Aconitase activity and expression during the development of lemon fruit

Citrus fruits are characterized by the accumulation of high levels of citric acid in the juice sac cells and a decline in acid level toward maturation. It has been suggested that changes in mitochondrial aconitase (EC 4.2.1.3) activity affect fruit acidity. Recently, a cytosolic aconitase (cyt-Aco) homologous to mammalian iron-regulated proteins was identified in plants, leading us to re-evaluate the role of aconitase in acid accumulation. Aconitase activity was studied in 2 contrasting citrus varieties, sweet lime ( Citrus limettioides Tan., low acid) and sour lemon ( Citrus limon var. Eureka, high acid). Two aconitase isozymes were detected. One declined early in sour lemon fruit development, but was constant throughout sweet lime fruit development. Its reduction in sour lemon was associated with a decrease in aconitase activity in the mitochondrial fraction. Another isozyme was detected in sour lemon toward maturation, and was associated with an increase in aconitase activity in the soluble fraction, suggesting a cytosolic localization. The cyt-Aco was cloned from lemon juice sac cells, but in contrast to the changes in isozyme activity, its expression was constant during fruit development. We present a model, which suggests that reduction of the mitochondrial aconitase activity plays a role in acid accumulation, while an increase in the cyt-Aco activity reduces acid level toward fruit maturation.     

Distribution ofGeotrichum candidum citrus race in citrus groves and non-citrus fields in Japan

The presence ofGeotrichum candidum citrus race, the citrus sour rot pathogen, was examined in soils of citrus groves and non-citrus fields of Japan. Soil samples were collected from 223 sites (118 sites in citrus groves, and 105 sites in fields cultivated with 33 species of non-citrus plants and in evergreen broad-leaved forest) in 11 main citrus-growing prefectures, and Hokkaido, a non-citrus-growing area. Of 236 soil samples from citrus groves, 95.76% containedG. candidum citrus race and 0.42% contained the non-citrus race; while of 210 samples from non-citrus fields, 62.85% and 4.76% contained the citrus race and the non-citrus race respectively. All of the citrus race isolates obtained either from citrus groves or non-citrus fields were pathogenic on lemon (Citrus limon) and satsuma mandarin (Citrus unshiu), but some of these isolates failed to infect orange (Citrus sinensis). The non-citrus races were pathogenic on ripe tomato fruit (Lycopersicon esculentum) and ripe muskmelon fruit (Cucumis melo var.reticulatus). Results indicated that citrus sour rot pathogen is widely distributed in citrus groves and non-citrus fields of diverse plant species in Japan.     

Contents of Sugars, Fruit Acids, Amino Acids and Phenolic Compounds of Apple Fruits i n Relation to their Susceptibility to Botryosphaeria ribis

Five apple cultivars showing different levels of susceptibility to Botryosphaeria ribis were used to study the relationship between susceptibility and contents of sugars, fruit acids, amino acids and phenolic compounds in the fruits at various stages of maturity. Immature fruits of all the cultivars tested were completely resistant until 10 July. The fungus grew better on the yellow-coloured cultivars than the red-coloured cultivars. The low amount of reducing sugars and also the high levels of fruit acids, amino acids and total phenols were found in immature apple fruits, irrespective of cultivar. No consistent differences between the cultivars were recognized with regard to the contents of soluble sugars, fruit acids and phenols in fruit flesh during the maturity of fruits. However, only the levels of total soluble amino acids in fruit flesh and of total phenols in fruit peel at late stage of maturity consistently varied between the cultivars. The dark red-coloured, resistant cultivars Miller spur and Starkrimson showed higher contents of amino acids and phenols in fruit tissues than did the yellow-coloured, susceptible cultivars.     

Cowpea Root Rot Severity and Metabolic Changes in Relation to Manganese Application

Severity of root rot (Rhizoctonia solani and Rhizoctonia bataticola) of cowpea (Vigna unguiculata L.) was reduced by 42.7 and 42.0%, respectively over control following the application of 10 μg/g Mn as manganese sulphate. Reduction in disease incidence was associated with increased levels of polyphenol oxidase (PPO), peroxidase (PO) and total phenols. PO activity was several times more as compared with PPO‐specific activity and increased markedly after infection either with R. solani or R. bataticola. Contrary to PPO and PO, the specific activity of catalase declined sharply. Infection also caused an increase in the content of reducing sugars, Cu, Zn and Mn but a decrease in o‐dihydric phenols, flavanols, total soluble sugars, non‐reducing sugars and Fe contents. It is suggested that Mn at the rate of 10 μg/g soil can be used to manage the root rot of cowpea.     

Effectiveness of preharvest application of submicron chitosan dispersions for controlling Alternaria rot in postharvest jujube fruit

The efficacy of submicron chitosan dispersions (SCD) on Alternaria alternata rot of the ‘Lingwu changzao’ jujube (Zizyphus jujuba Mill. cv. Lingwu changzao) fruit and possible mechanisms involved were investigated in this study. When jujube fruit at the preharvest stage were sprayed twice with SCD (10 mg/ml) water solution and then natural infections were allowed to develop, there was a significant reduction in disease incidence and lesion index compared to control fruit during storage period, and similar results were obtained from postharvest fruit inoculated with the Alternaria rot pathogen. Scanning electron microscopy of the pathogen revealed that hyphae and spores were damaged and deformed when growing on the surface of fruit pretreated with SCD or CHO. The slowed softening of jujube fruit resulted from the protopectin content increasing compared with the control. Furthermore, SCD sprays inhibited cell wall hydrolysing enzymes, pectinase activity was decreased, and the increase in cellulase activity was postponed (from 30 days to 45 days).It was concluded that preharvest application of SCD was a more effective alternative to conventional chitosan for preventing postharvest from Alternaria rot of ‘Lingwu changzao’ jujube fruit.     

脐橙果实贮藏过程中主要有机物质含量的变化

对朋那脐橙、纽荷尔脐橙和红肉脐橙果实采后室温贮藏过程中主要有机物质含量进行分析,结果表明,贮藏期间,果实可溶性固形物含量10d前略有上升,10d后的变化各品种间有差异;可滴定酸含量显著下降;固酸比显著上升;维生素C含量变化趋势因品种而异;可溶性蛋白质含量在贮藏过程中呈上升趋势。上述各指标在贮藏各时期不同品种间有明显差异。     

Control of green mold and sour rot of stored lemon by biofumigation with Muscodor albus

Control of postharvest lemon diseases by biofumigation with the volatile-producing fungus Muscodor albus was investigated. In vitro exposure to M. albus volatile compounds for 3 days killed Penicillium digitatum and Geotrichum citri-aurantii, causes of green mold and sour rot of lemons, respectively. Lemons were wound-inoculated with P. digitatum and placed in closed 11-L plastic boxes with rye grain cultures of M. albus at ambient temperature. There was no contact between the fungus and the fruit. Biofumigation for 24–72 h controlled green mold significantly, even when treatment began 24 h after inoculation. Effectiveness was related to the amount of M. albus present. In tests conducted inside a 11.7-m³ degreening room with 5 ppm ethylene at 20 °C, green mold incidence on lemons was reduced on average from 89.8 to 26.2% after exposure to M. albus for 48 h. Ethylene accelerates color development in harvested citrus fruit. M. albus had no effect on color development. Biofumigation in small boxes immediately after inoculation controlled sour rot, but was ineffective if applied 24 h later. G. citri-aurantii may be less sensitive to the volatile compounds than P. digitatum or escapes exposure within the fruit rind. Biofumigation with M. albus could control decay effectively in storage rooms or shipping packages.     

中华猕猴桃品种'Hort16A'的果实发育特征

To explore the fruit development characteristics of Actinidia chinensis'Hort16A' , fruit shape indexes during 2-154 d after anthesis, contents of soluble sugar and titratable acid in fruit during 30-154 d after anthesis, and contents of organic acid components in fruit during 44-147 d after anthesis were analyzed. The results show that fruit of 'Hort16A' grows rapidly during 30-44 and 58-72 d after anthesis. Content of soluble solid in fruit during 100-140 d after anthesis is slightly higher than that during 2-93 d after anthesis, and increases rapidly during 147-154 d after anthesis. Fruit firmness decreases rapidly during 147-154 d after anthesis. In general, during 30-154 d after anthesis, content of soluble sugar in fruit increases gradually, while content of titratable acid decreases firstly, then increases, and decreases again. In the fruit, tartaric acid is not detected, content of quininic acid is the highest, contents of malic acid and citric acid are higher, and contents of succinic acid and fumaric acid are very low. Total content of organic acids increases firstly and then decreases, and reaches the highest value at 140 d after anthesis. It is suggested that in order to improve fruit quality of'Hort16A' , its cultivation and management plans will be set up based on fruit development characteristics.     

八个贵州地方桃品种果实甜酸风味品质分析

为了评价贵州地方桃品种果实的甜酸风味品质,以主栽桃品种‘燕红’作对照,采用高效液相色谱法测定了贵州8个地方桃品种的果肉糖酸组分及含量。结果表明:(1)8个地方桃品种果肉中糖主要由蔗糖、葡萄糖、果糖和山梨醇组成,其中蔗糖的平均含量最高(55.62 mg/g),约占总糖的71.30%,但变异系数仅为17.92%;8个地方桃品种中,‘米桃’的葡萄糖与果糖含量差异较大,其果糖/葡萄糖的比值为1.21,而其它7个品种的葡萄糖与果糖含量相近。(2)8个地方桃品种果肉中有机酸主要由苹果酸、柠檬酸、奎宁酸和莽草酸组成,其中苹果酸含量最高,约占总酸的60.61%,但在‘白花桃’果实中有机酸含量以奎宁酸为主。(3)对8个地方桃品种果实的糖酸组分进行主成分分析发现,苹果酸含量和山梨醇含量的载荷系数分别为0.910和0.897,说明它们是影响果实甜酸风味的主导因素,且对改善果实的甜酸风味品质具有重要作用。8个贵州地方桃果实的甜酸风味分别为:‘黄腊桃’为甜,‘血桃’、‘青桃’、‘镇远桃’、‘红枫桃’为酸甜,‘白花桃’、‘西桃’和‘米桃’为酸。     

Hand position on the bunch and source–sink ratio influence the banana fruit susceptibility to crown rot disease

The postharvest development of crown rot of bananas depends notably on the fruit susceptibility to this disease at harvest. It has been shown that fruit susceptibility to crown rot is variable and it was suggested that this depends on environmental preharvest factors. However, little is known about the preharvest factors influencing this susceptibility. The aim of this work was to evaluate the extent to which fruit filling characteristics during growth and the fruit development stage influence the banana susceptibility to crown rot. This involved evaluating the influence of (a) the fruit position at different levels of the banana bunch (hands) and (b) changing the source–sink ratio (So–Si ratio), on the fruit susceptibility to crown rot. The fruit susceptibility was determined by measuring the internal necrotic surface (INS) after artificial inoculation of Colletotrichum musae. A linear correlation (r = −0.95) was found between the hand position on the bunch and the INS. The So–Si ratio was found to influence the pomological characteristics of the fruits and their susceptibility to crown rot. Fruits of bunches from which six hands were removed (two hands remaining on the bunch) proved to be significantly less susceptible to crown rot (INS = 138.3 mm ²) than those from bunches with eight hands (INS = 237.9 mm ²). The banana susceptibility to crown rot is thus likely to be influenced by the fruit development stage and filling characteristics. The present results highlight the importance of standardising hand sampling on a bunch when testing fruit susceptibility to crown rot. They also show that hand removal in the field has advantages in the context of integrated pest management, making it possible to reduce fruit susceptibility to crown rot while increasing fruit size.     

欧李果实发育期糖和酸组分及其含量的动态变化特性

以农大3号、农大4号、农大5号3个欧李品种为材料,测定果实发育过程中各组分糖、酸及总糖、总酸的含量,以明确欧李果实糖酸积累的动态变化特性.结果显示:(1)3个欧李品种果实成熟期糖含量、酸含量及糖酸比存在明显差异,其中农大3号品种的总糖含量最高,总酸含量最低,糖酸比值最高.(2)成熟期3品种各糖组分中均以果糖含量较高,葡萄糖和蔗糖含量较低,山梨醇含量微量;酸组分中均以苹果酸为主,柠檬酸少量.(3)3个品种果糖、蔗糖、葡萄糖、山梨醇含量在整个果实发育期均呈持续增加态势,并以果糖积累为主;农大3号果糖含量在8周后增幅明显高于另2个品种,且一直保持到果实成熟;3个品种蔗糖含量的变化趋势相近,在前期和中期增加缓慢,接近成熟的2～3周则迅速增加并占整个发育期积累量的70%以上.(4)3个品种酸含量的变化趋势较为相似,苹果酸和柠檬酸在果实发育的前期和中期含量均较低,在果实发育后期迅速增加,但接近果实成熟时又大幅下降.研究表明,果糖与苹果酸的含量及其动态变化是影响欧李果实糖酸比、决定果实风味的主要因素.     

Comparative responses of three fuel wood yielding plants to PEG-induced water stress at seedling stage

Three species of fast growing fuel wood yielding plants locally available (Acacia holosericea, Bauhinia variegata and Cassia siamea) were characterized in respect of their responses to water stress. Seedlings (25 days) of these species, exposed to two levels of water stress (−0.5 and −1.0 MPa) induced by PEG-6000 for 24 h, were analysed for relative water content (RWC) and the contents of chlorophyll, protein, soluble sugars and proline in leaves along with activities of catalase, peroxidase and superoxide dismutase (SOD). RWC was lower in stressed compared to the unstressed seedlings. However, stress-induced decline in RWC was lowest in B. variegata. Chlorophyll and protein contents declined with increasing levels of water stress, decline being least in B. variegata. Soluble sugar and proline contents increased under water stress particularly in B. variegata. The enzyme activity of catalase (EC-1.11.1.6), peroxidase (EC-1.11.1.7) and SOD (EC-1.15.1.1) decreased with increased levels of water stress. Such decline in the activity of these enzymes was least in B. variegata. Apparently, B. variegata is potentially the species most tolerant to water stress among these three fuel wood-yielding plants.     

Immobilization of bacteria in silica matrices using citric acid in the sol–gel process

The aim of this work was to use citric acid in the sol–gel process to generate an inorganic polymer that allows bacterial survival for long periods of time and to study the influence of different storage temperatures. We compared gram-negative Escherichia coli and gram-positive Staphylococcus aureus, immobilized and preserved at different storage temperatures in silica matrices prepared by the method proposed. Immobilized E. coli and S. aureus in silica matrices were stored in sealed tubes at 20, 4, −20, and −70°C for 4 months during which the number of viable cells was analyzed. Results show that the immobilization in silica matrices using citric acid, to neutralize the alkalinity of the silica precursors, makes the technique not only biocompatible but also easier to perform since polymerization does not occur immediately as it does when hydrochloric acid is utilized.     

