摘要:

SUMMARYWhen seven potato varieties susceptible toHeterodera rostochiensiswere grown every year on the same small plots for 6 years with precautions to minimize soil movements, yields were inversely proportional to the number of larvae in the soil before cropping in the first year only. With all the varieties, numbers of larvae after harvest fluctuated around mean values and the fluctuations became smaller in successive years. Although conditions from year to year were as uniform as possible, there were differences in weather, incidence of potato blight(Phytophthora infestans), seed size and quality, and in planting dates. Analysis of soil temperatures and of heat accumulation did not suggest that conditions after planting caused the fluctuations. The smaller fluctuations with repeated cropping probably reflect the influence of population density on the size of the root system and are what would be expected from the curve relating pre‐ to post‐cropping numbers, which reaches a maximum before the reproductive rate decreases to unity.A resistant potato hybrid exandigena, also grown every year, usually outyielded the susceptible varieties and, by the sixth year, yielded at least twice as much as the mean of the six susceptible variet

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05479.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYDevelopment and hatch of eggs ofMeloidogyne javanicawas independent of suction betweenpFo and 3·6 but decreased rapidly betweenpF3·6 and 4·2. Water was lost from the extracellular fluid of eggs containing developing embryos when the suction was abovepF3·6, causing a decrease in the mean volume of the eggs. The vitelline membrane of an egg is probably semipermeable and the osmotic pressure of the contents about 4 atmospheres (pF3·6). The volume of the cellular contents of an egg did not increase during development and so the hydraulic conductivity of the soil is probably unimportant in hatching.The results suggest that eggs ofM. javanicahatch over a wide range of soil moistures. The inhibition of hatch at high suctions, involving the reversible removal of water, is a likely survival mecha

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05480.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYThe percentage hatch of eggs ofMeloidogyne javanicaincreased asymptotically as the oxygen concentration increased from 0·2 to 21%. Hatch was unaffected by suction pressures of less thanpF3·4 at any oxygen concentration but was decreased by higher suctions. Both the development of embryos and the migration of larvae approached a maximum at an oxygen concentration of about 15%. Hatching was not limited by the rate oxygen diffused through the gelatinous matrix of the egg sac nor was the concentration of oxygen at the surface of an egg sac significantly lower than that within an individual egg. The maximum rate of metabolism appeared to need an oxygen concentration within the egg greater than 10

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05481.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYThe plant growth‐regulating activities of chloro‐, bromo‐ and iodo‐isomers in 2,5‐, 2,3,5‐ and 2,3,6‐substituted benzoic acids were assessed in the wheat cylinder, pea segment and pea curvature tests. Their effects in the tomato‐leaf epinasty test were also investigated.Replacing anortho‐chloro atom by bromine had little or no effect on activity. Anortho‐iodo substituent, however, reduced activity in the 2,3,6‐substituted series and almost completely inhibited it in the 2,5‐ substituted series. This decreased activity ofortho‐iodo‐substituted isomers is visualized as being due to a steric inhibition of the attachment of the carboxyl group to its receptor unit prior to the initia

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05482.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYWheat, pea and dwarf bean seedlings grown under controlled environmental conditions were used to assess the growth‐retardant activity of members of series of chloro‐substituted benzyl‐, trimethyl‐ and tri‐n‐butyl‐ ammonium bromides. The influence on activity of trialkyl groupings other than tri‐methyl and tri‐n‐butyl was also studied using compounds with the 4‐chloro‐benzyl ring structure. 3‐Chloro‐ and 4‐chloro‐benzyltributylammonium bromides were the most effective compounds. The activity was similar to that of 2,4‐dichlorobenzyltributylphosphonium bromide (Phosphon‐D) and they showed little phytotoxicity. A series of chlorophenoxymethyltributylammo‐nium and phosphonium salts were found to have lower activity than the corresponding chlorobenzyl derivatives. Allyldimethylsulphonium bromide retarded the growth of wheat seedlings but, like the aliphatic trimethylam‐monium bromides tested, it was only slightly active in the pea‐seedling test.The results are considered in relation to the chemical structure of the compounds studied. In particular, the influence of chlorine substitution in the ring of benzyltributylammonium salts on their growth‐retardant activity is compared with the effect of similar substitution o

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05483.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYExperiments were made to test the hypothesis that a toxin produced by or from apple roots is the causal factor of specific apple replant disease. In sand and vermiculite culture, apple leachates were not harmful to the growth of apples. In the field, apples exerted no effects on neighbouring apples other than competition effects. In pot and field experiments, the addition of apple root residues to fresh (unused) or fumigated soil depressed the growth of both apple and cherry test plants; similar additions to used (‘replant’) apple soil, however, improved the growth of apple, but not of cherry, test plants. It is concluded that specific apple replant disease is not caused by a toxin derived from root residues. It is suggested that the cause may rather be a rhizosphere microorgan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05484.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYPlum line‐pattern virus (PLV) was purified by homogenizing inoculated leaves ofNicotiana megalosiphonin 0·02 M phosphate buffer, pH 8·0 (1·5 ml/g leaf), containing 0·02 M 2‐mercaptoethanol. The homogenate was centrifuged at low speed and the supernatant liquid was clarified by adjusting the pH to 4·8 with 0·1 M citric acid. The green coagulum was removed by centri‐fugation and the extract adjusted to pH 6·5. After concentrating the virus by high‐speed centrifugation, remaining host protein was precipitated with the gamma‐globulin fraction of antiserum toN. megalosiphonprotein. Purification was completed with two cycles of high‐ and low‐speed centrifugation.Purified PLV had an A260/A280ratio ofc.1·7 and formed two zones when centrifuged in density gradients at pH 6·0–7·0. The virus was about 30 mμ in diameter in negatively stained preparations. The particles were easily disrupted. PLV was closely serologically related to cultures of plum line‐pattern virus from other areas, but no relationship was found to apple mosaic,Prunusnecrotic ringspot or prune dwarf viruses, or to a plum lin

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05485.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYFive short varieties of spring wheat derived from Norin 10: Lerma Rojo 64A (R), Penjamo 62 (P), Sonora 64 (S), Mexico 120 (M), and an unnamed selection obtained from Mexico (X), had grain yields equal to, or only slightly less than those of the taller European spring varieties Kloka (K) and Jufy I (J). Yields ranged from 500 to 580 g/m2of dry matter. The short variety NBJ115 (N) was severely infected with yellow rust and yielded only 290 g/m2. Total dry weight (excluding roots) of the short varieties was less than of J and K; hence grain accounted for 49 % of the total for the short varieties and 42 % for J and K. Most of the short varieties had fewer ears than the tall ones because sowing difficulties and poor germination produced fewer plants. The relative yields of X, P, R and S seemed to be correlated with their plant and ear densities.Leaf area duration after flowering(D), based either on total green area or on green area above the flag‐leaf node only, was less for the short varieties than for J and K. The apparent mean efficiency of this area in grain production (grain yield divided byD) was 50% greater for the short than for the tall varieties.The height of the short varieties ranged from 43 cm (M) to 79 cm (N). K was 92 cm and J 97 cm tall. Differences in height depended on the lengths of the top four internodes and not on number of internodes. Main shoots of all varieties produced seven or eight leaves. All varieties initiated spikelets 45–48 days after sowing. The short varieties flowered 103 days and matured 155 days after sowing; J and K flowered and matured about 1 week earl

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05486.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYA total of 5,250 acres of spring barley was sampled in proportion to the barley acreage in each of eight regions. The percentage leaf area ‘affected’ by each disease was recorded for the first (flag) and second leaves at a growth stage when the grain was milky ripe. The operation was automated by punching the data directly on to computer paper tape and a programme was written to analyse the results. Mildew was found to be the most important disease, causing an average loss in yield of approximately 18 %, followed in descending order by brown rust 3%, leaf blotch 1 %, yellow rust 1 %, halo spot 1 %. The total loss due to foliar diseases was estimated to be 20–25% of the national barley yield. Diseases were more severe in the southern than northern regions, e.g. mildew severity was three times higher because of the greater popularity of mildew‐susceptible varieties, and the prevalence of weather more conducive to mildew development. Disease severity was not related to previous cropping, and in general the February‐sown crops had more mildew than the April

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05487.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYPhytophthora injestansinfection of potato leaves causes abnormal opening of the stomata in the tissue colonized by the fungus before sporangiophores emerge through them. The affected area, which may be up to 7 mm wide, extends from the necrotic tissue to within 1–2 mm of the advancing edge of the colonizing mycelium. These stomata open wider than those in uninfected parts of the leaf, and do not close in the dark, but closure can be induced experimentally by a high water deficit. Affected guard cells have an increased osmotic value, reduced starch content, and show degradation of the chloro‐plasts. No direct infection of the guard cells has been observed. Autoradiography of infected leaflets which had been exposed to14CO2in the light, showed that a zone of increased photosynthesis occurs in the region of wide‐open st

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05488.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY