Pre- and postharvest treatment with alternatives to synthetic fungicides to control postharvest decay of sweet cherry

The effectiveness of alternatives to synthetic fungicides for the control of pathogens causing postharvest diseases of sweet cherry was tested in vitro and in vivo. When amended to potato dextrose-agar, oligosaccharides, benzothiadiazole, chitosan, calcium plus organic acids, and nettle macerate reduced the growth of Monilinia laxa, Botrytis cinerea and Rhizopus stolonifer. Treatment of sweet cherries three days before harvest or soon after harvest with oligosaccharides, benzothiadiazole, chitosan, calcium plus organic acids, nettle extract, fir extract, laminarin, or potassium bicarbonate reduced brown rot, gray mold, Rhizopus rot, Alternaria rot, blue mold and green rot of cherries kept 10 d at 20 ± 1 °C, or 14 d at 0.5 ± 1 °C and then exposed to 7 d of shelf-life at 20 ± 1 °C. Among these resistance inducers, when applied either preharvest or postharvest, chitosan was one of the most effective in reducing storage decay of sweet cherry, and its antimicrobial activity in vitro and in field trials was comparable to that of the fungicide fenhexamid. Benzothiadiazole was more effective when applied postharvest than with preharvest spraying. These resistance inducers could represent good options for organic growers and food companies, or they can complement the use of synthetic fungicides in an integrated disease management strategy.     

Effectiveness of postharvest treatment with chitosan and other resistance inducers in the control of storage decay of strawberry

This study compared the effectiveness of practical grade chitosan when used in solution with acetic, glutamic, formic and hydrochloric acids, and a water-soluble commercial chitosan formulation, in controlling postharvest diseases of strawberry. The commercial chitosan formulation and other resistance inducers based on benzothiadiazole, oligosaccharides, soybean lecithin, calcium and organic acids, and Abies sibirica and Urtica dioica extracts were also tested. The commercial chitosan formulation was as effective as the practical grade chitosan solutions in the control of gray mold and Rhizopus rot of strawberries immersed in these solutions and kept for 4 days at 20 ± 1 °C. Moreover, the treatment with commercial and experimental resistance inducers reduced gray mold, Rhizopus rot and blue mold of strawberries stored 7 days at 0 ± 1 °C and then exposed to 3 days shelf-life. The highest disease reduction was obtained with the commercial chitosan formulation, followed by benzothiadiazole, calcium and organic acids. The compounds that provided the best results in postharvest applications to control storage decay of strawberries, should be tested in further trials through preharvest treatments, applied at flowering and a few days before harvest.     

Applications of salt solutions before and after harvest affect the quality and incidence of postharvest gray mold of ‘Italia’ table grapes

The efficacy of some potassium and calcium based salts, namely potassium sulphate (PS), potassium sorbate (PSo), potassium carbonate (PC), potassium bicarbonate (PB), calcium sulphate (CS), calcium chelate (CCh), calcium chloride (CC) and calcium silicate (CSi) against gray mold of ‘Italia’ table grapes, was evaluated. In in vitro experiments, PSo, PC, PB, and CCh completely inhibited mycelial growth of Botrytis cinerea at 0.25%. Under artificial inoculation, salts at 1% (immersed or sprayed) showed a variable effect against the pathogen. For natural infection, salt solutions (1%, w/v) were applied according to three strategies: (a) spray (one week) before harvest, (b) immersion after harvest, and (c) combined treatments spray and immersion. The decay incidence of gray mold was evaluated after 30 days at 2 ± 1 °C and 90–95% RH, followed by 7 days of shelf-life at 22 ± 2 °C. All tested salts significantly reduced the decay incidence of gray mold as compared to a water control for the three strategies. The percentages of reduction ranged between 77–100, 91–98, and 61–100% for the preharvest treatment, in combined application, and in the postharvest treatment, respectively. PB and PSo were the most effective salts, completely inhibiting development of gray mold when applied before harvest and as a postharvest treatment. The influence of salts on physical and chemical properties of berry quality including total soluble solids, titratable acidity, pH, color index, weight losses and microbiological profiles was also investigated. New strategies are needed with the critical goal of controlling gray mold of grapes with no fungicide residues. Salts applied just before harvest may be an effective way to minimize gray mold during storage.     

Combination of postharvest antifungal chemical treatments and controlled atmosphere storage to control gray mold and improve storability of ‘Wonderful’ pomegranates

Common food additives (sodium bicarbonate (SB), sodium carbonate (SC), and potassium sorbate (PS)) were compared to the fungicide fludioxonil for the control of gray mold on California-grown ‘Wonderful’ pomegranates artificially inoculated with Botrytis cinerea and stored at 7.2 °C in either air or controlled atmosphere (CA, 5 kPa O₂ + 15 kPa CO₂) conditions. Fludioxonil was superior to other treatments. PS was the most effective additive. Synergistic effects between antifungal treatments and CA storage were observed. After 15 weeks of storage at 7.2 °C, the combination of PS treatment (3 min dip in 3% solution at 21 °C) and CA storage was as effective as the combination of heated fludioxonil (30 s dip in 0.6 g L⁻¹ of active ingredient at 49 °C) and air storage. Mixtures of PS with SB or SC did not improve the efficacy of either treatment alone. In tests conducted in commercial facilities, decay development and external and internal fruit quality were assessed on naturally infected pomegranates stored in either air or CA after application of a selected postharvest antifungal combined treatment (CTrt) integrating PS, SB + chlorine, and fludioxonil. CTrt was effective in controlling natural gray mold after 6 weeks of storage at 8.9 °C, but lacked persistence and it was not effective after 14 weeks. CA storage greatly enhanced decay control ability of CTrt. Skin red color was better maintained in CA-stored than in air-stored fruit. Juice color and properties (SSC, TA, and pH) were not practically affected by either postharvest treatment or storage condition. The integration of PS treatments with CA storage could provide an alternative to synthetic fungicides for the management of pomegranate postharvest decay.     

Combination of hot water,Bacillus amyloliquefaciens HF-01 and sodium bicarbonate treatments to control postharvest decay of mandarin fruit

An antagonistic isolate Bacillus amyloliquefaciens HF-01, sodium bicarbonate (SBC) and hot water treatment (HW) were investigated individually and in combination against green and blue mold and sour rot caused by Penicillium digitatum, P. italicum and Geotrichum citri-aurantii respectively, in mandarin fruit. Populations of antagonists were stable in the presence of 1% or 2% SBC treatment, and spore germination of pathogens in potato dextrose broth was greatly controlled by the hot water treatment of 45 °C for 2 min. Individual application of sodium bicarbonate at low rates and hot water treatment, although reducing disease incidence after 8 weeks or 4 weeks of storage at 6 °C or 25 °C respectively, was not as effective as the fungicide treatment. The treatment comprising B. amyloliquefaciens combined with 2% SBC or/and HW (45 °C for 2 min) was as effective as the fungicide treatment and reduced decay to less than 80% compared to the control. B. amyloliquefaciens HF-01 alone or in combination with 2% SBC or/and HW significantly reduced postharvest decay without impairing fruit quality after storage at 25 °C for 4 weeks or at 6 °C for 8 weeks. These results suggest that the combination of B. amyloliquefaciens HF-01, SBC and HW could be a promising method for the control of postharvest decay on citrus while maintaining fruit quality after harvest.     

Combination of peracetic acid and hot water treatment to control postharvest brown rot on peaches and nectarines

