摘要:

SUMMARYPotato mop‐top virus (PMTV) was best detected in field soils by air‐drying them for more than a week before remoistening and growing seedlings ofNicotiana tabacumorN. debneyifor a 6–10 week period. Infection ofN. tabacumwas assessed by inoculating sap from roots and shoots toChenopodium amaranticolor.Similar inoculations fromN. debneyiwere far less convenient for detecting PMTV than recording leaf symptoms, but slightly more efficient.Air‐dry soil retained PMTV infectivity for 9 months, when passed through a 50 μ sieve or when diluted with 103but not 104parts of steamed soil. Tobacco seedlings were not infected when their roots were steeped in PMTV‐containing tobacco sap. Infective soils containedSpongospora subterranea, spore balls of which resisted air‐drying for more than a year and passed a 50 μ sieve. Roots of susceptible seedlings were infected with PMTV when exposed to spore balls ofS. subterraneataken from powdery scabs on PMTV‐infected potato tubers, or to suspensions obtained by steeping, in nutrient solution, roots infected with virus‐carrying cultures ofS. subterranea.Plants in several families were hosts ofS. subterranea, but probabilities of infection when exposed to spore balls differed greatly between families and only species of Solanaceae were good hosts. The ten species infected with PMTV when grown in infective soil or when exposed to spore balls ofS. subterraneataken from PMTV‐infected potato tubers are all members of this family. PMTV seems to be carried internally inS. subterraneaspore balls and survived in them for at least a year.PMTV was transmitted byS. subterraneato Arran Pilot potato, causing yellow blotches in some leaves and spraing in many tubers. However, when newly infected with PMTV in the field, not all Arran Pilot tubers developed spraing. Also, although many spraing‐affected or symptomless but PMTV‐infected tubers carried PMTV‐containing spore balls ofS. subterranea, powdery scabs were rarely found near the centres of the rings of primary spraing. PMTV became established in virus‐free soil when PMTV‐infected tubers carryingS. subterraneawere planted as ‘seed’ but not when virus‐free tubers bearing powdery scabs were used. 5.subterraneaseems the main, and possibly the only, vector of PMTV in the soils examined.S. subterraneadid not transmit potato aucuba mosaic virus from p

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05461.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYWhen the natural incidence ofCladosporium fulvumCooke, occurring at a relatively late stage of cropping, was controlled with fungicides, comparisons with unsprayed control plants showed that there was an interval ofc.6 weeks between the incidence of severe infection, when the fungus was colonizing at least 50 % of the host's leaf area, and fruit yield decreases.Eye estimates made on separate leaves usually over‐estimated the percentage of infection. Correction factors were derived from the regression of eye estimates on infected areas calculated from leaf tracings. Whole‐plant infection indices were obtained by averaging corrected values of percentage infection separately assessed on leaves immediately above each fruit truss.Although dichlofluanid and tank‐mixed zineb decreased the incidence ofC. fulvummore than captan sprays, tomato yields (including green fruit) were increased similarly by all three fungicides from 2·99 to an average of 3·51 kg/plant duringc.3 months' picking. Decreasing the intervals between successive sprays from 21 to 7 days greatly decreased leaf mould infection but did not significantly affect yields. Restricting applications to plant tops (namely foliage from the fourth‐youngest truss to the mainstem apex) gave yield benefits equal to those gained from sprays applied to who

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05462.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYCalcium nitrate prolonged the saprophytic survival ofOphiobolus graminis(Sacc.) Sacc. in artificially colonized straws buried in soil in the laboratory, whether supplied to the soil (at 12·5 or 100 mg nitrogen/100 g soil) or to the straws before colonization (at 0·5 or 1·0 g nitrogen/100 g straw). Glucose (at 2·5 g/100 g soil, and at 10 g/100 g straw) shortened survival.When straws colonized in the presence of 0·5 g nitrogen/100 g straw were buried in soil supplied with 14·1 mg nitrogen/100 g soil, the level of soluble soil nitrogen reached equilibrium at 2–4mg/100g soil; this allowed rapid straw decomposition and, although the added soil nitrogen prolonged survival in straws that remained undecomposed, it also accelerated substrate exhaustion. Addition of 100 mg nitrogen/100 g soil was supra‐optimal for survival: although some nitrogen was necessary for maximum survival, the equilibrium concentration of soluble nitrogen (24–56 mg/100 g soil) was high enough in this case to have an inhibitory effect

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05463.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYUnder a glasshouse crop of red clover,Ophiobolus graminis(Sacc.) Sacc. in artificially colonized straws survived for longer on the soil surface than when buried, and for much longer when suspended above the soil; survival in buried straws was somewhat more prolonged in fallow soil than under clover. In field experiments with consecutive crops of winter wheat, under‐sowing with red clover was not effective in reducing the incidence of take‐all, possibly because of above‐ground survival of the pathogen in unploughed straw. Early rotavation, however, significantly reduced disease incidence, probably because of enhanced microbial activity and competition for nitrogen in the well‐aerated compost of soil and

