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91.
92.
93.
Summary Genetic variability in the apple [Malus] fruit disorder bitter pit and fruit calcium concentrations ([Ca]) was determined in 25 seedling families at each of two sites from 1999 to 2000 and again for one site, in 2001. Most trees were free of pit or had low pit incidence, which could be approximated by an over-dispersed binomial distribution. A genetic component to external and internal pit incidence was found across both sites and all years. This effect was irrespective of the use of several cropping factors, average fruit weight or fruit mineral concentrations as covariates in the analyses. Year and/or site always had substantial effects on pit incidence. Interactions of genetic effects with site or year were also detected with large differences in mean pit incidence between sites or years for some families but not others. No relationship was found between mean family pit incidence and mean family [Ca] or mean family harvest date. However fruit [Ca] and harvest date were usually important predictors of within-family variation in pit incidence. For any one seedling, family had the largest effect on bitter pit incidence followed by site and [Ca] and the smallest effect was that of harvest date. [Ca] showed a strong genetic component and estimated family means of [Ca] were consistent at different sites and years. These results suggest that susceptibility of apple genotypes to bitter pit in breeding programmes may be best assessed through screening across multiple sites and seasons. Fruit [Ca] might be useful as an indirect selection index for bitter pit within, but not among families. 相似文献
94.
Despite the phenomenon of heterosis having been used to improve crop productivity for almost a century, there is little understanding
of the molecular mechanisms involved. Heterosis has been described recently in the widely used plant model Arabidopsis thaliana. To assess the opportunity afforded by this system, we have developed, through pollination to a male sterile female parent
(Ler ms1), a range of hybrids of A. thaliana accessions. We tested this method of hybrid production in A. thaliana by comparing seed produced by natural pollination and hand pollination of emasculated plants. Our results demonstrate that
using male sterile lines, which more closely represent methods used for hybrid crop production, circumvents the problems associated
with the analysis of hybrids produced from emasculated plants. We identified hybrid combinations exhibiting mid-parent heterosis
for vegetative fresh weight ranging from −9 to 103% and characterised heterosis in the reciprocal hybrids of one strongly
heterotic combination. We found no evidence of a relationship between the extent of genetic relatedness of A. thaliana accessions and the strength of heterosis exhibited by their hybrids.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
95.
ABSTRACT In the international business literature location behavior has traditionally been analyzed using Dunning's (1977 ) OLI framework, which focuses on the nature, role, and behavior of multinational enterprise (MNE). In this paper it is argued that this approach is now no longer appropriate for discussing the spatial behavior of MNEs, because of the fundamental changes which have taken place either in MNE organization or in the global and institutional environment for foreign direct investment (FDI). At the same time, the paper argues that current location theory from regional economics and economic geography is also largely unsuitable for discussing these issues, such that the spatial behavior of the MNE provides a set of difficult challenges to location analysts. There appears to have been some response to these issues from the international business and management literature, most notably the Porter literature on clusters. However, it is also argued here that this literature provides few, if any, real answers to the problems set by the geographical behavior of the MNE. It is concluded that a fusion of traditional economic geography approaches with a focus on the information and organizational aspects of the firm and the region under consideration may be a way forward for both theory and empirical analysis. 相似文献
96.
Ian R. Crute 《Euphytica》1992,63(1-2):95-102
Summary Over the last 30 years, six resistance alleles (Dm2, Dm3, Dm6, Dm7, Dm11 andDm16) located in two linkage groups, have contributed to the control of downy mildew in lettuce crops grown under protection (glass or polythene) in northern Europe. More recently, an as yet genetically uncharacterised resistance factor, R18, has also begun to assume importance. The occurrence of the various combinations of these resistance alleles that exist in commercial cultivars has been dictated by the pathotypes ofBremia lactucae used in their selection but also restricted by linkage in repulsion. In the UK, a pathotype ofB. lactucae insensitive to phenylamide fungicides, such as metalaxyl, emerged in 1978 and became prevalent throughout lettuce production areas in subsequent years. The specific virulence of this pathotype was identical to the previously described phenylamide sensitive pathotype NL10 and cultivars carryingDm11, Dm16 or R18 were resistant. Consequently, an integrated control strategy based on the utilisation of metalaxyl on cultivars carryingDm11 provided effective control in UK until 1987 when a new phenylamide insensitive pathotype began to cause problems. The specific virulence of this second pathotype, which was first reported in the Netherlands and France, was identical to the previously described phenylamide sensitive pathotype NL15. Cultivars carryingDm6, Dm16 or R18, but notDm11, were resistant to NL15; consequently an appropriate change in the cultivar recommendations for use in the integrated control strategy was successfully promulgated. It is predicted that variations of this integrated control strategy involving the use of appropriately selectedDm gene combinations may prove effective for some time. This prediction is based on studies of the status of the avirulence loci in the two phenylamide insensitive pathotypes and of the specific virulence characteristics of phenylamide sensitive components of the pathogen population. 相似文献
97.
Soil communities are compartmentalized into pathways of trophic interactions and nutrient flows that originate from plant roots, bacteria and fungi. The pathways differ in terms of the organisms that comprise them, the habitats that the organisms occupy and the rates by which the organisms process and transfer material and energy. The fungi, nematodes and arthropods within the fungal pathway live in air-filled pore spaces and water films, while the bacteria, protozoa, and nematodes within the bacterial pathway occupy water-filled pore spaces and water films. Organisms within the fungal pathway have longer generation times and process matter at slower rates than those within the bacterial pathway. Empirical studies have shown that under natural conditions the pathways co-exist in a stable manner. The relative sizes (indexed by the densities of organisms) and activities (indexed by nutrient-flow rates, excretion rates and respiration rates) of the pathways may change seasonally and in response to minor disturbances, but they persist. However, large anthropogenic and natural disturbances induce shifts in the relative sizes and activities of the pathways. Coincident with these shifts are reports of changes in the aboveground plant community and the availability and retention of plant limiting nutrients. We developed simple models of the bacterial and fungal pathways to explore the consequences of the observed shifts on the dynamic stability of the system. The more stable configurations occurred when there was a balance in the flow of nutrients between the two pathways. Large shifts in nutrient cycling and community structure towards either the fungal pathway or toward the bacterial pathway resulted in less stable or unstable configurations. 相似文献
98.
99.
Joshua M. Tebbs Melinda H. McCann 《Journal of Agricultural, Biological & Environmental Statistics》2007,12(4):534-551
Insect-vectored plant diseases impact the agricultural community each year by affecting the economic value, the quantity,
and the quality of crops. Controlling the spread of disease is an important area in risk assessment, and understanding the
dynamics of vector populations helps researchers to develop effective treatments. In this article, we consider an experimental
design commonly used by researchers who study plant disease and examine large-sample, likelihood-based hypothesis tests that
can be used to characterize disease-transmission behavior in a stratified population. Small-sample size and power results
along with design considerations are provided. We illustrate our testing procedures using two real data examples and provide
recommendations for plant-disease researchers in the field. 相似文献
100.
Ilyas Siddique Caroline Gutjahr Gamini Seneviratne Broder Breckling Sudheera W. Ranwala Ian J. Alexander 《Biology and Fertility of Soils》2007,44(1):163-170
Topsoil properties were determined in forest gardens established about 20 years ago on eroded grassland soils (abandoned tea
lands) in the wet zone of the Sri Lankan highlands. They were compared with adjacent, eroded grasslands (abandoned tea lands)
on strongly weathered soils vs soils at earlier stages of pedogenic development in a two-way analysis of variance. Soil pH
in forest gardens was, on average, 6.1, nearly one unit higher than in the adjacent grasslands. In the garden soils, the cation
exchange capacity (CEC measured at pH 4.8) was nearly double, exchangeable calcium concentrations five times and exchangeable
magnesium three times as high as in the grasslands soils. Total soil N content was found to be nearly 40% higher in the gardens.
Topsoil gravel contents in the gardens were less than half as high as in the grasslands. The increases in exchangeable bases
and N in gardens, relative to grasslands, were attributed to increased nutrient retention and acquisition. Higher retention
was partly due to the higher CECpH4.8, and probably to reduced erosion and increased, continuous fine root density in the garden topsoils. Higher field CEC in
gardens was likely to result from generally higher C contents and from the reversal of acidification, presumably caused by
base accumulation and decomposition processes. Our results suggest that forest garden establishment on degraded grasslands
can lead to accumulation of mobile nutrients in the topsoil, probably due to increased nutrient retention, subsoil uptake
and litter input exceeding nutrient uptake by the standing biomass. 相似文献