Heat treatments and expansin gene expression in strawberry fruit

Heat treatments have been applied in fruit postharvest technology for insect disinfestations, decay control, ripening delay and modification of fruit responses to other stresses. Heat treatment affects several aspects of fruit ripening, such as ethylene production and cell wall degradation probably through changes in gene expression and protein synthesis. In this paper, strawberries (Fragaria × ananassa Duch., cv Camarosa) at 50–75% red stage of ripening were heat-treated at 45 °C during 3 h in an air oven and then stored at 20 °C for 0, 4, 18, 24 and 48 h. Fruit firmness was determined and the expression of a set of expansin genes (FaEXP1, FaEXP2, FaEXP4, FaEXP5 and FaEXP6) was analyzed. The firmness of treated fruit was higher than that of control fruit 24 h after treatment, though the differences disappeared after 48 h at 20 °C. The analysis by northern-blot indicated that heat treatments affected differently the expression of expansin genes. The expression of FaEXP1, FaEXP2 and FaEXP6 was lower in treated fruit during the following 24 h post-treatment. The lower expression of these expansin genes could contribute to delay softening after heat treatment.     

Expression of carotenogenic genes during the development and ripening of watermelon fruit

Five watermelon varieties with different flesh colors: “ZAOHUA” (red); “96B41” (pink); “307CHAOFENG” (yellow); “UNKNOWN” (orange); and “SANBAI” (white) were used to investigate the relationship between carotenoid profiles and expression of carotenoid-related genes during fruit development and ripening. In mature fruit, “ZAOHUA” and “96B41” accumulated high level of lycopene, “SANBAI” contained trace amounts of carotenoids. Through HPLC and dot blot hybridization, carotenoid content was analyzed and compared to the expression of carotenoid-related genes including Psy, Pds, Zds, CrtIso, Lcyb, Chyb, Nced1, Nced2, Nced3 during fruit development. All genes examined were expressed in all five watermelon varieties. In red and pink color varieties, the decrease of gene expression for Lcyb and Chyb at stage C (30 d after pollination) may be consistent with the high accumulation of lycopene and β-carotene. In the yellow variety, expression of the detected genes increased markedly with the onset of maturation, but little carotenoid accumulation was detected, which may be due to high level of carotenoid cleavage dioxygenases. Expression of all detected genes decreased rapidly in the white color variety upon fruit ripening, which may be attributed to a reduction in metabolic flux in the carotenoid pathway. These results imply the complex regulation of the carotenoid biosynthetic pathway in watermelon.     

Apple tree growth and overall fruit quality under organic and conventional orchard management

Two apple (Malus × domestica Borkh.) orchards, a conventional and an organic one, were compared in terms of plant growth, marketable fruit quality attributes (fruit weight, shape, color, phenolic compound concentration, nutrients) and yield. The two orchards were located nearby, in order to exclude possible pedoclimatic influences on the measured variables. The two management systems resulted in similar new season's shoot growth and similar fruit quality attributes, in terms of total soluble solids, juice pH, titratable acidity and color indexes, while the conventionally grown trees produced almost twice the yield of the organically managed ones. The flesh plus peel portion of the conventionally produced fruits exhibited higher total flavonoid and o-diphenols concentration, while the flesh portion presented higher flavonoid concentration. Nitrogen concentration was higher in all portions of conventionally grown fruits, while potassium, calcium, sodium and manganese concentrations were higher in the flesh portion of organically produced fruits. Significant differences were observed between management systems concerning fruit nutrient ratios, but their values were within the desired ranges, under both conventional and organic management systems.     

Isolation of a citrus ethylene-responsive element binding factor gene and its expression in response to abiotic stress,girdling and shading

Information about citrus ethylene-responsive element binding factor (ERF) genes and their functions in fruit ripening or in stress tolerance is still scarce. In the present study, one of ERF genes, CitERF was isolated from fruit of Citrus unshiu with a maximal putative open reading frame encoding 207 amino acids. The deduced protein contains a region rich in acidic amino acids, an AP2/ERF domain and a KRRK nuclear localization signal. It belongs to group B of Class I in the ERF subfamily in which MdERF2 (Malus × domestica ethylene-response factor 2) and PsERF1b (Prunus salicina ethylene-response factor 1b) were involved in the progress of fruit ripening. CitERF mRNA level in fruit peel and pulp increased obviously along with fruit ripening. However, its expression could be reduced significantly by treatments of total shading and fruit-bear-shoot girdling plus defoliation during fruit ripening. As for the response to abiotic stresses, CitERF expression was found to be induced continuously during the treatment of 10% polyethylene glycol. On the other hand, it could be induced to high level at 1 h after the treatment of 4 °C or 250 mM NaCl and then declined continuously. Taken together, the results suggested that CitERF may play an important role in some biological processes during fruit ripening and in improving tolerance to drought, low temperature and salt stress.     

Phytochemicals and antioxidant capacity of orange (Citrus sinensis (l.) Osbeck cv. Salustiana) juice produced under organic and integrated farming system in Greece

Organically and integrated produced orange (Citrus sinensis (l.) Osbeck cv. Salustiana) fruits were assayed in terms of fruit characteristics and juice phytochemicals over a period of two years. Fruit size and juice volume were higher under organic farming system. There were not any significant differences concerning either the carbohydrates’ or organic acids’ concentrations of the juice. Similar results were obtained concerning the total phenol, the total o-diphenol and the total flavonoid concentration of the juice, while neither hesperidin nor narirutin differentiated significantly. However, β-carotene concentration was detected in higher concentration in organically produced fruit (0.43 mg L⁻¹). Juice extracted from both integrated and organically produced fruits exhibited similar antioxidant capacity values (based on 2,2-diphenyl-1-picryl hydrazyl and ferric reducing/antioxidant power assays), while correlation analysis revealed the significant contribution of phenolic compounds to antioxidant capacity (r = 0.75–0.86). Most of the amino acids determined were quantified in similar concentration in the juice of both organic and integrated produced fruits (approximately 1600 mg L⁻¹). The present results indicate that integrated oranges cv Salustiana, under the cultivation management implemented in this experiment, present similar antioxidant and nutritional values to the organically produced ones.     

Response of evergreen perennial tree crops to gibberellic acid is crop load-dependent: II. GA3 increases yield and fruit size of ‘Hass’ avocado only in the on-crop year of an alternate bearing orchard

Despite problems of low fruit set, small fruit size and alternate bearing, the Hass cultivar dominates commercial avocado production worldwide. To increase yield and fruit size, gibberellic acid (GA₃) (25 mg L⁻¹) was applied at different stages of ‘Hass’ avocado tree phenology: (i) mid–late April (flower abscission), end of June–beginning of July (fruit abscission and beginning of the exponential phase of fruit growth), and mid-January (beginning of pre-harvest fruit drop); (ii) end of June–beginning of July; and (iii) mid-September (near the end of the major fruit abscission period; period of exponential fruit growth). In both years of the research, applications of GA₃ in April and June–July were within the periods of intense flower and fruit abscission, respectively; fruit abscission was low in September and January. Maximum air temperature was not related to flower or fruit abscission. In the on-crop year (391 fruit per untreated control tree), a single application of GA₃ at the end of June–beginning of July significantly increased total yield (kilograms only) and yield of commercially valuable fruit (178–325 g/fruit) (as kilograms and number per tree) compared with the control (P < 0.0001). GA₃ applied in September increased total yield (kilograms only) and yield of commercially valuable fruit (kilograms and number per tree) to values intermediate to and not significantly different from all other treatments, except trees receiving multiple applications of GA₃. This treatment reduced total yield and yield of commercially valuable fruit (kilograms and number per tree) relative to all treatments (P ≤ 0.0002). In contrast, during the off-crop year (32 fruit per control tree), no GA₃ treatment had a significant effect on yield or fruit size compared with the control and all other GA₃ treatments. For ‘Hass’ avocado, there was no negative effect from applying GA₃ at the end of June–beginning of July in both the off- and on-crop years; 2-year cumulative total yield and yield of commercially valuable fruit were increased by 27 kg (128 fruit) and 22 kg (101 fruit) per tree, respectively, above the yield of untreated control trees (P < 0.0001).     

Phenolic content and free radical scavenging activities in rambutan during fruit maturation

The 1,1-diphenyl-2-picrylhydrazyl (DPPH^•) scavenging activity, changes and accumulation of phenolic content were studied in the peel, seed and pulp of rambutan, Nephelium lappaceum L. (Rongrien and Seeechompoo cultivars) during fruit maturation. The IC₅₀ values of the radical scavenging activity of the peels, in both cultivars remained low through fruit development (1.42–4.75 μg/mL) but the values of the seed and pulps were low at the beginning and increased markedly toward fruit development until harvest (4.87 to >1000 μg/mL). The accumulation of phenolic compounds in rambutan peels of Rongrien and Seechompoo cultivars increased continuously until reaching a maximum of 1653 and 733 mg per fruit at the time of being harvested, at 112 and 98 days after full bloom (DAFB), respectively. Ellagic acid, corilagin and geraniin in the peels of both cultivars were observed and quantified. The major component in the peels of the two cultivars was geraniin. The accumulation of ellagic acid, corilagin and geraniin in the peels increased and reached the maximum at the harvest stage, especially the major constituent of geraniin (1011 and 444 mg/fruit for Rongrien and Seechompoo, respectively). The free radical scavenging property was observed to have a relationship with the phenolic content quantified in different parts of the rambutan fruit. This research demonstrates potential data on phenolic constituents through fruit development, especially in the peels at the time of harvest.     

Organic acid content and composition of the olive fruits during ripening and its relationship with oil and sugar

In this work, the contents of oil, sugar and organic acids of olive fruit samples (Domat, Memecik and Uslu) were determined by using HPLC at different maturation stages. Olive fruit samples presented a common organic acid profile, composed of four constituents: oxalic, citric, malic and succunic acids. Total organic acid content of Domat variety was found to be 4787.1 ± 4.53 mg/100 g in January. Memecik variety had the highest value at the beginning of the ripening period (6385.08 ± 4.90 mg/100 g). The amount of organic acid in Uslu variety reached up to the value of 10942.5 ± 30.41 mg/100 g. The results were evaluated statistically to determine relationship between the oil, sugar and organic acid content in three olive varieties during maturation. A positive correlation was found between the total sugar and organic acid (r = 0.54, p < 0.01) whereas a low positive correlation was observed between the contents of oil and total organic acids (r = 0.46, p < 0.05) in olive varieties.     

Decreased anthocyanin biosynthesis in grape berries grown under elevated night temperature condition

In grape cultivation, high night temperature generally reduces anthocyanin accumulation in berry skin. To clarify the regulatory mechanism of anthocyanin biosynthesis under the conditions of high night temperatures, we examined flavonoid accumulation, the activities of related enzymes and gene expression in the anthocyanin biosynthetic pathway in grape berries grown under cool and warm night conditions. Anthocyanin accumulation in the skin of berries grown at high night temperatures (30 °C continuous) was reduced as compared to that of berries grown at low night temperatures (30 °C in daytime/15 °C in night time). On the other hand, flavonol levels in the skin of berries were not significantly different between low and high night temperature conditions. High night temperatures also inhibited the gene expression of chalcone synthase (CHS), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), leucoanthocyanidin dioxygenase (LDOX) and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) at veraison and an increase in UFGT activity after veraison. These results suggest that the inhibition of anthocyanin biosynthesis in grape berries grown under high night temperature condition could be caused by lower expression levels of anthocyanin biosynthetic genes at an early stage of ripening and lower activities of anthocyanin biosynthetic enzymes, particularly UFGT.     

Multiple pre-harvest treatments with acibenzolar-S-methyl reduce latent infection and induce resistance in muskmelon fruit

Muskmelons (cv. Yindi) were sprayed with 100 mg a.i. L⁻¹ acibenzolar-S-methyl (ASM) four times at four different stages: flowering, the young fruit, the fruit enlarging period and the netting periods. Analyses were performed 1 week after each ASM treatment. Results showed that the incidence of total latent infection (caused by all observable fungi) and the incidence of relative latent infection (caused by Alternaria alternata or Fusarium spp.) were significantly lower in sprayed muskmelons than in the control fruit. Moreover, the reduction in the incidence of latent infection was greater with increased ASM treatments. The control of latent infection by ASM resulted in reduced incidence of postharvest decay and improved fruit appearance and firmness after 10 d of storage. In addition, the activities of peroxidase, phenylalanine ammonia lyase, β-1,3-glucanase and chitinase increased significantly in treated muskmelons. ASM treatments also contributed to the accumulation of phenolic compounds, lignin and flavonoids. Increases in defense-related enzyme activities and in particular metabolite levels were observed in plants with more ASM treatments. These results suggest that multiple ASM treatments could induce disease resistance in muskmelons and could be an ideal strategy for preventing latent infection in fruits.     

Response of evergreen perennial tree crops to gibberellic acid is crop load-dependent. I: GA3 increases the yield of commercially valuable ‘Nules’ Clementine Mandarin fruit only in the off-crop year of an alternate bearing orchard

Worldwide, gibberellic acid (GA₃) is used routinely to increase fruit number and size of seedless mandarins. The efficacy of seven combinations of GA₃ concentrations and application times to maximize total yield and yield of commercially valuable fruit (diameter 57.2–76.2 mm) of ‘Nules’ Clementine mandarin (Citrus reticulata Blanco) was determined in a commercial orchard. GA₃ applied during the period of intense flower abscission failed to reduce the total number of abscised flowers in both the light off- and heavy on-bloom years. No GA₃ treatment reduced fruit abscission when trees were setting the low yield off-crop. However, all trees receiving GA₃ in the high yield on-crop year had fewer abscised fruit than untreated control trees (P = 0.0188) and GA₃ applied 10 days after 75% petal fall and in July increased the number of fruit retained on tagged branches >20% compared to control trees (P = 0.0005). Maximum air temperature was not related to flower or fruit abscission. In the off-crop year (548 fruit per untreated control tree), it was necessary to apply 15 or 25 mg L⁻¹ GA₃ at 60% bloom, 90% bloom, 75% petal fall and 10 days after 75% petal fall to significantly increase the number of fruit per tree and yield of commercially valuable fruit (kilograms and number per tree) (P < 0.0001) above that of control trees, with no reduction in total kilograms per tree. In the following on-crop year, it was better not to apply GA₃: no treatment increased total yield or fruit size and five of seven GA₃ treatments tested reduced total yield as kilograms and number of fruit per tree (P = 0.0003). The results provide strong evidence that GA₃ efficacy is crop load-dependent and dictate that crop load should be considered when using GA₃ to increase fruit set or fruit size of mandarins.     

Biochemical changes associated with hardening of endocarp in Spondias mangifera Willd. fruits during developmental stages

Spondias mangifera is a unique, fleshy, drupe fruit with a mango flavor. The hardening of endocarp during development and maturation of hog plum is a major bottleneck, which reduces the edibility of the fruits by 80% and makes them unmarketable. For the first time, three distinct maturity stages were demonstrated. Distinct pattern in change in surface color, accumulation of carotene pigments and biochemical components in fruits were observed. The decrease in chlorophyll ‘a’ and chlorophyll ‘b’ correlated well with the downhill trend in Transmittance Refractory Spectroscopy (TRS) – ‘L’, ‘a’, ‘b’ values. The decrease in the total chlorophyll along with the accumulation of carotene pigment contributes significantly to the lightness of surface color and reflected in ‘L’ hue values. Confluence of carotene and total chlorophyll on the 9th week provides a distinct marker for maturity. Complete convergence of five carpells on the 9th week after fruit set, heralds the onset of maturation in Indian hog plum and which was adjudged as visual index of maturity. Hardening of endocarp begins after attainment of optimum maturity and last for 2 weeks. Pre-climacteric plunge in respiration along with coordinated changes in pigments, and accumulation of ascorbic acid, phenols, presets the optimum maturity period of 9th week after fruit set. Pre-climacteric falls in respiration with lowest output of 40.57 mg CO₂/kg-h concentration on 9th week after fruit set indicates the attainment of fruit maturity. Harvesting of hog plum between 9th and 11th weeks provides the fruit with soft endocarp and complete edibility.     

Phenotypic variations in fruits and selection potential in Sclerocarya birrea subsp. birrea

The domestication of indigenous fruits through agroforestry is seen as one of the important issues in the transformation in the way in which land is used within rural areas. A study of the variation in fruit traits is also important as it is a prerequisite for cultivar development in the domestication process. Following an aridity gradient, phenotypic variation was assessed in fruits of Sclerocarya birrea subsp. birrea, native to West African semi-arid areas. Fruits were collected from 42 trees of various diameters in agroforestry parklands from the dry and semi-humid Sudanian zones. They were partitioned into peel, flesh and pit. Each fruit was labelled and its components were measured and weighted. The overall mean fruit mass was 18.58 ± 0.24 g (mean ± SE) but fruits from the population in the drier zone were significantly larger (19.90 ± 0.37 g vs 17.02 ± 0.24 g; P < 0.001). The results showed a strong correlation between fruits and their components (P < 0.05). Tree diameter was very weakly correlated with fruit traits. There was a high level of variation in fruit characteristics and components within and between populations. The within-population variation accounted for the greatest part (67–100%) of the total variation. Many trees, mainly from the drier zones, showed superior phenotypic traits. Five groups of trees which represented different fruit morphotypes were identified for various prospective exploitations. The results strongly support the implementation of preliminary practical conservation action and domestication of S. birrea in West Africa.     

Seasonal changes of mineral nutrients and phenolics in pomegranate (Punica granatum L.) fruit

Pomegranate fruit is an important source of potentially healthy bioactive compounds and mineral nutrients. Changes in total phenolic compound, concentrations, and levels of macronutrients (P, K, N, Mg, Ca and Na) and micronutrients (Zn, Cu, Mn, Fe and B) in arils and peel of pomegranate fruit were recorded from 10 days after full bloom until harvest. Total phenolics levels increased at early stage of growth both in peel and arils of fruit, but thereafter generally decreased during maturation and reached to 3.70 and 50.22 mg g⁻¹ of dry weight in arils and peel, respectively, at harvest. The amount of total phenolics in peel was markedly higher than arils of pomegranate fruit. The concentration of most elements in arils and peel decreased during fruit growth and development. At harvest the relative order of concentration of macronutrients both in arils and peel was K > N > Ca > P > Mg > Na. The concentration of most micronutrients was greater in the arils than in the peel especially in early season. The relative order of concentration of micronutrients in arils was B > Fe > Zn > Cu > Mn. The accumulation of all the macro- and microelement within the fruit also increased during fruit growth and development. These results provide important data on total phenolics and macro- and micronutrient changes during fruit growth and development, emphasizing that pomegranate fruit can be a good source of bioactive compounds and minerals.     

GA3 increases fruit weight in ‘Yu Her Pau’ litchi

In order to increase the fruit weight of a shriveled-seed cultivar, trees of ‘Yu Her Pau’ litchi (Litchi chinensis Sonn.) growing in Taiwan were sprayed with Gibberellic acid (GA₃) (ProGibb^®, 20% of GA₃) at 5 and 10 mg/l 14 days after full bloom (AFB) over 2 years. Both concentrations of GA₃ significantly increased fruit longitudinal and transversal diameter, and fruit, aril and pericarp weight (40–41 and 37–38 mm, and 27.3–28.4, 21.7–22.7 and 5.0–5.3 g, respectively) compared with control (35–36 and 33–34 mm, and 22.3–22.4, 17.8–17.9 and 3.9–4.0 g), but had no significant effects on seed weight, percentage of aril weight of total fruit weight or total soluble solids (0.5–0.7 g, 78.9–80.3% and 18.1–19.0 °Brix, respectively). Fruit characteristics within the two concentrations of GA₃ showed no significant difference. The results indicated that sprays of GA₃ should be evaluated in ‘Yu Her Pau’ commercial orchards, and in other elite cultivars.     

