Effect of 1-methylcyclopropene (1-MCP) on reducing postharvest decay in tomatoes (Solanum lycopersicum L.)

1-Methylcyclopropene (1-MCP as SmartFresh™ technology), an ethylene antagonist, was evaluated for affecting postharvest decay caused by Alternaria alternata, Botrytis cinerea, and Fusarium spp. on ‘Quality 23’ and ‘Seminis 35’ tomatoes at green or pink stages. Fruit with natural or artificial infection were subjected to 1-MCP at 0.0 μL L⁻¹, 0.6 μL L⁻¹ for 12 h, and 1.0 μL L⁻¹ for 6 h. After 31-42 d storage, disease incidence and severity of individual diseases in 1-MCP treated fruit was significantly reduced compared with that of the untreated controls, except in one inoculated test for ‘Quality 23’ where severity of Alternaria rot in 1.0 μL L⁻¹ treated fruit were significantly higher than that of the untreated control. Fruit treated with 1-MCP at 1.0 L⁻¹ for 6 h also had significantly higher incidence of Alternaria rot in the inoculated ‘Quality 23’ and in the non-inoculated ‘Seminis 35’ compared with the fruit treated with 1-MCP at 0.6 μL L⁻¹ for 12 h. The results of this study indicate that 1-MCP can reduce postharvest decay within a certain storage period.     

采后UV-C处理对树莓贮藏保鲜效果的影响

以"September"树莓果实为材料,采用0.43、2.15、4.3和6.45 kJ/m2的UV-C进行辐照处理,并在4℃下贮藏,通过测定贮藏期间果实腐烂指数、失重率、可溶性固形物含量、总酚含量和抗氧化能力,研究UV-C处理对树莓果实保鲜效果的影响。结果表明,UV-C处理能够显著抑制果实腐烂指数、失重率的上升,减缓果实可溶性固形物含量、总酚含量的下降,增强果实的抗氧化能力,维持果实较好的品质。在4个UV-C处理剂量中,4.3 kJ/m2UV-C处理组果实的腐烂指数、失重率最低,可溶性固形物含量和总酚含量最高,抗氧化能力最强。适宜剂量的UV-C处理(4.3 kJ/m2)能维持树莓果实采后品质,增强抗性,延缓衰老。     

Chemical and flavour changes in jackfruit (Artocarpus heterophyllus Lam.) cultivar J3 during ripening

Chemical composition (titratable acidity, moisture content, crude fibre, colour, pH, soluble solids, sugars, organic acids) and flavour changes during ripening of jackfruit (Artocarpus heterophyllus L.) cultivar J3 were evaluated. Significant (p < 0.05) changes in titratable acidity and colour was obtained, but no significant changes were found in moisture and crude fiber contents during ripening. Total soluble solids and total sugars increased significantly (p < 0.05) throughout the ripening process. Total soluble solids at the top portion of the fruit were significantly (p < 0.05) higher than middle and bottom portions of the same fruit. A high content of malic acid was found in unripe fruit (day 1). In contrast, ripened fruit (days 5 and 6) contained a high amount of citric acid. Overall, the total amount of organic acids was found to decrease from the early to later stage of ripening. A total of 23 volatile compounds were tentatively identified by GC and GC–MS. The number of peaks was observed to increase throughout the ripening process. In this study, data obtained suggest that the ripening process of jackfruit was at its optimum at day 5 after harvest.     

ABA and UV-C effects on quality,antioxidant capacity and anthocyanin contents of strawberry fruit (Fragaria ananassa Duch.)

Effects of 1 mM abscisic acid (ABA) and 4.1 kJ/m² UV-C radiation on quality, antioxidant capacity, anthocyanin contents, and anthocyanin biosynthetic enzyme activities of large green strawberry fruit stored at 20 °C were evaluated. Results showed that ABA promoted color formation, firmness decrease, soluble solids content and anthocyanin accumulation while UV-C inhibited these processes. Activities of phenylalanine ammonia-lyase, tyrosine ammonia-lyase and p-coumarate ligase were immediately upregulated by approximately 50% with UV-C radiation but were inhibited, including dihydroflavonol 4-reductase especially on day 3 or 4. UV-C radiation had little effect on activity of cinnamate 4-hydroxylase (C4H). ABA enhanced activities of anthocyanin biosynthetic enzymes except C4H. These data indicated that the stimulatory effect of ABA on strawberry anthocyanin accumulation was related to enhancement of biosynthetic enzyme activities, while the effects of UV-C were more transient. In addition, it appeared that C4H was not a rate-limiting enzyme in the strawberry anthocyanin biosynthesis pathway.     

