Accelerated Fruit Ripening Research Articles

INFLUENCE OF INDUCED RIPENING AND COLD STORAGE PROTOCOLS ON THE INCIDENCE OF POSTHARVEST DISEASES OF DATE PALM FRUIT

Date palm (Phoenix dactylifera L.) is a crop of increasing importance in the Elx area (Southeast of Spain). Since in this area date fruit are commercialized for fresh consumption, the most important problems limiting their storability are irregular ripening, weight loss, and postharvest decay. Postharvest treatments to uniformly accelerate fruit ripening and avoid more than one harvest are economically mandatory for the most important date cultivars in the area. In this work, the incidence of major postharvest diseases was determined for two consecutive seasons on locally grown ‘Hayani’ and ‘Medjool’ dates sealed in multi-layer PE bags and cold-stored (CS) at -3°C for up to 3 months before or after exposure of non-bagged fruit to induced ripening treatments of 98% CO2 at 25°C for 2 or 4 days (CO2) or air at 25°C for 2 or 4 days (Heat). Determinations were performed after shelf-life of 10 days in an ambient air atmosphere at 20°C. Fungal pathogenic isolates were plated in PDA Petri dishes and incubated at 25°C for further macroscopic and/or microscopic identification. Irrespective of the protocol, all ‘Hayani’ dates exposed to CS, CO2+CS, and Heat+CS were infected by Penicillium spp. Although with variable incidence depending on the season, other frequent disease causal agents were Aspergillus niger, Alternaria spp., and Cladosporium spp., generally in this order. A. niger and Alternaria spp. were significantly less frequent on Heat+CS and CO2+CS-treated dates, respectively. On ‘Medjool’ dates, Penicillium spp. and A. niger were isolated from about 100 and 10%, respectively, of fruit treated with either CS+CO2 or CO2+CS. Severe microbial fermentation was observed on dates exposed to the sequence CS+Heat.

REST BREAKING AGENTS ON APPLE ENDODORMANCY RELEASE UNDER SOUTHERN URUGUAYAN CONDITIONS

Apple (Malus domestica Borkh) commercial production in Uruguay is mainly located in the southern area (35°SL), where winter conditions not always satisfy chilling requirements for adequate sprouting. Limitations as poor budbreak percentage and extended flowering period are usually overcome with rest breaking agent sprays. In the present work, we evaluate the response of four apple cultivars ('Royal Gala', 'Granny Smith', 'Red Chief' and 'Fuji'); to four or five rest breaking product sprays in three moments, during 2005 and 2006. A factorial experiment with two factors, product per moment, was applied. The products applied were: hydrogen cyanamide (1.25%), paraffin mineral oil (3.0%), paraffin mineral refined oil (2.0%) in all cases; and hydrogen cyanamide (0.75%) + paraffin mineral oil (2.0%) combination on 'Red Chief' (2005 and 2006), 'R. Gala' and 'Fuji' (2006). The first application was performed considering 250 CU (UTAH model) registered from sensors located in the trees (first 15 days of August). Following applications were performed on the first and third week of September. Budbreak percentage on field conditions was evaluated weekly. Bud type (reproductive or vegetative), position (lateral or apical) and branch age were registered. In addition, shoot length was quantified. At harvest, flesh firmness, soluble solid and starch contents were measured. For most cases, 'moment × product' interaction and the main 'product' effect on bud break were not significant, while the main 'moment' effect had high significance. Treatments applied at the second and third moment showed a significant rise in budbreak percentage, regarding the control; while treatments applied at the first moment, had precocious budbreak. Hydrogen cyanamide applied alone or combined in 'Royal Gala', also accelerated fruit ripening.

Effect of hydroxyl radical on the scission of cellular wall polysaccharides in vitro of banana fruit at various ripening stages

Fruit ripening is generally attributed to disassembly of cellular wall, particularly due to solubilisation and depolymerisation of pectin and hemicellulose. Experiments were conducted to test effects of hydroxyl radicals (·OH) on the scission of cellular wall polysaccharides from pulp tissues of banana fruit at different ripening stage. Cellular wall materials were isolated from pulp tissues of banana fruit at different ripening stages. Two pectic fractions, water soluble pectin (WSP) and acid soluble pectin (ASP), and two hemicellulosic fractions, 1 M KOH soluble hemicellulose (HC1) and 4 M KOH soluble hemicellulos (HC2), were obtained from the cellular wall materials from pulp tissues, respectively. Effects of ·OH induced by the Fenton reaction on the scission of pectin and hemicellulose in vitro were investigated. As fruit ripening progressed, the sugar components of the WSP, HC1 and HC2 attacked by ·OH showed obvious molecular-mass downshifts. Thus, ·OH caused the disassembly of polysaccharides (WSP, ASP, HC1 and HC2) from cellular walls of pulp tissues of banana fruit, demonstrated by the reduced molecular mass distribution. Moreover, ·OH production in pulp tissues increased significantly as banana fruit ripened, which further help account for the role of ·OH in accelerated fruit ripening.

Effect of tomato deleafing on mirids, the natural predators of whiteflies

Sustainability in Mediterranean greenhouse agrosystems involves environmentally-friendly techniques based on biological and non-chemical methods. Deleafing is a common agricultural practice used to accelerate fruit ripening and facilitate farming methods. However, deleafing may have an impact on mirids, a natural predator used to control whiteflies, which are considered among the most noxious insect pests of field and greenhouse crops worldwide. Here we studied the impact of leaf removal on populations of mirids. Two deleafing practices were tested: (a) regular deleafing, with the first removal of 2 leaves per plant 10 weeks after sowing; and (b) delayed deleafing, in which the first removal was delayed by 14 days. Our results show that regular deleafing had a strong negative impact on mirid populations. Indeed, the first deleafing of the regular method eliminated 74% of young nymphs. Such a loss was not observed with the delayed method because nymphs were older and already distributed on leaves which were never thinned. As a consequence of this initial difference, mirid populations were 60% higher in the delayed than in the regular deleafing treatments at the end of the crop. The biological control of whiteflies was less efficient in the regular deleafing crop for which densities were, on average, 30% higher than in the delayed deleafing crop. Such inefficiency could call into question the sustainability in protected tomato crops of environmentally-friendly techniques focused on reducing the pesticides used.

Roles of Intra-fruit Oxygen and Carbon Dioxide in Controlling Pepper (Capsicum annuum L.) Seed Development and Storage Reserve Deposition

Seeds developing within a locular space inside hollow fruit experience chronic exposure to a unique gaseous environment. Using two pepper cultivars, `Triton' (sweet) and `PI 140367' (hot), we investigated how the development of seeds is affected by the gases surrounding them. The atmospheric composition of the seed environment was characterized during development by analysis of samples withdrawn from the fruit locule with a gas-tight syringe. As seed weight plateaued during development, the seed environment reached its lowest O2 concentration (19%) and highest CO2 concentration (3%). We experimentally manipulated the seed environment by passing different humidified gas mixtures through the fruit locule at a rate of 60 to 90 mL·min-1. A synthetic atmosphere containing 3% CO2, 21% O2, and 76% N2 was used to represent a standard seed environment. Seeds developing inside locules supplied with this mixture had enhanced average seed weight, characterized by lower variation than in the no-flow controls due to fewer low-weight seeds. The importance of O2 in the seed microenvironment was demonstrated by reduction in seed weight when the synthetic atmosphere contained only 15% O2 and by complete arrest of embryo development when O2 was omitted from the seed atmosphere. Removal of CO2 from the synthetic atmosphere had no effect on seed weight, however, the CO2-free treatment accelerated fruit ripening by 4 days in the hot pepper. In the sweet peppers, fruit wall starch and sucrose were reduced by the CO2-free treatment. The results demonstrate that accretionary seed growth is being limited in pepper by O2 availability and suggest that variation in seed quality is attributable to localized limitations in O2 supply.

Effect of fruit maturity on the response of 'Kensington' mango fruit to heat treatment

The effects of conditioning and hot water treatments on immature and mature ‘Kensington’ mangoes were examined. A hot water treatment of 47°C fruit core temperature held for 15 min increased weight loss (50%), fruit softness (15%), disrupted starch hydrolysis and interacted with maturity to reduce the skin yellowness (40–51%) of early harvested fruit. Immature fruit were more susceptible to hot water treatment-induced skin scalding, starch layer and starch spot injuries and disease. Conditioning fruit at 40°C for up to 16 h before hot water treatment accelerated fruit ripening, as reflected in higher total soluble solids and lower titratable acidity levels. As fruit maturity increased, the tolerance to hot water treatment-induced skin scalding and the retention of starch layers and starch spots increased and susceptibility to lenticel spotting decreased. A conditioning treatment of either 22° or 40°C before hot water treatment could prevent the appearance of cavities at all maturity levels. The 40°C conditioning temperature was found to be more effective in increasing fruit heat tolerance than the 22°C treatment; the longer the time of conditioning at 40°C, the more effective the treatment (16 v. 4 h). For maximum fruit quality, particularly for export markets, it is recommended that mature fruit are selected and conditioned before hot water treatment to reduce the risk of heat damage.

The tomato ethylene receptors NR and LeETR4 are negative regulators of ethylene response and exhibit functional compensation within a multigene family.

The plant hormone ethylene is involved in many developmental processes, including fruit ripening, abscission, senescence, and leaf epinasty. Tomato contains a family of ethylene receptors, designated LeETR1, LeETR2, NR, LeETR4, and LeETR5, with homology to the Arabidopsis ETR1 ethylene receptor. Transgenic plants with reduced LeETR4 gene expression display multiple symptoms of extreme ethylene sensitivity, including severe epinasty, enhanced flower senescence, and accelerated fruit ripening. Therefore, LeETR4 is a negative regulator of ethylene responses. Reduced expression of this single gene affects multiple developmental processes in tomato, whereas in Arabidopsis multiple ethylene receptors must be inactivated to increase ethylene response. Transgenic lines with reduced NR mRNA levels exhibit normal ethylene sensitivity but elevated levels of LeETR4 mRNA, indicating a functional compensation of LeETR4 for reduced NR expression. Overexpression of NR in lines with lowered LeETR4 gene expression eliminates the ethylene-sensitive phenotype, indicating that despite marked differences in structure these ethylene receptors are functionally redundant.

The post-harvest ripening of water stressed banana fruits

Maintaining banana fruit in a low humidity environment accelerated fruit ripening. This was reflected in an earlier increase in respiration and ethylene production and more advanced peel colour and...