Ioannis Karapanos

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.

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.

Induced parthenocarpic cherry tomato fruits did not shown significant differences in l -ascorbate content but showed different pattern in GalLDH and GME expression

Parthenocarpy in tomato is often induced by auxins to overcome fertilization problems due to low temperatures. To estimate the effect of this agronomical practice on the physiology and dietary value of cherry tomato fruits we determined l-ascorbic acid, the expression and immunolocalization of galactono 1,4 lactone dehydrogenase and the expression of GDP-mannose 3′,5′-epimerase, key genes in l-ascorbic acid biosynthesis. The levels of l-ascorbic acid did not differ between seeded and parthenocarpic fruits while the relative expression of galactono 1,4 lactone dehydrogenase and GDP-mannose 3′,5′-epimerase gene transcripts showed some significant differences between seeded and parthenocarpic fruits. The galactono 1,4 lactone dehydrogenase immunohistolocalization signal was stronger in the ovules and mature embryos of seed-containing fruits. Our data suggest that although there were differences in the expression of the studied genes and in enzyme localization, these did not cause differences in the l-ascorbic acid content of parthenocarpic fruits produced by auxin application.

Cowpea fresh pods – a new legume for the market: assessment of their quality and dietary characteristics of 37 cowpea accessions grown in southern Europe

BACKGROUND Cowpea is traditionally cultivated in some regions of southern Europe for its dried seeds; however, there is a scarcity of information on the quality and dietary characteristics of fresh pods, which are occasionally used in folk diets. This paper aims at covering this gap in knowledge, thereby contributing to the dissemination of fresh cowpea pods as a novel product for the market. The quality and dietary characteristics of pods from 37 accessions (Vigna unguiculata ssp. unguiculata and ssp. sesquipedalis) grown in southern Europe were assessed in an attempt to provide information on pod quality and nutritional properties and to identify relationships between quality traits and accession origin. RESULTS Pods from the sesquipedalis accessions were heavier and larger, and reached commercial maturity 2 days later, than those from the unguiculata accessions. There were also large differences in the quality and dietary characteristics of the accessions. The pods of most accessions were rich in proteins, chlorophylls, carotenoids and phenolics, and showed high antioxidant activity and low concentrations of nitrates and raffinose-family oligosaccharides. Cluster analysis based on quality, dietary or antinutritional traits did not reveal any apparent grouping among the accessions. All the quality characteristics were independent of accession origin and subspecies. CONCLUSION Most of the accessions produced fresh pods of good quality and high dietary value, suitable for introduction in the market and/or for use as valuable genetic material for the development of new improved varieties.

Phenotypic diversity and evaluation of fresh pods of cowpea landraces from Southern Europe: Fresh pod variability of cowpea landraces

BACKGROUND Cowpea fresh pods are consumed as green vegetables in many countries in Southern Europe. Among cowpea cultivated material, a relatively large number of landraces can be found, maintaining species genetic diversity. To assess the value of these landraces in breeding programs, the characterization and estimation of diversity levels is therefore required. In the present study, an estimation of the diversity and evaluation of cowpea landraces originating from Portugal, Spain and Greece, in terms of their fresh pod traits, was performed, aiming to assist with the problem of low cowpea production in Southern Europe. RESULTS A notable mean total phenotypic diversity (HT = 0.57) was observed in the whole collection. The Spanish cv. - gr. unguiculata collection exhibited the highest value of total phenotypic diversity (0.56). Landraces did not differ significantly from each other regarding the three countries of origin. Landraces such as Cp4906, Vg60 and BGE038478 presenting higher values of some traits studied could contribute to the breeding of new cowpea varieties for fresh pod production. Positive correlations were observed, indicating the feasibility of breeding for preferable traits regarding fresh pod consumption. CONCLUSION The present study has revealed a wide diversity among and within cowpea landraces that could enhance fresh pod production in South European countries.

Seeded and Parthenocarpic Cherry Tomato Fruits Exhibit Similar Sucrose, Glucose, and Fructose Levels, Despite Dissimilarities in UGPase and SPS Gene Expression and Enzyme Activity

Farmers often resort to the production of auxin-induced parthenocarpic tomato fruits to overcome the adverse climatic conditions which are unfavorable for sufficient fertilization and to lengthen the production period. Even though this practice improves the out-of-season yield, it often undermines fruit quality. In the current study, we examined the effect of induced parthenocarpy in cherry tomato cv. Conchita on the concentration of the main sugars, and on the expression, the activity and the localization of UDP-glucose pyrophosphorylase (UGPase) and sucrose phosphate synthase (SPS), enzymes that are actively involved in sucrose metabolism. Minor differences were detected in sugar levels of seeded and parthenocarpic fruits, whereas considerable variances were found in transcript accumulation and enzyme activities of both UGPase and SPS. Moreover, both proteins were present in the developing seeds. Our data indicate that although induced parthenocarpy significantly influences sucrose metabolism, it has a negligible effect on sugar levels.

