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61.
The plant pathogenic single‐strand DNA‐containing geminiviruses have been the recent focus of intense investigation, owing both to their agronomic importance and to their potential as vectors for the expression of foreign genes in plants. Molecular genetic studies have provided detailed information on the genomic organization of many of these viruses. A greater genetic complexity has been demonstrated among the members of this viral family than had previously been suspected, as well as an apparently rapid rate of evolution of genetic diversity. We now recognize fundamental differences in the genome structure and organization of the whitefly‐ and leafhopper‐transmitted viruses, as well as among those geminiviruses infecting dicotyledonous or monocotyledonous hosts. This knowledge has provided new insights into the evolution of these viruses. The viral genes involved in replication and in systemic movement in the plant have been defined, and viral origins for single‐strand (ss) and double‐strand (ds) DNA replication have been mapped to small nucleotide regions. With the structural features of the viral genomes now well defined, current efforts are focused on elucidating the molecular aspects of viral gene regulation and interactions with host‐cell components that lead to the production of disease. Recent progress in determining the mechanism of replication and systemic movement and the contributions of these to symptom and disease development are discussed in the context of the potential for genetically engineering disease‐resistant plants. 相似文献
62.
The influence of prior ovipositional experience on host selection in four species of aphidiid wasps (Hymenoptera: Aphidiidae) 总被引:1,自引:0,他引:1
We evaluated the influence of prior ovipositional experience on host selection in four solitary parasitoids, Aphidius erviHaliday, A. pisivorusSmith, A. smithiSharma & Subba Rao, and Praon pequodorumViereck (Hymenoptera: Aphidiidae). When provided simultaneously with equal numbers of two species of aphids, Acyrthosiphon pisum(Harris) and Macrosiphum creeliiDavis (Homoptera: Aphididae), all four parasitoids showed a moderate to strong preference for A. pisum.This preference did not increase after sampling, except in P. pequodorum.Learning did not alter host selection behavior in A. erviand P. pequodorum.However, females of A. pisivorusconditioned on A. pisumselected fewer M. creeliithan unconditioned wasps and wasps conditioned on M. creelii.It is suggested that prior ovipositional experience influences a parasitoid's expectations of the kinds of hosts available, but it does not alter the (innate) rank order of hosts. 相似文献
63.
Summary We have isolated Saccharomyces cerevisiae mutants, smp, showing stable maintenance of plasmid pSRI, a Zygosaccharomyces rouxii plasmid. The smp mutants were recessive and were classified into at least three different complementation groups. The three mutants also showed increased stability of YRp plasmids and the mutations are additive for plasmid stability. One mutation, smp1, confers a respiration-deficient (rho
0) phenotype and several Rho– mutants independently isolated by ethidium bromide treatment of the same yeast strain also showed increased stabilities of pSR1 and YRp plasmids. The wild-type S. cerevisiae cells showed a strongly biased distribution of pSR1 molecules as well as YRp plasmids to the mother cells at mitosis, while the smpf mutant did not show this bias. Another mutation, smp3, at a locus linked to ade2 on chromosome XV, confers temperature-sensitive growth. The SMP3 gene encodes a 59.9 kDa hydrophobic protein and disruption of the gene is lethal. 相似文献
64.
The degree of intergradation between two species of Sulawesi macaques,Macaca tonkeana andM. hecki, was studied by examining the diagnostic external characteristics of more than 100 monkeys kept as pets by natives. Two possible
hybrid monkeys were found and both originated from the borderland between the two species, located in the most proximal region
of the northern peninsula of Sulawesi. The previously postulated wide area of integradation between the two species at the
possible contact zone was, however, not recognized, and typical examples oftonkeana orhecki were found to be present on the two sides of a narrow “hybrid” zone which was defined by direct observations. Furthermore,
despite considerable individual variations, we were able to allocate most monkeys to one or other of the species. Each of
ten external characteristics of the members of both species more or less encompassed the individual variations, but may undergo
changes with the development of the monkeys. The mechanisms of reproduction of hybrid monkeys and the maintenance of differences
between the species are discussed. 相似文献
65.