Brown rot caused by Monilinia spp. is the most important postharvest disease of stone fruit. From preliminary studies, the combination of 0.25% hydrogen peroxide, 0.02% peracetic acid (PAA) and 0.075% acetic acid, corresponding to 300 mg L⁻¹ of PAA, was selected to control Monilinia fructicola. Brown rot control was similarly controlled when the same concentration of PAA was applied with a PAA-based commercial product. In order to reduce PAA concentration, combinations of different concentrations and temperatures were evaluated. A treatment of 200 mg L⁻¹ of PAA at 40 °C for 40 s was selected to control pre-existing and future infections, different inoculum concentrations of M. fructicola and to control brown rot on naturally infected fruit. Brown rot was completely controlled with the selected treatment when peaches and nectarines were inoculated 0 h before the treatment but it was not controlled when infection time was increased to 24, 48 and 72 h. Also, the treatment significantly controlled brown rot at all inoculum concentrations evaluated (10³, 10⁴, 10⁵ and 10⁶ conidia mL⁻¹) in both peaches and nectarines, but no protection against future infections was observed. In naturally infected fruit, brown rot incidence was slightly but significantly reduced to 61 and 36% in ‘Roig d’Albesa’ and ‘Placido’ peaches, respectively, but not in nectarines. Immersion for 40 s in 200 mg L⁻¹ of PAA at 40 °C provides an alternative treatment to control only recent infections of Monilinia spp. whatever their concentration without generally affecting fruit quality.     

Salt strategies to control Botrytis mold of ‘Benitaka’ table grapes and to maintain fruit quality during storage

Gray mold is the most common postharvest disease of table grapes in most regions of the world. The effect of eight salts, namely sodium silicate (SSi), sodium sulphate (SS), sodium carbonate (SC), sodium bicarbonate (SB), iron chelate (Fech), iron sulphate (FeS), ammonium bicarbonate (AB), and ammonium oxalate (AO) was determined in vitro on mycelial growth and spore suspension of Botrytis cinerea. In particular, SSi, SC, SB, FeS, and AB completely inhibited pathogen growth at 0.25% concentration. Six salt solutions at 1%, immersion or spray, were tested to verify their effect on grapes artificially inoculated with B. cinerea. All salts significantly reduced the percentage of gray mold as compared to control except for Fech after one week at 22 ± 1 °C. Three salt solutions were applied, in vivo, according to different strategies: (i) spraying before harvest, (ii) immersion after harvest, and (iii) the combination of pre- and postharvest treatments. Water was involved as a negative control while Rovral (a.i. iprodione) and SO₂ served for comparisons. After one month of cold storage at 2 ± 1 °C followed by one week of shelf-life at 22 ± 2 °C, the natural incidence of postharvest mold was mostly caused by B. cinerea. The efficacy of preharvest applications was noticeably high and statistically was not enhanced by further treatments after harvest. Salts applied only after harvest were not effective in suppressing Botrytis mold, with the exception of FeS. The influence of salts on physicochemical properties for berry quality was also monitored. The field application of salts can be considered as an appropriate regime to enhance their activity since no negative impact of their application on quality profile was observed. The incidence of gray mold can be significantly reduced using some salts which are safe for consumers and the environment.     

Effects of hot water treatment on the storage stability of satsuma mandarin as a postharvest decay control

Satsuma mandarins (Citrus unshiu Marc., cv. Gungchun) of an early harvesting cultivar were treated by hot water dipping at 52 °C for 2 min, 55 °C for 1 min, and 60 °C for 20 s, and then stored at 5 °C for 3 weeks and subsequently at 18 °C for 1 week (simulated shelf-life) to examine the possible use of hot water treatment (HWT) as an environmentally benign method to maintain mandarin quality characteristics during postharvest storage and sale. The initial respiration rate, just after heat treatment, was significantly higher in the treated fruit than in the untreated controls. During storage, however, the respiration rate was at a similar level in all treatments. HWT also had no adverse effects on quality attributes, including pH, titratable acidity, soluble solids contents, weight loss, firmness and peel color. The development of stem-end rots, mold decay, and black rots was manifestly lower in heat-treated fruit than in untreated controls. Sensory evaluation showed that HWT at 60 °C for 20 s markedly improved fruit appearance, making them cleaner and glossier. The results confirmed that hot water dipping could be applied to satsuma mandarin as an effective pretreatment to maintain postharvest quality during storage and marketing.     

Pre-storage hypobaric treatments delay fungal decay of strawberries

Fungal decay is a major cause of postharvest losses in strawberries. The traditional approach for controlling fungal decay is the use of fungicides. However, the use of fungicides has been questioned as a sustainable and safe method, and is also prohibited in many countries. One potential physical method for reducing fungal decay is application of a short-term hypobaric treatment prior to storage. In this study efficacy of postharvest hypobaric treatments to control natural rot development in strawberries was evaluated. Strawberries were treated with hypobaric pressures (25 kPa_a, 50 kPa_a and 75 kPa_a) for 4 h at 20 °C and subsequently stored at 20 °C or 5 °C. A 50 kPa_a treatment consistently delayed rot development in samples stored at either temperature confirming that the technique has potential as a non-chemical treatment. Moreover 50 kPa_a treatments did not affect weight loss and firmness at either 20 °C or 5 °C. An initial increase in respiration rate was observed in 50 kPa_a treated samples potentially indicating mild stress due to hypobaric treatment. An in vitro fungal study found that 50 kPa_a treatment for 4 h did not affect the rate of radial growth of colonies of Botrytis cinerea and Rhizopus stolonifer, providing further evidence that the potential mechanism of hypobaric treatment is induction of the defence system within the fruit rather than a direct effect on fungal viability. Further molecular and biochemical research is required to evaluate the possible stimulation of resistance in fruit through short-term hypobaric treatments.     

Effectiveness of a short hyperbaric treatment to control postharvest decay of sweet cherries and table grapes

The effectiveness of short hyperbaric treatments to control postharvest decay of sweet cherries (Prunus avium L., cv Ferrovia) and table grapes (Vitis vinifera L., cv Italia) was investigated. Sweet cherries and table grape berries were exposed to the pressure of 1140 mmHg (1.5 atm) for 4 and 24 h, respectively, in 64 L gas-proof tanks. Fruit kept at ambient pressure (near 760 mmHg, 1.0 atm) served as a control. Postharvest rots of sweet cherries arose from naturally occurring infections, whereas table grape berries were artificially wounded, exposed to the hyperbaric treatment, then the wounds inoculated with 20 μL of a Botrytis cinerea conidial suspension (5 × 10⁴ spores mL⁻¹). Sweet cherries were stored at 0 ± 1 °C for 14 d, followed by 7 d at 20 ± 1 °C. Table grapes berries were kept at 20 ± 1 °C for 3 d. On sweet cherries, hyperbaric treatment reduced the incidence of brown rot, grey mould, and blue mould, with respect to the control. Similarly, on treated table grapes a significant reduction of lesion diameter and percentage of B. cinerea infected berries was observed. Induced resistance was likely to be responsible for the observed decay reduction. To our knowledge, this is the first report on the effectiveness of short hyperbaric treatments in controlling postharvest decay of sweet cherries and table grapes.     

Prestorage application of high carbon dioxide combined with controlled atmosphere storage as a dual approach to control Botrytis cinerea in organic ‘Flame Seedless’ and ‘Crimson Seedless’ table grapes

Pre-storage application of 40% CO₂ at 0 °C for 24 or 48 h and controlled atmosphere (12% O₂ + 12% CO₂) storage at 0 °C for up to eight weeks on decay control and quality of organic ‘Flame Seedless’ and ‘Crimson Seedless’ table grapes were studied as a postharvest disease control alternative. To simulate different potential field conditions, these organic treatments were applied to organic-grown grapes that were naturally infected (without inoculation), surface inoculated (berries inoculated by spraying with a conidia suspension), and nesting inoculated (clusters inoculated by placing in the middle an artificially infected berry) with the pathogen Botrytis cinerea, the cause of grape gray mold. Under these three conditions, a 40% CO₂ for 48 h pre-storage treatment followed by controlled atmosphere reduced the gray mold incidence from 22% to 0.6% and from 100% to 7.4% after four and seven weeks, respectively. High CO₂ pre-storage alone limited botrytis incidence in both naturally and artificially infected grapes, but was more effective when combined with CA. These treatments did not affect visual or sensory fruit quality. Exposure to high CO₂ for 24 or 48 h effectively inhibited mycelial growth of B. cinerea in PDA plates incubated at 22 °C for up to 72 h. Conidia germination in PDA plates was reduced ∼60% after 12 h incubation. In vitro studies demonstrated a fungistatic effect, but further studies on the mechanism of action could improve treatment performance. This novel high CO₂ initial fumigation followed by controlled atmosphere during storage or transportation could be a commercially feasible alternative for postharvest handling of organic and conventional table grapes. Our results encourage validating this combined physical treatment in other cultivars and under commercial conditions.     