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05464.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYIn laboratory, greenhouse and field experiments, mancozeb and copper compounds controlled the leaf‐spot phase of zebra disease caused byPhytophthora arecae, one of the pathogens responsible for this serious disease in Tanzania's high‐yieldingAgavehybrid no. 11648. As the copper compounds were phytotoxic, Dithane M‐45 (Mancozeb) is recommended as a protectant during the rainy s

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05465.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYEpidemic attacks ofPhytophthora parasiticaon papaya fruits developed during wet, windy weather, but declined rapidly when the weather became dry. During rain, abundant sporangia were liberated from the mycelial mats on infected fruits, but none was trapped in dry air.Collar rots and tree collapse caused by root rot occur irrespective of spray treatments and previous aerial infections on the same tree: they are no more prevalent in blocks with abundant aerial infections than in blocks with none. Basal rots occurred earlier and more frequently on plantings near abandoned diseased fields: they were scattered randomly and appeared before aerial infections.It is suggested that new outbreaks might be initiated from seeds of infected fruit, in which chlamydospores have been found, or from infected nursery seedlings.Drosophilaspp. were found to be occasional vectors of sporangia.Control of aerial infections was obtained with maneb, basic copper sulphate, captan or difolatan. Spraying only the upper half of the acropetally developing fruit cluster gave much better control than spraying only the lower fruits.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05466.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYA patchy degeneration of weed mats ofSalvinia auriculatain the sheltered mouths of rivers draining into Lake Kariba was reported in 1962 to be associated with a fungal attack. Laboratory isolations from degenerating plants yielded a saprophyticAlternariasp. and a parasiticSpicariopsissp. Degenerating plants failed to transmit the disease when placed among healthy plants, and the results of inoculation experiments with spores ofSpicariopsissp. were inconsistent with this fungus being a primary pathogen.The characteristic feature of degeneration in the field was a mosaic of alternating ‘islands’ of diseased and healthy plants. Although the diseased plants showed the symptoms associated withAlternariasp. andSpicariopsissp., their characteristic distribution provided circumstantial evidence that degeneration was physiological in origin. This view was strengthened by the fact that sudd plants growing on degenerating areas of theSalvinia‘carpet’ were usually chlorotic. The presence of symptoms caused by the parasiticSpicariopsissp. on degenerating plants could be explained by postulating that, after the plants have begun to degenerate, they are predisposed to infection by this fungus.The association of degeneration with a particular type of riverine site suggests that a seasonal investigation of the hydrobiological conditions accompanying the development of weed mats at such sites would indicate the type of factor responsible for the disease. The original hope for a biological control ofSalvinia auriculataby means of a parasitic fungus remains a theoretical poss

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05467.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYA laboratory technique is described for the production of drops of simulated rain in which fungal spores were suspended. When such drops containing conidia ofBotrytis fabaeimpacted on a target leaf the secondary droplets produced infections on receptor broad bean leaves. The capacity of fungicides applied to the target leaf to redistribute in secondary splash droplets was examined in terms of the infectivity of the spores in the droplets. The extent to which a copper fungicide reduced infection on the receptor leaves was related to the level and tenacity of the fungicide deposit on the target leaf. The effect of wetting agents on the redistribution of this fungicide could probably be explained by their influence on the tenacity of the initial deposit. In general the capacity of different fungicides to inhibit infection by the secondary droplets was related to the inherent toxicity of the fungicides toB. fabae.Implications of the dispersal of spores and fungicides by rain splash are briefly considered with reference to field conditions.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05468.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYPlots were fumigated with various amounts of D‐D or 85% dazomet dust and sown with spring wheat given various amounts of nitrogenous fertilizer. Dazomet increased yield and decreased take‐all disease in the first crop after application, but increased the disease in the second crop. Although D‐D increased take‐all slightly, it increased yield in 1966, but in 1967 it decreased yield and its use was associated with a severe ear deformity. Fumigation had little effect on eyespot, sharp eyespot, root browning (Fusariumspp.), or browning root rot (Pythiumspp.), but decreased nematode damage where nematodes were n

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05469.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYImproved pathogen‐free seed germination and better seedling growth were obtained by hot‐water treatments at 60 °C for 10 min of seed of the cotton varieties Karnak and Ashmouni, and at 45 °C for 5 min of seed of the flax varieties Giza 4 and Baladi.These treatments also reduced pre‐ and post‐emergence losses due toRhizoctonia solaniandFusarium oxysporumf.sp.vasinfectumin cotton, and toF. oxysporumf.sp.liniin flax, and resulted in better growth of the survivi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb05470.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY