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961.
Two wide hybrids, Diplotaxis erucoides (2n = 14) × Brassica rapa (2n = 20) and B. maurorum (2n = 20) × B. rapa, were developed using the sequential ovary–ovule culture. Reciprocal crosses failed, possibly as a consequence of strong
unilateral incompatibility. The F
1 hybrids in each combination were completely male sterile and morphologically intermediate to the respective parents. DNA
marker polymorphism and chromosome counts confirmed their hybrid nature. High frequency of bivalents in the F
1 and the presence of trivalents/quadrivalents in the derived amphiploids suggested genomic duplications and homoeology of the
parental genomes. Up to three homoeologous pairs between the D. erucoides (DeDe) and B. rapa (AA) genomes, and one between B. maurorum (BmBm) and B. rapa genomes were observed. Successful synthesis of the F
1 hybrids and amphiploids of B. rapa with D. erucoides and B. maurorum, and allosyndetic chromosome pairing are expected to permit introgressions of desirable loci into the cultivated Brassica
germplasm, especially for resistance to Alternaria
brassicae and Albugo candida. 相似文献
962.
Eddy covariance (EC) systems are being used to assess the accuracy of remote sensing methods in mapping surface sensible and
latent heat fluxes and evapotranspiration (ET) from local to regional scales, and in crop coefficient development. Therefore,
the objective was to evaluate the accuracy of EC systems in measuring sensible heat (H) and latent heat (LE) fluxes. For this
purpose, two EC systems were installed near large monolithic weighing lysimeters, on irrigated cotton fields in the Texas
High Plains, during the months of June and July 2008. Sensible and latent heat fluxes were underestimated with an average
error of about 30%. Most of the errors were from nocturnal measurements. Energy balance (EB) closure was 73.2–78.0% for daytime
fluxes. Thus, daylight fluxes were adjusted for lack of EB closure using the Bowen ratio/preservation of energy principle,
which improved the resulting EC heat flux agreement with lysimetric values. Further adjustments to EC-based ET included nighttime
ET (composite) incorporation, and the use of ‘heat flux source area’ (footprint) functions to compensate ET when the footprint
expanded beyond the crop field boundary. As a result, ET values remarkably matched lysimetric ET values, with a ‘mean bias
error ± root mean square error’ of −0.03 ± 0.5 mm day−1 (or −0.6 ± 10.2%). 相似文献
963.
964.
Conservation strategies should be based on a solid understanding of processes underlying species response to landscape change.
In forests fragmented by agriculture, elevated nest predation rates have been reported in many forest bird species, especially
near edges. In intensively-managed forest landscapes, timber harvesting might also be associated with negative edge effects
or broader “context” effects on some species when the matrix provides additional resources to their major nest predators.
In this study, we hypothesized that proximity to a forest edge and proportion of cone-producing plantations will increase
nest predation risk in fragments of relatively undisturbed forest. We focused on the Brown Creeper (Certhia americana), an indicator species of late-seral forests. We compared habitat configuration and composition at four spatial scales (0.14,
0.5, 1 and 2 km) around 54 nests and related daily nest survival rate to the distance to the nearest forest edge, mean patch
size of late-seral forest (r = 141 m), proportion of non-forested lands (r = 141 m), density of maintained roads (r = 1 km), proportion of cone-producing spruce plantations (r = 2 km), and year. The best model included distance to the nearest edge and proportion of cone-producing plantations. Distance
of nests to the nearest edge was the best individual predictor of daily nest survival. A larger sample of nests showed a significant
threshold in distance to the nearest forest edge; nests located at least 100 m away were more likely to fledge young. These
results suggest that even in managed forest landscapes, matrix effects can be important and some bird species may exhibit
negative edge effects. 相似文献
965.
Neutral models for testing landscape hypotheses 总被引:5,自引:0,他引:5
Neutral landscape models were originally developed to test the hypothesis that human-induced fragmentation produces patterns
distinctly different from those associated with random processes. Other uses for neutral models have become apparent, including
the development and testing of landscape metrics to characterize landscape pattern. Although metric development proved to
be significant, the focus on metrics obscured the need for iterative hypothesis testing fundamental to the advancement of
the discipline. We present here an example of an alternative neutral model and hypothesis designed to relate the process of
landscape change to observed landscape patterns. The methods and program, QRULE, are described and options for statistical
testing outlined. The results show that human fragmentation of landscapes results in a non-random association of land-cover
types that can be describe by simple statistical methods. Options for additional landscape studies are discussed and access
to QRULE described in the hope that these methods will be employed to advance our understanding of the processes that affect
the structure and function in human dominated landscapes. 相似文献
966.
Zhi-Wei Wang Lei Gao Hai Zhou Liu Shi Yong Mei Yuan Zhou Chang Ping Xiang Ting Wang 《Euphytica》2012,186(2):313-320
A male sterile plant appeared in the radish breeding program at the Hubei Academy of Agricultural Sciences, Hubei, China.
In its progeny, a two-type (half of plants male sterile, the other half male fertile) line 01GAB was established. An F2 population of 260 plants from a cross of male-sterile 01GAB and a male fertile line 9802H segregated for male fertility in
a 3:1 ratio indicating that fertility was restored by a single dominant gene, here designated RsMs. A PCR-based DNA marker specific to the male fertility Rfob gene in 9802H was absent in 01GAB. Linkage analysis placed the RsMs locus 10.7 cM away from the Rfo locus. In an F2 population of hybrids between 01GAB and male fertile 9802B, a co-dominant DNA marker for the RSultr3.2A (a radish sulfate transporter gene) locus was linked to the RsMs locus at 1.5 cM suggesting that fertility restoration in 01GAB was located in the region with known male sterility restorers
in radish. However, no maintainer for the 01GAB source of male sterility has been identified so far. Cytological observations
have shown that the abnormalities in male sterile anthers first appeared in tapetum at the tetrad stage, followed by a hypertrophy
of the tapetal cells at the vacuolate microspore period. These results suggest that male sterility in 01GAB is likely to be
genetic in nature, or it may represent a new type of the cytoplasmic male sterility. 相似文献
967.
