摘要:

SUMMARYSix rice cultivars (lines (TKM6, OS6, ADNY 11, IR28, Rexero and IR579‐48‐1) were used to determine the pupation sites ofDiopsis thoracicaand their effects on pupal parasitism. There was a general preference for pupation on the first three outer leaf sheaths. Preference was also observed for healthy tillers compared with damaged ones, except in OS6 where there was no significant difference between pupation on healthy and damaged tillers. Pupae on the first two outer leaf sheaths were heavily parasitised by the eulophidTetrastichus (Neotrichoporoides)sp. (Hymenoptera). The level of parasitism ranged from 17·6% in OS6 to 58·8% in Rexero, with an overall mean of 38·9% for the entire experimental plot. The number of parasites per pupa ranged from 0·5 in OS6 to 3·0 in Rexero, with an overall mean of 1·37. There was a strong relationship between (a) parasitism (%) (r = 0·68); (b) number of parasites per pupa per variety (r = 0·90) and pupal length. The relationship between parasitism (%) and parasite density was very strong (r = 0·89), but a marginal improvement in relationship was obtained when parasitism (%) was correlated with log parasite density (r = 0·94), thus possibly suggesting weak interaction between

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03043.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYCircumstantial evidence from field experiments at Rothamsted suggested that effects of powdery mildew on grain filling in spring barley may be determined partly by temperature during the grain‐filling period. An experiment was, therefore, done which compared the effects of fungicides applied to control powdery mildew on grain filling in early‐ and late‐sown spring barley plants kept either out‐of‐doors throughout their growth (‘cool’ environment) or under the same conditions until the start of grain filling and then transferred to a heated glasshouse (‘warm’ environment) until harvested. Fungicides that controlled mildew increased the total grain yield of the late‐sown barley more than that of the early‐sown and much more in the warm environment than in the cool. On average, the effect of the fungicides in the cool environment was to increase grain yield by 17·7%. Small increases in numbers of grains/ear (+ 3·4%) and thousand‐grain weight (TGW) (+ 2·3%) contributed to this increase but it could be attributed principally to an average increase in numbers of ears/plant of 12·4%. Contrastingly, fungicides increased average grain yield in the warm environment by 58·2%. Effects of the fungicides on numbers of ears/plant (+ 27·8%) and on numbers of grains/ear (+ 4·5%) were not significantly different to those in the cool environment, and the much greater responses in the warm than in the cool environment could be attributed mostly to much larger effects on grain size (+ 19·2%)The greater benefits of the fungicides and, by implication, the greater damage done by powdery mildew in the warm than in the cool environment cannot, unequivocally, be attributed to differences in temperature during grain‐filling because the two environments clearly differed in other ways and especially in light intensity. Nevertheless, the results obtained do illustrate the potential risks involved in using data obtained under one set of circumstances to predict what will happen in another, especially when environments differ as

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03044.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYStudies on the epidemiology of arabis mosaic (AMV), prunus necrotic ringspot (PNRSV) and strawberry latent ringspot (SLRV) viruses were made in relation to commercial production of standard and bush roses. AMV or SLRV apparently induced either symptomless infection in rose cultivars andRosaspp., or leaf symptoms ranging from small chlorotic flecks to severe chlorotic mosaic and, occasionally, plant death. Infection ofR. canina ‘inermis’orR. corymbiferaby an isolate of SLRV fromR. corymbiferaalso severely depressed flowering and hip formation. In addition, whereas this isolate could be graft‐transmitted to allRosaspp. tested, isolates fromR. rugosaandR. multiflorafailed to be graft‐transmitted toR. canina ‘inermis’orR. corymbifera.No difference was detected in graft‐transmission tests ofRosaspp. with several isolates of AMV or PNRSV.In plantings of up to 7 yr none of the viruses was transmitted through pollen to healthy roses grown in nematode‐free soil, and only SLRV was readily seed‐transmitted, particularly inR. rugosa.Nevertheless, in soil containing viruliferous nematodes, AMV and/or SLRV were transmitted toc.80% of healthy plants.AMV and particularly SLRV were each damaging to field‐grown maiden rose bushes cv. Fragrant Cloud. SLRV delayed the onset of flowering, and reduced the number and size of blooms. Diseased bushes were less vigorous, and half or none of the AMV‐ or SLRV‐ infected bushes respectively, conformed to the British Standards Institution specifications for maiden bush roses.These results are discussed in relation to the commercial production of fiel

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03045.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYA virus was transmitted from broad bean plants in Apulia (Southern Italy) with leaves showing yellow rings, line patterns or yellow vein banding and malformations and necrosis of pods. Symptoms in some, but not all, test plants were similar to those induced by tobraviruses. Purified virus preparations contained two classes of rod‐shaped particles containingc.5% nucleic acid with sedimentation coefficients of 186S and 276S. After centrifugation to equilibrium in CsCl gradients, two components were resolved, with buoyant densities of 1·298 and 1·316 g/cm3. Unfractionated virus preparations contained two species of single‐stranded RNA with mol. wts ofc.1·06 × 106and 2·48 × 106and one species of coat protein with mol. wt ofc.21 300. The modal lengths of the two classes of particles, both in plant sap and in purified preparations, were 77 nm (S particles) and 202 nm (L particles). L particles accumulated in infected cells in paracrystalline aggregates, whereas S particles were randomly distributed in the cytoplasm of cells. The virus was serologically unrelated to two isolates of tobacco rattle virus and two isolates of pea early‐browning virus. The virus, named broad bean yellow band, is considered a distinct

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03046.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYIn sandy loam infested withGlobodera rostochiensis(2–95 eggs g‐1soil) the yield of Desiree potatoes was decreased by 8·2 t ha‐1for every increment of 20 eggs g‐1soil. Oxamyl incorporated in the seedbed at 5 kg ha‐1before planting prevented significant loss of yield and damage to the tubers and minimised nematode increase. Cara and Maris Piper potatoes, which were resistant and tolerant toG. rostochiensisusually responded less to oxamyl than did susceptible cultivars. In a range of cultivars, yield responses to oxamyl treatment of soil infested withG. rostochiensisoften differed from those in soil infested withG. pallida.In field experiments, oxamyl controlledG. pallidaless thanG. rostochiensis.In pots, such differential control of the two species by oxamyl was no

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03047.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe effects of aldicarb and benomyl on plant‐parasitic nematodes, vesicular arbuscular mycorrhiza and the growth of forage maize were measured in 1980—1982 in two field experiments at Woburn, Bedfordshire and in a pot experiment using loamy sand soil from the field site. The most numerous migratory nematode,Tylenchorhynchus dubiusincreased three to four‐fold during each season in untreated soil and was effectively controlled by aldicarb.Pratylenchusspecies were fewer but equally well controlled. The cereal cyst‐nematode (Heterodera avenae), a serious maize pathogen in Northern France, was relatively scarce in untreated roots and was further decreased by aldicarb treatment; post‐harvestH. avenaeegg numbers were not affected by treatments; they declined equally because maize is such a poor host. Significant yield benefits (up to 37%) followed aldicarb treatment and were ascribed to nematode control in the absence of attribution to insect or other pests. Benomyl did not increase yields nor did it significantly affect the incidence of mycorrhiza.The results confirm that considerable losses of forage maize can be caused by nematodes in light soil and that aldicarb is an effective nematicide even at the rate of 1·7

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03048.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYIn field samples taken on a grid pattern during four winters over an 80 ha farm there were manyTrichodorus viruliferus(up to 3000/litre soil) in light soils but few in heavier soils. Depth samples taken during the summer showedTrichodorusto be the only nematode genus which was more numerous below plough depth than in the plough layer. In field experiments in the most heavily infested part of the farm, soil‐applied granular pesticides did not increase sugar yields following the dry spring of 1982; aldicarb increased sugar yields in one experiment following the wet spring of 1983 although it, and other granular pesticides, did not affect yield in an adjacent experiment whereT. viruliferuswere fewer. Irrigation during the dry summer of 1983 maintained relatively large populations ofT. viruliferus, whereas in unirrigated plots without aldicarb populations declined by over 50%. Economic thresholds forT. viruliferusin 1983 at Broom's Barn were about 700/litre in unirrigated soil and 300/litre in irrigated soi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03049.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYIn experiments over 3 years, separate field plots were cultivated once only at 2‐wk intervals. Cultivation resulted in a flush of weed seedlings, representing usually less than 6% of the apparently viable seeds in the top 10 cm of soil and with a species composition which varied with the time of year. Subsequent flushes coincided in timing and extent with those on soil which had been undisturbed and were related to significant rainfall events. In each year there were periods when lack of soil moisture restricted emergence. At these times, seeds were released from dormancy by cultivation but germination of some or all of them was delayed. There was a general correspondence in the emergence patterns of weeds and of carrot and onion sown after each cultivation. On occasions when the seedbed was drying out, establishment of the comparatively rapidly‐germinating radish and cabbage was greater than that of carrot, onion or weeds. Effective initiation of germination of both crops and weeds was traceable to rainfall events. Emergence was reduced or delayed on more than half of the 45 cultivation occasions during the three growing seasons, and the results emphasise the importance of soil moisture in determining the extent and timing of seedling emerge

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03050.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYTwo laboratory methods of testing for resistance toBotrytis squamosainAllium cepa, A. fistulosumand hybrid material derived from them were developed. In one method, seedlings were sprayed with conidiospores, incubated for 3 days at 15°C (2 days at 100% r.h.) and the numbers of lesions per leaf assessed. This test was destructive. The second method was non‐destructive, the plants being retained for breeding purposes. Leaf segments (25 × 15 mm) or leaf discs (14 mm diameter) were inoculated individually with a drop (0·014 ml) of spore suspension, and maintained at 15°C and 100% r.h. with a 12 h photoperiod. The length of the latent period, denned as the number of days for 50% of the leaf portions to produce lesions bearing visible mycelium, was determined for each onion line in a test. The reciprocal (1/t) of the latent period was used to test for significant differences between lines by analysis of variance.With both test methods, spores were applied at concentrations that discriminated relative resistance most readily.In both seedling and leaf segment testsA. fistulosumwas more resistant thanA. cepatoB. squamosa.The leaf disc test indicated that cultivars ofA. fistulosumdiffered in their resistance. In hybrid material resistance was intermediate or more like that ofA. fistu

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03051.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYIn Brussels sprouts, yields of up to 357 embryos per 100 anthers cultured were obtained using a thermal shock treatment of 16 h at 35°C at the start of the culture period. Treatments of 48 h at 35°C and 14 days at 30°C gave no embryos. The F1hybrid cv. Gower consistently gave higher embryo yields than the F1hybrid cv. Nym, the differences being 3 to 10‐fold. Differences in embryo yield of 3‐fold or less were usually not statistically significant because of great variation within a treatment. This variation was less with donor plants raised in a growth room than with those raised in a glasshouse, where temperature and light intensity could not be so accurately controlled.From 842 embryos cultured, 270 plants were regenerated, mostly via hypocotyl explants, which developed from the anther‐derived embryos. Most of the regenerants were haploid or diploid, with a few of highe

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1984.tb03052.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY