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971.
The emergence pattern and life cycle of four major species growing in a non–irrigated almond tree grove were analysed in relation to ploughing frequencies and environmental factors. At the community level, the overall emergence pattern was found to be much the same whether or not the soil was disturbed. Nevertheless, soil disturbance in late winter and early spring produced peaks of seedling emergence and brought about an increase in germination. Winter annuals such as Lolium rigidum Gaudin and Diplotaxis erucoides (L.) DC., which emerged in the autumn, started to grow rapidly in winter and spring and were able to pre–empt the environmental resources of the habitat and suppress spring–germinating plants such as Chenopodium album L. and Amaranthus blitoides S. Watson. Late–winter and early–spring disturbances favoured the dominance of summer annuals such as C. album and A. blitoides S. Watson. The different ploughing regimes applied during the first year had effects on plant development and seed production which brought about changes in plant population size during the second year. 相似文献
972.
A Japanese powdery mildew isolate with exceptionally large infection efficiency on Mlo-resistant barley 总被引:1,自引:2,他引:1
A Japanese field isolate (Race I) of Erysiphe graminis f.sp, hordei was tested on 17 barley lines carrying the mlo powdery mildew resistance gene. Race I produced many successful infections with infection type larger than or equal to 2 on six lines (M66, MC20, SRI, SR7, A tem and Totem), On the remaining 11 lines it reacted with infection type 0. Colony numbers on the Mlo-lines were between 26% and 12 9% of the numbers on a susceptible cultivar Manchuria, These numbers were larger than, or similar to those produced by isolate HL3/5, which has the highest recorded infection efficiency on Mlo-resistant cultivars. The interaction between isolates and lines was highly significant. The isolate GE3, from which HL3/5 was derived by selection, gave rise to occasional colonies corresponding to less than 03° o of the number produced on cv. Manchuria. 相似文献
973.
Stuart A. MacFarlane Derek J. F. Brown John F. Bol 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(5):535-539
The coat protein gene of the nematode non-transmissible, SP5 isolate of pea early-browning tobravius was replaced with that of the highly nematode transmissible, PPK20 isolate of tobacco rattle tobravirus. Plants were infected with the recombinant virus when mechanically inoculated and the virus invaded the plants systemically. However, although the PPK20 isolate of TRV was transmitted by nematodes from these plants, the recombinant virus was not transmitted. Therefore, the virus coat protein is not the exclusive determinant of nematode transmission. 相似文献
974.
The antiphytoviral activity of 1-morpholinomethyl-tetrahydro-2(1H)-pyrimidinone (DD13) in a test system including protoplast cultures, surviving tissues and greenhouse plants was examined. The inhibitory effect was quantitatively investigated by immunofluorescence and enzyme linked immunosorbent assay. The antiviral action in vitro was 96%. The first 6 h after inoculation was the most sensitive period of the tomato mosaic virus (ToMV) reproduction cycle. DD13 possessed a protective effect in 97–100% plants infected with ToMV and cucumber mosaic virus (CMV). 相似文献
975.
Gopalan C. Unnithan John F. Andersen Tomomi Hisano Eiichi Kuwano Ren Feyereisen 《Pest management science》1995,43(1):13-19
Seventeen substituted imidazoles were tested as inhibitors of juvenile hormone (JH) III synthesis by cockroach corpora allata in an in-vitro radio-chemical assay. Most of these 1,5-disubstituted imidazoles were highly potent, with IC50 values of less than 100nM. The compounds differed in their ability to cause an accumulation of the precursor methyl farnesoate in the glands. Four of the imidazoles were tested by topical application to previtellogenic adult females, and all caused a significant inhibition of JH synthesis and an accumulation of intraglandular methyl farnesoate for at least three days after treatment. Methyl farnesoate epoxidase activity of homogenates of corpora allata was inhibited by the compounds TH -14 and TH -27. This P450-dependent epoxidase activity was inhibited at less than 10 nM. The results show that the 1,5-disubstituted imidazoles are powerful inhibitors of the last step of juvenile synthesis in this cockroach. 相似文献
976.
Suzanne J. Clark Nicola P. Coward Glenn W. Dawson Ian F. Henderson Andrew P. Martin 《Pest management science》1995,44(4):381-388
Two related iron chelates, one toxic to slugs by ingestion, the other not, were introduced into the foregut of D. reticulatum. The subsequent movement and redistribution of the metal within the slug tissues was studied by labelling the chelates with the radioactive isotope 55Fe. In slugs which survived treatment approximately half of the 55Fe was voided in faeces. The iron retained became unevenly distributed, the highest concentration occurring in the digestive gland, irrespective of the chelate used. At high doses, slugs treated with tris(1-oxo-1,2-diazabutan-2-oxido)Fe(III) were fatally poisoned while those treated with the homologue, tris(1-oxo-1,2-diazaoctan-2-oxido)Fe(III) were not. Slugs killed by the toxic chelate consistently contained proportionally less iron in the digestive gland and proportionally more in the body wall and reproductive system. Dosing slugs already killed by carbon dioxide asphyxiation gave a similar pattern, suggesting that the greater mobility of the iron from the toxic chelate was not a function of the slugs' metabolism. 相似文献
977.
978.
Rapid and sometimes extensive mortality and decline of oak, principally Quercus suber and Q. ilex , has occurred in parts of southern Spain and Portugal in recent decades. We report here isolation of the aggressive root pathogen Phytophthora cinnamomi from roots of diseased oaks or from soil at eleven out of thirteen decline foci examined. It is proposed that the introduction and spread of P. cinnamomi may be a major factor in the Iberian oak decline, interacting with drought and other site factors, and leading to stress-related attacks by insects and other fungi. By analogy, it may also be involved in the similar oak declines occurring elsewhere on the Mediterranean. 相似文献
979.
Japanese leaf beet Beta vulgaris var. cicla cv. Fudanso plants were found to contain four double-stranded RNA (dsRNA) components in apparently healthy beet plants. Two were identified as from beet cryptic virus 1 (BCV1), but the other two showed different mobilities on gel electrophoresis and were transcribed into complementary DNA (cDNA) and cloned. Hybridization analysis showed no significant sequence homology between these two dsRNAs and the dsRNA components of BCV1 or the other known cryptic virus of beet, BCV2. Slot- and dot-blot hybridization were used with cDNA clones as probes to identify plants containing these two dsRNA components. Virus particles were purified from these plants and were shown to contain the two new dsRNA components, thus demonstrating the existence of a new beet cryptic virus, which we have called BCV3. 相似文献
980.
A study on the population dynamics of broom-rape (Orobanche crenata Forskal) in faba bean (Viciafaba L.) was conducted in two locations for 8 years. The O. crenata seed bank increased every year in the 20-cm depth arable layer until it reached approximately 4 million (M) seeds m?2. Seed viability ranged between 53% and 68%, approximately half of the seeds remaining dormant. About 3 × 10?3% of the seed bank became attached to the root system of the faba beans. Only 9% of the attached broomrapes developed and emerged from the soil, possibly reflecting high levels of intraspecific competition. Maximum broomrape seed production for a population of 53 emerged broomrapes per m2 was approximately 4 M seeds m?2. About 43% of the seeds produced were not incorporated into the soil, most probably as a result of their degradation, decomposition or dispersion. Stock semencier et autres paramètres démographiques de I'orobanche crénelée (Orobanche crenata Forsk.) dans des cultures de féverolle (Vicia faba L.) Une étude de la dynamique de populations d'orobanche crénelée (Orobanche crenata Forsk.) dans des cultures de féverolle (Viciafaba L.) a été menée pendant 8 années sur deux sites. Le stock semencier de O. crenata a augmenteéchaque année dans la couche (20 cm) arable du sol jusqu'à atteindre 4 millions (M) de graines m?2. La viabilité des graines était comprise entre 53 et 68%, approximativement la moitié d'entre elles présentaient une dormance. Environ 3 × 10?3% du stock semencier adhérait au système racinaire de la féverolle. Seulement 9% des orobanches adhérantes se développaient et levaient, ce qui pourrait refléter une compétition intraspécifique importante. La production maxi-male de graines par une population de 53 orobanches levées au m2était d'environ 4 M graines m?2. Environ 43% des graines produites n'étaient pas incorporées au sol, très prob-ablement en raison de leur dégradation, de leur décomposition ou de leur dispersion. Bodensamenbank und andere populationsde-mographische Parameter der Sommerwurz Orobanche crenata Forsk. in Bestanden der Acker-Bohne (Vicia faba L.) Bei einer Untersuchung der Populationsdy-namik der Sommerwurz Orobanche crenata Forsk. in Beständen der Acker-Bohne (Vicia faba L.) an 2 Orten über 8 Jahre hin nahm die Bodensamenbank in der Pflugzone von 20 cm Tiefe jedes Jahr zu, bis sie rund 4 Millionen Samen m?2 erreichte. Die Lebensfähigkeit der Samen lag bei 53 bis 68%, etwa die Hälfte war dormant. Ungefähr 3 × 10?3% kamen mit den Bohnenwurzeln in Berührung. Nur 9% davon entwickelten sich und wuchsen heran, worin vielleicht der hohe Grad intraspezifischer Konkurrenz zum Ausdruck kommt. Die höchste Zahl gebildeter Samen eines Sommer-wurzbestands von 53 Pflanzen m?2 war rund 4 Millionen. Etwa 43% der gebildeten Samen gelangten nicht in den Boden, wahrscheinlich weil sie zerstört oder verweht wurden. 相似文献