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981.
农业网络资源的开发与利用 总被引:1,自引:0,他引:1
本文阐述了开发利用网上农业信息资源的重要意义,并对开发利用的方法与途径进行了探讨。 相似文献
982.
Reyes Tárrega Leonor Calvo Ángela Taboada Elena Marcos José Antonio Marcos 《European Journal of Forest Research》2011,130(6):949-957
We compared the structure of the arboreal layer and the diversity and species composition of the understory vegetation of
three types of mature forest communities: oak (Quercus pyrenaica) and beech (Fagus sylvatica) forests and Scots pine (Pinus sylvestris) plantations. Our main aim was to determine whether differences in these variables existed and were due to the identity of
the dominant tree species. We selected four stands or replicates per forest type located geographically close and with relatively
similar conditions. We found no differences in the arboreal structure of oak and beech forests, which were characterised by
great variability in tree size, while in case of plantations, this variability was lower at both the intra-stand (estimated
by the coefficient of variation) and inter-stand (i.e. the four replicates harboured trees of similar sizes) scales. However,
the highest variability in the canopy layer of natural forests was not consistently linked to greater understory species richness.
Indeed, the lowest plant species richness was found in beech forests, while oak forests harboured the highest value at either
the sampling unit (per m2) or stand scales. The greatest negative correlation between plant diversity and the environmental variables measured was
found for litter depth, which was the highest in beech forests. The results obtained by the CCA indicated that the four replicates
of each forest type clustered together, due to the presence of characteristic species. We concluded that pine plantations
did not approach the environmental conditions of native forests, as plantations were characterised by singular understory
species composition and low arboreal layer variability, compared to natural woodlands. 相似文献
983.
984.
Xiaojie Wang Wenming Zheng Heinrich Buchenauer Jie Zhao Qingmei Han Lili Huang Zhensheng Kang 《European journal of plant pathology / European Foundation for Plant Pathology》2008,120(3):241-247
Stripe rust of wheat caused by Puccinia striiformis f. sp. tritici is one of the most important diseases on wheat worldwide, especially in temperate regions with cool moist weather conditions.
A rapid and reliable detection of the pathogen in latent infected wheat leaves during overwintering of the fungus in the dormant
stage will contribute to determine the initial inoculum potential and thus to predict early outbreak and to improve effective
management of the disease. To achieve this aim, a PCR-based method was developed for specific and sensitive detection of P. striiformis. Specific primers were designed according to a genome-specific sequence of P. striiformis. To evaluate the specificity of the primers, seven different isolates and races of P. striiformis as well as six other pathogens of wheat were tested. All isolates of P. striiformis yielded a distinct band of a fragment of 470 bp, while using DNA of the other wheat pathogens as a template no amplification
product was detected. The sensitivity of the primers was tested using serial dilutions of total DNA from P. striiformis; the limit of detection was 10 pg of DNA. Using extracts from P. striiformis-infected wheat leaves, the fungus could be determined in the leaves before symptoms appeared. The stripe rust could also
be detected in the dormant stage by the PCR assay in samples of wheat leaves taken during the winter season. The application
of the PCR assay may be useful for rapid and reliable detection of P. striiformis in latent infected leaves of overwintering wheat plants. 相似文献
985.
Epizootic hemorrhagic disease virus (EHDV) is a vector-borne disease of ruminants disseminated in the tropic and subtropic
zone of the world. Gazella subgutturosa subgutturosa (goitered gazelle) is native species of Anatolia. Due to risk of extinction, captured gazelles have been taken under protection
in a restricted area at Ceylanpinar state farm. In this study, the presence of EHDV was investigated serologically in 82 goitered
gazelle and 399 cattle. Seropositivity rates in goitered gazelle and cattle were detected as 2.43% and 3.50%, respectively. 相似文献
986.
Faba bean (Vicia faba L.) has high utility as a food and soil fertility improving crop. One of the major fungal pathogens of faba bean is Botrytis fabae, the causative agent of chocolate spot. The disease affects significantly the leaf, stem, pod and seed of faba bean compromise its productivity in the smallholder farming sector. Nonetheless, there are limited resistant/tolerant faba bean varieties available and disease control technology options. Therefore, it was prudent to evaluate faba bean landraces for chocolate spot resistance. Fifty landraces together with ten improved varieties were evaluated both in the field and in the greenhouse under natural and artificial inoculation with previously selected aggressive Botrytis fabae isolate (Iso-016) from West Gojjam, in Ethiopia. There were highly significant differences (p?<?0.001) among the landraces for reaction to the disease and agronomic traits. Significant positive correlation was recorded between reaction of genotypes in the field and greenhouse disease data. The overall mean disease epidemics varied from 92.5 to 697.5 for the area under disease progress curve (AUDPC). The highest level of resistance was found in the ICARDA lines, ILB-4726, ILB-938 and BPL-710. Of all 18 landrace collections displayed significantly lower disease reaction than the susceptible check. However the resistance was moderate. The selected eighteen landraces will be recommended for use in breeding for chocolate resistance. Overall, resistance was highly heritable, suggesting that phenotypic selection can be exploited to improve chocolate spot resistance in faba bean varieties. 相似文献
987.