UV-C照射采后番茄果皮细胞超微结构变化与抗病性研究

为揭示UV-C诱导采后果蔬抗病性机制的细胞结构基础,对比观察经2.4 kJ/m2UV-C照射后存于24℃下第4天和第8天的绿熟番茄佳粉15果皮细胞超微结构变化及人工接种链格孢菌的抗病性。结果表明,UV-C处理可使果皮细胞中叶绿体等细胞器衰老延缓,细胞壁和细胞质变得致密和粘稠,电子透明度减小,中胶层分解推迟;人工接种后第3天,处理果发病率较对照降低31.67百分点,第10天降低15.27百分点,病情指数降低16.90。2.4 kJ/m2UV-C照射可提高番茄果实抗病性,增强果皮细胞壁防御能力。     

UV-C辐射玉米种子对叶片保护酶活性及叶表皮形态的影响

以嫩单18玉米种子为实验材料,研究了不同时间的UV-C辐射对玉米叶片中保护酶活性和叶表皮特征的影响。结果显示:SOD、POD和CAT的活性变化趋势相似,即随辐射时间增加活性降低,辐射4h或6h时降到最低,之后有所上升,但是都低于对照组。UV-C辐射能缩小气孔的长、保卫细胞宽、表皮长细胞的长度和长细胞宽度;而叶长、叶宽和根条数明显增加(p<0.05),表明玉米在受到UV-C辐射时可通过增加叶面积和根条数来缓解辐射带来的伤害。     

Factors affecting the postharvest soluble solids and sugar content of tomato (Solanum lycopersicum L.) fruit

Although a large component of tomato fruit taste is sugars, the choice of tomato cultivar and the postharvest practices implemented by industry are designed to reduce crop loss and lengthen shelf-life and do not prioritize sweetness. However, because there is a growing recognition that taste and flavor are key components of tomato marketability, greater emphasis is now being placed on improving traits like sugar content. In this review the factors, both pre-, post and at harvest that influence sugar content in fruits sold at market are broadly outlined. Lines of investigation that may maximise the outcome of current practices and lead, long-term, to enhanced postharvest fruit sugar contents are suggested.     

Influence of aqueous 1-methylcyclopropene concentration, immersion duration, and solution longevity on the postharvest ripening of breaker-turning tomato (Solanum lycopersicum L.) fruit

The influence of aqueous 1-methylcyclopropene (1-MCP) concentration, immersion duration, and solution longevity on the ripening of early ripening-stage tomato (Solanum lycopersicum L.) has been investigated. Tomato fruit at the breaker-turning stage were fully immersed in aqueous 1-MCP at 50, 200, 400 and 600 μg L⁻¹ for 1 min, quickly dried, and then stored at 20 °C. Ethylene production, respiration, surface color development, and rate of accumulation of lycopene and polygalacturonase (PG) activity were suppressed and/or delayed in fruit exposed to aqueous 1-MCP. Suppression of ripening was concentration dependent, with maximum inhibition in response to 1 min immersion occurring at concentrations of 400 and 600 μg L⁻¹. Climacteric ethylene peaks were delayed approximately 6, 7, and 9 d and respiration was strongly suppressed in fruit treated with aqueous 1-MCP at 200, 400, and 600 μg L⁻¹, respectively, compared with control fruit. Fruit firmness, lycopene content, PG activity, and surface hue of fruit treated at the three higher levels remained strongly suppressed compared with control. Skin hue values and pericarp lycopene content in response to treatment at the subthreshold 50 μg L⁻¹ provided evidence for differential ripening suppression in external versus internal tissues. Maximum delay of softening and surface color development in response to 50 μg L⁻¹ aqueous 1-MCP occurred following immersion periods of between 6 and 12 min. Factors affecting fruit penetration by aqueous 1-MCP and mechanisms contributing to recovery from 1-MCP-induced ripening inhibition are discussed.     

Inheritance of resistance to two isolates of sterility mosaic pathogen in pigeonpea (Cajanus cajan (L.) Millsp.)

The resistant reaction to tomato spotted wilt virus (TSWV) was found to be determined by a single dominant gene in three Capsicum chinense Jacq. accessions (‘PI 152225’, ‘PI 159236’, ‘7204’). Allelism studies indicated that all C. chinense lines bear the same allele located at the Tsw locus. All the inoculated plants in the allelism tests displayed a resistant hypersensitive phenotype characterized by necrotic local lesions followed by abscission of the inoculated organ. However, a small proportion of them showed late systemic infection. Nine TSWV isolates obtained from these individual plants with systemic symptoms were backinoculated to the three resistant parents. All isolates were able to infect systemically all the resistant accessions without inducing local necrotic lesions. Serological analysis confirmed that these nine viral isolates belong to the TSWV species (serogroup I). Consequently, the susceptible plants in the allelism tests could not be interpreted as possessing a recombinant genotype because of the virulence change in the viral strain. Hobbs et al. (1994) already reported the existence of TSWV pathotypes overcoming the resistance of C. chinense resistant accessions. Practical consequences for pepper breeding associated with the emergence of these resistance-breaking isolates are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Wound-induced H2O2 and resistance to Botrytis cinerea decline with the ripening of apple fruit

Fruit ripening is a developmental process and is associated with increased susceptibility to mechanical injury, which favours Botrytis cinerea infection. Using ‘Gala’ apples harvested at different stages of ripening, we demonstrated that wounding can activate initial H₂O₂ accumulation and wound healing ability to defend against B. cinerea penetration. Delaying the harvest date attenuated those responses. Superoxide dismutase, peroxidase and catalase, which are all involved in H₂O₂ metabolism, were differentially activated by wound stress depending on the stage of fruit maturity. Mature fruit were less able to respond to wounding by increasing phenylalanine ammonia lyase and peroxidase activity, which are associated with reduced phenolics and lignin content in local wound sites. The reduced response in late-harvested fruit contributes to the fruit ripening-induced loss of wound healing ability and increases susceptibility to B. cinerea. In addition, the rapid increase of H₂O₂ content immediately after wounding in early-harvested fruit was followed by increased phenylalanine ammonia lyase and peroxidase activity. In late-harvested fruit, the reduced ability to increase phenylalanine ammonia lyase and peroxidase activity in response to wounding was consistent with ripening-reduced generation of H₂O₂ early after wounding, leading to reduced resistance to B. cinerea. Thus, H₂O₂ accumulation in response to wounding is modulated by fruit maturity and is required for efficient wound healing and resistance to B. cinerea.     

不同热处理方式对冬枣货架期品质的影响

以山东沾化冬枣为试材,研究了不同热处理方式对冬枣货架期好果率、腐烂指数、转红指数、软化率、热伤害程度、失水率的影响.结果表明,在热空气、热蒸汽和热水3种热处理方式中,热水处理的效果最好,其最佳条件为50～55℃处理6～8 min,能显著提高冬枣货架期品质,抑制腐烂指数、软化率、发酵率上升和好果率的下降,延长冬枣的货架寿命.但热水处理又促进了冬枣货架期转红指数的上升.     

Effect of high temperature stress on ethylene biosynthesis, respiration and ripening of ‘Hayward’ kiwifruit

Temperatures up to 35°C have been shown to increase ethylene production and ripening of propylene-treated kiwifruit (Stavroulakis, G., Sfakiotakis, E.M., 1993. We attempted to study the regulation by high stress temperature of the propylene induced ethylene biosynthesis and ripening in ‘Hayward’ kiwifruit. ‘Hayward’ kiwifruit were treated with 130 μl/l propylene at temperatures from 30 to 45°C up to 120 h. Ethylene biosynthesis pathway and fruit ripening were investigated. Propylene induced normal ripening of kiwifruit at 30–34°C. Fruit failed to ripe normally at 38°C and above 40°C ripening was inhibited. Propylene induced autocatalytic ethylene production after a lag period of 24 h at 30–34°C. Ethylene production was drastically reduced at 38°C and almost nil at 40°C. The 1-aminocyclopropane-1-carboxylic acid (ACC) content was similar at 30–38°C and was very low at 40°C. The 1-aminocyclopropane-1-carboxylate synthase (ACC synthase) and 1-aminocyclopropane-1-carboxylate oxidase (ACC oxidase) activities decreased with a temperature increase above 30°C, but ACC oxidase decreased at a faster rate than ACC synthase. Fruit not treated with propylene showed no ripening response or ethylene production. However, kiwifruit respiration rate increased with temperature up to 45°C, reaching the respiration peak in 10 h. At temperatures up to 38°C, propylene treatment enhanced the respiration rate. After 48 h at 45°C, fruit showed injury symptoms and a larger decrease in CO₂. The results suggest that high temperature stress inhibits ripening by inhibiting ethylene production and sensitivity while respiration proceeds until the breakdown of tissues.     

1-MCP extends the storage and shelf life of mangosteen (Garcinia mangostana L.) fruit

Mangosteen (Garcinia mangostana L.) fruit were harvested when the peel (pericarp) was light greenish yellow with scattered pinkish spots. Fruit were exposed to 1 μL L⁻¹ 1-methylcyclopropene (1-MCP) for 6 h at 25 °C and were then stored at 25 °C (control) or 15 °C. The 1-MCP treatment only temporarily delayed softening of the fruit flesh, during storage. Storage life, defined as the time until the pericarp was dark purple, was much longer in fruit stored at 15 °C than in fruit stored at 25 °C. It was also longer in 1-MCP treated fruit (storage life at 15 °C: control 18 d, 1-MCP-treated fruit 27 d). The 1-MCP treatment also increased the length of shelf life, defined as the time until the pericarp turned blackish purple or showed calyx wilting, at 25 °C. 1-MCP treatment reduced ethylene production. It also reduced pericarp levels of 1-aminocyclopropane-1-carboxylic acid (ACC), and the pericarp activities of ACC synthase (ACS) and ACC oxidase (ACO). In the fruit flesh, in contrast, 1-MCP did not affect ACC levels and ACS activity, but the treatment reduced ACO activity. Taken together, both the storage life and the shelf life of the fruit were extended by the 1-MCP treatment. A decrease in ACO activity largely accounted for the effects of the 1-MCP on ethylene production in the pericarp.     

Inheritance of resistance to Didymella lycopersici Klebb. in tomato (Lycopersicon Mill.)

Summary The inheritance of the resistance to Didymella lycopersici was studied on F₃- and Bc₁-lines from interspecific crosses of L. esculentum with L. hirsutum and with L. hirsutum glabratum. The resistance is not monogenic and is inherited in dominant fashion. The high h² values based on line means offer possibilities to seleet efficiently for enhanced levels of resistance.     

Chilling-injury of harvested tomato (Solanum lycopersicum L.) cv. Micro-Tom fruit is reduced by temperature pre-treatments

Heat-shocks were used to reduce the development of chilling injury symptoms during ripening of tomato fruit (Solanum lycopersicum L. cv. Micro-Tom). Mature green tomatoes were immersed in 30-50 °C water for 3-9 min before being chilled at 2.5 °C for 0, 0.5, 1, 2, 3, or 14 days, and then held at 20 °C for an additional 7-14 days. The affect of both heat-shock and chilling treatments were independent of fruit weight. Measured at 20 °C after 14 days of chilling, fruit exposed to 40 °C for 7 min exhibited reduced chilling injury symptoms, as measured by their advanced ripening score and decreased rate of ion leakage into an isotonic 0.2 M mannitol solution. Reduced rates of leakage from the symplastic compartment probably contributed to the 2-fold decrease in the amount of ions in the apoplastic space, when compared to the control. A subsequent paper will report the results of metabolic profiling of Micro-Tom tomato fruit subjected to treatments that significantly decreased their development of chilling injury symptoms.     

Effects of UV-C treatment on inactivation of Escherichia coli O157:H7, microbial loads, and quality of button mushrooms

This study investigated the effects of ultraviolet-C (UV-C) light applied to both sides of mushrooms on microbial loads and product quality during storage for 21 d at 4 °C. Microflora populations, color, antioxidant activity, total phenolics, and ascorbic acid were measured at 1, 7, 14 and 21 d of storage. Additionally, the inactivation of Escherichia coli O157:H7 by UV-C was determined. Results showed that UV-C doses of 0.45-3.15 kJ m⁻² resulted in 0.67-1.13 log CFU g⁻¹ reduction of E. coli O157:H7 inoculated on mushroom cap surfaces. UV-C radiation also reduced total aerobic plate counts by 0.63-0.89 log CFU g⁻¹ on the surface of mushrooms. Although mushrooms treated with UV-C had more severe browning with increasing dosage after initial treatment, the control mushrooms also browned as indicted by lower L* and higher a* values after 21 d of storage at 4 °C. In addition, the UV-C treatments apparently inhibited lesion development on the mushroom surface. During the first 7 d, irradiated mushrooms had lower antioxidant activity, total phenolics, and ascorbic acid content compared to non-radiated samples. However, irradiated mushrooms reached similar amounts of these nutrients as the control after 14 d of storage at 4 °C. In summary, UV-C radiation could potentially be used for sanitizing fresh button mushrooms and extending shelf-life.     

Development of flavor-related metabolites in cherimoya (Annona cherimola Mill.) fruit and their relationship with ripening physiology

Flavor is one of the most important attributes of fresh fruit for the consumer, and is affected by several factors, including genotype, maturity stage, and environmental conditions. Flavor-related metabolites were characterized in two important cherimoya varieties, cv. Concha Lisa and cv. Bronceada, during fruit ripening. The most important sugars present were glucose, fructose and sucrose, and only fructose and glucose increased during ripening. The most important acids were tartaric, malic and citric acids, and all increased as ripening progressed. Overall aroma profile was mainly determined by esters and terpenes in both varieties. Ester compounds such as ethyl hexanoate, butyl butyrate and hexyl propanoate increased during ripening. The activity of alcohol acyl transferase also increased during fruit ripening concomitant with ester accumulation. Terpenes, such as α and β-pinene, showed a reduction during ripening, whereas others, such as myrcene and limonene, increased.     

Andean beans (Phaseolus vulgaris L.) with resistance to the angular leaf spot pathogen (Phaeoisariopsis griseola) in southern and eastern Africa

Common beans (Phaseolus vulgaris) are separated into two distinct groups: Andean and Middle American. We identified CAL 143 as the first Andean bean with resistance to angular leaf spot disease caused by Phaeoisariopsis griseola. Angular leaf spot is the most widespread and economically important bean disease in southern and eastern Africa, and it is especially severe on the extensively grown Andean beans. Cal 143 was resistant in Malawi, South Africa, Tanzania, and Zambia, but it was susceptible in Uganda. This was attributed to the presence of races of P. griseola in Uganda not present in the other countries. We identified two additional Andean bean lines, AND 277 and AND 279, with resistance to angular leaf spot in Malawi. We also characterized the virulence diversity of 15 isolates of P. griseola from southern and eastern Africa into nine different races. Five of six isolates from Malawi and two of seven from Uganda, obtained from large-seeded Andean beans, were characterized into four different races considered Andean. These were compatible only or mostly with large-seeded Andean cultivars. The other eight isolates from Uganda, Malawi, and the Democratic Republic of Congo, obtained from a small- or medium-seeded Middle American beans, were characterized into five different Middle American races. These were compatible with Middle American and Andean cultivars. CAL 143 was resistant or intermediate under greenhouse conditions to all but one of the same 15 isolates from southern and eastern Africa, but it was susceptible to an isolate from Uganda obtained from a medium-seeded Middle American bean. This revised version was published online in July 2006 with corrections to the Cover Date.