EFFECT OF NITROGEN APPLICATION ON GROWTH PARAMETERS, YIELD AND LEAF NITRATE CONTENT OF GREENHOUSE LETTUCE CULTIVATED DURING THREE SEASONS

Lettuce (Lactuca sativa L., cv. ‘Parris Island’) was grown hydroponically in autumn, winter and spring under five levels of nitrogen (N) fertilization. Plant biomass was highest in spring and lowest in autumn at N rates of 200 and 260 mg L−1, respectively. Increasing N application correlated positively with rates of photosynthesis, transpiration, stomatal carbon dioxide (CO2) conductance and leaf chlorophyll concentration. Photosynthetic rate, stomatal CO2 conductance, and chlorophyll a/b ratio were higher in spring than in autumn or winter. Nitrate concentrations within the leaves increased with increasing N application in all seasons. It is concluded that lettuce growth and yield is higher in spring than in winter or autumn due to enhanced photosynthesis thanks to increasingly favorable photoperiod. Regardless of season, high N rates promote yield but increase leaf nitrate concentrations. Therefore, for the production of healthy produce the recommended N rate should be based not just on yield but also on the nitrate content.

Application of β-naphthoxyacetic acid ( β-NOA) improves fruit yield and marketable quality in out-of-season cherry tomatoes (Solanum lycopersicum L. var. cerasiforme (Dunal) D. M. Spooner, G. J. Anderson and R. K. Jansen) cultivated in unheated greenhouses in the Mediterranean Basin

Summary The effects of truss vibration, and the application of β-naphthoxyacetic acid ( β-NOA) to flowers, on fruit-set, total and marketable yields, and fruit quality were studied in two cherry tomato [Solanum lycopersicum L. var. cerasiforme (Dunal) D. M. Spooner, G. J. Anderson and R. K. Jansen] hybrids ‘Conchita F1’ and ‘Cherelino F1’, grown in an unheated plastic greenhouse during the Winter/Spring and Spring seasons in Southern Greece. Fruit-set was high in the Winter/Spring crop but, due to unfavourable conditions (i.e., night-time temperatures below 10ºC, which impaired microsporogenesis, pollination, and fertilisation), most fruit contained few seeds, were small and unmarketable. Although both truss vibration and β-NOA significantly increased mean fruit weights, and total yields, in both cultivars, the application of β-NOA gave the greatest increase in mean fruit weight and percentage of marketable fruit. In contrast, in the Spring crop, neither treatment affected the number or weight of fruit per plant because the climatic conditions were more favourable for pollination and fertilisation. The application of β-NOA did not adversely affect fruit quality, as previously reported in large-fruiting tomato cultivars. β-NOA did not induce any malformation or puffiness in the fruit and, while these seedless fruit showed higher dry mass percentages, higher total soluble solids contents, and lower titratable acidity levels than seeded tomato fruit, their colour, firmness, sugar, and phenolics contents were not affected. Conditions that are unfavourable for fruit set frequently occur in unheated greenhouses in the Mediterranean Basin during the Winter and early Spring; therefore, we conclude that the application of β-NOA to the flowers of cherry tomato at that time will ensure higher yields, better market quality, and higher market returns.

Nutritional value and antioxidant content of seed‐containing and seedless eggplant fruits of two cultivars grown under protected cultivation during autumn‐winter and spring‐summer

BACKGROUND Due to their low carbohydrate and high antioxidant content, eggplants are beneficial for the human diet. At <15 °C, pollen production and fertility are reduced and plant-growth regulators may be used to set seedless fruit. Because only the agronomic effects of hormone are well-documented, we investigated the composition and metabolism during the development/maturation of seed-containing and seedless fruits of two cultivars grown over two seasons. RESULTS The respiration rate of both seedless and seed-containing fruit decreased with development and maturation. In seedless fruit, starch content decreased at market maturity, whereas in seed-containing fruit starch increased. Respiration and starch were higher in spring-summer than in autumn-winter. Disaccharides were highest at market maturity, with sucrose generally higher in seed-containing fruit; monosaccharides were variable and protein content was reduced in seedless fruit. Phenols closely correlated with antioxidant activity and decreased with development; at market maturity in spring-summer phenols were higher in seedless fruit (Tsakoniki) or unaffected (Emi). Polyphenol oxidase and peroxidase activities were mostly higher in seed-containing fruit, but browning was higher in seedless fruit. CONCLUSIONS Notwithstanding reduced protein and increased browning, seedless fruit at market maturity presented less starch, hence fewer calories, and more antioxidants (phenols) for the human diet than the corresponding seed-containing fruit.

Cultivar-Dependent Responses of Eggplant (Solanum melongena L.) to Simultaneous Verticillium dahliae Infection and Drought

Several studies regarding the imposition of stresses simultaneously in plants have shown that plant responses are different under individual and combined stress. Pathogen infection in combination with drought can act both additively and antagonistically, suggesting a tailored-made plant response to these stresses. The aforementioned combination of stresses can be considered as one of the most important factors affecting global crop production. In the present research we studied eggplant responses to simultaneous Verticillium dahliae infection and drought with respect to the application of the individual stresses alone and investigated the extent to which these responses were cultivar dependent. Two eggplant cultivars (Skoutari and EMI) with intermediate resistance to V. dahliae were subjected to combined stress for a 3-week period. Significant differences in plant growth, several physiological and biochemical parameters (photosynthesis rate, leaf gas exchanges, Malondialdehyde, Proline) and gene expression, were found between plants subjected to combined and individual stresses. Furthermore, plant growth and molecular (lipid peroxidation, hydrogen peroxide, gene expression levels) changes highlight a clear discrimination between the two cultivars in response to simultaneous V. dahliae infection and drought. Our results showed that combined stress affects significantly plants responses compared to the application of individual stresses alone and that these responses are cultivar dependent.