摘要:

Eight series of aryloxyacetic, α‐aryloxy‐propionic, ‐butyric and ‐isobutyric acids have been synthesized, and their growth‐regulating activity has been assessed using six different test methods, viz. tomato‐leaf epinasty,Avenacylinder,Avenacurvature, tomato parthenocarpy, tomato‐leaf rooting and the Went pea test. The ability to induce morphogenic effects in tomato plants was also studied. The results are critically discussed and shown to be consistent with the view that in tests involving only cell extension the presence of an α‐hydrogen atom is usually necessary for growth‐regulating activity to be shown. In tests in which cell division occurs this effect is not so clearly defined, though the presence of an α‐hydrogen does, in general, correlate with grow

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01078.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The physiological activity of all the mono‐, di‐ and trichloro‐phenoxyacetic acids has been investigated using the pea curvature andAvenacylinder tests. The highest activity was shown by the 4‐chloro‐, 2:4‐dichloro‐ and 2:4:5‐trichloro‐ acids, though the 2‐ and 3‐chloro, 2:3‐, 2:5‐ and 3:4:dichloro‐ and the 2:3:4‐trichloro‐ derivatives were appreciably active in both tests. Significant activity was also shown in either one or both tests by the 2:6‐dichloro‐, 2:3:5‐, 2:3:6‐ and 3:4:5‐trichloro‐ acids.The activity of such compounds is considered in relation to two recent theories which attempt to relate capacity to induce a growth response with the position of substituents in the aromatic ring. It is concluded that neither theory can satisfactorily explain the relative activities of these

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01079.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

A technique for the propagation of Brussels sprout by means of root cuttings is described. Adventitious shoots arise exogenously on callus tissue which develops around the base of side roots. Cuttings sometimes rot without forming adventitious shoots, and cuttings which remain sound do not all produce shoots. Rotting may largely be prevented by planting cuttings with the proximal end exposed above the surface of the medium, and by allowing the root portions to dry before planting. Surface sterilization with mercuric chloride controls rotting but reduces bud formation. Individual plants differ in their capacity to form buds on root cuttings, and this difference is carried by the clones derived from them. Portions of root form more buds if cut into several pieces than if planted intact.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01080.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The epidemiology of club‐root disease of cabbages has been studied by growing plants in naturally and artificially contaminated soils under varying conditions of moisture, temperature, spore load, soil reaction and lime content.The disease can occur in both acid and alkaline soils. By attention to the interaction of factors influencing infection the presence or absence of an attack, as well as its extent and severity, can be predetermined.In acid soils, very favourable conditions for the incidence of the disease are a moisture content equal to about 70 % of the maximum water‐holding capacity and a mean air temperature of 18–23° C. Fluctuations in soil moisture at high levels provide as favourable conditions for infection as a high constant moisture. The level of spore load (within the limits of 103to 2.5 × 107spores per g. of soil) does not influence the number of diseased plants in acid soils when favourable conditions for an attack and for good growth of the host are provided. Under less favourable conditions spore load does exercise an effect.The disease occurred in both naturally and artificially contaminated soils showing a pH of 7.8 at planting time; in the former, the pH was adjusted to 7.8 by liming in the field over a period of years, and in the latter by treatment with pure calcium hydroxide shortly before planting. In alkaline soils infection is favoured by high moisture content, high temperature and high spore load. Satisfactory conditions for infection are provided, as in acid soils, at a moisture content of 70% of the maximum water‐holding capacity, it being immaterial whether this level is constantly maintained or fluctuating at high levels. No diseased plants occurred when the soil moisture fluctuated or remained constant at low levels. Severe attacks occurred in alkaline soils when the air temperature fluctuated between points much higher and lower than the mean temperature of 23° C. It is suggested that the optimum temperature for infection is higher than 23° C. In alkaline soils at moisture contents and temperatures favourable for infection a heavy attack can develop only in the presence of a high spore load.In general, it was found that the conditions which were most favourable for the incidence of the disease also favoured the intensity of its development.No substantial differences in the incidence of the disease in different soils were found, but more plants contracted club root in the lighter soils when conditions were less favourable for infection.The results obtained suggest that while liming in the field may control the disease if the spore load is low, even very heavy applications of lime may not be effective if the soil is heavily contaminated and soil moisture and temperature do not operate as limit

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01081.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The ability of four cereal root‐rot fungi,Helminthosporium sativum, Curvularia ramosa, Ophiobolus graminisandFusarium culmorum, to colonize wheat straw as saprophytes has been investigated. Test pieces of straw were buried in a graded dilution series of maizemeal‐sand culture of the test fungus with unsterilized soil. For assessing percentage straws colonized, three methods were compared: (1) isolation on agar plates, (2) Garrett's (1938b) wheat‐seedling test and (3) incubation on moist sand, to promote sporulation (the ‘sand‐plate’ test).Curvularia ramosaandFusarium culmorumwere found to behave as vigorous competitive saprophytes of the soil‐inhabiting type, whereasHelminthosporium sativumandOphiobolus graminisproved to be weak saprophytic colonizers of the specialized root‐

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01082.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

Factors influencing the saprophytic colonizing ability of two cereal root‐rot fungi,Curvularia ramosa, a vigorous competitive saprophyte, andHelminthosporium sativum, a weak competitive saprophyte, have been investigated. The observed difference in their competitive saprophytic ability could not be ascribed either to a difference in rate of growth or to the ability of the stronger saprophyte,C. ramosa, to produce an antibiotic. The weaker saprophyte,H. sativum, proved, however, to be more sensitive than C.ramosato antibiotics produced by other soil micro‐organisms. Thus, in spore germination tests with purified fungal antibioticsin vitro, H. sativumproved more sensitive to eight of the ten substances tested than didC. ramosaand was only slightly less sensitive thanC. ramosato the remaining two antibiotics.H. sativumwas found also to be generally more sensitive thanC. ramosato the antagonistic effects of certain common soil bacteria. Of the seven bacterial species tested, five caused an appreciable reduction in germ tube development and two reduced germination inH. sativumwhereas none of the bacterial species inhibited either spore germination or germ tube development ofC. ramosa, and three actually stimulated germ tube development by this fun

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01083.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

Records are given of the survival ofHelminthosporium sativum, Curvularia ramosaandOphiobolus graminisas saprophytes in infected wheat straw buried in un‐sterilized soil of different nitrate nitrogen content. Ample nitrogen supply prolonged the survival ofO. graminisand C.ramosabut shortened that ofH. sativum.Both the Australian isolate ofH. sativumused for the survival experiment and a Canadian isolate of the fungus were able to utilize nitrate, as well as ammonium and peptone nitrogen; neither isolate required either thiamin or biotin for growth in pure culture. The depressing effect of nitrate nitrogen upon survival ofH. sativumis ascribed to its encouragement of competing micro‐organisms also present in the infected str

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01084.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The wheat variety Red Standard was more susceptible to infection byErysiphe graminisat 14–20° C. than atc.7° C. Conidia were produced per unit area of pustule more than ten times as rapidly at 14° C. as at 7° C.The increased susceptibility of wheat to mildew after applying nitrogenous fertilizer (N) was associated with changes in its growth rate. Both growth rate and susceptibility increased to a maximum and then declined; the curves for the two were parallel, with a lag of some days between effect on growth rate and effect on susceptibility. Plants that had passed through the susceptible phase and became resistant to mildew, again became susceptible when supplied with more N. Nitrogen‐deficient plants continuously resisted infection.The higher the average growth rate during an experiment the greater was the total amount of infection. Increasing the average growth rate was soon followed by a sharp increase in the amount of infection. When plants of two size groups received the same amount of N the initially smaller plants became more heavily infected than the larger

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01085.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

A canker disease of cypresses, caused byMonochaetia unicornis, was first observed in Kenya in 1942. Outbreaks appear to have followed a spread from south‐east to north‐west, the direction of the south‐east monsoon, and the disease has now been recorded in nearly all the cypress‐growing areas of Kenya, Tanganyika and Uganda, in Southern Rhodesia and the Union of South Africa. The oldest known infections occurred in 1937.The fungus grows in the bark and sapwood, forming cankers which spread rapidly up and down the stem or branch, more slowly round, frequently causing girdling. Cankered trees produce large amounts of resin and a periderm may be initiated in advance of the fungus. Infections occur most commonly at main branch crotches, but cankers also start at the tree collar, on the stem and at minor branch crotches.The fungus exists in nature in three strains having differing levels of virulence, growth rate in culture, size of acervuli and conidia, and retention of viability in conidia. The distribution of one strain appears to be limited by ecological conditions.Acervuli ripen and conidia are liberated from 3 to 8 weeks after the start of the rains. Infections start during the rains and misty weather, the slimy spores being dispersed for short distances only. Conidia may retain their viability for up to 28 months.The local spread of the disease in Kenya has been traced and differing levels of virulence east and west of the Great Rift valley, associated with differences of climate, have been observed.Trees 2 years old are the most susceptible and older trees are only infected in the rapidly growing parts.Cupressus macrocarpais more susceptible thanC. lusitanica, the latter species being heavily infected only where it is growing close to diseasedC. tnacrocarpa.Occlusion of cankers occurs in both species but is more effective in halting the spread of the fungus inC. lusitanica.It is suggested that the disease originated from a single focus and may represent the mutation of a strain ofMonochaetia unicornisparasitic on cypresses from a strain only parasitic on an indigenous host,Juniperus procera.The fungus may, however, have been imported from

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01086.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY

摘要:

The two hop varieties Fuggle and OR55have respectively low and high resistance to wilt caused by virulent strains ofVerticillium albo‐atrum.When the pathogen enters through the roots it grows vigorously in the stems of Fuggle plants and slightly in the stems of OR55plants. Leaf symptoms are correspondingly severe and mild.If Fuggle stems are grafted on to OR55roots andvice versa, and the fungus thus invades the stems from roots of the opposite resistance type, it now grows slightly in the Fuggle stems and vigorously in the OR55stems. Leaf symptoms are correspondingly mild and severe, and thus wilt intensity is related to the variety of root and not to the variety of stem. Evidence is available which shows that this is not due to the transfer of a ‘resistance factor’ generated in the resistant roots.The variety Fuggle has low resistance to virulent strains ofV. albo‐atrumbut high resistance to mild strains. As in the case of varietal type this resistance is expressed by vigorous or slight growth of the fungus in the stems (and corresponding leaf symptoms) when the fungi are introduced through Fuggle roots. When they are directly inoculated into the stems there is no differentiation of the strains. If a small inoculum is used both strains induce mild wilt. If a large inoculum is inserted into a pith cavity both strains induce severe wilt. The reaction of the Fuggle stem is thus governed by conditions relating to the type of invasion and not to the strain of pathogen.It is suggested that this also applies with root inoculations. Normal stems of both Fuggle and OR55varieties have a high resistance to invasion from a weak source of the pathogen (such as exists in a highly resistant root), and the fungus can invade the stems heavily only from a suitable inoculum source (i.e. a root of low resistance).Heavy invasion of the stem from a root may be due to1A lowering of stem resistance by:(a) toxins diffused from the invaded root,(b) an impairment of normal root function.2An increase in invasive power of the pathogen by:(a) the establishment of a ‘food base’ in the root,(b) the diffusion of a ‘fungal accelerator’.The main conclusions that the primary focus of the disease is in the root and that the normal stems of all varieties possess a similar (and possibly high) resistance is supported by other researches onFusariumwilt of tomatoes and other wilt diseases and may be

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1953.tb01087.x

出版商:Blackwell Publishing Ltd    

年代:1953

数据来源: WILEY