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排序方式: 共有1334条查询结果,搜索用时 31 毫秒
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中国水果供给结构性变化的实证研究 总被引:1,自引:0,他引:1
为分析中国水果供给的结构性变化,本文构造中国水果的供给模型,将1978-2001年24年划分为两个时期,利用Chow检验分别回归后发现我国水果供给的各种弹性均发生了明显的结构性变化,从而得出果农对价格的反应能力和敏感性增强、对农资投入的依赖性增强等重要结论。 相似文献
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Atsushi NAKAMURA Kenji TOGASHI Naoyuki YAMAMOTO Akiko NISHIURA 《Animal Science Journal》2002,73(3):175-184
In order to control rates of response and inbreeding, mate selection using fuzzy selective mating criteria (FMC) was investigated in adult multiple ovulation and embryo transfer nucleus schemes for dairy cattle. Stochastic simulation was used to model the closed nucleus scheme. This mate selection was examined in four alternative mating and male selection schemes: (i) a hierarchical scheme; (ii) a hierarchical sibship scheme (two males per sibship); (iii) a factorial scheme (two sires per dam); and (iv) a factorial sibship scheme (two males per sibship and two sires per dam). Genetic response and inbreeding rate tended to be reduced by increasing the trade-off parameter of FMC between the expected breeding value and inbreeding of progeny. Inbreeding rates in all schemes were reduced by reducing the variance of family size through selection and the average coancestry of mating pairs through mate allocation. 相似文献
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After about 25 years of intensive research a substantial moment of information has accumulated on the basic biology of Prostephanus truncatus in stored products. This article reviews the literature on the geographical distribution, biotypes, symbiotic associations, mating and flight behaviour, oviposition, and development on both agricultural and non-agricultural hosts. The current knowledge about the nutritional biology (including the role of symbionts) and host finding behaviour (including the inter-linked roles of plant chemicals and the insect's own pheronones) are highlighted as research areas which deserve future attention. In addition, few studies have been conducted to determine the extent to which the biology of P. truncatus permits it to survive and reproduce in non-agricultural environments. These areas of study should be pursued as possible routes to providing more effective integrated pest managements strategies for the larger grain borer. 相似文献
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To determine the potential of sexual reproduction among host-adapted populations of Phytophthora infestans sensu lato in Ecuador, 13 A1 isolates belonging to clonal lineages US-1, EC-1 and EC-3, and 11 A2 isolates belonging to the clonal lineage EC-2, were paired on agar plates to induce crossing. In the first experiment, six A1 isolates (three US-1, two EC-1 and one EC-3) were each crossed with three A2 isolates (total = 18 crosses). Matings involving isolates of the EC-1 lineage produced more oospores of healthy appearance than did matings with isolates of US-1 or EC-3. In the second experiment, the oospores of 35 crosses (21 EC-1 × EC-2; 10 US-1 × EC-2; four EC-3 × EC-2) were dispersed on water agar to assess oospore germination. Overall, germination percentages were low. Only one cross produced enough progeny for evaluation. Twenty-three single-oospore offspring were isolated and evaluated for mating type; electrophoretic patterns of glucose-6-phosphate isomerase ( Gpi ) and peptidase ( Pep ) alloenzyme loci; mitochondrial DNA haplotype; and genomic DNA fingerprint. Multilocus genotype data indicated that all 23 isolates resulted from meiotic recombination. Four progeny with homothallic phenotype appeared to be unstable heterokaryons. Markers at several loci segregated according to simple Mendelian expectations for a diploid organism, but the ratios of three RFLP loci and the Pep locus were not consistent with Mendelian expectations. All progeny were nonpathogenic on hosts of the parental genotypes. Reduced mating success and reduced pathogenic fitness of progeny appear to be postmating mechanisms of reproductive isolation in populations of P. infestans sensu lato in Ecuador. 相似文献
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云南省马铃薯晚疫病菌的交配型、抗药性及生理小种分布的研究 总被引:17,自引:2,他引:17
从云南省陆良县、建水县和南涧县采集2000年秋播的马铃薯晚疫病标本,分离获得124个致病疫霉菌株,连同1999~2000年分离自昆明、曲靖等地的春播马铃薯晚疫病的10个菌株共134个,采用常规技术对这些菌株进行了交配型、抗药性及生理小种的研究。交配型测定结果为:陆良县的18个菌株中有3个为A2交配型,其余15个菌株为A1交配型,建水县和南涧县的106个菌株及昆明、曲靖1999~2000年的10个菌株都是A1交配型。测定了83个菌株对瑞毒霉(metalaxyl)和烯酰吗啉(dimethomorph)的抗药性,结果有12.0%的菌株对瑞毒霉表现抗性,16.9%表现中抗,71.1%表现敏感,其中陆良、昆明和曲靖的抗瑞毒霉菌株的比例大于建水和南涧的抗药性菌株的比例;所测定的83个菌株都对烯酰吗啉表现敏感。生理小种鉴定结果表明,云南晚疫病菌为3.4、0、3和4生理小种,分别占鉴定菌株总数的48.0%、32.5%、15.6%和3.9%。但南涧仅发现3.4和0小种,而昆明有0、3、3.4和4小种,陆良有0、3和3.4小种,可见昆明和陆良地区的晚疫病菌生理小种比南涧地区的生理小种的组成更趋多样。 相似文献
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桑叶养猪实用技术分为桑树种植技术和桑叶干粉发酵养猪技术两个部分。利用荒地种植桑树,降低生猪养殖饲养成本,桑叶养猪种养结合,成为生态农业典范。桑叶干粉发酵技术,提高了桑叶干粉的可消化率和饲料功能。桑叶干粉发酵料占配方6%~10%,做成桑叶猪饲料,替代3%~5%鱼粉、豆粕等蛋白质饲料,节约了饲料成本。桑叶喂养猪(简称桑叶猪,下同)的猪肉中含有肌苷酸等风味物质,显著提高猪肉胴体品质和猪肉风味。设计猪尿处理,采用红泥膜沼气池降解工程工艺应用后,降解水兑2倍清水对桑树喷灌工艺,减少人工处理劳力和成本费用。设计10%抗非洲猪瘟中药饲料添加剂+桑叶饲料,预期防治非洲猪瘟总效果85%以上。桑叶养猪实用技术可行,供同行参考。 相似文献