Dimitrios Savvas

Effects of NaCl or nutrient-induced salinity on growth, yield, and composition of eggplants grown in rockwool

The effects of increasing the salt concentration of a basic nutrient solution from 2.1 up to 4.7 dS m ˇ1 by providing either additional amounts of nutrients or 25 mmol l ˇ1 NaCl on growth, yield, fruit quality and mineral composition of eggplants were investigated. The extra nutrients used to raise the electrical conductivity were added either at the same ionic concentration ratio as in the basic nutrient solution or at an increased ratio of K to total cation concentration. The vegetative growth and the number of flowers per plant were not influenced by any of the salinity treatments. In contrast, the fresh fruit yield of eggplant was significantly reduced to the same extent in all salinity treatments. The yield depression was a result of a decline in mean fruit weight, whereas the number of fruits per plant was not affected. However, recalculation of the data on dry weight basis revealed no significant differences between the treatments. The percentage of eggplant fruits graded Class 1 was significantly reduced at 4.7 dS m ˇ1 , whilst the kind of salts used to induce salinity had no significant effect on fruit quality. The increase of electrical conductivity up to 4.7 dS m ˇ1 by the addition of extra nutrients did not result in a higher nutrient uptake, with the exception of P in roots, and P and organic N in the petioles of older leaves. In contrast, the concentrations of Mg and NO3‐N were reduced in some plant parts when salinity was increased by the addition of extra nutrients, regardless of the proportions of cations in the nutrient solution. All salinity treatments reduced the concentration of Mg in the leaves to the same degree, thus indicating that this salt effect is not ion specific. # 2000 Elsevier Science B.V. All rights reserved.

Response of hydroponically grown gerbera to nutrient solution recycling and different nutrient cation ratios

Abstract The effects of recycling the drainage solution by adding nutrients to replenish it at three different K:(K+Ca+Mg) ratios (0.40, 0.48, 0.56, equivalent basis) on yield, flower quality and nutritional status of soilless-grown gerbera were investigated. The recycling treatments were compared also to a control with free drainage and a standard K:(K+Ca+Mg) equivalent ratio of 0.40 in the irrigation solution. The ratios between NH 4 and total N, Ca and Mg, macronutrient anions, and micronutrients, were identical in all treatments when injecting concentrated solutions of fertilizers to prepare fresh nutrient solution, and similar to standard recommendations for open systems, regardless of recycling or not. Furthermore, the target electrical conductivity and pH in the irrigation solution were identical in all treatments. When the drainage solution was recycled, the highest yield was obtained with the highest K:(K+Ca+Mg) injection ratio. However, both the number of flowers per plant and the flower stem length were significantly lower in all recycling treatments compared to those obtained when the effluents were discharged. This was attributed to a profound decline of the NH 4 concentration in the drainage solution and, thus, also in the irrigation solutions prepared by reusing it, which resulted in increased pH in the root environment and restricted supply of Mn to the plants. In addition to Mn, the leaf P and Fe concentrations were also reduced by the increased pH in the root zone when recycling was applied. Hence, to prevent nutrient imbalances in closed hydroponic systems, it is suggested to supply potassium and nitrogen at higher K:(K+Ca+Mg) and NH 4 /total-N ratios than those recommended for open systems.

Automated management of nutrient solutions based on target electrical conductivity, ph, and nutrient concentration ratios

Abstract An algorithm to automatically formulate the composition and prepare nutrient solutions for soilless cultures based on desired characteristics given as target values is proposed. To formulate the complete ionic composition of a nutrient solution, standard recommendations referring to the following solution characteristics should be available: (i) electrical conductivity (EC), (ii) pH, (iii) concentration ratios of macronutrients (meq basis), and (iv) micronutrient concentrations. Moreover, the mineral composition of the water used to prepare the nutrient solution should be taken into account. To develop the main steps of the algorithm, the total salt concentration (meq L‐1) of the nutrient solution is related to the desired electrical conductivity. The target pH indicates the concentration of HCO3 − in the nutrient solution, whereas the absolute concentration of each macronutrient is derived from the desired concentration ratios and the total salt concentration. The necessary calculations are stan...