CPPU application on size and quality of hardy kiwifruit

For the purpose of determining the appropriate conditions of application to increase the size of a hardy kiwifruit, Actinidia arguta ‘Mitsuko’, N₁-(2-chloro-4-pyridyl)-N₃-phenylurea (CPPU) was applied at three different growth stages of the crop: at petal fall, 10 and 25 days after petal fall (DAPF), and three different concentrations: 1, 5 and 10 mg l⁻¹. A significant increase in fruit size was obtained by treatment at the concentrations of 5–10 mg l⁻¹ and at 10 DAPF. The fruit weight doubled. Although a significant reduction in the concentrations of total soluble solids (TSS), titratable acids (TA) and ascorbic acid (AsA) in the CPPU-treated fruits was recorded, the TSS/TA ratio and AsA content per fruit increased by the treatment. CPPU application at petal fall induced abnormally protruding fruit tip.     

Changes in antioxidants and fruit quality in hot water-treated ‘Hom Thong’ banana fruit during storage

The effects of hot water treatment on antioxidants and fruit quality were investigated in banana fruit of cv. Gros Michel (Musa acuminata, AAA Group, locally called cv. Hom Thong) by immersing fruits in hot water (50 °C) for 10 min, before storage at 25 °C for 10 days or 14 °C for the first 8 days followed by storage at 25 °C for the second 8 days until ripening. Quality parameters including peel color and pulp firmness indicated that hot water treatment helped to delay banana fruit ripening at both storage conditions. Hot water treatment decreased the levels of hydrogen peroxide (H₂O₂) and malonydialdehyde (MDA) during storage at 25 °C. Glutathione (GSH and GSSG) contents and the ratio of GSH/GSSG during fruit approaching ripening were significantly induced in hot water-treated fruits while ascorbic acid (AA) contents were slightly increased. In addition, the combined treatment increased free phenolics and flavonoids during storage. Results suggest that hot water treatment has led to an induction of antioxidants in banana fruits as indicated by an increase of antioxidants and a decrease of H₂O₂ during ripening, and all of which result in a delayed ripening of banana fruit.     

Leaf pruning intensities at flowering of banana (Musa AAA,cv. Grande Naine) did not influence fruit green and yellow life and quality

This study examined the effects of leaf pruning intensities at flowering on the green and yellow life and fruit quality of bananas (Musa AAA, cv. Grande Naine). The fruit from banana plants that retained 7, 9, 11 and 13 leaves after pruning were packed in carton boxes of 13.7 kg and stored in a cold room at 14 °C for 21 days to simulate transportation conditions. During this period, eight visual evaluations of fruit peel colour were made. Next, fruits were induced to commercial ripening using ethylene at 100 μl/ml. Four evaluations (every 2 days) on fruit firmness, soluble solids, titratable acidity, fruit weight and peel colour were made to assess fruit yellow life. No interaction between evaluations and number of leaves retained was found for pulp firmness, soluble solid percentage, fruit acidity, fruit weight and maturation grade. The fruit green life and peel colour was similar for plants retaining different number of leaves. After the application of ethylene, there were no differences in fruit firmness (P > 0.62), percentage of soluble solids (P > 0.24) nor in the percentage of acidity (P > 0.32). No difference in fruit weight (P > 0.07) and ripening grade (P > 0.17) were observed among plants retaining different number of leaves. The results suggest that in tropical commercial banana plantations, producing for international markets, it is possible to defoliate the banana plants to seven leaves at flowering without causing a reduction on the green and yellow life and quality of fruit.