The effects of starvation on biochemical composition and gametogenesis were investigated in the Pacific oyster Crassostrea gigas. Histological analysis, combined with oocyte examination and measurements of protein, glycogen and lipid levels and RNA/DNA
ratio from gonad, adductor muscle and mantle tissue of each sex were performed. In the starved groups, C. gigas showed gonad development, but the progress was delayed during the experiment. Glycogen was the first substrate used by C. gigas for dealing with lack of food. While glycogen was rapidly consumed, protein and lipid contents decreased gradually. A decrease
in the RNA/DNA ratio in the starved groups in all the body components was found during starvation, illustrating that RNA/DNA
ratio was a valid indicator of nutritional condition in C. gigas. A significant increase in water and ash contents and a corresponding decrease in condition index were observed in the starved
groups, showing that the water and ash content and condition index were related to the usage of glycogen, lipid and protein
reserves in body composition. During starvation, energy reserves were mobilized for survival and gonad development, but spawning
was arrested. The information obtained in this study is useful for broodstock management in the Pacific oyster industry. 相似文献
988.
Ai Jin Cai-xia Lei Jing-jing Tian Jian Sun Hong Ji 《Fish physiology and biochemistry》2018,44(1):197-207
The purpose of this study was to explore the mechanism of by which docosahexaenoic acid (DHA) inhibit the accumulation of adipose tissue lipid in grass carp (Ctenopharyngodon idella). We therefore designed two semi-purified diets, namely DHA-free (control) and DHA-supplemented, and fed them to grass carp (22.19 ± 1.76 g) for 3 and 6 weeks. DHA supplementation led to a significantly lower intraperitoneal fat index (IPFI) than that in the control group by reducing the number of adipocytes but significantly higher adipocyte size (P < 0.05). In the intraperitoneal adipose tissue, the DHA-fed group showed significantly higher peroxisome proliferator-activated receptor (PPAR)γ, CCAAT enhancer-binding protein (C/EBP)α, and sterol regulatory element-binding protein (SREBP)1c mRNA expression levels at both 3 and 6 weeks (P < 0.05). However, the ratio of the expression levels of B cell leukemia 2 (Bcl-2) and Bcl-2-associated X protein (Bax) was significantly lower in the DHA-fed group than in the control group (P < 0.05), and the protein expression levels of the apoptosis-related proteins caspase 3, caspase 8, and caspase 9 were also significantly higher (P < 0.05). Overall, although DHA promotes lipid synthesis, it is more likely that DHA could suppress the lipid accumulation in adipocytes of grass carp by inducing adipocyte apoptosis. 相似文献
989.
Pablo A. Conejeros Carlos Calderón Daniela Gómez Luis Nilo Sergio H. Marshall 《Aquaculture International》2011,19(5):999-1005
As with any other intensively farmed animal species, the Atlantic salmon has been selectively bred and cross-bred to maximize
desirable traits. Selection tends to diminish genetic diversity in target populations, which among other negative effects
is hypothesized to decrease their capacity to confront a broad variety of pathogens. We have analyzed mitochondrial (mtDNA)
as well as major histocompatibility complex (MHC) DNA sequences from individuals collected from a single aquaculture cage
in southern Chile. Interestingly, only two mtDNA haplotypes were obtained; however, several different MH alleles were detected,
with divergence values that were compared with those of natural populations of salmonids. Thus, it seems evolutionary processes
responsible of keeping MH diversity in the wild managed to retain MH variability in farmed Atlantic salmon, maintaining high
immune diversity despite the generally lower levels of observed neutral genetic diversity. 相似文献
990.
Megumu Tanahashi Takashi Nakano Hajime Akamatsu Motoichiro Kodama Hiroshi Otani Kumiko Osaki-Oka 《European journal of plant pathology / European Foundation for Plant Pathology》2016,145(4):787-795
A disease caused by Alternaria alternata occurred on the leaves of European pear cultivar Le Lectier in Niigata Prefecture, Japan, and was named black spot of European pear. In conidial inoculation tests, the causal pathogen induced not only small black lesions on the leaves of European pear cultivar Le Lectier, but severe lesions on the leaves of apple cultivar Red Gold, which is susceptible to the A. alternata apple pathotype (previously called A. mali) causing Alternaria blotch of apple. Interestingly, the apple pathotype isolate showed the same pathogenicity as the European pear pathogen. HPLC analysis of the culture filtrates revealed that A. alternata causing black spot of European pear produced AM-toxin I, known as a host-specific toxin of the A. alternata apple pathotype. AM-toxin I induced veinal necrosis on leaves of Le Lectier and General Leclerc cultivars, both susceptible to the European pear pathogen, at 5?×?10?7 M and 10?6 M respectively, but did not affect leaves of resistant cultivars at 10?4 M. PCR analysis with primers that specifically amplify the AM-toxin synthetase gene detected the product of expected size in the pathogen. These results indicate that A. alternata causing black spot of European pear is identical to that causing Alternaria blotch of apple. This is the first report of European pear disease caused by the A. alternata apple pathotype. This study provides a multiplex PCR protocol, which could serve as a useful tool, for the epidemiological survey of these two diseases in European pear and apple orchards. 相似文献