Youssef Rouphael

Alleviation of salt stress by arbuscular mycorrhizal in zucchini plants grown at low and high phosphorus concentration

With the aim of determining whether the arbuscular mycorrhizal (AM) inoculation would give an advantage to overcome salinity problems and if the phosphorus (P) concentration can profoundly influence zucchini (Cucurbita pepo L.) plant responses to AM, a greenhouse experiment was carried out with AM (+AM) and non-AM (−AM). Plants were grown in sand culture with two levels of salinity (1 and 35xa0mM NaCl, giving electrical conductivity values of 1.8 and 5.0xa0dS m−1) and P (0.3 and 1xa0mM P) concentrations. The percentages of marketable yield and shoot biomass reduction caused by salinity were significantly lower in the plants grown at 0.3xa0mM P, compared to those grown at 1xa0mM P. However, even at high P concentration, the absolute value of yield and shoot biomass of +AM zucchini plants grown under saline conditions was higher than those grown at low P concentration. The +AM plants under saline conditions had higher leaf chlorophyll content and relative water content than −AM. Mycorrhizal zucchini plants grown under saline conditions had a higher concentration of K and lower Na concentration in leaf tissue compared to −AM plants. The P content of zucchini leaf tissue was similar for +AM and −AM treatments at both low and high P concentrations in the saline nutrient solution. The beneficial effects of AM on zucchini plants could be due to an improvement in water and nutritional status (high K and low Na accumulation).

Yield, fruit quality and mineral composition of grafted melon plants grown under saline conditions

Summary In many irrigated areas of the Mediterranean region, farmers are forced to use saline water to irrigate their crops due to an inadequate supply of fresh water. Grafting may represent an effective tool to improve crop tolerance to salinity. Two greenhouse experiments were carried out to determine yield, fruit quality and mineral composition of melon plants (Cucumis melo L. cv. ‘Cyrano’), either ungrafted or grafted onto the commercial rootstock ‘P360’ (Cucurbita maxima C. moschata) and cultured in pumice. Plants were supplied with nutrient solutions having electrical conductivities (EC) of 2.0, 4.0, 5.9, 7.8 or 9.7 dS m–1. The saline nutrient solutions (those > 2.0 dS m–1) had the same basic composition, plus an additional 20, 40, 60 or 80 mM NaCl, respectively. In both years (2003 and 2004), increased salinity in the nutrient solution resulted in a linear decrease in marketable yield compared to controls that was due to reductions in the size and number of marketable fruits. Averaged across years and nutrient solution concentrations, marketable fruit yield was 44% higher in grafted than in ungrafted plants. The lowest marketable yield recorded in ungrafted plants was associated with a reduction in both mean fruit weight and in the number of fruits per plant compared to grafted plants. Salinity improved fruit quality in both grafting combinations by increasing firmness, dry matter (DM), acidity and total soluble solids (TSS) contents. The nutritional qualities of grafted melons such as fruit DM, titratable acidity and TSS content were slightly inferior compared to those of ungrafted plants, whereas physical qualities such as fruit firmness and Hunter colour values (L* and a*/b*) were superior compared to those of plants grown with their own roots. Grafted plants could reduce leaf Na+ ion, but not Cl– ion, concentrations. However, the sensitivity to salinity was similar between grafted and ungrafted plants, and the higher marketable yield from grafted plants was mainly due to grafting per se.

Leaf area estimation of sunflower leaves from simple linear measurements

Simple, accurate, and non-destructive methods for determining leaf area (LA) of plants are important for many experimental comparisons. Determining the individual LA of sunflower (Helianthus annuus L.) involves measurements of leaf parameters such as length (L) and width (W), or some combinations of these parameters. Two field experiments were carried out during 2003 and 2004 to compare predictive equations of sunflower LAs using simple linear measurements. Regression analyses of LA vs. L and W revealed several equations that could be used for estimating the area of individual sunflower leaves. A linear equation having W2 as the independent variable provided the most accurate estimate (r2 = 0.98, MSE = 985) of sunflower LA. Validation of the equation having W2 of leaves measured in the 2004 experiment showed that the correlation between calculated and measured areas was very high.

Leaf area estimation from linear measurements in zucchini plants of different ages

Summary Simple, accurate and non-destructive methods to determine individual leaf areas of plants are a useful tool in physiological and agronomic research. Determining the individual leaf area (LA) of zucchini squash (Cucurbita pepo L.) involves measurements of leaf parameters such as length (L) and width (W), or some combinations of these parameters. Three greenhouse experiments were carried out during Spring-Summer 2001, Spring-Summer 2002 and Summer-Autumn 2003 to compare predictive models for zucchini leaf areas using simple linear measurements that could accommodate the effects of changes in leaf shape during different plant ages. The L:W ratio (leaf shape parameter) of zucchini squash decreased with increasing leaf area and became constant, with a similar pattern between growing seasons. Leaf area was predicted accurately from the product of L and W (R2 = 0.97 and Mean Square Error, MSE = 1,526 cm2), but this model was dependent on plant age. A linear model having W2 as the independent variable provided the most accurate estimate (R2 = 0.98, MSE = 972 cm2) of zucchini LA, independent of plant age. Validation of the model having the W2 of leaves measured in the 2002 and 2003 Experiments showed that the correlation between calculated and measured areas was very high.

Modeling individual leaf area of rose ( Rosa hybrida L.) based on leaf length and width measurement

Accurate and nondestructive methods to determine individual leaf areas of plants are a useful tool in physiological and agronomic research. Determining the individual leaf area (LA) of rose (Rosa hybrida L.) involves measurements of leaf parameters such as length (L) and width (W), or some combinations of these parameters. Two-year investigation was carried out during 2007 (on thirteen cultivars) and 2008 (on one cultivar) under greenhouse conditions, respectively, to test whether a model could be developed to estimate LA of rose across cultivars. Regression analysis of LA vs. L and W revealed several models that could be used for estimating the area of individual rose leaves. A linear model having L×W as the independent variable provided the most accurate estimate (highest r2, smallest MSE, and the smallest PRESS) of LA in rose. Validation of the model having L×W of leaves measured in the 2008 experiment coming from other cultivars of rose showed that the correlation between calculated and measured rose LA was very high. Therefore, this model can estimate accurately and in large quantities the LA of rose plants in many experimental comparisons without the use of any expensive instruments.

Improving melon and cucumber photosynthetic activity, mineral composition, and growth performance under salinity stress by grafting onto Cucurbita hybrid rootstocks

The aim of the current work was to determine whether grafting could improve salinity tolerance of melon and cucumber, and whether possible induction of tolerance to salt stress was associated with the protection of the photosynthetic apparatus. Two greenhouse experiments were carried out to determine gas exchange, mineral composition, growth and yield of melon (Cucumis melo L. cv. Cyrano) and cucumber (Cucumis sativus L. cv. Akito) plants, either ungrafted or grafted onto the Cucurbita hybrid rootstocks (Cucurbita maxima Duch. × Cucurbita moschata Duch.), ‘P360’, and ‘PS1313’, respectively. Plants were grown hydroponically and supplied with two nutrient solutions — a nonsalinized control and a salinized solution which contained 40 mmol L−1 of NaCl. Salinity induced a smaller decrease in leaf area index (LAI), in grafted-compared to ungrafted plants. Similarly, the PN and gs reduction in NaCl treatment compared to control were significantly lower in grafted plants (34% and 34%, respectively, for melon and 14% and 15.5%, respectively, for cucumber) compared to ungrafted plants (42% and 40%, respectively, for melon and 30% and 21%, respectively, for cucumber). In all grafting combinations, negative correlations were recorded between Na+ and Cl− in the leaf tissue and PN. Grafting reduced concentrations of sodium, but not chloride, in leaves. Under saline conditions a smaller reduction in melon and cucumber shoot biomass dry mass and fruit yield were recorded, with positive correlations between shoot biomass, yield and PN. These results suggest that the use of salt tolerant Cucurbita rootstock can improve melon and cucumber photosynthetic capacity under salt stress and consequently crop performance.

Yield, water requirement, nutrient uptake and fruit quality of zucchini squash grown in soil and closed soilless culture

Summary The effects of soil and closed soilless systems (cocofibre, perlite and pumice culture) on precocity, productivity, water use, plant mineral composition and fruit quality were studied on zucchini plants (Cucurbita pepo L. ‘Afrodite’ grown in a greenhouse at Viterbo, central Italy. The plants grown in a soilless system exhibited higher yield (total, marketable and fruit number), harvest index, and water-use efficiency compared with those grown in soil. Among soilless treatments, pumice had the lowest water requirement and hence the highest water use efficiency. Use of cocofibre led to the earliest yield compared with the other substrates due probably to the higher minimal temperatures recorded on the organic substrate. Plants grown in soilless culture had a higher uptake of N, Mg, Na, Fe, Cu, Mn, Zn than those grown in soil. After 73 d of solution recycling in soilless treatments, N-NO3, K, P, Fe and Mn were depleted by 26, 16, 40, 92, and 25% respectively, while Ca, Mg, Na, Cu and Zn increased by 6, 69, 113, 360, and 981 % respectively. Carbohydrate concentration (glucose, fructose, sucrose and starch) increased in soilless over soil culture. No significant differences were observed in dry matter or total protein content. Nitrate concentration of fruits was lower in soil than in soilless treatments. The results demonstrated that the growers may improve water and nutrient control, yield and fruit quality by switching from soil to closed soilless culture.

