摘要:

SUMMARYDevices are described which were used to catch rain‐dispersedColletotrichumconidia within and between coffee trees infected with coffee berry disease (CBD). The amount of CBD inoculum dispersed was related to the number of diseased and sporulating berries but not to the sporulating capacity of the fungus in maturing bark. Wet conditions encouraged spore production and dispersal, and spraying with fungicides prolonged sporulation of diseased berries.The amount of pathogenic inoculum, subsequent disease development and crop losses were greatly increased by the presence of only a few diseased berries during growth of the young crop. Spore concentrations were greatest close to diseased berries, but most spores within trees were dispersed downwards through the canopy. Some spores were dispersed between trees by wind‐driven rain‐splash and vectors such as pickers.Inoculum sources in tree tops are most important during CBD epidemics and disease can be restricted by removing or spraying the tops of multiple‐stem trees. Fungicide applied to tree tops effectively controls CBD, because spores dispersed during rain are accompanied by redistributed f

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04712.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYThe development of infection byPeronospora viciae(Berk.) Casp. was studied in field and plot experiments during 1967, 1968 and 1969. Numbers of primary systemically infected plants appeared shortly after emergence and reached a maximum by the end of May. Such plants acted as primary infectors and did not survive more than 3 weeks.Maximal sporangial release occurred between 06.00 and 08.00 h BST with a peak at 07.00 h, after 1–2 h insolation. Inoculation of leaves at 10.30 h resulted in greater infection than inoculation at 20.00 h. The result suggested a possible maturation requirement of sporangia following release from the sporangiophore.Initially the spread of foliar (local lesion) infection in the crop was sporadic and localized in cvs. Jade, Gregory, Dark Skinned Perfection (D.S.P.) and Frühe Kleine Pfälzerin (F.K.P.) during the 3 years. The number of plants of all cvs. with foliar infection reached 100% by mid‐June. Lesions rarely exceeded 15% of the leaf and stipular area of the mature plant. No effect of foliar lesions, at the highest level of infection, in haulm or seed fresh weight could be detected in cvs. F.K.P., Jade and D.S.P.Secondary systemic infection occurred sporadically in field crops usually with dense haulm growth. Plants of Jade with systemic infection were rated according to the number of nodes affected. There was a small but significant increase in haulm and seed fresh weight in plants with up to two nodes affected. But plants with three to five nodes showed a progressive reduction in the yield of green seed (resulting from a reduction in the number of podding nodes) and in pod size and haulm fresh weight. Total losses in Jade during 1968 and 1969 with all grades of infection did not exceed 4 % of the green seed crop. Systemic infection in some plants resulted in the death of the apex and the production of healthy, normally podding tillers. Such plants had no commercial value due to delayed maturation. Pod infection in Jade occurred largely independently of systemic symptoms: the overall level during 1969 did not exceed 16 % and only 2 % were severely infected.Total losses (from both systemic and pod infection) in Jade during 1968 and 1969 represented only a negligible part of the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04713.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYIncidence and severity of the take‐all disease in spring wheat and spring barley caused byGaeumannomyces graminis (syn. Ophiobolus graminis) were studied during seven years of monoculture.The fungus apparently survived for much longer periods in the soil under non‐susceptible break‐crops than previously recorded. The incidence and severity of infection increased progressively with each successive cereal crop from initially low levels to a maximum within 3–7 years, which was followed by a progressive but limited decline in the disease. Spring wheat was more susceptible to take‐all than spring barley and the development of take‐all decline (TAD) was recorded earlier in the sequences of wheat than of barley crops. Nitrogen did not influence the disease until the point of maximum incidence and severity, when it caused a reduction in disease levels in addition to that associated with TAD. Factors influencing the time of onset and the rate of development of take‐all and of TAD are discussed and possible explanations for TAD

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04714.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYPlants with symptoms of potato mop‐top virus (PMTV) occurred in many commercial seed stocks of Arran Pilot and Red Craig's Royal potato in Scotland, but their incidence rarely exceeded 5%. In nuclear stocks of seed potatoes, most varieties examined in 1967 and 1968 were infected at one or more locality, but infected plants did not occur in all clones or at all stages of propagation of any one variety. infection of nuclear stocks resulted both from propagation on virus‐infested land and from unwitting selection of infected plants to start new clones. PMTV was detected in farm soils ranging from light sands to heavy loams, in five Scottish counties. Soil was infested throughout the ploughed layer but the severity of infestation varied greatly within any one field; some sites of former potato clamps were heavily infested. PMTV was detected in field soil 12 years after potatoes were grown.In glasshouse tests many British crop and wild plants were colonized bySpongospora subterranea.Within some families all species tested were moderate to good hosts. (Solanaceae, Chenopodiaceae and Cruciferae), in others, species differed greatly in susceptibility (Compositae and Umbelliferae), and in a few, species were poor hosts or were not infected (Caryophyllaceae and Gramineae). Of the British crop and weed species that were moderate to good zoosporangial hosts ofS. subterranea, onlySolanum nigrum, potato, spinach and sugar beet were hosts of vector‐borne PMTV. Potato probably survives between potato crops mainly in the resting spores ofS. subterranea.PMTV was probably first brought to Europe with potatoes from South or Central Am

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04715.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYAn experiment in a field where sugar beet in 1965 had suffered from Docking disorder caused byLongidorus attenuatustested the effect of fumigating the soil with 3741/ha D‐D and two amounts of nitrogen fertilizer on different crop sequences between 1966 and 1969. Although severe Docking disorder did not recur in sugar beet, fumigation increased yield in each of the three following years. Yield of barley was increased for 4 yr and of wheat, potatoes and ryegrass for 1 or 2 yr after treatment. All plant parasitic nematodes were controlled by the first fumigation and the numbers of those in unfumigated plots 3 yr after treatment. Fumigation also largely prevented infection of sugar beet by the fungusHelicobasidium purpureu

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04716.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYA model is deveolped relating photosynthesis taking place in successive layers of the canopy of a wheat crop to the intensity of the radiation incident on the crop, the elevation of the sun, and to the angle to the horizontal and photosynthetic area of ears, leaves and leaf sheaths. The validity of the model is tested by comparing the rate of photosynthesis, pattern of translocation and solid geometry of a semi‐dwarff wheat (TL 365a/25) with those of a variety of conventional height (Cappelle‐Deprez). The model gives realistic estimates of crop yield and indicates that the greater yield of the semi‐dwarf selection is caused by faster photosynthesis, despite less photosynthetic surfaces of ears and leaves. It also indicates that selection for erect leaves may lead to further increases in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04717.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYWhite clover, red clover, lucerne, sainfoin and Italian ryegrass were grown in a series of culture solutions in which 0, 25, 50, 75 and 100% of the potassium was replaced by sodium. In the shoots, the potassium: sodium ratios indicated selectivity for potassium which decreased in the order: sainfoin>lucerne>red clover>white clover>Italian ryegrass. In the roots only sainfoin showed selectivity for potassium: with the other species the ratio of potassium to sodium in the roots was similar to that in the other species the ratio of potassium to sodium in the roots was similar to that in the culture solution. All species showed selective transport of potassium to the shoots in preference to sodium: this was least in Italian ryegrass and white clover and greatest in sainfoin, which in contrast to other species also showed restricted transport of potassium to the shoots. Replacement of potassium by sodium slightly increased the magnesium concentration in the shoots but had no effect on the calcium concentration.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb04718.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY