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991.
992.
Spatial heteroscedasticity may arise jointly with spatial autocorrelation in lattice data collected from agricultural trials
and environmental studies. This leads to spatial clustering not only in the level but also in the variation of the data, the
latter of which may be very important, for example, in constructing prediction intervals. This article introduces a spatial
stochastic volatility (SSV) component into the widely used conditional autoregressive (CAR) model to capture the spatial clustering
in heteroscedasticity. The SSV component is a mean zero, conditionally independent Gaussian process given a latent spatial
process of the variances. The logarithm of the latent variance process is specified by an intrinsic Gaussian Markov random
field. The SSV model relaxes the traditional homoscedasticity assumption for spatial heterogeneity and brings greater flexibility
to the popular spatial statistical models. The Bayesian method is used for inference. The full conditional distribution of
the heteroscedasticity components can be shown to be log-concave, which facilitates an adaptive rejection sampling algorithm.
Application to the well-known wheat yield data illustrates that incorporating spatial stochastic volatility may reveal the
spatial heteroscedasticity hidden from existing analyses. 相似文献
993.
Gemechu Keneni Mussa Jarso Tezera Wolabu Getnet Dino 《Genetic Resources and Crop Evolution》2005,52(5):539-549
An experiment was conducted in 2001 at Holetta and Kulumsa, Ethiopia, to study the extent and pattern of genetic diversity
in Ethiopian field pea (Pisum sativum L.) landraces. One hundred forty-eight germplasm accessions were grown in an alpha lattice design with 2 replications. Data
on 12 traits were collected and analyzed. Differences among the accessions were significant for most of the traits (except
number of seeds/ pod) at each location even though differences pooled over location were mostly non-significant. The accessions
were grouped into five clusters of different sizes. Accessions from the southern part of the country (Arsi) distributed overall
clusters while those from the northern half (North and South Wello, North Gonder and North Shewa) fell into clusters C1 to C3. Cumulative effects of a number of characters dictated differentiation of the accessions into clusters. There was no definite
relationship between geographic diversity and genetic diversity as overlapping was encountered in clustering pattern among
accessions from different parts of the country. Accessions from different regions might have similar genetic background and
those from the same origin might also have different genetic background. Therefore, geographic diversity should not necessarily
be used as an index of genetic diversity and parental selection should be based on a systematic study of genetic diversity
in a specific population. Genetic distances among most of the clusters were significant that crosses between parents selected
out of them are expected to generate desirable genetic recombination. Selection should also consider the special advantages
of each cluster and each accession within a cluster. Future germplasm collection, conservation and breeding efforts should
focus not only on inter-regional diversity but also on intra-regional diversity. 相似文献
994.
Gemechu Keneni Mussa Jarso Tezera Wolabu Getnet Dino 《Genetic Resources and Crop Evolution》2005,52(5):551-561
A field experiment was conducted in 2001 at Holetta and Kulumsa, Ethiopia, to study genetic diversity in Ethiopian faba bean
(Vicia faba L.) landraces. One hundred sixty random germplasm accessions were grown in an alpha lattice design with two replications. Data
on 12 traits were collected and analyzed. Significant differences were observed among the accessions for most of the traits
(except number of pods/podding nodes) at each location even though differences pooled over location were mostly non-significant.
Cluster analysis distinguished seven diversity classes of different sizes. Accessions from the northern half of the country
(North and South Wello, North Gonder and North Shewa) were closely related while those from the southern part of the country
(Arsi) were highly diverse. Cumulative effects of a number of characters dictated differentiation of the accessions into clusters.
Some overlapping were encountered between accessions from the northern and those from the southern parts of the country. The
study revealed that accessions from different regions might have similar genetic background and those from the same origin
might also have different genetic background. Therefore, geographic diversity should not necessarily be used as an index of
genetic diversity and parental selection should be based on a systematic study of genetic diversity in a specific population.
Genetic distances between most of the clusters were significant that crosses between parents selected out of them are expected
to generate desirable progenies. Future germplasm collection, conservation and utilization strategies should put more focus
not only on inter-regional diversity in the country as a whole but also on intra-regional diversity in Arsi. 相似文献
995.
Hongjie Li Robert L. Conner Qin Chen Robert J. Graf André Laroche F. Ahmad A. D. Kuzyk 《Genetic Resources and Crop Evolution》2005,51(8):827-835
Wheat streak mosaic virus (WSMV), vectored by the wheat curl mite (WCM),Aceria tosichella Keifer, is one of the most destructive viral diseases of wheat found in many wheat producing areas of the world. Host resistance is the most effective method for controlling this disease and its vector. Symptomatological analysis and enzyme-linked immunosorbent assay (ELISA) were used to characterize WSMV-resistance in wheat-alien partial amphiploid lines and their derivatives. The results showed that most of partial amphiploids derived fromThinopyrum ponticum andTh. intermedium were free of systemic symptoms with very low ELISA readings that were similar to that of the non-inoculated Chinese Spring control. While the partial amphiploid lines 693 and PWM706 were identified as new genetic resources of resistance to WSMV. The present study demonstrated that both symptomatological and ELISA methods efficiently assessed WSMV-resistance in the wheat-alien hybrids and systemic symptom incidence and ELISA absorbance readings were highly correlated (r
2 = 0.8658–0.9323) over time following inoculation. The ELISA results also indicated that the virus did not buildup in the plant tissues of these virus-resistant partial amphiploids. Similar results were observed in chromosome translocation and substitution lines that have the geneWsm1 conferring WSMV resistance. However, the lines containing the geneWsm1 and all the partial amphiploid lines, except Agrotana, were susceptible to the WCM. One line derived from a cross of wheat and Agrotana, was effective in controlling the spread of WSMV and was highly resistant to the WCM. Another line and an accession ofTriticum dicoccoides (Koern.) Schweinf. were highly susceptible to WSMV and WCM. Early disease development was delayed in a new hard red winter cultivar McClintock. The partial WSMV-resistance of McClintock was demonstrated by initially low ELISA readings, and a lower percentage of infected plants than other WSMV-susceptible wheat. The use of the identified promising sources of resistance to WSMV and the WCM in wheat breeding is discussed.LRC Contribution No. 387-01061. 相似文献
996.
Purpose
Soil macropores play a principal role in water infiltration but they are highly variable. The objectives of this study were (1) to investigate the temporal change in macropores of an Ultisol as affected by land use and slope position and (2) to analyze contribution of macropores to water infiltration.Materials and methods
Water infiltration was measured at upper and lower slopes in citrus orchard and watermelon field once every 2 months for 1 year using tension infiltrometers at a successive pressure head from ?12, ?6, ?3, to 0 hPa.Results and discussion
Hydraulic conductivity (K) was significantly affected by land use and slope position except at 0 hPa pressure head, showing a significant temporal variation. Effective macroporosity, derived from the increment of hydraulic conductivity between ?3 and 0 hPa, showed a significant temporal variation. Such temporal variation was land use (P?<?0.05) and slope position (P?<?0.001) dependent. Despite of low proportion in total soil volume (averaged 3.5 cm3 m?3), the macropores contributed 47 % of water flux on average. The macroporosity was more stable and higher in the citrus orchard (2.43 cm3 m?3, coefficient of variance (CV)?=?75 %) than in the watermelon field (1.72 cm3 m?3, CV?=?117 %) and contributed more to infiltration in the citrus orchard (60 %, CV?=?16 %) than in the watermelon field (33 %, CV?=?43 %) as well, because tillage was operated only in the watermelon field.Conclusions
No-tillage increased water conducting macropores but did not increase hydraulic conductivity irrespective of slope position.997.
Xiaoyan Cao Charisma Lattao Klaus Schmidt-Rohr Jingdong Mao Joseph J. Pignatello 《Journal of Soils and Sediments》2016,16(7):1841-1848
Purpose
Sorbate-induced swelling and plasticization of sorbent have been linked to sorption hysteresis of organic compounds in the natural organic matter of isolated humic acids, soils, and coals. The above processes, which have important implications for the fate and bioavailability of organic and inorganic contaminants, are mostly based on macroscopic changes and require molecular-level confirmation. This study aimed to investigate the presence or absence of sorbate-induced plasticization of Pahokee peat soil as a function of different sorbates.Materials and methods
The plasticization of Pahokee peat soil was studied upon sorption of different proton-free solutes including C6D6, CDCl3, CCl4, C2Cl4, CBr4, C6D5Cl, and C5D5N, covering apolar and polar aromatic and aliphatic compounds. The swelling and plasticization of Pahokee peat soil were verified at the molecular level by 1H wideline and two-dimensional wideline separation (2D WISE) NMR. The use of 1H wideline shapes is the traditional technique for studying molecular dynamics but hampered by the lack of spectral resolution, with one dimension displaying 13C chemical shifts and the second showing 1H wideline shapes, is capable of providing information on molecular dynamics of specific functional groups.Results and discussion
Our results showed that the segments of Pahokee peat soil sorbed with C6D6, C2Cl4, and C5D5N became more mobile, but the changes due to the plasticization were small. Both C6D6 and C5D5N selectively increased the mobility of specific components, C6D6 of the nonpolar alkyl domains, and C5D5N of both the nonpolar alkyl domains and aromatic components.Conclusions
Some liquid solutes at high concentrations (2–5 wt%) are capable of slightly “softening” natural organic matter of a soil, and this provides support for the hypothesis that natural organic matter in Pahokee peat soil is in a glassy state that is subject to plasticization.998.