Effects of saline stress on mineral composition, phenolic acids and flavonoids in leaves of artichoke and cardoon genotypes grown in floating system

BACKGROUNDnCynara cardunculus is a species native to the Mediterranean basin. It includes globe artichoke and cultivated cardoon as well as their progenitor wild cardoon. The species is a source of biophenols, and its leaf extracts have been widely used in herbal medicine as hepatoprotectors and choleretics since ancient times. The aim of this study was to determine the effect of increasing the level of salinity in the nutrient solution (1 or 30 mmol L⁻¹ NaCl) on biomass production, mineral composition, radical-scavenging activity, caffeoylquinic acids and flavonoids in three artichoke (Romolo, Violetto di Provenza and Violetto di Romagna) and three cultivated cardoon (Bianco Avorio, Bianco Gigante Inerme and Gigante di Romagna) cultivars grown in a floating system.nnnRESULTSnIncreased salinity in the nutrient solution decreased the leaf dry biomass and leaf number of artichoke and cultivated cardoon cultivars. Salinity reduced macro- and microelement accumulation in leaves (e.g. N, K, Ca, Mg, Fe, Mn and B) but improved their antioxidant activity, total polyphenols, chlorogenic acid, cynarin and luteolin. The cultivated cardoons, especially Bianco Avorio and Gigante di Romagna, showed higher biomass and leaf number than those observed in artichoke genotypes. Violetto di Provenza exhibited the highest content of chlorogenic acid, closely followed by Violetto di Romagna, whereas for cynarin content the highest values were recorded in Violetto di Provenza, Bianco Avorio and Gigante di Romagna. The highest content of luteolin was recorded in Gigante di Romagna and Bianco Avorio, while the highest content of apigenin was observed in Gigante di Romagna.nnnCONCLUSIONnThe results showed that the floating system could be considered an effective tool to improve quality aspects through proper management of the salt concentration in the nutrient solution. They also suggest that specific cultivars should be selected to obtain the desired profile of bioactive compounds.

Enhancement of alkalinity tolerance in two cucumber genotypes inoculated with an arbuscular mycorrhizal biofertilizer containing Glomus intraradices

The aim of the present study was to determine whether arbuscular mycorrhizal (AM) inoculation with a biofertilizer containing clays as granular carriers, leek root pieces and Glomus intraradices spores could improve alkalinity tolerance of two cucumber genotypes, and to study the changes induced by AM at agronomical and physiological level. A greenhouse experiment was carried out to determine yield, growth, fruit quality, net photosynthesis (ACO2), electrolyte leakage, and mineral composition of two cucumber (Cucumis sativus L.) genotypes (hybrid “Ekron” or open-pollinated variety “Marketmore”) with inoculated and noninoculated arbuscular mycorrhizal biofertilizer. Plants were supplied with nutrient solutions at two pH values (6.0 or 8.1). The high pH nutrient solution had the same basic composition with an additional 10xa0mM NaHCO3 and 0.5xa0gu2009l−1 CaCO3. The percentage root colonization was higher in “Marketmore” (21.8%) than “Ekron” (12.7%). Total and marketable yield and total biomass were significantly higher by 189%, 213%, and 77%, respectively, with Ekron in comparison to those recorded with Marketmore. The highest crop performance with Ekron in comparison to Marketmore was due to the improved nutritional status (higher N, P, K, Ca, Mg, Fe, Mn, and B), higher leaf area, and net photosynthesis. Increasing the concentration of NaHCO3 from 0 to 10xa0mM in the nutrient solution significantly decreased yield, plant growth, ACO2, N, P, Fe, Cu, Zn, Mn, and B concentration in leaf tissue, whereas the electrolyte leakage increased. The inoculated plants under alkaline conditions had higher total, marketable yield, and total biomass than noninoculated plant. Mycorrhizal cucumber plants grown under alkaline conditions had a higher macronutrient concentration in leaf tissue compared to noninoculated plants. The highest yield and biomass production in inoculated plants seems to be related to the capacity of maintaining higher net ACO2 and to a better nutritional status (high P, K, Mg, Fe, Zn, and Mn and low Na accumulation) in response to bicarbonate stress with respect to −AM plants.

Effects of Drought on Nutrient Uptake and Assimilation in Vegetable Crops

Scarcity of water is a severe environmental limit to plant productivity. Drought-induced loss in crop yield probably exceeds losses from all other causes, since both the severity and duration of the stress are critical. Nutritional imbalance under drought conditions depresses plant growth and therefore productivity by affecting nutrient uptake, transport, and distribution. Despite contradictory reports on the effects of nutrient supply on plant growth under drought conditions, it is generally accepted that an increased nutrient supply will not improve plant growth when the nutrient is already present in sufficient amounts in the soil and the drought is severe. A better understanding of the role of mineral nutrients in plant resistance to drought will contribute to improve fertilizer management in arid and semiarid areas and in regions suffering from temporary drought. Considering that vegetables are concentrated in semiarid zones where water stress is frequent, it is important to ascertain how this type of stress affects the nutrient uptake and assimilation of these crops. This chapter starts with an overview of the recent literature on plant nutrition of vegetables under drought conditions, stressing mainly the effects of drought on nutrient availability, uptake, transport, and accumulation in plants, and also the interactions between nutrient supply and drought response; it then proceeds to identify the means to increase nutrient availability under drought conditions through breeding, grafting, and fertilization.