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91.
92.
传统上 ,孵化机都是设计成机内各处都保持均匀一致的温度。为使现代高产肉鸡的孵化能够取得最佳结果 ,这一概念有其局限性 相似文献
93.
Pigs infected with an African swine fever field isolate of modified virulence became acutely thrombocytopenic four to five days after the onset of fever and viremia. By eight days after inoculation, all pigs were thrombocytopenic. Immunofluorescence microscopy demonstrated that 2 to 10% of the megakaryocytes were infected. By 13 days after inoculation, platelet counts returned to within normal limits, and there was megakaryocytic hyperplasia despite a continued viremia. Secondary complications delayed the return of normal circulating platelet levels in some pigs. The clinical findings of African swine fever are discussed in light of the gross and histologic lesions. 相似文献
94.
95.
Summary Four varieties of lupins were sown at three planting dates and the level of Phomopsis leptostromiformis measured on the mature stems. When averaged over planting dates the varieties did not differ in resistance to this disease, however there were highly significant interactions between varieties and planting dates for level of disease. The implications of this result for resistance breeding to Phomopsis leptostromiformis are discussed. 相似文献
96.
M. Santalla M. Lema A. P. Rodiño A. M. González A. B. Monteagudo A. M. De Ron 《Euphytica》2005,142(1-2):85-95
Approaches are needed to broaden the genetic base and improve earliness and yield potential of large-seeded beans under sustainable cropping systems. The objective of this research was to develop adapted dwarf bean populations having a commercial seed quality and yield suitable for the production in the South of Europe. The original base populations were produced from crosses between genotypes within each Mesoamerica, Nueva Granada and Peru races, and between Peru and Nueva Granada, and Mesoamerica and Nueva Granada races. Visual mass selection for plant performance was practised in the F2 and F3 generations. In the F4 and F5, single plants were harvested under two cropping systems (sole cropping and intercropping with maize). From F4, selection was based on precocity, combined with seed yield and seed commercial type. The F4:7 selected lines from each original population were compared with their parents and five checks at four environments and two cropping systems. Differences among environments, populations, parents and checks were observed for all traits. Under intercropping with maize, there was a 50% reduction in seed yield. Yield of parents and checks belonging to Andean South American races, intraracial (Nueva Granada × Nueva Granada) and interracial (Nueva Granada × Peru) populations, was higher than that of those of Middle American origin. Intraracial crosses within large-seeded Andean South American (Peru race) and Middle American gene pools (Mesoamerica race) did not produce lines yielding more than the highest yielding parent. Only two large-seeded lines selected from crosses between small- and large-seeded gene pools out-yielded the best parent and check cultivar. 相似文献
97.
Summary Narrow-leafed lupin or lupine (Lupinus angustifolius L.) is one of the three species of the genus Lupinus that grows naturally in Galicia (northwestern Spain). In this region, with more than one million of cattle heads, almost
20% of Spanish total, there is no cultivation of any protein legume for feed. Lupins are widely used as a source of protein
and energy in livestock feed and would contribute to the supply of vegetable protein at low cost. A 2-year study of natural
narrow-leafed lupin germplasm was conducted under winter Mediterranean conditions in northwestern Spain. Fifty-nine wild populations
and two cultivars developed in Poland were evaluated for major morphological, phenological, and agronomical characteristics.
The objectives were to assess the agronomic potential of this germplasm for the future production and breeding, and to know
the relationships among populations studied. Lupin populations showed significant differences for most of the traits studied.
Genotype × environment interaction was significant for plant height, green and dry mass, pod length, seeds per pod, seed length
and width, and water permeability of seed coat, indicating that some genotypes were better fitted to a specific environment
than others.
Three narrow-leafed lupin populations (LUP-0098, LUP-0138 and LUP-0200) were identified with suitable agronomical characteristics
for their possible future cultivation in the region and breeding purposes. The accession LUP-0138 presented the best behaviour
for seed production. These results open the way for the winter narrow-leafed lupin to become a promising crop in the future
for the northwestern Spain. 相似文献
98.
Summary Powdery mildew development was assessed on squash (Cucurbita pepo) plants of a susceptible cultivar, a resistant accession, their F1, and their F2 in an early summer planting in the field, covered or not covered with a shading net. Three reaction types were observed: susceptible, powdery mildew on stems and on both, the upper and lower leaf surfaces, as in the susceptible parent; resistant, no powdery mildew on leaves or stems, as in the resistant parent; and partially resistant, powdery mildew on upper leaf surfaces only, as in the F1. Disease presence on the stem was associated with susceptibility. Shading hastened the appearance of powdery mildew and increased the severity of infection on partially resistant and susceptible plants, facilitating identification of resistant individuals in the F2 population.Contribution No. 1613-E from the Agricultural Research Organization, Bet Dagan, Israel 相似文献
99.
Relationships among American and Spanish populations of maize 总被引:1,自引:0,他引:1
Summary Two experiments were carried out with two objectives. First, to establish the phenetic relationships among the maize (Zea mays L.) landraces from Galicia (Northwestern Spain) maintained at the Misión Biológica de Galicia. Second, to assess the resemblance between a collection of Spanish populations (including the landraces from Galicia) and a set of US Corn Belt varieties. For the first objective 73 varieties from Galicia, along with 9 hybrid checks, were grown in 9×9 simple lattices at two locations for two years. For the second objective 131 populations from the US Corn Belt and Spain, along with 9 hybrid checks, were grown for three years in unreplicated experiments. Cluster analyses were carried out with the first principal components that accounted for a significant amount of the total variation. Four groups were found among the landraces from Galicia. The populations from Spain and America were classified as belonging to nine main groups. The replicated experiment was more accurate than the unreplicated one. However, it is concluded that an unreplicated test grown in several environments is accurate enough to detect the main groups, although some inaccuracies should be expected. 相似文献
100.
Fifty sloping fields of barley with different short-term cropping histories across Prince Edward Island were examined for variations in root-zone depth and the severity of soil parasitic nematodes as part of a wider study of relationships between cropping sequence, topographic position, soil physical conditions and crop performance. Root lesion nematode (Pratylenchus penetrans) density in the roots was significantly greater (13%) at foot slopes than at top slopes, and stunt nematode (Tylenchorhynchus spp.) was significantly greater (8%) at top slopes where the soil was drier. The density of stunt nematodes and root lesion nematodes in the soil was significantly greater (>15%) under miscellaneous cereals-barley sequences than under potato-barley or hay-barley, attributable to level of carryover. Root lesion nematode density in the roots was significantly greater (12%) under hay-barley than either of the other two sequences. This nematode also showed a strong tendency to increase in number with increasing root-zone depth, and may be explained on the basis that increased root-zone depth provides increased host root mass (substrate). Stunt nematodes, on the other hand, increased with decreasing root-zone depth and may be explained by the known propensity of these organisms for drier, shallower soil conditions. 相似文献