摘要:

SUMMARYThe tolerance of spring and winter cultivars of wheat, barley and oats to infection by barley yellow dwarf virus (BYDV) was examined in field tests. Sererely affected plants were stunted and grain yields were considerably reduced. These changes in infected spring barley cultivars were associated with decreases in both ear length and number and sizes of grain. Most barley and oat cultivars were more susceptible than wheat cultivars. Yield losses decreased with successively later dates of inocultaiton, the yield response being characteristic of the tolerance of individual cultivars. Differences between tolerant and susceptible cultivars were insignificant in most cases where infection occurred after growth stage 7.Individual seedling symptoms assessed in April and May were more closely related to each other and to yield losses than those recorded in March and June. The incorporation of seedling symptoms into indices of infection permits estimates of decrease in yield to be made by applying the formulae,DY = (LC+LA+SH)/3to barley cultivars andDY = 1.7 × (LC+LA+SH)/3 ‐ 7to oat cultivars. Thus decreases in grain yield (DY) can be related to decreases in seedling height (SH) and increases in percentage of leaf area discoloured (LA) and intensity of discoloration (LC).Plot symptoms of infection, scored on a 0–7 scale, offered a more convenient method of assessment than individual seedling symptoms. Plot scores (PA) were closely correlated with other seedling symptoms and with decreases in grain yield (DY), and can thus be used to estimate yield losses by substituting into the formula, DY = 14PA (April)‐8. This formula was found to be applicable to all cereal cultivars examined in N.I.A.B. trials, there being no distinction between wheat, barley an

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04615.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYElectron microscopy of thin sections ofXiphinema diversicaudatumandX. indexfed on plants infected respectively with arabis mosaic and grapevine fanleaf viruses showed that the viruses are retained as a monolayer of particles adsorbed on to the cuticle lining the lumina of the odontophore (stylet extension), anterior oesophagus and oesophageal bulb. During the moult of the nematode the cuticular lining is shed and together with the detached virus particles is ingested into the intestine through the oesophago‐intestinal valve; this supports the limited experimental evidence that viruses transmitted byX. diversicaudatumandX. indexare not retained through the moul

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04616.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYCucumber mosaic virus (CMV) was transmitted in the seed of infectedStellaria mediaplants. The rate of seed transmission varied both in manually infected plants (3–21%) and in plants grown from infected seed (21–40%). In naturally infected plants the rates of transmission found were 4–29%.Seeds recovered from field soil carried 4–5% infection and in infected seed placed in the soil the virus persisted for at least 5 months.Seed transmission of CMV also occurred in infectedLamium purpureum(4%),Cerastium holosteoides(2%) andSpergula arvensis(2%) but it could not be demonstrated in six other more common weed species in five botanical families.Seed transmission inStellaria mediaoccurred with a British (W) and an American (Y) strain of CMV. The virus was shown to occur inS. mediapollen.The importance of CMV‐infectedS. mediaseed in the soil in relation to the epidemiology of the virus is

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04617.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYRapid phage and serological methods were compared with biochemical and bean‐pod inoculation tests for the identification ofPseudomonas phaseolicola. Phages II P, 12 P and 48 P were highly specific and did not lyse any of forty‐five other isolates from bean or the sixteen species ofPseudomonastested. They were also, however, unable to lyse the rough colony forms ofP. phaseolicolawhich were occasionally isolated. Phage 12 S lysed a wide range ofPseudomonasspp., including a proportion ofP. phaseolicolaisolates, the majority of which were race 2. Serological tests showed that the heat‐labile antigen possessed byP. phaseolicolawas common to twelve other species of plant pathogenic pseudomonads. The heat‐stable antigen was more specific and was detected only inP. mors‐prunorumandP. primulae, neither of which occurs on bean. The two races ofP. phaseolicolawere indistinguishable in serological tests. It was concluded that both phage and antiserum tests provide specific, rapid and easily applied methods for the routine identification ofP. phaseolicolaisolates from plant and seed

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04618.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYIrrigation applied early during tuberization significantly decreased scab on tubers of Majestic, King Edward and Record, but not on Pentland Crown, a resistant cultivar, where tubers had little scab even from the driest soil. There was little benefit from keeping soils wetter than 0.6 in (15.24 mm) soil moisture deficit (S.M.D.) for more than 3 weeks after tuber initiation, and irrigation to 0.8 in (20.32 mm) S.M.D. gave economic control. Irrigating only after the ‘marble stage’ increased yield but the tubers were scabbed. Irrigation did not alter the rate eyes (nodes) separated from the apical bud but speeded the swelling of tub

