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Ignazio Infantino and Riccardo Lo Bianco*

Peel color is a critical index of external fruit quality and consumer appreciation level. Traditional methods for determination of peel color are based on visual analysis or punctual measurements by colorimeter. In this study we present a method based on digital image analysis that integrates the accuracy of an interactive measurement and the efficacy of an image analysis that descibes entire sides of the fruit. A sample of apple, mandarin, grape, and peach fruit was photographed (each fruit on two opposite sides) with a digital camera for determination of peel color. Digital images were converted from RGB to CIE L*a*b* format, and color characteristics were indexed and quantified. The implemented method uses a reference color image cropped from the best fruit (interactively chosen) to calculate a color index for each fruit of the image set. The final index is the weighted sum of the number of pixels of the fruit, where pixels closer to the reference color (distance in the CIE L*a*b space) are considered more relevant. This color index gives integrated information on fruit color quantity (% of cover color) and quality (hue and saturation). The method represents a rapid and efficient way of determining color of the entire fruit surface and overcomes difficulties and approximation of traditional methods. A modification of the same method can be used to determine peel rugosity (mandarin) and average size and number of grape berries per bunch.

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Michelangelo Policarpo and Riccardo Lo Bianco*

Five different types/combinations of foliar fertilizers were tested on eight-year-old trees of `Nocellara del Belice' olive grown in central Sicily. Trees were sprayed four times during Summer and Fall 2002 with Floral 20-20-20 (mineral N, P, K, and microelements; FLO) in combination with Alga Cifo (extract of brown algae; ALG), Floral 20-20-20 alone, Alga Cifo alone, Azomin (organic N, amino acids and peptides; AZO), Supernat93 (organic N and K, distillation residue; SUP), and water (control). Yield and trunk circumference were measured during Fall 2002, whereas other vegetative and reproductive parameters were measured during Spring-Fall 2003. AZO and SUP trees produced more than control and ALG trees, whereas only AZO trees showed higher yield efficiency than control. The number of inflorescences per shoot was greatest in FLO and ALG trees and smallest in control trees. Percentage of ovary abortion and June drop were lowest in AZO trees and highest in FLO+ALG and ALG trees, whereas ALG was the only fertilizer that caused a greater fruit drop at harvest. Shoot growth was significantly reduced in ALG and FLO trees, and AZO trees presented leaves with reduced specific weight. Organic foliar fertilization with AZO and SUP generally improved yield and growth of `Nocellara del Belice' olive trees by reducing ovary abortion and June drop and increasing shoot growth.

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Riccardo Lo Bianco and Mark Rieger

The peach [Prunus persica (L.) Batsch (Peach Group)] fruit is a sink organ comprised of different types of tissue, which undergoes three distinct developmental stages during the growth season. The objective of this study was to characterize the activity and partitioning of sorbitol and sucrose catabolism within `Encore' peach fruit to determine whether the two forms of translocated carbon play different roles in the various fruit tissues and/or stages of development. Sorbitol catabolic activity was defined as the sum of NAD-dependent sorbitol dehydrogenase (SDH) and sorbitol oxidase (SOX) activities, whereas sucrose catabolic activity was defined as the sum of sucrose synthase (SS), soluble acid invertase (AI), and neutral invertase (NI) activities. Partitioning of sorbitol and sucrose catabolism in each tissue was calculated as percentage of total sorbitol or sucrose catabolic activity in the entire fruit. At cell division, sorbitol catabolic activity was similar in the endocarp and mesocarp, but lower in the seed. However, sorbitol catabolism was mostly partitioned into the mesocarp, due to its large size compared to that of other tissues. SDH was more active in the mesocarp, while SOX was more active in the endocarp. Sucrose catabolism was most active and partitioned mainly into the endocarp. At endocarp hardening, both sorbitol and sucrose catabolic activities were highest in the seed, but despite this, sucrose catabolism was partitioned mostly in the mesocarp. At cell expansion, sorbitol and sucrose catabolic activities were still higher in the seed only when expressed on a weight basis and similar in mesocarp and seed when expressed on a protein basis. Both sorbitol and sucrose catabolism were partitioned mostly into the mesocarp. Sorbitol and sucrose contents were generally higher in the tissues that exhibited lower catabolic activities. All carbohydrates were always partitioned mostly into the mesocarp. Our results show that, at the cell division and endocarp hardening stages, sorbitol and sucrose catabolism are partitioned differently in the fruit and that SDH activity may play an important role in mesocarp cell division and final fruit size determination.

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Riccardo Lo Bianco and Mark Rieger

In peach [Prunus persica (L.) Batsch (Peach Group)], both sorbitol and sucrose are used for source to sink carbon (C) transport, yet their specific functions in fruit growth and development remain unclear. Growth rate (GR), respiration rate (R), carbohydrate content, and the activities of sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX), sucrose synthase (SS), acid invertase (AI), and neutral invertase (NI) were determined in `Encore' peaches to study the specific functions of sorbitol and sucrose in each phase of fruit development (an early period of rapid cell division, a relatively inactive intermediate stage where endocarp (pit) hardening occurs, and a final swelling due to cell expansion). Fruit growth and respiration rates (mol C/fruit per day) were always positively correlated, but the growth coefficient (gc) relating them was significantly higher at cell division, when maintenance respiration (Rm) was nearly absent. Sorbitol and sucrose appeared to participate equally in growth and maintenance respiration. Contents of sorbitol and sucrose both correlated positively to GR, and their rates of accumulation increased from early to late growth stages in similar fashion. SDH activity was always positively correlated with sink strength and GR, but with R only at endocarp hardening (r = 0.632). SOX activity was also correlated with sink strength and GR in the early (r = 0.514 and 0.553) and late (r = 0.503 and 0.495) growth phases, but not at endocarp hardening, and was correlated with R in two of three growth phases. Among sucrose cleavage enzymes, AI activity was positively correlated with sink strength, GR, and R more strongly than the others (r = 0.51 to 0.80), but only in the cell division and cell expansion periods. SS activity was correlated with sink strength and R only at endocarp hardening, and NI activity was generally not correlated to sink strength, GR, or R. We conclude that sorbitol and sucrose play similar roles in fruit development, and the enzymes associated with their metabolism work in concert to produce the observed changes in growth and respiration.

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Bedri Karakas, Riccardo Lo Bianco and Mark Rieger

The effect of specific ion toxicity during salt stress was tested in the present study. The experiment was repeated twice, in 1996 and 1998, with `Nemaguard' peach seedlings and rooted cuttings grown in hydroponics under two NaCl concentrations (50 and 30 mm). Foliage was separated in symptomatic and symptomless leaves and the amount of sodium (Na+) and chloride (C1) was determined. Significantly higher Na+ content was found in symptomatic than in symptomless leaves in both experiments, whereas in only two of the six cases was Cl content higher in symptomatic than in symptomless leaves. The Na+ threshold for leaf scorch was somewhere between 4 and 6 mg·g–1 dry weight. Results indicated that Na+ accumulation, rather than Cl accumulation, was associated with the familiar marginal and interveinal scorch symptoms seen in salt-stressed peach leaves.

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Vittorio Farina, Riccardo Lo Bianco and Paolo Inglese

Canopy shape and depth may influence crop uniformity of peach trees at harvest. To test this hypothesis we examined yield distribution and fruit quality changes at different canopy levels of peach trees trained to delayed vase (DV) and perpendicular Y (Y). Trees of both training forms were divided vertically into six or seven 50-cm-deep layers and fruit was harvested at commercial ripening from each layer separately. Regardless of training form, number of fruit and yield per layer were highest in the central part of the canopy, but more evenly distributed among canopy layers in Y trees. In DV trees, fruit weight decreased linearly from top to bottom, whereas it remained constant along the top and middle portion of Y canopies to decrease rapidly at the bottom. In DV trees, 83% of the fruit fell into AAA, AA and A size categories, whereas fruit of Y trees was more evenly distributed among all size categories. Hue of fruit peel color increased linearly with distance from canopy top in both training forms, but more sharply in DV trees. Fruit soluble solid content decreased linearly from canopy top to bottom, regardless of training form. A more uniform crop load distribution within the canopy in combination with a light penetration gradient resulted in greater variability of quality parameters for Y than DV trees.

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Riccardo Lo Bianco, Brunella Morandi and Mark Rieger

Along with sucrose, sorbitol represents the major photosynthetic product and the main form of translocated carbon in peach. The objective of the present study was to determine whether in peach fruit, sorbitol and sucrose enzyme activities are source-regulated, and more specifically modulated by sorbitol or sucrose availability. In two separate trials, peach fruit relative growth rate (RGR), enzyme activities, and carbohydrates were measured 1) at cell division stage before and after girdling of the shoot subtending the fruit; and 2) on 14 shoots with different leaf to fruit ratio (L:F) at cell division and cell expansion stages. Fruit RGR and sorbitol dehydrogenase (SDH) activity were significantly reduced by girdling, whereas sucrose synthase (SS), acid invertase (AI), and neutral invertase (NI) where equally active in girdled and control fruits on the fourth day after girdling. All major carbohydrates (sorbitol, sucrose, glucose, fructose and starch) were reduced on the fourth day after girdling. SDH activity was the only enzyme activity proportional to L:F in both fruit developmental stages. Peach fruit incubation in sorbitol for 24 hours also resulted in SDH activities higher than those of fruits incubated in buffer and similar to those of freshly extracted samples. Overall, our data provide some evidence for regulation of sorbitol metabolism, but not sucrose metabolism, by photoassimilate availability in peach fruit. In particular, sorbitol translocated to the fruit may function as a signal for modulating SDH activity.

