Harold C. Passam

The effects of osmoconditioning on the germination emergence and early plant growth of cucumber under saline conditions

Abstract Osmoconditioning improved the rate of germination of cucumber ( Cucumis sativus L. cultivar ‘Telegraph’) seeds at 25°C and 15°C in water and NaCl solutions of upto 200 mM (16.5 dS m −1 ). At 15°C, the total percentage of germination was also increased. Osmoconditioning promoted the rates of radicle extension, seedling emergence and expansion of the cotyledons and first leaf. However, no effect was observed on the rate of growth of the second leaf or on the photosynthetic activity of either the first or the second leaf. The promotive effects of osmoconditioning on germination were retained by seeds that were stored for 2 months after treatment and were observed in seeds of other cultivars too. It was concluded that although osmoconditioning alleviated NaCl-induced stress during germination, emergence and early growth of cucumber, the benefits of treatment did not persist beyond the seedling stage.

Effects of nitrogen form and concentration on the distribution of ions within cucumber fruits

Abstract The objective of this study was to determine the influence of nitrogen concentration and the ratio of NO 3 to NH 4 on the distribution of inorganic elements within the tissues of cucumber fruit grown on rockwool. Nitrogen was supplied at three N concentrations and four ratios of NO 3 to NH 4 . Increases in the total nitrogen concentration within the nutrient medium significantly increased the NO 3 content of all the fruit tissues, but this effect was most pronounced in the skin, neck and apical region. The concentration of K, Ca, Mg and NO 3 in all regions of the fruit was higher when NO 3 constituted 75% or more of the total N in the nutrient medium, but was reduced by increasing concentrations of NH 4 . The Mn content of the tissue in the central region of the fruit was reduced by NH 4 ions, whereas the Cu content of this tissue increased. No significant effect of N form on the B, Fe, Zn content of fruits was detected. In contrast, the B content of the apical tissue and the Zn content of the skin declined significantly with increasing N level. The highest concentrations of K and NO 3 were found in the neck and skin tissues, whereas the highest concentrations of Mn and Cu were observed only in the fruit skin. Mg concentrations were lowest in the tissues of the fruit neck, while B concentrations were highest in tissues near to the site of style abscission.

Effects of Nitrogen Form and Concentration on Yield and Quality of Cucumbers Grown on Rockwool During Spring and Winter in Southern Greece

ABSTRACT The influence of nitrogen concentration and the ratio of NO3 to NH4 on the marketable yield and fruit quality characteristics of cucumbers (Cucumis sativus L. cv. Palmera) grown on rockwool during spring and winter in southern Greece were studied. Nitrogen (N) was supplied at three N concentrations and four ratios of NO3 to NH4. During the spring, increasing total nitrogen or NH4 concentration within the nutrient solution significantly decreased the mean total yield and fruit size. However, during the winter, the yield and number of fruits per plant were not affected by N concentration, but were reduced by increasing NH4:NO3 ratio. Fruits that were produced under low N concentrations were lighter in color, but only the color of the apical tissues of the fruit was affected by the NH4:NO3 ratio. Flesh firmness of the fruit was not affected by N source or concentration, except for the apical tissue, the firmness of which declined with increasing N concentration. On the basis of the present results, for highest yield and fruit quality during both the spring and winter seasons of southern Greece, 100 ppm N applied solely in the form of NO3 is indicated.

Flowering, fruit set and fruit and seed development in two cultivars of aubergine (Solanum melongena L.) grown under plastic cover

Abstract Two cultivars of aubergine (Solanum melongena L.) were cultivated in plastic-covered greenhouses over three seasons. Cultivar ‘Long Negro’ (producing oblong fruits) showed a very high rate of flowering but fruit set was low since most flowers aborted soon after anthesis. Cultivar ‘Emi’ (producing oval fruits) flowered less profusely, but fruit set was higheer owing to the ability of this cultivar to form fruits parthenocarpically or at a low level of fertilisation. Because fruit set in ‘Long Negro’ required abundant fertilisation, the seed content of this fruit was invariably high. Maximum fertility of ‘Emi’ occurred at anthesis 8–13 weeks after planting and fruit set during this time contained the most seed. It is concluded that genotype is an important factor in the regulattion of flowering and fruit set in aubergine, with concomitant implications for fruit and seed production.

Effect of plant growth regulators on the tuberisation and physiological age of potato (Solanum tuberosum L.) tubers grown from true potato seed

The effects of plant growth regulators [6-benzyl amino purine (BA), indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), gibberellic acid (GA3), chlormequat chloride (CCC), daminozide] and their time of application on tuberisation and physiological age of cv. Chacasina F1 grown from true potato seed (TPS) were studied in four experiments conducted in spring or autumn in Greece. BA, IAA and 2,4-D did not affect plant development, tuberisation or the physiological age of the tubers produced. Daminozide and CCC reduced plant height when applied 30 but not 60 d after transplanting (DAT) in both spring and autumn. Neither substance affected tuberisation or the physiological age of the tubers formed. Application of GA3 30 DAT significantly increased plant height and the number, but not the weight, of tubers formed per plant. Tubers from GA3-treated plants tended to be elongated with a low dry matter content. When GA3 was applied at 60 DAT, plant height was increased, but tuber number, weight and ...

Flower morphology and number of aubergine (Solanum melongena L.) in relation to fruit load and auxin application

The effect of fruit load and auxin application on the flower morphology and flower number of two aubergine cultivars was investigated under greenhouse conditions. The flowers of plants that did not set fruit showed only minor fluctuations in flower and pistil mass, and in style and anther length. However, when plants were allowed to set fruit by pollination, flower and pistil mass, and style (but not anther) length were significantly reduced during the stage of fruit growth. Style length was also reduced in flowers formed after fruit had been set parthenocarpically by the application of auxin (IAA), but there was no significant effect of IAA on style length in the absence of fruit development. The number of flowers was reduced in the presence of IAA (with or without fruit set), or following fruit set by pollination. It is suggested that fruit load and development affect flower mass and style length of aubergine whereas auxin influences the number of flowers.

Factors affecting the efficacy of agar-based substrates for the study of tomato pollen germination

Summary The present work examines the effects of substrate additions and incubation conditions on in vitro germination of tomato pollen on semi-solid, agar-based substrates with the ultimate aim of defining a standard semi-solid substrate for tomato pollen germination studies. Partial replacement of sucrose by polyethylene glycol (PEG-6000) for osmotic regulation of the substrate significantly increased pollen germination of both the low temperature-susceptible F1 cultivar ‘Dombito’, and the more temperature-resistant cv.‘Supermarmande’, to a level that varied according to the season of pollen harvest. In contrast, partial substitution of sucrose by mannitol was inhibitory to an extent that depended on the final concentration of mannitol in the medium. The optimum pH for germination was 6.5 and the optimum incubation temperature was 15°C. Among the vitamins (riboflavin, thiamine, pyridoxine, niacin, pantothenic acid, p-aminobenzoic acid), amino acids (glutamic acid, aspartic acid), casein hydrolysate, plant growth regulators (gibberellic acid, indole-3-acetic acid, indole-3-butyric acid, indole-3-propionic acid, 1-naphthaleneacetic acid, kinetin) and flavonoids (naringin, myricetin, naringenin, quercetin, rutin) tested, a significant increase in pollen germination was induced only by the flavonoids quercetin and myricetin and, to a lesser extent, by indole-3-acetic acid. In contrast, both kinetin and naringenin were inhibitory, as were both amino acids at 100 mg l–1 and casein hydrolysate (at 1.0 – 10.0 g l–1). On the basis of the above results, we conclude that, for both tomato cultivars tested, the most suitable semi-solid substrate among those examined was that containing 10% (w/v) sucrose, 15.1% (w/v) PEG-6000 and 1.5% (w/v) agar, with the possible addition of 5 mg l–1 quercetin, or 5 mg l–1 myricetin.

l -Ascorbic acid metabolism in parthenocarpic and seeded cherry tomatoes

The auxin treatment in tomato plants during anthesis has been extensively used for setting fruits in adverse climatic conditions (e.g., low temperatures and inadequate light), which is well known that reduces pollen availability and fertility. Since auxin application may affect fruit composition and quality, we examined l-ascorbic acid metabolism in seeded fruit (set by natural pollination) and parthenocarpic fruit (set by auxin) in cherry tomato cv. Conchita. Specifically, we studied the oxidized and total ascorbic acid contents, the expression of all characterized genes of l-ascorbic acid metabolism, the activity of ascorbate peroxidase and dehydroascorbate reductase and the immunolocalization of ascorbate peroxidase. Differences were detected between seeded and parthenocarpic fruits, in the expression of some of the genes of ascorbic acid metabolism. However, strong presence of l-ascorbic acid peroxidase protein was detected on the developing seeds. Our data indicate that induced parthenocarpy in auxin treated plants has a significant influence in ascorbic acid metabolism comparing to seeded tomato fruits.

Bromoethane-induced changes in respiration rate, ethylene synthesis, and enzyme activities in potato tubers in relation to dormancy breakage

Summary This paper describes the effect of bromoethane, which promotes the breakage of dormancy of potato tuber buds, on the metabolic activity of tubers, up to the stage of visible sprouting. The respiratory activity of treated tubers increased to a maximum 2 d after treatment, which, despite a subsequent decline, remained at a higher level than that of untreated controls for a further 8 d. Similarly, bromoethane induced a higher level of ethylene release from tubers over 10 d from its application compared to the controls. With the exception of invertases (acid and alkaline), all the other enzymes studied (i.e., hexokinase, fructokinase, glucose-6-phosphate dehydrogenase, uridine-5-diphosphoglucose pyrophosphorylase, adenosine-5-diphosphoglucose pyrophosphorylase and -glucosidase) exhibited higher rates of activity in bromoethane-treated tubers than in the controls. From the results of this study, it appears that the application of bromoethane increased the metabolic activity of potato tubers prior to the first visible sign of bud sprouting, which occurred approx. 10 d after treatment.

Storage of Tomatoes in Low Oxygen Atmospheres Inhibits Ethylene Action and Polygalacturonase Activity

The effect of low concentrations of O2 (1%) with or without the application of exogenous ethylene (10 μl/l) on the production of endogenous ethylene, the activity of polygalacturonase (PG), and the ripening of tomato fruits during storage for three weeks at 20°C and four weeks at 10°C, followed by one week under ambient conditions (25°C) was studied. The internal ethylene concentration in the fruits stored under low O2 at 10 or 20°C was low during storage and increased only when fruits were transferred to ambient conditions. The application of exogenous ethylene to fruits stored under low O2 at 10 or 20°C did not induce autocatalytic ethylene synthesis. By contrast, the internal ethylene concentration of fruits stored in air was high at 20°C and somewhat lower at 10°C. Under low O2 conditions, PG activity was low and the fruits remained firm and green throughout storage, whereas, during storage in the air, PG activity increased and the fruits softened and developed their characteristic red color.