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04619.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYInoculation of seed potato tubes withVerticillium nubilumproduced infection on the underground stem bases to subsequent growth in the form of brown lesions, often accompanied by longitudinal or transverse cracking. Some inoculation tests provided further evidence of a causal relationship between infection withV. nubilumand coiled sprout, but it was not possible to define the conditions in which the fungus gave rise to coiling.Seed tubers sprouted in light before planting produced more coiling than unsprouted or desprouted tubers. Sprouting had this effect whetherV. numbilumwas present or not and coiling induced by sprouting and that induced byV. nubilumoccurred independently. The increased coiling of stem bases from sprouted tubers was often accompanied by fasciation, whereas this symptom was not usually associated with the coiling from unsprouted or desprouted seed tubers inoculated with the fungus. Brown lesions associated withV. nubilumwere readily distinguishable from those ofRhizoctonia solanibut not from those caused byOospora pustulans. Neither of these fungi was found to cause coiling.Different varieties of potatoes showed differences in the incidence of coiling in response to sprouting treatment. There was no apparent differences in varietal response to infection byV. nubilum.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04620.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYGermination ofPeronospora viciaesporangia washed off infected leaves varied from 20% to 60%. Sporangia shaken off in the dry state gave 11–19% germination. Most sporangia lost viability within 3 days after being shed, though a few survived at least 5 days. Infected leaves could produce sporangia up to 6 weeks after infection, and sporulating lesions carried viable sporangia for 3 weeks.Sporangia germinated over the range 1–24 °C, with an optimum between 4 and 8 °C. Light and no effct.The temperature limits for infection were the same as for germination, but with an optimum between 12 and 20 °C. A minimum leaf‐wetness period of 4h was required, and was independent of temperature over the range 4–24 °C. Maximum infectivity occurred after 6h leaf wetness at temperatures between 8 and 20 °C. Infection occurred equally in continuous light or in darkness.After an incubation period of 6–10 days sporangia were produced on infected leaves at temperatures between 4 and 24 °C, with an optimum of 12–20 °C. Exposure to temperatures of 20–24 °C for 10 days reduced subsequent sporulation. Sporangia produced at suboptimal temperatures were larger, and at 20 °C. smaller, than those produce at 12–16 °C. Viability was also reduced. No sporangia were produced in continuous light, or at relative humidities below 91%. For maximum sporulaiton an r.h. of 100% was required, following a lower r.h. during incubation.Oospores wre commonly formed in sporulating lesions, and also where conditons limited or prevented sporulation.The results are discussed briefly in relaiton to disease developme

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04621.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYGermination rate and total germination ofPuccinia graminisuredospores were directly related to pustule age and duration between spore collections. Partial drying of the spores enhanced germination rate; keeping them for 18 h at 100% r.h. reduced both rate and total germination. Spores germinated in polystyrene dishes between 4 and 29 °C and optimally between 15 and 23 °C Light (3 cal/cm2/h) had little effect on germination on moist surfaces but inhibited germination on the leaf. In Hybrid 229/8 wheat this effect was more pronounced than in var. Little Club. The number of primary infections increased linearly with duration of surface wetness with a narrow temperature optimum at 23.5 °C.Two phases of infection could be distinguished: germination (requiring darkness and capable of taking place over a wide temperature range) and penetration (requiring light and slightly higher temperature than for germination). Stomatal closure caused by subjecting the plants to water stress led to proporational reductions in infection. The results are discussed in relation to dew formati

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04622.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYIn tests to find a replacement for creosote, widely used for painting conifer stumps to prevent colonization byFomes annosus, the best all‐round results were given by sodium nitrite. This has therefore been introduced in the forest, though, as it is poisonous to man and to animals, urea or disodium octoborate (‘Polybor’) may be used instead where labour cannot be well controlled, or there appears to be a danger to unattended livestock or to water su

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04623.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

SUMMARYA lethal bole, rot disease of coconut, caused byMarasmiellus cocophilusPegler, sp. nov., reaches epidemic proportions in several areas along the coasts of Kenya and Tanzania.The first symptoms noticed on palms 8 or more years old are a frond wilt and a crown rot, but these follow a primary bole rot. Highest mortality is among seedlings and young palms up to 8 years old.Where the disease occurs sporophores are sometimes common on exposed roots, dead seedlings and the soil surface where diseased palms have been dug out. The fungus appears to be a persistent colonizer of coconut debris in the soil.Mycelial cultures from infected bole tissues and from sporophores were highly pathogenic to seedlings, and slowly invaded older tissue.M. cocophilusreaches the inner bole tissues only through the roots, and wounding of roots of their aerenchymatous protuberances is important in infection.Seedlings may become infected through roots damaged during transplanting from nurseries to the field; movement of seedlings from affected areas is one certain method of dispersal.Suggested control measures are: (1) selection of seedlings in nurseries and subsequent transplanting should be as early as possible; (2) seedlings should be transplanted very carefully, and damaged roots pruned and disinfected; (3) seedlings should never be taken from affected areas; (4) periodic soil sterilization of nurseries; and (5) no cultivation should be done between palms, especially where disease is present.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1970.tb04624.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY