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Copyright of Weed Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper considers the problem of estimating the short-run effects of nominal tariff and domestic production levels on the levels of imports and final market prices of fresh tomatoes in the UK during the period 1959-1968. Prior to EEC entry, tariff protection was used as the main policy instrument for horticultural support; horticultural goods being exempt from guarantee or intervention price schemes. In retrospect it would, therefore, seem useful to consider the theoretical requirements for its effective use in such a market situation. The paper consists of two parts. The first section discusses a simple comparative-static specification of a simultaneous equation market model determining the prices and import levels of a single horticultural good and goes on to derive measures of the effects of tariff rate and domestic production changes on market equilibrium. The second section presents several sets of alternative estimates of the specified market model and calculated effects for the specific case of fresh tomatoes during the period 1959-68. [ABSTRACT FROM AUTHOR]

The article provides information on the results of a study on the effects of the substituted urea herbicides diuron and linuron on sap flows in tomato roots. Samples of radioactive exudate and pure herbicide were applied into Whatman chromatogram paper and developed with benzene-acetone. It found that major disruption of the root tissues does not occur following application although pressure-induced sap flows may be identical to sap transport in the intact plant. It concludes that herbicide absorption is determined by their structure.

This article presents the results of an experiment on the control of potato root eelworm in a glasshouse soil with a formulation of methyl isothiocyanate. A formulation of 20 per cent methyl isothiocyanate in xylol was applied at 125 milliliter/square meter to plots of glasshouse soil infested with potato root eelworm, 34 days before planting with tomatoes. Live eggs, hatched larvae, larvae in roots and larvae in soil after treatment, and live eggs after harvest, were counted. Assays agreed in their estimates of kill, but counts of live eggs underestimated kill. Injection gave a 93-99 per cent kill and was superior to surface sprinkling of the sterilant and sealing with waterproof paper, which gave a kill of 82-85 percent. Plant height and tomato fruit production were increased by treatment.

Glucose pre-treatment enhances ageing in excised roots of tomato on subsequent sub-culture in sucrose medium to a much greater extent than pre-treatment in sucrose or fructose. However, continual sub-culture in glucose medium causes much less ageing than continual sub-culture in sucrose or fructose. Sugar concentrations used were such as to preclude effects due to osmotic potential changes. Pre-treatment in mixtures of glucose and sucrose caused less ageing than glucose alone, but this may be due to the demonstrated reduction in glucose absorption caused by sucrose. A two-stage system for the development of ageing is proposed and this is discussed in the light of earlier studies on ageing in cultured tomato roots. [ABSTRACT FROM AUTHOR]

The effect of aspermy virus infection the water status of tomato leaves was studied. Infected leaves had a higher relative water content than controls, the increase being related to inoculum concentration. This was shown to be caused by an inability to take up water rather than a truly higher water content. It is suggested that this may be the result of a reduction in the permeability of cell membranes. [ABSTRACT FROM AUTHOR]

1. Young cocklebur plants grown under various short cycles of alternating light and dark periods of equal length (each period 6 seconds, 1 minute, 5 minutes, 30 minutes, 60 minutes, or 120 minutes in length) for two to three weeks showed the best growth as measured by increase in dry weight under cycles of 1 minute of light and 1 minute of darkness (1-minute cycles). One-hour cycles were also favorable to growth, while growth was relatively poor under 5-minute. 30-minute, and 2-hour cycles. 2. Young tomato plants grew best under the shortest cycle employed (6-second) and also well under 5-minute cycles, but growth was relatively poor under 1 minute cycles and quite poor under 30-minute and 60-minute cycles of the ones employed. 3. The growth patterns under a series of various cycles were not changed by the application of a daily spray of 10 per cent sucrose solution, by a spray of 5X10-4 M solution of IAA applied every third day, not by a single spray of 0.5 or 5.0 mg/I of TIBA applied at the beginning of the experimental period in either plant, except for some depression of growth in the tomato by the applied IAA. 4. Chlorophyll deficiencies appeared in leaves of cocklebur piants grown under 5-minute and 15-minute cycles and in the leaves of tomato plants grown under 5-minule and 30-minute cycles (a 15-minute cycle was not used with the tomato), while plants under the other cycles used were normal in color. The application of the various sprays did not affect this chlorophyll deficiency. [ABSTRACT FROM AUTHOR]

Culture of roots for 7 days in 1.5% glucose medium drastically enhanced ageing on subsequent subculture in 1% sucrose medium. NAA, GA, BA, ABA and ethylene enhanced the ageing of roots cultured in I% sucrose medium, but counteracted the effect of pretreatment in 1.5% glucose. Reduction of growth during the glucose pretreatment by low temperature counteracted the effect of glucose on ageing; in contrast, reduction of growth by a high concentration of mannitol did not affect ageing. Exposure of roots to glucose for 72 h was required to produce the effects of glucose. It is postulated that cell division may be required during the glucose treatment for glucose to affect ageing. [ABSTRACT FROM AUTHOR]

Examination of the effect of CO2-concentration and time of day on the content of malic acid, citric acid, aconitic acid, isocitric acid, succinic acid and fumaric acid in tomato leaves, revealed that the total content of these acids will rise with the CO2-concentration up to 0.10 vol% Co2. In the morning up to 0.22 vol% CO2 was needed for optimal effect. Samples of leaves picked at 1 a.m. showed the lowest content of these acids. At 9 a.m. the content had increased, and at 4 p.m. the increase was considerable. The content of malic and citric acid constituted 36 and 34% of the total acid content. In the afternoon and the night the aconitic acid represented 14% and in the morning 20% of the total acid content. Isocitric acid, fumaric acid and succinic acid occurred only in relatively small concentrations. [ABSTRACT FROM AUTHOR]

The light saturation curves for photosynthesis in Lycopersicon esculentum have been studied for a yellow-green mutation and for hormone treated plants. comparisons have been made between saturation point and the size of the photosynthetic unit in these plants. These data suggest a function in the regulation of photosynthetic rates. [ABSTRACT FROM AUTHOR]

T3238fer (Fe-inefficient) and T3238FER (Fe-efficient) tomato plants differ in their ability to utilize Fe and therefore can be used as test genotypes to locate sites of Fe uptake or to characterize changes that occur in roots in roots in response to Fe stress (Fe deficiency). T3238fer does not respond to Fe stress. Release of hydrogen ions and reduction of Fe3+ to Fe2+ are two primary responses of T3238FER roots to Fe stress. Fe reduction sites were predominantly in the young lateral roots, and between the regions of root elongation and maturation of the primary root. The use of BDPS (bathophenanthrolinedisulfonate) to trap Fe2+ did not affect the release of H+ ions or reduction by T3238FER roots. BPDS did not decrease Fe uptake until it exceeded the Fe concentration in the nutrient solution. A sevenfold increase in BPDS caused a threefold decrease in Fe taken up by the plant. Fe3+ is reduced to Fe2+ at root sites accessible to BPDS. Adding Zn decrease the response to Fe stress. Iron stress initiates the development of lateral roots, and we propose that most Fe enters the plant through these roots. The iron moves through protoxylem into the metaxylem of the primary root and then to the top of the plant as Fe citrate. Root environmental factors that are competitive or inhibit Fe-stress, response, or genotypes that fail to respond to Fe stress, contribute to the development of Fe deficiency in plants. [ABSTRACT FROM AUTHOR]

In experiments with intact tomato plants the effect of potassium on the translocation of photosynthates was studied. Four series of plants were grown in nutrient solutions with two different potassium levels (K1 and K2 treatments). When the fruits of the first truss had developed the plants were treated with labelled CO2 for 2 h in a glove box. The plants were then divided in roots, stems, fruits and leaves, which were prepared for chemical analysis. In all experimental series the plants with the higher K supply grew better and therefore assimilated higher amounts of labelled CO2 (cpm/plant). The assimilation rates per g fresh material, however, were not increased in each experimental set by the K2 treatment. The absolute quantities of labelled photosynthates transported from leaves and stems to the fruits were also greater in the plant with the higher potassium supply. In all experimental series the proportion of labelled material found in the fruits was higher in the plants of the K2 treatment (total label of the plant = 100%) than in the plants of the K1 treatment. This beneficial effect of potassium was also observed in cases, where potassium had not affected the CO2 assimilation rate. Expressing the distribution of labelled material in relative terms (percentage proportions) means that the effect of CO2 assimilation on the transport of photosynthates was excluded to a high extent. The higher percentage proportions of labelled material found in fruits and roots of the K2 as compared to the K1 treatment is, therefore, predominantly dependent on a specific effect of potassium on the translocation of assimilates. The labelled material found in the soluble fraction of the stems consisted of about 90% sugars, nearly half of which was sucrose, the rest being mainly glucose and fructose. This finding suggests that sucrose is the most important... [ABSTRACT FROM AUTHOR]

Copyright of Weed Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Weed Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Weed Research is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Endotrophic mycorrhiza in tomato and maize, induced by chlamydosporic varieties of Endogone macrocarpa, were examined quantitatively by estimating infection of roots, pigmentation of roots and production of ectocarpic chlamydospores. When the size of the root system was taken into account, estimates of infection showed a relationship to growth of the host. The amount of pigmentation within the root system gave a good indication of mycorrhizal intensity and was related to the size of the host at high levels of infection. The numbers of spores produced on an individual root system, given a particular treatment, were positively correlated with the size of the host. The relative merits of these different assessments of mycorrhiza are discussed. [ABSTRACT FROM AUTHOR]

During the months of May, June and July, when the demand for tomatoes is at its highest, British consumers' needs are met by supplies coming from heated glasshouses in South Holland, in Guernsey, and in England and Scotland. The island of Jersey also sends a small amount of glasshouse tomatoes, but for all practical purposes Southern England and the two off-shore territories command the supply. [ABSTRACT FROM AUTHOR]

Gibberellin A4&7 was more effective than gibberellic acid in increasing shoot elongation when applied to the apex of intact Lycopersicum esculentum seedlings of Tiny Tim, a dwarf cultivar, and Winsall, a tall cultivar. After 14 days, gibberellic acid and gibberellin A4&7 stimulated growth of the dwarf more than the tall tomato. In tall tomato the application of indole-3-acetic acid alone (6.1 μg/plant) showed an inhibitory growth effect, but when applied with 17.5 μg per plant of gibberellic acid, it had a synergistic effect at 7 days but not at 14 days. When the auxin concentration was reduced to 0.61 μg per plant a synergistic effect was observed on tall plants at 7 and 14 days between indole-3-acetic acid and gibberellic acid. Application of gibberellin A4&7 with auxin did not give a synergistic response in tall or dwarf tomato. [ABSTRACT FROM AUTHOR]

Lycopene biosynthesis of parenchyma chromoplasts was studied in detached tomato fruits, Lycopersicum esculentum Mill. cv. Waltham forcing, and found to be phytochrome mediated. A few minutes of red light during the day enhanced lycopene formation. Far-red irradiation did not enhance lycopene biosynthesis. Far-red following red nullified the promotive effect of red light. Lycopene content increased two-fold in the presence of abscisic acid. Ripening of tomatoes was inhibited when gibberellin, kinetin and ascorbic acid were applied to green tomatoes. Gibberellin (A3) was more inhibitory to lycopene synthesis than kinetin. [ABSTRACT FROM AUTHOR]

Carotenoid synthesis in the fruit of tomato mutants is under gene control. Since undifferentiated plant cells are presumably totipotent, the callus tissue should be able to produce the carotenoids typical of the genotype. The carotenoids of masses of callus derived from hypocotyls of the red ghost and tangerine tomatoes were extracted and characterized by means of column and thin layer chromatography, chemical and spectral properties. The red ghost callus contained predominntly phytoene and phytofluene; the tangerine callus had primarily ζ-carotene and prolycopene. Thus under our cultural conditions, carotenoids typical of the fruit rather than the leaf were produced, albeit in much reduced quantities. [ABSTRACT FROM AUTHOR]

Measurements were made of phosphorus uptake by intact tomato plants from solutions labelled with 32P. The plants were exposed to low water potentials by the addition of mannitol to culture solutions. The amounts of labelled phosphorus in the roots and in the shoots were determined after a one- or two-hour period. Down to -5.4 atmospheres, the amount of labelled phosphorus in the roots remained constant, but the amount transported to the shoots was reduced. However, potentials of -10.4 atm reduced the amount of labelled phosphorus in both the root and the shoot. Similar results were obtained when plants were tested immediately after water stress was imposed and when tested after water potentials had been lowered gradually. Plants were treated for one hour at low water Potentials and then returned to control solutions (-0.4 atm). For a considerable time, these plants had a much lower phosphorus uptake than plants which had remained continuously at -0.4 atm. These data support the idea that a disturbance in mineral nutrition is partly responsible for reduced growth in plants which experience a moderate water deficit. [ABSTRACT FROM AUTHOR]

Research was carried out concerning the cell-physiological backgrounds of the disease blossom-end rot of tomatoes, which, like bitter pit of apple and tipburn of lettuce, is a Ca-deficiency disease. In our experiments tomatoes with the least amounts of Ca were attacked by the disease. We estimated the ion permeability of tissues with different Ca levels. Permeability was found to increase with decreasing Ca contents in the tissue. The increase accelerated with the beginning of the disease. The artificial rise in the permeability caused by ether and decenylsuccinic acid resulted in an increased occurrence of the disease. It is probable that the Ca-deficiency causes the necrosis of the tissue in blossomend rot and that the shortage of calcium among others affects the disorganization of membranes and organells in the cell. [ABSTRACT FROM AUTHOR]

The effects of uracil and its analogue 5-nitrouracil on growth and flowering of tomato have been studied. A few drops (0.3 ml) of solutions containing 15, 30, 60, 90 and 150 μg of each prepared from a stock of 500 mg/l in glass redistilled water were applied per plant on 3-4 top leaves and the apex of one month old seedlings with 6-7 leaves. A second application double in volume of the same chemicals was made on the same plants a week later. The controls were given a distilled water treatment. Treatments with uracil and 5-nitrouracil significantly increased the plant height and the fresh and dry weights of the shoot. Higher concentrations (500 mg/l) had no promotive effect. Although there had been a significant promotion of the leaf and stem growth, the root growth and the nodes were unaffected. Flowering was significantly hastened by both bases. Treatments with uracil also resulted in the formation of more flowers. Uracil and 5-nitrouracil also caused significant increases in the total-N of the leaf and the stem, and the effect on protein metabolism seems to be localised where they act as RNA metabolites. The presence of the nitro-group in 5-nitrouracil does not act as an additional source of nitrogen for protein metabolism as it did not have more promotive effects than uracil. [ABSTRACT FROM AUTHOR]

The carbohydrate content (starch, glucose and sucrose) in tomato plants grown in air containing 0.04, 0.10, 0.15, 0.22, 0.32, or 0.50 vol. per cent CO2 was studied at 2 hours' intervals over a period of 24 hours. The highest starch content was found at 0.22 vol. per cent CO2, while the highest content of soluble sugars were reached at a concentration of 0.10 vol. per cent CO2. A few observations of the morphogenic effects of carbon dioxide were also made. [ABSTRACT FROM AUTHOR]

In excised tomato roots submerged in solution, mannitol at -2.8 atm increased the phosphorus uptake and decreased the loss of previously absorbed phosphorus. Separate collection of the xylem exudate demonstrated that these mannitol effects were due entirely to a reduced phosphorus flow via exudation. For example, in the case of previously absorbed phosphorus, the high loss of phosphorus at -0.3 atm could be contributed to phosphorus transport via the exudation stream, which was higher at -0.3 than at -2.8 atm. In contrast, loss from the root surface to the external medium was identical for the two different water potentials. The neglect in measuring ion flow in the exudate might have confounded ion transport studies by other workers. Some particular cases were re-examined, such as chloride uptake at high external concentrations and ion loss from different cell compartments. [ABSTRACT FROM AUTHOR]

Seedlings of loblolly pine were grown in sand culture at two concentrations of nitrogen 110 and 75 ppm N) and calcium (0 and 200 ppm Cal for a four month period in order to determine which form of nitrogen was used most readily and to learn if there was an effect of calcium on nitrogen metabolism. Three sources of nitrogen were employed: nitrate. ammonium, and urea. A number of indicators of growth were followed, and chemical analyses were made of foliage and roots. The results are summarized as follows: 1.Urea, when supplied at 75 ppm of N, resulted in production of the greatest height. diameter, fresh weight. dry weight. and the lowest root/ shoot ratio of any of the treatments. 2.A number of seedlings died when ammoniinn nitrogen was supplied in the presence of calcium. but not in its absence. .3. Use of urea was associated with the highest total nitrogen content of foliage and nitrate with the least. Nitrogen source, however, did not have a major influence on the total nitrogen content of roots. 4.The soluble nitrogen content of foliage and roots was greatest with urea, and least with nitrate. when nitrogen was supplied at 75 ppm and calcium at 200 ppm. 5.Total and individual free amino acids, especially arginine, glutamine. asparagine. and praline. varied greatly with the nitrogen source. Seedlings supplied with ammonium had the largest amount of free amino acids. while those receiving nitrate had the smallest reserves. Nitrogen deficiency symptoms were produced in all 10 ppm nitrogen treatments. There was very little difference in the appearance of the plants in any of the 10 ppm series. 7. Calcium deficiency symptoms were not produced at 0 ppm calcium. However. 200 ppm calcium in the nutrient solution resulted in slight increases in almost all indices of growth that were used. 8. The foliage total nitrogen content in most treatment sequences was influenced positively by the presence of calcium in the nutrient solution, whereas the root nitrogen content was generally influenced negatively when calcium was supplied. O. The calcium content of the foliage was influenced not only by calcium level, but also by the nitrogen source. Nitrate was associated with the greatest foliage calcium content at each level of nitrogen supplied. [ABSTRACT FROM AUTHOR]

Tomatoes and eggplants used as top-scions, inter-stocks and stocks were grafted on potato plants, in order to evaluate their effects on tuberization of potato. There was some tuber inhibiting substance in tomato and eggplant which was formed in young leaves. The tuber forming stimulus moved readily downward from potato scions to potato stocks through tomato inter-stocks without young leaves. Tomato inter-stocks with young leaves resulted in an inhibition of tuberization of potato stocks regardless of supply of tuber forming stimulus from potato lop-scion. Apparently an inhibition of tuberization of potato plants grafted with tomato or eggplant may depend on not only a lack of tuber forming stimulus but formation of tuber inhibiting substance. [ABSTRACT FROM AUTHOR]

The relation between water uptake and nitrate ion uptake was studied in experiments with excised root systems of tomato plants. For the preliminary culture of the sample plants and for the experiments proper we used nutrient solution the concentration and composition of which was kept as nearly constant as possible. The regulating effect of transpiration on water uptake was replaced by a vacuum established above the cut surface of the stump of the stem. The results show that root systems absorb water and nitrate at uniform rates when a constant vacuum is established above the stump of the stem. This applies throughout the vacuum range used from 0-70 cm, Hg. The degree of vacuum (suction) determines the rate of uptake, The higher degree of Vacuum, the higher the rate of uptake, and this applies to water as well as nitrate. Thus a relation exists between the rate of water uptake and the rate of nitrate uptake: but the relation is not a simple straight-line function. since the rates of uptake for water and nitrate are not affected in the same way by a given change in vacuum values within the range of 0-70 cm. Hg. The discussion concludes that the area of the root active in the uptake of water varies with the degree of suction. and that the ratio permeability to nitrate/permeability to water does not remain constant in the different parts of the root system activated for water uptake as the vacuum increase. [ABSTRACT FROM AUTHOR]

An attempt was made to determine the rate of active and that of passive ion uptake processes in tomato plants. Experimentally this was accomplished by investigating the nitrate uptake and the respiration rate on root systems with and without top (transpiration). The measurements were performed with short intervals in 2 to 3 hour periods prior to and after detopping. The results showed a considerable change in the rate of nitrate uptake when the tops were removed. The respiration of the root system, however, remained unaffected during the entire experimental period. It is concluded that under the conditions of the present experiments the passive uptake of nitrate amounts to at least three quarters of the total uptake of nitrate. [ABSTRACT FROM AUTHOR]

Root respiration in intact tomato roots was studied by simultaneous determinations of carbon dioxide release and oxygen consumption. When the root remained in undisturbed nutrient solution for a short time preceeding the determinations (20 minutes), the rate of carbon dioxide release was higher during the initial experimental period (20-30 minutes) than during the subsequent period. The oxygen uptake proceeded at a constant rate throughout the experiment. The hypothesis is advanced that the "extra" carbon dioxide release during the initial experimental period is due to a delayed release of carbon dioxide produced and accumulated in the root tissue prior to the experiment. It is concluded that determination of oxygen consumption is the most reliable method of measuring root respiration in short time experiments. [ABSTRACT FROM AUTHOR]

1. In a particular experiment (Street, McGonagle and Roberts 1953, Expt. No. 3), involving repeated subculture of the main axis meristems, excised tomato roots were obtained after 15 successive passages, which had a high growth rate and which appeared to have a high survival expectation. These tip cultures were sectored and the growth and survival on repealed subculture of roots derived from the sectors studied. A marked contrast in growth behaviour between roots derived from the survivors of Expt. No. 3 above ('habituated' roots) and roots derived directly from the clonal sectors ('clonal' roots) has been demonstrated. The 'habituated' roots have a higher survival expectation on repeated subculture and the high level of growth characteristic of the first few passages is maintained in the 'habituated' roots, but not in the 'clonal' roots. 2. The distinctive growth behaviour of the 'habituated' roots is not lost when the roots are maintained for a number of passages as sector cultures. 3.By studying the growth of individual roots in successive passages it has been shown that the decline in mean growth values associated with loss of meristematic activity of 'clonal' roots is due to a general fall in growth rate and not merely to a low level of growth in these roots about to cease activity. 4. Study of the growth values for individual roots has also shown that both 'clonal' and 'habituated' roots undergo a cyclic pattern of growth behaviour. Within the same set of cultures the growth patterns of individual roots are 'out of phase' with one another and are considered to be determined, in their major features, by internal factors. The growth behaviour of the 'habituated' roots differs from that of the 'clonal' roots in that the general level of growth of the individual 'habituated' roots is higher and the peak and minimal growth values which occur at intervals during repeated subculture, are less contrasted. Cessation of meristematic activity in a 'clonal' root generally occurs when the growth is very low or is declining. 5. Further data are presented showing that illumination of the cultures during incubation enhances main axis growth and suppresses lateral development. Both 'habituated' and 'clonal' roots are affected in the same way. Cessation of meristematic activity is accentuated in the 'clonal' roots by incubation in the dark and under these conditions the contrast in growth behaviour between 'clonal' and 'habituated' roots is most marked. 6. In the present series of experiments, the 'clonal' roots, when submitted to repeated subculture by excision of the main axis meristems. showed no evidence of the 'habituation" to culture such as occurred in the experiment from which the present 'habituated' roots are derived. [ABSTRACT FROM AUTHOR]

1. The growth-promoting activity of White's medium 'staled' by the growth of excised tomato roots and then adjusted to favourable pH, is not increased by the addition of sucrose or vitamins or the 'solution of inorganic salts'. Addition of ferric sulphate, however, causes a marked increase in growth-promoting activity. With medium 'staled' by supporting root growth for only 7 days this addition almost restores the activity to that of new medium. 2. The alkaline drift occurring in White's medium as a result of root growth causes iron to be precipitated and the consequent iron deficiency cannot be prevented by increasing the initial concentration of ferric sulphate. pH drift operates as a 'staling' factor primarily by its effect on iron availability. 3. White's medium modified by supplying the nitrogen as ammonium nitrate does not support as high an initial growth rate as the standard medium, but since its pH does not increase during culture, no iron deficiency intervenes to cause an early decline in its growth activity. 4. Other soluble inorganic ferrous and ferric salts can be effectively substituted for the ferric sulphate of White's medium but they do not prevent the development of iron deficiency as the pH increases. A slight extension of the pH range over which iron is available can be achieved by using ferrous phosphate which acts as a constant source of ferrous ions. Iron supplied as ferric citrate or as ferric sodium ethylenediamine tetra-acetate remains available over a much wider pH range and their use as iron sources allows root growth to continue for much longer periods than in standard White's medium. 5. Commercial ferric citrate scales were found to contain copper at a concentration which, because of its toxicity seriously limited the concentration of iron which could be supplied in this form. Using a specially prepared ferric citrate solution it was found that either increasing the ferric citrate concentration up to ×1O the standard iron concentration or increasing the citrate : iron ratio reduced the growth-promoting activity of medium of low pH but enhanced the level of growth at the higher pH values tested. 6. Ferric sodium ethylenediamine tetra-acetate undergoes some decomposition when autoclaved in White's medium, but if the medium is sterilised by filtration, the complex is non-toxic up to ×4 the standard iron concentration and supports growth up to at least pH 6.5. 7. From a study of the growth achieved when iron is supplied in the form of these complexes at different concentrations and at different pH values, it is, suggested that the complex ions act as direct donors of ferric iron to chelating substances at the surface of the absorbing cells. 8. It was found that sterilisation of media by autoclaving, as compared with filter-sterilisation, caused, particularly at pH values higher than 4.8, a loss of iron by precipitation from both standard medium and medium containing ferric citrate. The effect was most marked with standard medium. 9. The development of iron deficiency in White's medium as a result of root growth is, in the pH range 4.9-5.1, checked by the simultaneous formation of monosaccharides. Monosaccharides added to new medium of initial pH within this range, in quantities such as arise during the 7-day culture period, increase its growth promoting activity. By purification of the commercial samples of dextrose and laevulose used it has been shown that this effect is not due to iron contamination in the sugar samples. 10. Roots developed in standard White's medium are able to continue a slow rate of growth for some time after the rise in pH of the medium has rendered iron unavailable. It is suggested that this is made possible by utilisation of iron absorbed earlier in the culture period. 11. The bearing of the results on the technique and potentialities of excised root cultures for physiological research is discussed. [ABSTRACT FROM AUTHOR]

This article cites a study that compared several methods of introducing the predator, Phytoseiulus persimilis, to control red spider mite on glasshouse tomatoes in Yorkshire, England in 1971. Introducing the red spider mite on to every tenth plant three days before placing the predator on the same plants was the most effective method of preventing red spider mite damage. The methods of assessing predator and red spider mite populations as well as red spider mite damage on tomatoes are also described.

In glasshouse soils infested with grey sterile fungus, the cause of brown root rot of tomato, and the potato cyst nematode, methyl bromide fumigation increased yield, and controlled the nematode at all except the lowest treatment applied. In the experiments described here methyl bromide did not affect the development of brown root rot. [ABSTRACT FROM AUTHOR]

The article presents a study on the resistance and susceptibility of tomatoes to the leaf mould fungus Cladosporium fulvum (C. fulvum). It was found that resistance to C. fulvum is well known, and a number of resistant varieties of tomato are grown in glasshouse culture. The study showed a general similarity in the progress of physiologic specialization of the leaf mould fungus in Canada and in Great Britain. In Canada, where autumn tomato crops are exposed to heavy infection, resistance is of greater consequence. The increasing use of hybrid tomato varieties may enable the acceleration of the recombination of desired resistance genes into new varieties.