C. Olympios

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.

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.