M. Paula Sotelano Gustavo A. Lovrich Federico Tapella 《Aquaculture International》2016,24(4):1025-1037
Losses of king crabs (deaths) in massive rearing conditions are frequently attributed to cannibalism. As several factors could influence cannibalism intensity during culture, the aim of the present study was to determine the effect of molt condition, stage and density on cannibalism among Lithodes santolla juveniles. Comparisons between intermolt and molt conditions and between C1 and C2 stages during intermolt were performed at three densities (6, 12 and 18 individuals per flask; that is equivalent to 236, 472 and 708 individuals m?2). After 16 days of juvenile coexistence, cannibalism (injured + dead) was higher during molting (33.9 ± 4.5 %) than intermolt (21.7 ± 3.9 %), even though only 36 % of crabs had molted. Although cannibalism was similar in C1 and C2 stages, the proportion of dead animals was higher by a factor of three in C1 stage, probably due to the fact that animals reach the first juvenile stage with low energetic reserves, after the lecithotrophic larval development. Density was the main factor influencing cannibalism in our experiments. Higher densities promoted higher deaths, while agonistic interactions evidenced by injured crabs remained constant. Walking appendages were lost more often than chelipeds during first agonistic encounters. We recommend the use of intermediate densities (450 crabs m?2 at most), the early detection of exuviae and the sorting of crabs after molting, for L. santolla rearing. 相似文献
968.
Effects of seasonal and environmental changes on aquaculture production in tropical Lake Volta,Ghana
Emmanuel T. D. Mensah Hederick R. Dankwa Lauridsen L. Torben Ruby Asmah Benjamin B. Campion Regina Edziyie 《Aquaculture International》2018,26(6):1387-1400
Globally, aquaculture production is faced with numerous challenges, notable among which is water quality. The study determined seasonal environmental changes in Lake Volta and its implications on cage production of Nile tilapia, Oreochromis niloticus in experimental and commercial farm (Sun Woo Farm) set-ups. For each set-up, three cages were used, each measuring 81 and 162.5 m3 for experimental and commercial, respectively. The cages were stocked with 22.5 g fingerlings at a rate of 40 and 80 m?3 in experimental and commercial cages, respectively, and fed commercial diet. The growth performance, yield, economics, and selected water quality parameters were monitored during the dry and wet seasons between November 2014 and July 2015. There were no differences in water quality parameters between dry and wet seasons (p?>?0.05). Water quality for both seasons remained within limits required for good Tilapia growth in both set-ups. There were minimal variations in growth characteristics between seasons which were not significant; however, final mean weight and yields were high in the dry seasons in both set-ups. The cost of feed and fingerling accounting for about 80% of total costs were the major components identified to affect cost of production. A higher profit index and returns on investment were observed in the dry season in both set-ups and was linked to higher survival rates in the season. Production of Nile tilapia in cages can be cultured throughout the year without any adverse effects as exhibited in similar production patterns in both experimental and commercial set-ups. 相似文献
969.
Wim Verbeke Isabelle Sioen Karen Brunsø Stefaan De Henauw John Van Camp 《Aquaculture International》2007,15(2):121-136
The increasing number of marketable fish being supplied from aquaculture is a response to the increasing demand for healthy
food and is filling the gap left by depleting natural fish stocks. Little is known about the awareness and perception of the
consumer in terms of farmed fish versus fish from capture fisheries. The consumer's subjective point of view is of overriding
importance for the production system and product acceptance as well as for future market success. In this paper consumer perception
in Belgium is explored and compared against scientific evidence of farmed versus wild fish. Primary data were collected through
a consumer survey (April 2003) and focus group discussions (May 2004) with Belgian consumers. The majority of the consumer
sample reported no perceived differences between farmed versus wild fish. However, mean perception scores were slightly in
favour of wild fish on the attributes taste, health and nutritious value, in particular among consumers aged 55 years and
older. The availability of farmed fish was perceived to be better than that of wild fish, while the consumer's perception
of safety did not differ between farmed and wild fish. The focus group discussions indicated that consumers’ opinions and
beliefs about farmed fish are mainly based on emotion and image transfer from intensive terrestrial livestock production rather
than on awareness and factual knowledge of aquaculture.
相似文献
John Van CampEmail: |
970.
In contrast to schooling behavior in fish, which is well documented, the schooling behavior of an evolutionary counterpart,
squid, has not been adequately described in the literature. In the current study, we investigated the ontogeny of schooling
behavior in the oval squid Sepioteuthis lessoniana reared from hatching to about two months of age. During the two months of development, the distance and angle between nearest-neighbor
individuals decreased from 5.3 mantle lengths (ML) to 1.8 ML and from 42.7° to 24.2°, respectively. In addition, the swimming
distance of individuals in experimental duration decreased from 530.4 to 79.9 ML, and the relative swimming speed also decreased
from 17.1 to 4.6 ML/s during the same period, with increasing synchronized hovering of individuals. These observations clearly
suggest that oval squid swim randomly until 20 days after hatching, then form a school 30–60 days after hatching with an inter-individual
distance of 2.0 ML. At two months after hatching, oval squid individuals swam in a parallel orientation and formed a belt-shaped
arrangement, similar to the adult schooling behavior observed in natural populations. 相似文献