Interactions between ammonium and pH of the nutrient solution supplied to gerbera (Gerbera jamesonii) grown in pumice

The interactions between the NH4-N/total-N supply ratio (Nr) and the pH of the nutrient solution delivered to the plants regarding the nutrient availability and its influence on plant growth and yield were investigated in a gerbera crop grown in pumice. Four treatments obtained by combining a low and a high Nr (0.02 and 0.13 on a molar basis, respectively) with two different levels of nutrient solution pH (5.0 and 5.8, respectively) were compared in a long-term glasshouse experiment. The low Nr resulted in significantly higher pH levels in the rhizosphere, as indicated by the values measured in the drainage water. A high nutrient solution pH further increased pH in the root zone at low Nr but had no influence on it at the higher Nr level. The high pH in the root zone restricted significantly the Cu, Mn, and Zn uptake as indicated by both analytical results and visual symptoms, which were typical for Cu- and Mn-deficiencies. Mn-deficiency was induced only when a low Nr was combined with a high nutrient solution pH. The Cu-deficiency symptoms appeared earlier, were more severe and occurred also when the low Nr was combined with a low nutrient solution pH, but to a lesser extent. As a result of these nutrient deficiencies, both the growth and the flower yield were severely restricted when Nr was low. These results indicate that gerbera is prone to Cu- and Mn deficiencies at pH values above 6 in the rhizosphere. The maintenance of root zone pH below this level in soilless culture is most successfully attained by properly adjusting the NH4-N/total-N supply ratio rather than the pH of the nutrient solution delivered to the plants.

Response of eggplants grown in recirculating nutrient solution to salinity imposed prior to the start of harvesting

Summary The effects of exposing eggplants grown in recirculating nutrient solution to salt stress (6.1 dS m–1) from planting until the beginning of harvesting, on plant growth, yield and macronutrient status was investigated. The salinity was imposed by adding to a basic nutrient solution either additional nutrients at two cation ratios or NaCl. The results showed that the exposure of plants to salinity prior to the beginning of harvesting reduced both vegetative growth during that time and early fruit yield, but the depression of the latter was more severe. The restriction of the early yield was a result of a reduced mean fruit weight due to a lower fruit water content. The detrimental effects of salinity on the mean fruit weight disappeared 25 d after discontinuing the salinity treatments. As a result, the total yield obtained after five months of harvesting was not influenced by exposing the plants to salinity prior to the beginning of harvesting. The salinity source had no specific effect on plant growth. Moreover, the increase of salinity up to 6.1 dS m–1 did not cause any specific nutritional imbalance or toxicity to the plants, irrespective of the salts used to achieve it. It is suggested that the electrical conductivity of the nutrient solution may be raised to 6.1 dS m–1 to control excessive vegetative growth in eggplants grown hydroponically. However, salt treatment should be terminated either at the first harvest, if the total yield is more important than the early yield, or three weeks earlier, if the opposite is true.

Influence of NaCl-salinity imposed on half of the root system of hydroponically grown tomato on growth, yield, and tissue mineral composition

Summary The effects of splitting the root system of tomato grown in recirculating nutrient solution into two compartments receiving raw water (0.3.dS m–1) and saline nutrient solution (13.0.dS m–1, 100.mM NaCl), respectively, on growth, yield and tissue mineral composition were investigated. The water/salinity treatment was compared with standard nutrition for tomatoes (2.2.dS m–1) or supply of the entire root system with the above saline nutrient solution. The exposure of all or part of the root system to NaCl-salinity reduced the K concentration initially in the roots and, later, in the old leaves. The total-N concentration was restricted only in the older leaves by the exposure of all or half the root system to high NaCl concentrations. In all plant parts, the concentration of Na was more markedly raised when the entire root system was exposed to NaCl-salinity as compared with the root-splitting treatment. The P concentration was restricted in the part of the roots supplied solely with raw water. The leaf Ca and Mg concentrations were diminished on some sampling dates only when the entire root system was exposed to NaCl-salinity. Further, the root Mg concentrations were significantly increased in both root parts of plants subjected to root splitting as compared with those measured in plants receiving exclusively standard or saline nutrient solution. The obtained results indicated also an intensive retranslocation of K, Na, Mg and N between the two root compartments. The exposure of the entire root system of tomato to salinity depressed the fresh fruit yield mainly because of a restricted mean fruit weight but had no effect on the dry fruit production. Splitting the root system into two compartments receiving raw water and NaCl-enriched nutrient solution, respectively, also depressed the fresh fruit yield but to a slightly lesser extent than complete exposure to salinity. However, the yield decline was exclusively due to fewer fruits per plant, while the mean weight and the dry-matter content of fruit were not affected. As a result, the dry fruit yield was also markedly restricted in the water/salinity treatment. It is suggested that a moderate salt stress imposed on the entire root system of tomato restricts yield due to a lower water content of fruit owing to osmotic adjustment, while the exposure of the roots partly to salinity and partly to raw water diminishes the dry biomass production due to lack of osmotic adaptation.