Kunio Watanabe Shuichi Matsumura Tsuyoshi Watanabe Yuzuru Hamada 《Primates; journal of primatology》1991,32(3):385-389
Morphological observations of pet and wild monkeys were made in the area that was inferred to be the borderland betweenMacaca tonkeana andM. ochreata in Sulawesi. Almost all individual monkeys could be classified into one of two species by their external characteristics.
The possible borderland was estimated to extend from the La River in the east and to around Karaena River in the west. These
two species may make contact in the forest in the western area of the borderland. Some external characteristics exhibited
wide individual variations in the two species. Some monkeys originating from the borderland showed external characteristics
that were intermediate between those of the two species. The possible intergradation between these two species is discussed
in terms of the morphological variations found in the two species. 相似文献
66.
Naive and experienced Diglyphus isaea were attracted by host plant odours of lettuce and chrysanthemum to search and probe on infested and uninfested leaves. A slight preference was shown for leaves infested with Chromatomyia syngenesiae. At close range, visual stimuli were unnecessary for oviposition and host‐feeding. Contact with uninfested lettuce and chrysanthemum elicited searching and probing behaviour whereas host frass did not. Host larval movement appeared to aid host detection at close range. The number of ovipositor probes increased with proximity to live hosts but not for stationary, dead hosts. Dead hosts were frequently walked over or missed when D. isaea passed within 0.5 cm of the stationary larvae. Dead hosts were also rejected for oviposition but not for host feeding. Both naive and experienced females discriminated between healthy hosts and those which had been attacked by conspecifics or encountered previously. 相似文献
67.
榆中贝母(Fritillaria yuzhongensis)生长于马啣山的高山地带,全生育期约100 d左右,是一种生育期较短的类短命植物。在果实成熟时,种子的胚发育不全,具有后熟作用的特点,包括形态后熟和生理后热两个阶段;因此,需要一定时期的低温处理,才能完成后熟过程,以解除休眠,促使种子发芽。本试验表明:榆中贝母完成形态后熟过程的最佳温度是7℃左右,经过100d以上的低温处理才能使原胚发育成熟,继续在7℃低温下处理70d以上,才能完成生理后熟过程。榆中贝母种子休眠时间长,需要经过170d以上的低温处理,种子才能萌发。本试验结果为榆中贝母种子的萌发提出了适宜的温度范围和低温处理时间,为提高种子的出苗率和缩短栽培年限提供了科学依据。 相似文献
68.
对武汉东湖三个定点观测站和潜江市一深水机井中异养细菌群落的种群组成、对不同基质的反应、菌株和群落的生理特征和活力水平等方面比较研究结果表明:环境差异较小的东湖Ⅰ、Ⅱ、Ⅲ站异养细菌群落间的差异亦较小,具有类似的结构特征和生理活力水平,对特定基质表现了相似的作用模式;地下水中的异养细菌群落在上述几方面均显示了明显的差别。此外,在异养细菌群落结构和功能研究方法上亦是有益的探讨。 相似文献
69.
70.
Elena Fernandez Garcia 《Entomologia Experimentalis et Applicata》1988,48(2):173-178
The suitability of different host plants for Pieris rapae L. in the South of the Iberian Peninsula, was studied in relation to host plant phenology, female behaviour, and larval development. Capparis spinosa is the only host plant available during the dry season of the year in the area studied. D. virgata, R. raphanistrum, H. incana and S. alba being suitable spring hosts. Comparative studies on mortality, larval development and larval growth between C. spinosa and the spring hosts revealed no significant differences.
Résumé L'adéquation de différentes plantes comme hôtes de P. rapae a été examinée en fonction de la phénologie des végétaux, du comportement de la femelle et du développement larvaire dans le sud de la péninsule ibérique. Pendant la saison sèche, C. spinosa est la seule plant convenable dans la zone étudiée. Diplotaxis virgata, Raphanus raphanistrum, Hirschfeldia incana et Sinapis alba sont des hôtes printaniers convenables. La mortalité, le développement et la croissance larvaires ne sont pas différentes sur C. spinosa et sur les hôtes de printemps.相似文献