Effects of postharvest treatments on gene expression in Prunus persica fruit: Normal and altered ripening

Peach (Prunus persica) fruit have a short shelf-life, and the most common method employed to delay ripening and increase their postharvest life is cold storage. However, after extended storage at low temperature some cultivars have alterated ripening processes, resulting in a lack of juice and a woolly texture. To improve our understanding of the molecular mechanisms involved in the responses of peach fruit to cold storage we determined gene expression changes of fruit (cv. O’Henry) under different postharvest conditions: ripening (5 days at 21 °C), cold storage (21 days at 4 °C) and induction of woolliness (21 days at 4 °C followed by 5 days at 21 °C).Cluster analyses of genes differentially expressed between treatments revealed unique patterns associated with biological processes that operate during postharvest treatments. Genes up-regulated during postharvest ripening and woolliness include components of ethylene, and aroma biosynthesis as well as oxidative stress response. During cold storage treatment and woolliness, several genes linked to the oxidative stress response increased in abundance, suggesting changes in redox status. Quantitative RT-PCR analysis showed a sequential increase levels of mRNAs encoding key components of cellular stress response. Moreover, after 21 days of cold storage, expression of genes encoding oxidoreductase, catalase, superoxide dismutase and gluthatione reductase was still significantly higher than before cold treatment, suggesting that fruit cells were able to respond to the increased production of ROS that was induced by extended cold storage. In the woolly fruit, up-regulation of stress response genes was accompanied by down-regulation of key components of metabolic pathways that are active during peach ripening. The altered expression pattern of these genes might account for the abnormal ripening of woolly fruit.     

Effect of hot water treatment on leaf extension growth,fresh weight loss and color of stored minimally processed leeks

Freshly harvested leeks (Allium porrum L.) were heated by immersion in water at 50, 52.5, 55 or 57.5 °C for 0–60, 0–35, 0–20 and 0–15 min, respectively. After hot water treatment, leeks were cooled in water at ambient temperature for 10 min and then cut at 22 cm from the compressed stem of the root base, weighed, had color measured and stored at 4 °C for 9 days. Untreated stalks (without immersion in a hot water bath) were used as controls. Hot water treatments at 50 °C for 40–60 min, 52.5 °C for 25–35 min, 55 °C for 17.5–20 min and 57.5 °C for 10–15 min efficiently controlled postharvest leaf extension growth in stalks stored for 9 days. However, treatments that controlled leaf extension growth showed fresh weight loss significantly higher than the control. There was only a slight effect of heat treatment on color attributes of stored minimally processed leek.     

Hot water dipping treatments on Tarocco orange fruit and their effects on peel essential oil

The most common and serious diseases which affect citrus fruit after harvest in Italy are induced by Penicillium digitatum Sacc. and Penicillium italicum Weh., responsible respectively for green and blue mold rots. This paper deals with the effectiveness of hot water dipping (HWD) treatments as alternative means to control postharvest decay on Tarocco orange fruit [Citrus sinensis (L.) Osbeck], and their effect on fruit quality with special regard to peel essential oils. Selected treatments were HWD at 52 °C for 180 s and at 56 °C for 20 s. These treatments were compared with an effective fungicide standard treatment (Imazalil) and an untreated control. The results showed that HWD at 56 °C for 20 s was more effective in inhibiting P. digitatum spore germination than HWD at 52 °C for longer exposure time. In addition, HWD treatment at 56 °C significantly increased the level of alcohols, esters and aliphatic (fatty) aldehydes. Therefore, the lowest values of decay incidence recorded in HWD fruit treated at 56 °C may be due to the increase in oxygenated monoterpenes, esters and aldehydes. Finally, HWD treatments did not cause surface damage or color change and did not influence internal quality parameters.     

Effect of nitric oxide (NO) and associated control treatments on the metabolism of fresh-cut apple slices in relation to development of surface browning

Surface browning is an important cause of deterioration of fresh-cut apples during postharvest handling. ‘Granny Smith’ apple slices treated with NO gas (10 μL/L) and the NO donor compound 2,2′-(hydroxynitrosohydrazino)-bisethanamine (diethylenetriamine nitric oxide (DETANO) (10 mg/L) dissolved in phosphate buffer (pH 6.5) showed delayed development of surface browning during storage at 5 °C and also resulted in a lower level of total phenols, inhibition of PPO activity, reduced ion leakage and reduced rate of respiration but had no significant effect on ethylene production or lipid peroxide level as measured by malondialdehyde (MDA) and hydrogen peroxide levels. The two control treatments of phosphate buffer (pH 6.5) and water dips also had significant effects compared to untreated slices. The relative effectiveness of treatments in extending postharvest life and reducing total phenols, PPO activity, ion leakage and respiration was DETANO > NO gas > phosphate buffer > water > untreated. Apple slices dipped in chlorogenic acid dissolved in water showed surface browning soon after application but dipping in DETANO solution negated the effect of chlorogenic acid whether applied before or after dipping in chlorogenic acid solution while the buffer and NO gas were also effective. It is suggested that an increase in phenols occurs on the apple surface soon after cutting, possibly as a defensive mechanism of the apple to limit damage to surface cells. The effectiveness of the applied treatments to inhibit development of surface browning may relate to their ability to minimize the level of phenols active on the cut surface possibly in conjunction with a reduced PPO activity.     

Can hot water treatments enhance or maintain postharvest quality of spinach leaves?

It has been reported that a short duration hot water treatment, applied as a heat shock, improves subsequent postharvest quality in bagged spinach and rocket leaves. This study has established that the maximum hot water temperature and duration before spinach leaves showed damage, was 45 °C for 60 s. Subsequent detailed studies compared postharvest quality of leaves treated at 45 °C for 60 s immediately after harvest with untreated leaves after 5 and 10 days of storage at 4 °C. Heated leaves were significantly lighter and more yellow suggesting enhanced senescence, but leaf membrane integrity and associated gas composition of the storage atmosphere were not significantly different. Hot water treatment at 45 °C for 60 s applied immediately after harvest had a mixed effect on the biochemical constituents of the leaves; total carotenoid concentration was maintained compared to untreated leaves but the contents of ascorbic acid, dehydroascorbic acid, chlorophyll a and b were not affected. These observations suggest that in contrast to other reports, hot water treatments have limited commercial potential for postharvest quality improvement of spinach leaves.     

A multispectral vision system to evaluate enzymatic browning in fresh-cut apple slices

Increased regulation of chemical fumigants has forced the almond industry to seek alternatives for postharvest control of insect pests in raw almonds. This paper reports developments of non-chemical treatment for postharvest disinfestation of almonds using radio frequency (RF) energy. A pilot-scale 27 MHz RF unit was used to evaluate effects of a RF treatment protocol on quality attributes in treated in-shell and shelled almond samples. The RF treatment protocol used 0.75 kW RF power, a forced hot air at 63 °C, back and forth movements on the conveyor at 0.56 m/min, and single mixing, which all improved the final heating uniformity. RF treatments sharply reduced the heating time from 86 and 137 min for hot air heating to only 6.4 and 8.8 min for the center of 1.5 kg in-shell and 2.4 kg shelled almond samples to reach 63 °C, respectively. Almond quality was not affected by the RF treatments because peroxide values, fatty acid and kernel color of treated almonds were better than or similar to untreated controls after 20 d at 35 °C, simulating 2 years of storage at 4 °C. RF treatments did not significantly affect the kernel moisture content of both types of almonds but reduced the moisture content in the shell. RF treatments may hold great potential to replace chemical fumigation for disinfesting almonds.     

