摘要:

Xanthomonas malvacearumspread more rapidly along vascular tissue than into mesophyll when inoculated to the main veins of susceptible cotton leaves. The extent of spread varied with the concentrations of inocula, tissue age and cotton variety.Increasing concentrations of inocula accelerated the initial spread of disease.Bacteria spread more rapidly in young leaves than in old—increasing age greatly decreased disease in the mesophyll. The initial invasion was quicker in young leaves of young plants than in young leaves of old plants.Three types of behaviour, according to the host's reaction, distinguish Knight's resistance factors: (a) whereX. malvacearumspread extensively along veins and into mesophyll of plants containing factors B3and B5; (b) where it was restricted to the point of inoculation in plants containingB4, B9and combinations withB6m; and (c) where it spread along veins but not appreciably into mesophyll in varieties containingB2andB2B3.From this and four other different types of tests, factorsB2andB3seem to increase mesophyll resistance but onlyB2gives appreciable vascular resistance. Further, the vascular bundles in varieties withB2seem to be surrounded by an additional ‘barrier’ which resistsX. malvac

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03481.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

A bacterial disease of mahogany (Khaya senegalensisandK. grandifoliola) is reported for the first time. The disease causes rough or scabby leaf spots and small knob‐like cankers on the branches, which may die back as a result of infection. The symptoms of the disease differ to some extent with locality and host species. The causal organism is readily isolated from the leaves and young branches. Infection of the leaves takes place through the stomata at any time of the year. Several methods of inoculation into green shoots and woody branches were attempted but typical shoot infections were produced only when young green shoots were rubbed with the pathogen; the resulting blisters change to the typical knob‐like cankers when the shoots become woody.The disease is attributed to a new species ofXanthomonas, namely,X. khayaesp. nov., a description of which is gi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03482.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Antibacterial substances active againstCorynebacterium fascianshave been shown to be present in the coats of various seeds. There were considerable differences in activity between the seeds of different genera and species and between individual seeds of a single species.C. fasciansalso showed strain variation in sensitivity to the antibacterial substances of the seeds of any one species. An inverse relationship was demonstrated between the sensitivity of a strain to the sweet‐pea seed substances and its ability to infect sweet‐pea seedlings under laboratory conditi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03483.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The incidence and symptoms of a disease of lucerne induced byVerticilliumspp. are much less severe immediately after the crop has been first cut than later when the crop has matured. Infection becomes more marked as the season advances and the age of the ley increases, and cuts taken in the third harvest year are proving unprofitable.In cross‐inoculation studies the causal organisms of lucerne wilt,V. albo‐atrumandV. dahliaeprove to be only mild pathogens to hop, potato, tomato and antirrhinum, and are not pathogenic to sainfoin and clover. The last two may therefore be cultivated as fodder crops in those areas most severely affected by lucerne wilt, but the cultivation of potatoes after lucerne should be discouraged, particularly if lucerne is to be sown in future years, since the potatoes might build up a reservoir of inoculum of the lucerne pathogen. In studies of host‐parasite relations it is shown thatV. albo‐atrumandV. dahliaefrom lucerne,V. albo‐atrumfrom hop,V. tricorpusfrom tomato andV. nigrescensandV. nubilumfrom potato vary in their effects upon lucerne seedlings growing on agar media,V. albo‐atrumfrom lucerne being, as in the field, the most virulent and the only one to reach the xylem vessels under the conditions of the experiments.The dressings Agrosan‐GN (containing mercury) and Fernasan (containing thiram) are toxic both to spores ofVerticilliumon lucerne seed coats and to infected plant material carried with seed, and although they are also toxicin vitrotoRhizobium mellelotusthis did not prevent dressed seeds which had been inoculated with the bacterium from developing into healthy seedlings bearing normal

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03484.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Experiments were made during 1955‐57 on the fungicidal control ofBotrytisattack on lettuce, cv. May Queen, matured in frames from November to April, and cv. Trocadero Improved, grown as seedlings in frames from November to March and then matured in the field from March to June. The frame lettuce were treated during their whole period of growth and the field lettuce in the seedling stage only.On both types, 0.33% thiram sprays applied on up to five occasions gave the best control of disease: 5% tecnazene dust was effective on the frame crop, in 2 out of 3 years when applied to the plants and also when incorporated in the top soil at the rate of 15 g. per sq.yd. Tecnazene applications did not give a good control of the disease on the field crop. Sprays with 0.25% captan were almost as effective as the thiram treatments on the field lettuce but not on the frame cro

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03485.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Results of laboratory tests in Southern Rhodesia indicate thatColletotrichum tabacum, Böning, the causal organism of tobacco anthracnose, could survive in dry soil for 13–17 weeks and therefore might survive from one season to the next in dry soil in the absence of tobacco‐plant residue. The most favourable conditions for survival arose when soils of high organic content dried out fairly soon after being infected; soils which remained moist were the least favourable.Chemical control of soil infection with methyl bromide gas at 1 lb./100 sq.ft. was effective and not phytotoxic. Of the wettable powders used as soil disinfectants, thiram was more effective than zineb or maneb, but all were phytotoxic at certain concentrations. Phytotoxicity to tobacco, which took the form of stunting and poor root growth, varied with different commercial preparations of thiram and z

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03486.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Supplementary methods of controlling black‐pod disease (Phytophthora palmivora) of cocoa in Nigeria are considered, because fungicide application is not always economic.There is no evidence that resistance occurs within the local population of Amelonado‐type trees.Although the percentage of diseased pods was greater with trees closely spaced (5 times 5 ft. to 8 times 8 ft.), than with widely spaced trees (10 times 10 ft. to 15 times 15 ft.), the closer spacings often gave more healthy pods per acre.Loss of pods from black‐pod was decreased when trees were inspected frequently (alternate days) and infected pods were removed when showing the earliest symptoms. However, this procedure may not be economic, except when potential yields are relatively small (fewer than twelve pods per tree).Satisfactory control of black‐pod was obtained with copper fungicides, applied with either hand‐sprayers or a power‐sprayer. The monetary return depends on yield level, rather than on disease incidence or on spraying costs. It is recommended that spraying should be practised when the potential yield is twelve or more po

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03487.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Growth analysis of wild oats (Avena fatuaandA. ludoviciana) grown in pots with different levels of nitrogen supply showed many similarities to spring barley, winter oats and winter wheat.Small differences that could affect competition between wild oats and cereals occurred mainly in the seedlings. Wild oat seedlings were smaller than the corresponding cultivated cereals in total dry weight, total nitrogen content, leaf area and number of shoots. However, very young wild oat plants had higher net assimilation rates than the cultivated cereals and soon caught up and passed them. The difference in net assimilation rate did not persist, and in the later stages of growth differences in dry‐matter production depended mainly on differences in leaf area. Another important difference between wild oats and cultivated cereals was that 98–100% of the wild oat seeds and none of the crop seeds were dormant 2 months after harvest.Ear emergence in wild oats spread over a longer period, the range of ear heights was greater and the tallest ears were taller than in the corresponding cultivated cereals. Assimilation in the ear appeared to account for less of the total dry matter of the plants of wild and cultivated oats than of wheat. The wild oats produced more seeds per plant than the cultivated cereals, but the 1000‐grain weight, and hence the total dry weight of seeds, was lower in the weeds than in the crop.Addition of nitrogen to the soil affected the growth of the wild oats in the same ways as the cultivated cereals; they took up the same amount of nitrogen per plant as winter oats and winter wheat but more than spring barley.It is concluded that wild oats are most susceptible in the seedling stage to competition from the crop and that nitrogenous fertilizer applied to an infested field is unlikely to alter the balance between the yields of crop and of wild

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03488.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

During the first year of growth of timothy, variations in nitrogen supply affected the number of tillers and leaves, leaf area and dry weight, but had little influence on relative growth and net assimilation rates, except at very low levels of nitrogen. Differentiation and ear emergence occurred slightly earlier at high nitrogen and ear length was increased; there was also an increase in the proportion of fertile tillers among the total number produced after the first few weeks of tillering. The effect of nitrogen supply on the number, dry weight and ear length of early primary tillers was small but became larger in later tillers. Irrespective of the level of nitrogen supply, tillers had particularly high net assimilation rates during the first few weeks following their appearance.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03489.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The cress‐root test and the maize‐root segment tests, both of which depend on the measurement of root‐growth inhibition, have been used to assess the growth‐regulating activity of a wide range of phenoxyalkanecarboxylic acids. The results are presented and compared with those obtained with the same compounds in other tests in which shoot tissues were employed. The results are also discussed in relation to current theories on mode of action and structure/activity relationship. These studies included the ‘α‐hydrogen’ effect, the activity of stereoisomers and activity of homologues of seventeen series of ω‐phenoxyalkanecarboxylic acids, considered in relation to their degradation within the tissues by β‐oxidation. Earlier findings were largely confirmed. Compounds which had previously been shown to be active in shoot tests such as the wheat‐cylinder, the pea‐curvature and the pea‐segment tests, were found to be active in the root‐growth inhibition tests and, furthermore, the degree of activity was usually similar.It is concluded that the two root tests investigated are of real value in assessing the activity of phenoxy acids in studies on the relationships between chemical structure and plan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb03490.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY