in observing these processes as they occur in situ. To identify potential soil management practices to minimize losses associated with cereal root failure, an understanding of the nature of root-soil interactions attributed to lodging is needed. An experiment was conducted that involved field impregnation and subsequent thin sectioning of lodged and unlodged root-soil complexes from contrasting soils, cereal crops, and management practices to elucidate the effects of lodging on soil structure and porous architecture. Using image analysis, size and distribution of pores in soils were quantified at both meso- (100,30 ,m) and microscales (<30 ,m). A significant effect of lodging on porosity was recorded whereby lodging reduced total porosity through compaction created by movement of the stem base, although this was variable among soil types. Pore-size distributions comprehensively supported these trends since alteration in the relative frequency of pores within specific size classes was clearly observed. The effects of lodging were more pronounced at the mesoscale because the data were more susceptible to variations created by natural soil heterogeneity at the microscale. These data suggested that sideways movement of the subterranean stem within the soil is a significant factor which is likely to affect the propensity for a cereal plant to lodge, indicating soil strength in the upper part of the soil profile is crucial. [source]

Environmental conditions influencing Sclerotinia sclerotiorum infection and disease development in lettuce

PLANT PATHOLOGY, Issue 4 2004
C. S. Young
The environmental factors that influence infection of lettuce by ascospores of Sclerotinia sclerotiorum, and subsequent disease development, were investigated in controlled environment and field conditions. When lettuce plants were inoculated with a suspension of ascospores in water or with dry ascospores and exposed to a range of wetness durations or relative humidities at different temperatures, all plants developed disease but there was no relationship between leaf wetness duration or humidity and percentage of diseased plants. Ascospores started to germinate on lettuce leaves after 2,4 h of continuous leaf wetness at optimum temperatures of 15,25°C. The rate of development of sclerotinia disease and the final percentage of plants affected after 50 days were greatest at 16,27°C, with disease symptoms first observed 7,9 days after inoculation, and maximum final disease levels of 96%. At lower temperatures, 8,11°C, disease was first observed 20,26 days after inoculation, with maximum final disease levels of 10%. Disease symptoms were always observed first at the stem base. In field-grown lettuce in Norfolk, 2000 and 2001, inoculated with ascospore suspensions, disease occurred only in lettuce planted in May and June, with a range of 20,49% of plants with disease by 8 weeks after inoculation. In naturally infected field-grown lettuce in Cheshire, 2000, disease occurred mainly in lettuce planted throughout May, with a maximum of 31% lettuce diseased within one planting, but subsequent plantings had little (, 4%) or no disease. Lack of disease in the later plantings in both Norfolk and Cheshire could not be attributed to differences in weather factors. [source]

Epidemiology and management of Leptosphaeria maculans (phoma stem canker) on oilseed rape in Australia, Canada and Europe

PLANT PATHOLOGY, Issue 1 2001
J. S. West
Phoma stem canker (blackleg), caused by Leptosphaeria maculans, is an important disease on oilseed rape (canola, rapeseed, Brassica napus, Brassica juncea, Brassica rapa) causing seedling death, lodging or early senescence in Australia, Canada and Europe, but not in China. The two forms of L. maculans (A group and B group) that occur on oilseed rape are now considered to be separate species. The epidemiology and severity of phoma stem canker differs between continents due to differences in the pathogen population structure, oilseed rape species and cultivars grown, climate and agricultural practices. Epidemics are most severe in Australia, where only the A group occurs, and can be damaging in Canada and western Europe, where both A and B groups occur, although their proportions vary within regions and throughout the year. Epidemics are slight in China, where the A group has not been found. Dry climates (Australia, western Canada) lengthen the persistence of infected debris and may synchronize the release of airborne ascospores (after rain) with seedling emergence. L. maculans spreads from cotyledon and leaf infections down petioles to reach the stem, with infections on cotyledons and leaves early in the season producing the most damaging stem cankers at the stem base (crown). Development of both crown cankers and phoma stem lesions higher up stems is most rapid in regions with high temperatures from flowering to harvest, such as Australia and Canada. Breeding for resistance (genetic, disease escape or tolerance), stubble management, crop rotation and fungicide seed treatments are important strategies for control of phoma stem canker in all areas. Fungicide spray treatments are justified only in regions such as western Europe where high yields are obtained, and accurate forecasts of epidemic severity are needed to optimize their use. [source]