Immersion of fruit in water to improve radio frequency treatment to control brown rot in stone fruit

Brown rot caused by Monilinia spp. is the most important postharvest disease of stone fruit. Currently, no chemical fungicides are allowed in the European Union to be applied to stone fruit after harvest, which has increased the need to develop alternative methods. Radio frequency (RF) treatment at 27.12 MHz with fruit immersed in water was studied to control brown rot in peaches and nectarines artificially inoculated with M. fructicola. Additionally, RF treatment in air was also investigated to evaluate the benefit of water immersion to reduce the effect of fruit size on treatment efficacy. RF treatment with fruit immersed in water at 20 °C applied for 9 min significantly reduced brown rot incidence in both peaches and nectarines and no significant differences in RF efficacy were observed depending on fruit size. However, when RF treatment was applied in air for 18 min, brown rot reduction was significantly higher in large fruit than in small fruit. Finally, the decrease in exposure time of radio frequency treatment with fruit immersed in water with increasing water temperature was also studied. Reduction of treatment time to 6 and 4.5 min was achieved by increasing water temperature at 35 and 40 °C, respectively, to control brown rot without adverse external and internal damage in both ‘Baby Gold 9’ peaches and ‘Autumn Free’ nectarines.     

Evaluation of postharvest treatments with chemical resistance inducers to control green and blue molds on orange fruit

Preventive and curative activities of postharvest treatments with selected chemical resistance inducers to control postharvest green (GM) and blue (BM) molds on oranges (cvs. ‘Valencia’ or ‘Lanelate’) artificially inoculated with Penicillium digitatum and Penicillium italicum, respectively, were evaluated. In vivo primary screenings to select the most effective chemicals and concentrations were performed with benzothiadiazole (BTH), β-aminobutyric acid (BABA), 2,6-dichloroisonicotinic acid (INA), sodium silicate (SSi), salicylic acid (SA), acetylsalicylic acid (ASA) and harpin. INA at 0.03 mM, SA at 0.25 mM, BABA at 0.3 mM and BTH at 0.9 mM were selected and tested afterwards as dips at 20 °C for 60 or 150 s with oranges artificially inoculated before or after the treatment and incubated for 7 d at 20 °C. Although it was an effective treatment, SSi at 1000 mM was discarded because of potential phytotoxicity to the fruit rind. Preventive or curative postharvest dips at room temperature had no effect or only reduced the development of GM and BM very slightly. Therefore, these treatments cannot be recommended for inclusion in postharvest decay management programs for citrus packinghouses.     

Effects of X-ray irradiation and sodium carbonate treatments on postharvest Penicillium decay and quality attributes of clementine mandarins

The integration of sodium carbonate (SC; dips at 20 °C for 150 s in aqueous 3% SC solutions) treatments and X-ray irradiation (at doses of 510 and 875 Gy) was evaluated on artificially inoculated ‘Clemenules’ clementine mandarins for the control of postharvest green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively. Although significant, the reduction of both disease incidence (number of infected fruit) and severity (lesion diameter) on fruit either incubated at 20 °C for 7 days or cold-stored at 5 °C for 21 days was not sufficient for satisfactory disease control under hypothetical commercial conditions. Therefore, the combined treatments could not be a substitute for conventional chemical fungicides. However, pathogen sporulation was greatly inhibited on infected clementines, thus X-irradiation could be of value for management of Penicillium resistant strains and to reduce inoculum levels in citrus packinghouses. X-ray irradiation at 195, 395, 510, and 875 Gy did not influence either decay incidence or the area under the disease progress curve (AUDPC) of lesions of green and blue molds on mandarins inoculated with the pathogens 2, 3, or 6 days after irradiation and incubated for 7 days at 20 °C. Therefore, X-ray treatment did not induce disease resistance in the rind of irradiated fruit. Although X-irradiation at doses up to 875 Gy followed by either 14 days at 20 °C or 60 days at 5 °C caused very slight rind pitting, minor decreases in fruit firmness, and modest increases in juice acetaldehyde and ethanol contents, these changes had no practical impact on fruit quality. Rind color, titratable acidity, soluble solids concentration, maturity index and juice yield were not influenced by irradiation. ‘Clemenules’ can be considered as a clementine cultivar highly tolerant to X-irradiation.