Giuseppe Colla

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.

Biostimulant action of a plant-derived protein hydrolysate produced through enzymatic hydrolysis

The aim of this study was to evaluate the biostimulant action (hormone like activity, nitrogen uptake, and growth stimulation) of a plant-derived protein hydrolysate by means of two laboratory bioassays: a corn (Zea mays L.) coleoptile elongation rate test (Experiment 1), a rooting test on tomato cuttings (Experiment 2); and two greenhouse experiments: a dwarf pea (Pisum sativum L.) growth test (Experiment 3), and a tomato (Solanum lycopersicum L.) nitrogen uptake trial (Experiment 4). Protein hydrolysate treatments of corn caused an increase in coleoptile elongation rate when compared to the control, in a dose-dependent fashion, with no significant differences between the concentrations 0.75, 1.5, and 3.0 ml/L, and inodole-3-acetic acid treatment. The auxin-like effect of the protein hydrolysate on corn has been also observed in the rooting experiment of tomato cuttings. The shoot, root dry weight, root length, and root area were significantly higher by 21, 35, 24, and 26%, respectively, in tomato treated plants with the protein hydrolysate at 6 ml/L than untreated plants. In Experiment 3, the application of the protein hydrolysate at all doses (0.375, 0.75, 1.5, and 3.0 ml/L) significantly increased the shoot length of the gibberellin-deficient dwarf pea plants by an average value of 33% in comparison with the control treatment. Increasing the concentration of the protein hydrolysate from 0 to 10 ml/L increased the total dry biomass, SPAD index, and leaf nitrogen content by 20.5, 15, and 21.5%, respectively. Thus the application of plant-derived protein hydrolysate containing amino acids and small peptides elicited a hormone-like activity, enhanced nitrogen uptake and consequently crop performances.

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.

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.

Phytochemical constituents and in vitro radical scavenging activity of different Aloe species.

The phytochemical profile of Aloe barbadensis Mill. and Aloe arborescens Mill. was investigated using colorimetric assays, triple quadrupole and time-of-flight mass spectrometry, focusing on phenolic secondary metabolites in the different leaf portions. Hydroxycinnamic acids, several characteristic anthrones and chromones, the phenolic dimer feralolide and flavonoids such as flavones and isoflavones were identified. The stable radical DPPH test and the ORAC assay were then used to determine the in vitro radical scavenging. The outer green rind was the most active, while the inner parenchyma was much less effective. The 5-methylchromones aloesin, aloeresin A and aloesone were the most active among the pure secondary metabolites tested. The results suggest that several compounds are likely to contribute to the overall radical scavenging activity, and indicate that leaf portion must be taken into account when the plant is used for its antioxidant properties.

Mild Potassium Chloride Stress Alters the Mineral Composition, Hormone Network, and Phenolic Profile in Artichoke Leaves

There is a growing interest among consumers and researchers in the globe artichoke [Cynara cardunculus L. subsp. scolymus (L.) Hegi] leaf extract due to its nutraceutical and therapeutic properties. The application of an abiotic stress such as salinity can activate the stress-signaling pathways, thus enhancing the content of valuable phytochemicals. The aim of this study was to assess the metabolic changes in artichokes by probing the leaf metabolome of artichoke plants grown in a floating system and exposed to a relatively mild (30 mM) potassium chloride (KCl) salt stress. Potassium chloride treatment decreased the leaf dry biomass of artichoke, macro- and microelements in leaves (e.g., Ca, Mg, Mn, Zn, and B) but increased the concentrations of K and Cl. Metabolomics highlighted that the hormonal network of artichokes was strongly imbalanced by KCl. The indole-3-acetic acid conjugates, the brassinosteroids hormone 6-deoxocastasterone, and even more the cytokinin precursor N6-(Delta-2-isopentenyl)-adenosine-5′-triphosphate, strongly increased in leaves of KCl-treated plants. Moreover, KCl saline treatment induced accumulation of GA4, a bioactive form additional to the already known GA3. Another specific response to salinity was changes in the phenolic compounds profile, with flavones and isoflavones being decreased by KCl treatment, whereas flavonoid glycosides increased. The osmotic/oxidative stress that salinity generates also induced some expected changes at the biochemical level (e.g., ascorbate degradation, membrane lipid peroxidation, and accumulation of mannitol phosphate). These latter results help explain the molecular/physiological mechanisms that the plant uses to cope with potassium chloride stress exposure.

Co‐inoculation of Glomus intraradices and Trichoderma atroviride acts as a biostimulant to promote growth, yield and nutrient uptake of vegetable crops

BACKGROUND The application of beneficial microorganisms at transplanting can promote rapid transplant establishment (starter effect) for achieving early and high yields. The aim of this study was to evaluate the biostimulant effects of Glomus intraradices BEG72 (G) and Trichoderma atroviride MUCL 45632 (T) alone or in combination on plant growth parameters, yield, chlorophyll index (SPAD), chlorophyll fluorescence and mineral composition of several vegetable crops. RESULTS The T. atroviride strain was capable of producing siderophores and auxin-like compounds under a wide range of substrate pH conditions (5.5-8.0). The highest shoot, root dry weight, SPAD and chlorophyll fluorescence in lettuce, tomato and zucchini was observed in the G + T combination, followed by a single inoculation of G or T, whereas the lowest values were recorded in the uninoculated plants. Under greenhouse conditions, the shoot dry weight was significantly increased by 167%, 56%, 115%, 68% and 58% in lettuce, melon, pepper, tomato and zucchini, respectively, when supplied with both beneficial microorganisms in comparison with the control. This increase in root and shoot weight was associated with an increased level of nutrient uptake (e.g. P, Mg, Fe, Zn and B). Under open field conditions, the lettuce shoot and root dry weight increased by 61% and 57%, respectively, with biostimulant microorganism application in field conditions. For zucchini, early and total yields were significantly increased by 59% and 15%, respectively, when plants were inoculated with both microorganisms. CONCLUSION The application of the biostimulant tablet containing both G and T can promote transplant establishment and vegetable crop productivity in a sustainable way.

The effect of growing spinach (Spinacia oleracea L.) at two light intensities on the amounts of oxalate, ascorbate and nitrate in their leaves

Summary The effect of growing spinach at two light intensities on the content of oxalate, ascorbate and nitrate in their leaves was determined. Plants were grown for five weeks in a growth cabinet under a 10 h light/14 h dark photoperiod and a photon flux density of either 800 or 200 µmol quanta m–2 s–1. The content of oxalate, ascorbate and nitrate in the fourth and fifth fully expanded true leaves was then determined at three times during the photoperiod. Spinach plants grown at the lower light intensity showed decreased growth, a decreased leaf area per plant and an increased shoot to root ratio. Leaves from plants grown under low light contained less ascorbate but more oxalate and nitrate. Our data show that the nutritional quality of spinach is thereby decreased by growth in low light intensities and suggest that the content of oxalic acid in leaves may depend on the rate of its catabolism.