Biology of suckers: late-formed shoots in sugarcane

ANNALS OF APPLIED BIOLOGY, Issue 1 2001
G D BONNETT
Summary Suckers in sugarcane are tillers that form late in the growing season after the population of main stalks has been established. Their biology has rarely been studied, though unsubstantiated comments relating to their morphology, development and number are abundant. In this paper, the literature is reviewed and new experiments presented. Comparison of suckers, emerging plant and ratoon cane showed that suckers have a different leaf and stem morphology. Suckers have a greater diameter at their stem base and shorter and wider leaves than primary stalks of a similar age. In 1 -year-old crops, suckers have been demonstrated to decrease the net sucrose concentration of harvested material by diluting sucrose in the main stalks. By comparing main stalks without suckers to those that have initiated suckers, evidence is presented that suckers may also be decreasing the sucrose content of the stalks from which they are growing. Genotypic and environmental factors influence sucker number. Several experiments were designed to identify environmental stimuli for suckering. Increased nitrogen, through application late in the growing season, was found to increase the numbers of suckers present. Manipulation of the light environment of main stalks showed that a change in light quality (but not necessarily quantity) stimulated suckering. Further work is underway to define how these environmental stimuli lead to sucker initiation and growth. Major scientific questions that should be addressed are: the identification of other potential environmental stimuli, how the signals are perceived and translated into sucker initiation, and why suckers have different morphology. The practical challenge is to combine the new information about sucker biology and develop from it strategies to alter agronomy and select new cultivars that results in decreased suckering. [source]

Adult large pine weevils Hylobius abietis feed on silver birch Betula pendula even in the presence of conifer seedlings

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2006
Riitta Toivonen
Abstract 1,The feeding preference of the adult pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) for Betula pendula Roth was studied in no-choice and paired-choice feeding experiments. 2,In the first no-choice test, large quantities of silver birch bark in Petri dishes were consumed; on average, the daily consumption of each weevil was 67 mm2. 3,In the second no-choice test, the weevils were offered 1-year-old silver birch seedlings for 6 days. Initially, the weevils fed mostly on the stem bases; later, they moved upward to feed on other parts of the stems. In addition to the main shoots, scars caused by gnawing were also found on leaf bases, blades, veins and petioles. Feeding resulted in the death of the main stems in 15% of the seedlings. 4,In the paired-choice tests, the conifers were preferred to silver birch, even though a large amount of silver birch was also consumed in the presence of conifers. 5,In the paired-choice tests, equal amounts of Scots pine and Norway spruce were always consumed. When hybrid aspen was offered, only small amounts were gnawed. [source]

Vascular colonization patterns in susceptible and resistant tomato cultivars inoculated with Fusarium oxysporum f.sp. lycopersici races 0 and 1

PLANT PATHOLOGY, Issue 2 2003
M. C. Rodríguez-Molina
The vascular colonization pattern of Fusarium oxysporum f.sp. lycopersici races 0 and 1 in tomato was studied in five susceptible and five resistant cultivar,fungus combinations during a 26-day period after inoculation by root immersion. Propagules spread discontinuously along the stems in all five cultivars 1 day after inoculation, irrespective of cultivar resistance. Five days later the fungus was limited to the stem bases in all cultivars. Between the fifth and 12th days, stem colonization by the fungus stopped in all cultivar,race combinations. Thereafter, the situation remained stable in resistant combinations, with inoculum distributed discontinuously, and no disease symptoms were apparent. By contrast, in the susceptible combinations a gradual upward colonization of the stems was seen such that fungal distribution was no longer discontinuous and disease symptoms appeared. These results suggest that a fungal ,incubation' period in the base of the vascular system is required before a secondary invasion of tissues occurs in susceptible genotypes. The slope of the regression line fitted between the height reached by the fungus up the stem (y) and the time after inoculation (x) provides a measure of the horizontal (polygenic) resistance in tomato cultivars [source]

Effects of crop debris and cultivations on the development of eyespot of wheat caused by Oculimacula spp.

ANNALS OF APPLIED BIOLOGY, Issue 3 2010
J.F. Jenkyn
Results from a series of crop sequence and single-year experiments that tested different straw and cultivation treatments in a total of 11 site,season combinations confirmed previous evidence that the development of eyespot disease in cereals can be decreased by debris in the seed bed even if that debris includes eyespot-infected stem bases, which are the principal sources of primary inoculum. Two of the experiments, which followed non-cereal break crops and tested the effects of crop debris applied after ploughing or tining on eyespot in winter wheat that was artificially inoculated with Oculimacula spp., provided convincing evidence that the effects can be attributed to the debris per se, and not to any associated husbandry practices. There were often larger effects on disease in summer than in spring or on severity than on incidence suggesting that the effects of debris cannot be explained solely by effects on inoculum or initial infection, and that debris has a disease-suppressive effect. [source]