摘要:

Bacteria isolated from Sri Lankan cowpea fields significantly reducedin vitromycelial growth and sporangial production ofPhytophthora vignaeby producing agar-diffusable and volatile inhibitors. Bacterial volatile inhibitors were evolved when the bacteria were grown on tryptic soy agar, nutrient agar, or King's B medium, although relatively less on the latter two media. The pH of agar exposed to the volatiles rapidly increased, suggesting that ammonia was involved in the inhibition. Volatile inhibitors were produced by the bacteria in soil amended with tryptic soy broth or cowpea seed extract, but not in unamended soil. Oospore—induced disease byP. vignaewas inhibited byBrevibacteriumstrain DF-3101 in soil.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754719

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Koinobiotic parasitoids are said to be unresponsive to host resources as measured by external host dimensions and, therefore, are unable to allocate sexes of progeny differentially into smaller versus larger hosts. The present paper examines the effect of host size on the sex allocation by a koinobiotic parasitoidLysiphlebus delhiensis(an aphid parasitoid). It tests the following hypotheses, assumed in host size model: (1) a greater proportion of females will emerge from larger hosts, (2) survival of the developing parasitoid stages differ between the sexes in relation to host size and (3) fitness of female offspring is better in large hosts. The results demonstrate thatL. delhiensisdeposits fertilised (diploid) and unfertilised (haploid) eggs differentially in response to host size. The female laid more haploid eggs in unsuitable host stages (I, II and IV instar nymphs, and adult apterous), than in suitable host size (III instar nymphs). However, perception of host size by females was not absolute and was dependent on the amount of temporal variation in the host size distribution and on the previously experienced host size. The measurement of certain performance criteria of the progeny ofL. delhiensisemerging from small versus large hosts (developmental period, survival, mating ability, fecundity and OSR) indicates that the host size related characters have a greater effect on the fitness of the female than male progeny. No evidence of differential mortality of the sexes ofL. delhiensisin small versus large hosts was observed. This implies, therefore, that while ovipositing in growing stages of the host,L. delhiensisexhibits maternal adjustment of OSR as a function of host size. By adjusting the sex ratio of the progeny in response to host size the female maximises her fitness without knowing about the future host quality.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754720

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Selective harrowing is introduced as a new concept in weed harrowing. It is defined as inter-row harrowing in late growth stages of the crop. Selective harrowing is expected to operate with a high selectivity, which means that a high degree of weed control can be obtained without associated crop damage resulting in crop yield reductions. Two questions with respect to weed harrowing in cereals are emphasised: How can selective harrowing be complemented with other principles of weed harrowing in order to achieve efficient weed control with a low number of passes; and how can the selectivity between crop and weeds be improved? Experiments in spring barley and winter wheat showed that high degrees of weed control could be achieved with weed harrowing giving results comparable to herbicide spraying. An increase of the row distance from 12 to 20 cm improved the selectivity of harrowing carried out in early growth stages whereas the selectivity of selective harrowing was unaffected by row distance. The total number of passes could not be reduced by combining different weed harrowing principles. Crop damage due to selective harrowing could not be totally avoided with high intensities of harrowing in spring barley but there was no detectable crop damage due to selective harrowing in winter wheat. Tractor hoeing combined with selective harrowing gave very high degrees of weed control without associated crop damage.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754721

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Manures (sewage sludge, swine, rabbit and poultry manures) from four farm or homestead wastes were analyzed for their chemical composition and were compared with NPK fertilizer for their ability to supply nutrient elements to tomato plants under field conditions.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754722

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The purposes of the present study were to search for antagonistic fungi to control seed-borne diseases of cereals caused byFusarium culmorum(W.G.Sm) Sacc. and to use these results to compare the distribution of non-pathogenicFusariumspp. and other fungi antagonistic toFusarium culmorumin soil and on straw particles in an organically and a conventionally cultivated field. The organic farm had been cultivated according to the principles of Steiner (1963) since 1952. The sites were similar with respect to climatic conditions, soil type and vegetation. There was no difference in the total number of antagonistic fungi isolated from the two differently cultivated fields, but the results forFusariumspp. showed effects of the actual crop as well as the cropping system. Soil sampling over a three year period at the organically cultivated farm in two crops—winter wheat or a mixture of grass and clover—showed almost twice as many species ofFusariumin the mixed crop compared to monoculture. In mixed crop fields, the percentage ofF. culmorumin relation to total isolations of fusaria was 20% in the organically cultivated field compared with 45% in the conventionally cultivated field. These results indicate that pathogenic fusaria may be suppressed by antagonistic fusaria to a larger extent in the organically cultivated field than in the conventionally cultivated field. In accordance with this, a higher number of antagonistic fusaria was found in the organically farmed field (14) compared to three in the conventionally farmed field. This was partly a result of a higher number of isolated fusaria and a higher number of different species ofFusariumin the organically cultivated soil (total number of non-pathogenic fusaria was 10 in the conventionally cultivated field and 56 in the organically cultivated field). However, it also seems to reflect an enrichment of fusaria with antagonistic properties towardsF. culmorum. Thus, the occurrence ofF. culmorumwas 1.7 times higher in the organically cultivated field while the occurrence of its antagonists was 4.6 times higher in the organically compared with the conventionally cultivated field.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754723

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Exposure of differently-aged (3, 5, 10 or 15 days) nymphs ofDysdercus Koenigiito eucalyptus oil vapours for a brief period once during rearing (2, 3, 4 or 5 hours) respectively), variously affected their mortality in the course of development. A significant shortening of the total postembryonic developmental time of surviving nymphs was noted if they were exposed for four or five hours to the oil volatiles of 10 and 15 days of age respectively. The concept of hormoligosis is put forth to explain this phenomenon. Adults of both sexes metamorphosing from treated nymphs showed appreciable loss in their fresh weight compared to controls. Pronounced reduction in the fecundity of the adult and the hatchability of eggs occurred in certain nymphal treatments. A “carry over” of the detrimental effect of oil volatiles on the breeding efficiency of the insect is suggested to account for such phenomena.

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754724

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754725

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754727

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0144-8765    

DOI:10.1080/01448765.1995.9754718

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor