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31.
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The septate gregarine Nematopsis marinus n. sp. (Apicomplexa: Cephaline) heavily infected the midgut of cultured Pacific white shrimp Litopenaeus vannamei (Boone) in Ecuador. It is morphologically similar to other species of the genera Nematopsis, but it can be distinguished from them, by having gamonts with a prominent hemispherical protomerite that contained numerous refractile granules and unusual strong gliding movement. There is evidence that shrimp acquired the infection in the ponds, as larval or postlarval stages do not showed infection. Juveniles and adult shrimp had a prevalence and intensity of infection ranging from 50% to 80% and 10 to > 5000 parasites respectively. When voided from the gut, the gregarine keep alive in seawater. This gregarine have been associated with the marine environment and there are no records of this species in low salinity waters or freshwater. Results suggest that N. marinus could have most of the life cycle of the species within the host L. vannamei. 相似文献
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E. W. M. Van Breukelen 《Euphytica》1982,31(3):585-590
Summary Pollen competition in vivo was studied by placing two pollen samples on one stigma and comparing the length of the tubes under a U.V. microscope. Comparisons involving pollen of Solanum tuberosum and S. phureja showed that 2x pollen grew faster than x pollen, both in 2x and x styles. Consequences for induction of dihaploids in S. tuberosum are discussed. 相似文献
35.
A Solatium tuberosum dihaploid that proved to be a 2n pollen producer, exhibited two types of meiotic abnormality involved in 2n pollen formation: premature cytokinesis at prophase II and parallel/tripolar spindles in meiosis II. For this reason such a dihaploid was preferentially used as a seed parent in crosses with the diploid species S. tarijense, S. sanctae-rosae, and S. phureja. Diploid interspecific hybrids were evaluated for male fertility, for 2n pollen production and stability over three years and for meiotic nuclear restitution mechanisms. Pollen stainability ranged from 6 to 85% and 2n pollen from 5 to 35% among hybrids. The meiotic mechanism generating 2n pollen was that of spindle abnormality in meiosis II and consequent dyad/triad formation. High correlation was found between fused/parallel spindles and dyads. 相似文献
36.
Transmission of resistance to common scab from the diploid to the tetraploid level via 4x-2x crosses in potatoes 总被引:1,自引:0,他引:1
Summary Diploid potato clones selected for their reaction to common scab and their ability to produce 2n male gametes were used in a series of crosses to a susceptible tetraploid female parent (cv. Shepody). In addition, two tetraploid clones were also selected for their reaction to common scab and crossed with Shepody as a female parent. Results indicated that resistance to common scab can be effectively transmitted from the diploid to the tetraploid level via 4x-2x crosses. Diploid parents producing 2n pollen via either first division or second division restitution can be used to transmit scab resistance. A relatively small proportion of resistant individuals could be recovered from susceptible x susceptible crosses in both 4x-2x and 4x-4x combinations. The data support a previously developed hypothesis that scab resistance is relatively simply inherited. 相似文献
37.
Summary The production of 2n pollen (pollen with the sporophytic chromosome number) was evaluated in 4x and 6x taxa of Vaccinium section Cyanococcus. Mean frequencies of 2n pollen producers were 17.1% and 8.3% in natural 4x and 6x populations, respectively. The frequency of 2n pollen producers in the 4x species ranged from 8.6% (V. angustifolium) to 23.8% (V. pallidum). Level of 2n pollen production was genotypically variable (1% to 37.4%). The widespread occurrence of 2n pollen in 2x, 4x and 6x taxa suggests that sexual polyploidization was widespread and responsible for the origin of the polyploid species found in this genus. The frequency of 2n pollen producers was not significantly different between the 4x species and their putative 2x ancestors. These results support the origin of 4x and 6x taxa as a consequence of sexual polyploidization. Polyploids derived from sexual polyploidization would be expected to have increased fitness and flexibility due to the mode of 2n pollen formation. In blueberry species the predominant mode of 2n pollen formation is genetically equivalent to a first division restitution mechanism (FDR). FDR 2n pollen transmits a high percentage of the heterozygosity and a large fraction of the epistasis from the 2x parent to the 4x offspring. 相似文献
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Summary Nobilization in sugarcane is viewed from a genetic angle considering the significance of 2n gametes. The inbreeding coefficients resulting from 2n gametes, for first and second nobilizations are worked out. The implication of 2n gametes to sugarcane breeding are discussed. 相似文献
39.
Summary InDactylis glomerata L. subsp.lusitanica, triploid and tetraploid plants were obtained by bilateral sexual polyploidization in crosses between diploid parents known to produce 2n gametes. The polyploid and diploid progeny were compared for allozyme diversity (allele number and heterozygosity), phenological (pollen fertility, inflorescence emergence date), cellular (stomatic cell size) and morphological characters (vegetative biomass, seed weight, total seed number per plant, panicle number and seed number per panicle length) in four contrasting growing conditions. Stomatal cell size and the total number of alleles were significantly lower in diploids than in polyploids which sometimes recovered more than two distinct alleles at a locus via 2n gametes possessing heterozygous loci. Pollen fertility was similar in diploids and tetraploids, but significantly lower in the triploids. Seed weight was significantly higher in polyploids, although the average number of seeds per panicle length and the total number of seeds was higher in the diploid sibs. No phenological differences occurred among ploidy levels whereas such differences were observed inDactylis in all the natural areas of sympatry between diploids and their related polyploids. Our results provide evidence for an instantaneous effect of polyploidization on certain traits and suggest that natural selection would act subsequently on several other traits to allow the establishment of new polyploids. 相似文献
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