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91.
In the province of Bolívar in the Andean region 212 farmers, six salesmen and 14 technicians, involved in maize production,
were interviewed. The majority of the farmers interviewed were small-holders; 64% of the farmers had a farm size of less than
4.5 ha. Maize is the most important crop and is often grown in association with beans. Most maize, 96%, is soft maize meant
for human consumption. The cultivars grown are open pollinated ones. One cultivar, ‘Guagal’, was grown extensively. A few others, among which an improved version of Guagal were of some importance. In the production
of maize the farmers consider damage due to insects, wind (lodging), diseases, drought and hail, the low prices for their
surplus maize and the high costs of fertilizers, chemicals, sowing seed and labour as the most important constraints. The
seed for sowing the next crop mainly came from seed kept from the last harvest. Farmers indicated that they select from the
harvested ears the healthy looking larger ones. Kernel type also was a selection criterion. Selection for plant type in the
field was rarely done. Of the farmers 71% stored the maize as kernels while 29% stored the seed kept on the ears. The storage
was predominantly done somewhere in the house in plastic (56%) or cloth bags (14%), in a pile (13%), just on the floor (4%)
or in cans (4%). Some farmers still had seed left from the last sowing and were willing to give a sample for testing. From
32 such samples the quality was assessed by INIAP, the Ecuadorean governmental research and breeding organisation. The samples
were consistently of a low quality. Especially the vigour of the seedlings was poor and most of the seeds were infected or
contaminated by fungi. In the region a few salesmen offer maize seed for sale of cultivar Guagal at prices affordable by the
farmer. Of improved cultivars the prices were higher than most farmers are willing to pay. The technicians considered good
seed quality and good maintenance of the cultivars effective methods in obtaining better yields. Many farmers do not have
access to seed of INIAP and are not familiar with the improved cultivars. 相似文献
92.
93.
The use of grain protein deviation for identifying wheat cultivars with high grain protein concentration and yield 总被引:2,自引:0,他引:2
James M. Monaghan John W. Snape A. Jan S. Chojecki Peter S. Kettlewell 《Euphytica》2001,122(2):309-317
The relationship between grain protein concentration and grain yield in different cultivars of winter wheat was examined in
a series of field experiments carried out over three years, in which 13, 12 and 8 cultivars were studied in each year, respectively.
The plants were grown at sites located in Shropshire, west-central England, in years 1 and 2, and at three other locations
in eastern England in year 3. Above ground plant samples were collected at an thesis and again at maturity, when they were
separated into grain and straw, and analysed for dry matter and N content. Analysis of residuals from regression of grain
protein concentration on grain yield (grain protein deviation, GPD) showed that some cultivars had a higher grain protein
concentration than was predicted from grain yield alone. It was deduced that the capacity to accumulate a higher grain protein
concentration than predicted from grain yield is under genetic control and thus may be improved through breeding. Other factors
(weight of N accumulated in the biomass at anthesis, weight of N accumulated in the biomass between anthesis and maturity
and the concentration of N remaining in the straw at maturity) were added step-wise into the regression to enable statistical
analysis of their relative contributions to grain protein. High GPD may be achieved through increased N accumulation after
anthesis, combined with efficient re-translocation of vegetative N reserves. The use of GPD provides a selection criteria
in wheat breeding programs to screen for increased grain protein concentration without a concurrent grain yield reduction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
94.
The aim of this paper is to challenge the characterization of paid informal work as a form of employment based on exploitative relations that should be eradicated. Using empirical evidence gathered through structured interviews with 511 households in deprived and affluent neighborhoods in British cities, this paper reveals that paid informal work in deprived areas is mostly conducted for kin, neighbors, and friends for co‐operative reasons and is thus more like unpaid community exchange in the private sphere than exploitative employment. In consequence, the challenge for social and labor market policy is argued to be not to try to eradicate such work but to harness it in these deprived urban neighborhoods. 相似文献
95.
Jan Rouwendal 《Growth and change》2004,35(3):391-418
ABSTRACT This paper argues that search theory is a useful addition to the way economists and geographers have approached the study of commuting behavior. This is illustrated by showing that introduction of a spatial element into the standard model of job search leads to the prediction of critical isochrones. Moreover, in the context of an urban economy with decentralized employment, the spatial search model predicts excess commuting. Search theory also suggests that regression toward the mean may play a confusing role in data describing the development of commutes over time, such as has been used in recent empirical work. Finally, the paper develops a simple spatial equilibrium search model in which employers set their wages optimally and searchers determine their reservation wages optimally in mutually consistent ways. The spatial element is crucial for the existence of such an equilibrium in which reservation wages of all searchers and wages set by all employers are identical. 相似文献
96.
In order to reveal the molecular genetic diversity of wheat wild relatives, an AFLP analysis was conducted with 16 accessions
of five Triticum andAegilops species originating from the Near East. Variation within population was studied with at least seven individuals per accession.
Four primer combinations were used for selective amplification. Based on the scored bands, we estimated percentage of polymorphic
bands, 1 – proportion of shared bands (1-psb) and nucleotide diversity (π). Of the five species used in this study, Ae.
speltoides had the highest level of `within population' variation. This species had also the highest value of the variation among populations.