Susheel Verma Jawahar L. Karihaloo Shailesh K. Tiwari Rani Magotra Awtar K. Koul 《Genetic Resources and Crop Evolution》2007,54(2):221-229
Eremostachys superba Royle ex Benth. (Lamiaceae) has undergone a severe decline in population size since its discovery in the North-western Himalayas
in late 19th century. One hundred and seventy-two plants from six populations in the Indian states of Uttar Pradesh and Jammu
& Kashmir, located between 0.45 km and 455.72 km apart from each other were evaluated for RAPD polymorphism. Sixteen random
primers generated 92 bands overall, 77 of which were polymorphic. Shannon’s index of genetic diversity within populations
(H
o) ranged between 0.305 and 0.421; the average within-population diversity (H
pop) was 0.389; and the total species diversity (H
sp) was 0.478. The population from Mohand (representing the type locality) had the fewest plants, at 18, and was genetically
the most depauperate. Among the other populations, ranging in size between 52 and 1,022 individuals, no relation between population
size and genetic diversity was evident. It is suggested that these six populations represent relics of a larger, extended
population, in which the presence of perennating rootstocks has helped preserve historic patterns of genetic diversity. AMOVA
revealed that 83.01% of the variation exists within populations, which was consistent with earlier studies on the reproductive
biology of E. superba, which indicated this species is predominantly allogamous. FST distances between all populations were significant, indicating
geographic differentiation despite some of them being closely separated. Habitat restoration and protection from indiscriminate
harvesting are proposed as primary strategies for conserving E. superba. Rejuvenation of the Mohand population through intrapopulation crossing between plants bearing diverse molecular phenotypes
is also suggested. 相似文献
999.
Xiao-Ping Jia Yun-Su Shi Yan-Cun Song Guo-Ying Wang Tian-Yu Wang Yu Li 《Genetic Resources and Crop Evolution》2007,54(2):233-236
The development of EST-SSR in foxtail millet (Setaria italica) for polymorphism and transferability study was reported here. From 1213 EST sequences, 30 SSRs were obtained and primers
were designed for 26 SSRs. Among them, four pairs of SSR primers amplified polymorphic products in 12 foxtail millet cultivars
and one accession of Setaria viridis, a wild relative of foxtail millet, with 10 alleles detected for the four loci and 2.5 alleles per locus. In addition, ten
SSR markers could be transferred to other nine Gramineae species. The putative functions of 11 ESTs containing polymorphic
and transferable SSRs were also identified. 相似文献
1000.
Louise Willemen Xavier Scheldeman Víctor Soto Cabellos Simón Rafael Salazar Luigi Guarino 《Genetic Resources and Crop Evolution》2007,54(7):1599-1612
This study evaluates quantitatively the suitability of the use of site-specific socio-economic and environmental data as indicators
to rapidly assess patterns of diversity and genetic erosion risk in cassava. Socio-economic data as well as farmers’ estimation
of genetic erosion were collected in the study area, the Ucayali region of the Peruvian Amazon, through interviews with 285
cassava farmers in 50 communities, while diversity was assessed based on agromorphological characterization of 295 cassava
accessions. Using multivariate regression analyses, 50 and 45% of the variation in respectively diversity and genetic erosion
estimation could be explained by a selected set of socio-economic and environmental indicators. In both regression models
four out of the total of 38 variables proved to contribute significantly (at p < 0.10 level). Additionally, the study revealed that farmers are a good direct source of information on the diversity present
at community level, which can contribute to the development of methodologies to assess diversity more rapidly. The results
of this study are valuable for the development of models to rapidly assess diversity dynamics in large areas. 相似文献