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Riccardo Lo Bianco, Mark Rieger and She-Jean S. Sung

Sorbitol is the major photosynthetic product in peach [Prunus persica (L.) Batsch.]. In sink tissues, sorbitol is converted to fructose via NAD+-dependent SDH. A new procedure is described that allows rapid, simple quantification of SDH activity in growing tissues. The procedure uses only 0.01 to 5 g of fresh tissue per sample, such that a single shoot tip, a single root tip, or ≈5 g of fruit flesh can be assayed for SDH activity. Storage of samples at 4 or -20 °C overnight resulted in significant loss of enzyme activity. Thus, freshly harvested tissues were ground with sand in buffer at 2 °C in a mortar and pestle, and the homogenate was centrifuged at 3000 g n to remove particulate matter and sand. The supernatant was desalted on a Sephadex G-25 column, and the eluent was assayed for SDH activity immediately. Activity was determined by measuring the production of NADH per minute in the assay mixture using a spectrophotometer (340 nm). Tris buffer at pH 9.0 was the best for extraction of peach SDH. Activity of SDH was strongly inhibited by dithiothreitol (DTT) in the extraction mixture and by DTT, L-cysteine, or SDI-158 in the assay mixture, similar to results reported for SDH from mammalian tissues. Peach SDH has a Km of 37.7 mm for sorbitol and a pH optimum of 9.5, similar to those reported for apple (Malus × domestica Borkh.) SDH. Unlike older protocols for SDH activity in plant tissues, the new procedure features reduced sample size (1/10 to 1/100 of that which was previously used), smaller volumes of buffer, fewer buffer ingredients, greatly reduced time for sample preparation, yet comparable or higher values of SDH specific activity. Following the same procedure, SDH activity was also measured in Prunus fremontii Wats., Prunus ilicifolia (Nutt.) Walp., and Marianna 2624 plum (P. cerasifera Ehrh. × P. munsoniana Wight & Hedr.).

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Riccardo Lo Bianco, Mark Rieger and She-Jean S. Sung

Terminal portions of `Flordaguard' peach roots [Prunus persica (L.) Batsch] were divided into six segments and the activities of NAD+-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX), sucrose synthase (SS), soluble acid invertase (AI), and soluble neutral invertase (NI) were measured in each segment 10, 15, and 20 days after seed germination. The same type of experiment was conducted with terminal portions of `Flordaguard' and `Nemaguard' peach shoots except that one of the six segments consisted of the leaflets surrounding the apex. Independent of the age of individual roots, activities of SDH and AI were consistently highest in the meristematic portion and decreased with tissue maturation. In shoots, AI was the most active enzyme in the elongating portion subtending the apex, whereas SDH was primarily associated with meristematic tissues. A positive correlation between SDH and AI activities was found in various developmental zones of roots (r = 0.96) and shoots (r = 0.90). Sorbitol and sucrose contents were low in roots regardless of distance from tip, while sucrose showed a decreasing trend with distance and sorbitol, fructose, and glucose increased with distance from the meristem in shoots. Activity of SDH in internodes, but not apices, correlated with shoot elongation rate of both cultivars, whereas activities of other enzymes did not correlate with shoot elongation rate. We conclude that AI and SDH are the predominant enzymes of carbohydrate catabolism and the best indicators of sink growth and development in vegetative sinks of peach.

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Tiziano Caruso, Francesco Guarino, Riccardo Lo Bianco and Francesco Paolo Marra

Peach trees trained to modified spanish bush (MSB) and Y-trellis (Y) were evaluated and compared in the Mediterranean settings of southern Italy. The observations included two peach (Rich May and Summer Rich) and two nectarine (Big Bang and Nectaross) cultivars. In the MSB system, trees were spaced at 4.5 × 2.5 m (888 trees/ha), whereas in the Y system, trees were spaced at 5.5 × 2 m (909 trees/ha). Costs at planting, yield per tree, fruit size grade, unit price of sold peaches for each size grade, amount and cost of materials and labor for cultural management, and grower’s profit were quantified throughout all 6 years from planting and at full crop (year 4–6). Fixed costs of the MSB system were 45% lower at planting, 11% lower for fertilization, and 33% lower for pest control than in the Y system. Regardless of cultivar, the MSB system reported 19% lower yields, 29% less management labor, and 12% higher labor efficiency (kg fruit/h) than the Y system. The yield gap between the two systems tended to decrease after the 5th year. A greater percentage of fruit fell into large size categories in the MSB than in the Y system. Fruit unit value and yearly profit were similar in the two systems. Even for the most profitable cultivar under the Y system (i.e., Nectaross), the time needed to pay off the additional investment for establishing a Y by its additional profit was ≈11 years, indicating an advantage of the Y system over the MSB only by the 12th year from planting. Yield trends, along with the high initial investment and management labor and costs in the Y system, indicate better financial performance and more sustainable production in the MSB than in the Y system.