As for Triticum species, the level of variation within population was low in diploid species (T. urartu and T. boeoticum),whereas two tetraploid species (T. dicoccoides and T. araraticum) had relatively high levels of variation within population. While the two diploid Triticum indicated a clear interspecific divergence, the two tetraploid wild wheats were not clearly divergent in this study. The
variance portioning analysis indicated that the variation detected for diploid Triticum species was mainly composed of `between species' variation, on the other hand that for tetraploid Triticum was mostly composed of `within population' variation. In conclusion, AFLP analysis reveals molecular variation in all accessions
used in this study, suggesting a potential genetic diversity of the wheat wild relatives in natural populations. These results
have implications for the design of strategies to maintain genetic diversity within genebank collections.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
97.
中国水稻白叶枯病菌系染色体DNA的RFLP谱型的初析 总被引:5,自引:0,他引:5
用2个DNA探针pJEL101和pBASavrXa10对78个水稻白叶枯病菌系进行RFLP分型,以分析其群体结构和遗传多样性。分别鉴定出16种RFLP标记带的谱型。以彼此的带位相似率达85%为界,可分为簇。参试菌系的群体遗传多样性为0.77(用pJEL101),和0.83RFLP谱型分析表明:我国多数病原型为杂合组群。白叶枯病菌系的分子表现型的变异,远远大于致病型,两个探针都能有效分析我国菌系的群 相似文献
98.
The residual effect of 2-year-old swards of clover-ryegrass mixture and ryegrass in monoculture on yield and N uptake in a subsequent winter wheat crop was investigated by use of the 15N dilution method and by mathematical modelling. The amount of N in the wheat crop, derived from clover-ryegrass residues was 25–43% greater than that derived from residues of ryegrass which had been growing in monoculture. Expressed in absolute values, the N uptake in the subsequent winter wheat crop was 23–28 kg N ha −1 greater after clover-ryegrass mixture than after ryegrass in monoculture. Up to about 54 kg N ha−1 of the N mineralised from the clover-ryegrass crop was calculated to be leached, whereas only 11 kg N ha−1 was leached following ryegrass in monoculture. 相似文献
99.
Growth and photosynthetic performance were analyzed in alloplasmic tomato at a high- (25/17 °C; HTR) and low-temperature regime (12/6 °C; LTR) in order to establish the role of cytoplasmic variation on low-temperature tolerance of tomato (Lycopersicon esculentum Mill.). Four alloplasmic tomato lines, containing the nuclear genome of tomato and the plastome of L. hirsutum LA 1777 Humb. & Bonpl., an accession collected at high-altitude in Peru, were reciprocally crossed with 11 tomato entries
with a high inbreeding level and a wide genetic variation, resulting in a set of 44 reciprocal crosses. Irrespective of growth
temperature, alloplasmic families with alien chloroplasts of L. hirsutum (h) were on average characterized by a high shoot biomass, a large leaf area, and a low specific leaf area in comparison with
their euplasmic counterparts. These results do not directly point to an advantageous effect of h-chloroplasts on biomass accumulation at low temperature but rather towards a small general beneficial effect on growth and/or
distribution of assimilates. Significant chloroplast-related differences in photosynthetic performance, however, were not
detected at both temperature regimes, indicating that h-chloroplasts can properly function in a variable nuclear background of L. esculentum. It is concluded that chloroplast substitution is not an effective method for breeding tomato plants with improved low-temperature
tolerance.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
100.
Anna Pretova Norbert C.A. de Ruijter André A.M. van Lammeren Jan H.N. Schel 《Euphytica》1992,65(1):61-69
Summary The capacity of the maize genotype 4c1 to regenerate microcalli and embryos from cultured microspores has been examined by comparing various cold pretreatments and culture media, using microspores and pollen at different stages of development. Viability of cultured cells was tested with FDA and their development was traced with light and fluorescence microscopy using DAPI as a nuclear dye.It was found that a pre-incubation of dissected flowers floating in a liquid nutrient medium at 8°C during 10–14 days was most successful for the induction of cell division. Among the developmental stages tested only the microspores appeared to regenerate. Subculture at 25°C in the same liquid medium, supplemented with 0.1 mg/l TIBA, gave highest rates of microspore division, i.e. up to 70% at 4 to 6 days of culture.All pathways described earlier for maize androgenic embryogenesis were observed within the 4c1 genotype. Symmetric divisions occurred in cultured microspores but most frequently asymmetric divisions lead to the formation of microcalli within 12 days of culture. In at least 60% of all dividing microspores cells were derived from the generative nucleus. Microcalli further developed either into loose or compact calli. Compact calli formed embryo-like structures.Abbreviations DAPI
4,6-diamidino-2-phenylindole
- Dicamba
3,6-dichloro-2-methoxy benzoic acid
- 2,4D
2,4 dichlorophenoxyacetic acid
- FDA
fluorescein diacetate
- PAA
phenylacetic acid
- TIBA
2,3,5-triiodobenzoic acid
- YP medium
Yu-Pei basal salt medium 相似文献