Phylogenetic multilocus sequence analysis of indigenous slow-growing rhizobia nodulating cowpea (Vigna unguiculata L.) in Greece

Cowpea (Vigna unguiculata) is a promiscuous grain legume, capable of establishing efficient symbiosis with diverse symbiotic bacteria, mainly slow-growing rhizobial species belonging to the genus Bradyrhizobium. Although much research has been done on cowpea-nodulating bacteria in various countries around the world, little is known about the genetic and symbiotic diversity of indigenous cowpea rhizobia in European soils. In the present study, the genetic and symbiotic diversity of indigenous rhizobia isolated from field-grown cowpea nodules in three geographically different Greek regions were studied. Forty-five authenticated strains were subjected to a polyphasic approach. ERIC-PCR based fingerprinting analysis grouped the isolates into seven groups and representative strains of each group were further analyzed. The analysis of the rrs gene showed that the strains belong to different species of the genus Bradyrhizobium. The analysis of the 16S-23S IGS region showed that the strains from each geographic region were characterized by distinct IGS types which may represent novel phylogenetic lineages, closely related to the type species of Bradyrhizobium pachyrhizi, Bradyrhizobium ferriligni and Bradyrhizobium liaoningense. MLSA analysis of three housekeeping genes (recA, glnII, and gyrB) showed the close relatedness of our strains with B. pachyrhizi PAC48T and B. liaoningense USDA 3622T and confirmed that the B. liaoningense-related isolate VUEP21 may constitute a novel species within Bradyrhizobium. Moreover, symbiotic gene phylogenies, based on nodC and nifH genes, showed that the B. pachyrhizi-related isolates belonged to symbiovar vignae, whereas the B. liaoningense-related isolates may represent a novel symbiovar.

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.

Impact of rhizobial inoculation and reduced N supply on biomass production and biological N2-fixation in common bean grown hydroponically

BACKGROUND Testing rhizobial inoculation of common bean (Phaseolus vulgaris L.) in hydroponics enables accurate quantification of biological N2 fixation (BNF) and provides information about the potential of reducing inorganic N fertilizer use. In view of this background, common bean grown on pumice was inoculated with Rhizobium tropici CIAT899 (Rt) and supplied with either full-N (total nitrogen 11.2 mmol L-1 ), 1/3 of full-N or N-free nutrient solution (NS). BNF was quantified at the early pod-filling stage using the 15 N natural abundance method. RESULTS Full-N supply to Rt-inoculated plants resulted in markedly smaller nodules than less- or zero-N supply, and no BNF. Rt inoculation of full-N-treated plants did not increase biomass and pod yield compared with non-inoculation. Restriction (1/3 of full-N) or omission of inorganic N resulted in successful nodulation and BNF (54.3 and 49.2 kg N ha-1 , corresponding to 58 and 100% of total plant N content respectively) but suppressed dry shoot biomass from 191.7 (full-N, +Rt) to 107.4 and 43.2 g per plant respectively. Nutrient cation uptake was reduced when inorganic N supply was less or omitted. CONCLUSION Rt inoculation of hydroponic bean provides no advantage when full-N NS is supplied, while 1/3 of full-N or N-free NS suppresses plant biomass and yield, partly because the restricted NO3- supply impairs cation uptake.