Use of organic acids and salts to control postharvest diseases of lemon fruits in Egypt

Abstract

Postharvest diseases caused by Geotricum candidum (sour rot), Penicillium digitatum (green mould), and P. italicum (blue mould) are the most important negative factors affecting handling and marketing of citrus fruits in Egypt. The effect of organic acids (ascorbic, benzoic, citric and sorbic) as well as organic salts (potassium sorbate and sodium benzoate) were evaluated on the growth of causal agents and their disease incidence under in vitro and in vivo conditions. Complete inhibition was observed in the linear growth of all tested fungi when exposed to benzoic, citric and sorbic organic acids at concentrations of 4% and 2% of either sodium benzoate or potassium sorbate, respectively. Minimizing the tested concentration of organic acid down to 2%, the tested fungi fluctuated in their response such that only benzoic and sorbic acids could completely inhibit the growth of either P. digitatum or P. italicum only. Different organic acids and salts showed various levels of either protective or therapeutic effect for coated lemon fruits against mould infection whatever the time of their artificial inoculation under in vivo conditions. All treated fruits showed reduction in sour rot and green and blue mould diseases when compared with untreated fruits. Complete inhibition of mould incidence was obtained in coated lemon fruits with 4% of water or wax mixtures of sodium benzoate and potassium sorbate 24 hours before inoculation. Also, high reduction in mould incidence was observed in lemon fruits coated with the same concentration at 48 hours after inoculation under the same conditions. On the other hand, the tested organic acids showed a lesser effect on mould incidence. Moreover, they were more effective against mould incidence when dissolved in water than wax, that only 4% of water mixture of sorbic and benzoic acids showed 100% protection against mould incidence. Furthermore, the severity of infection records followed the same trend. The present findings demonstrate that potassium sorbate and sodium benzoate have potential as environmentally friendly products, nontoxic postharvest fungicides against sour rot, green and blue mould incidence of stored citrus fruits and could be suggested for commercial use in packing-houses in consideration to their wide consumption as safely food preservatives.     

Physical postharvest treatments in the control of stem‐end rot of mango

Botryosphaeria dothidea is the major pathogen of mango in Brazil, causing stem‐end rot, which causes significant losses during transportation and storage. The current strategy to control this particular disease using synthetic fungicides has been ineffective, leaving residues in the fruit. The objective of the research was to study the effect of physical treatments, with hot water rinse brushing (HWRB) and ultraviolet C irradiation (UV‐C), individually and in combination, to control stem‐end rot of mango. Physicochemical parameters, respiration and resistance induction of the fruit were also analysed. The in vitro trials demonstrated that B. dothidea is a thermoresistant fungus. The individual treatments with HWRB at 65°C for 15 s and 2.5 kJ/m² of UV‐C presented the best results, showing less symptoms of the disease during 18 days of storage. The combination of HWRB with UV‐C did not improve the control of the disease when compared to the treatments applied individually. The physicochemical parameters and the consumer acceptance evaluation showed that both physical treatments preserved the appearance of the fruit and delayed the ripening–senescence process. The induction of defence‐related enzymes revealed that induced resistance was an important mechanism involved in the control of stem‐end rot of mango.     

Occurrence and Latent Infection of Alternaria Rot of Pingguoli Pear (Pyrus bretschneideri Rehd. cv. Pingguoli) Fruits in Gansu, China

Alternaria rot of Pingguoli pear occurred after latent infection. Fruit surfaces were asymptomatic within 60 days storage under cold condition (0°C, RH 85–90%), but black‐grey hyphae could be seen in the lenticels or calyx tube of Pingguoli pear after 90 days of storage. The tissue collapsed and resulted in visible black spots as the hyphae spread over the fruit. Average incidence of Alternaria rot of fruits from an orchard in Gansu was 28.86% at 100 days of storage. The main fungus isolated from the Alternaria rot on stored Pingguoli pear was identified as Alternaria alternata (Fr. : Fr.) Keissl. This pathogen was able to initially infect the fruit via two pathways during the growing season, and then remain in a latent state. The fungus first colonized the styles at the full‐blossoming stage, and then grew into the carpel cavities progressively after 50 days from petal fall. The percentage latent infection of A. alternata was up to 45% in the carpel cavity until the harvest time. The fungus also attacked fruit surfaces and remained latent in the fruit peel during fruit development. The percentage of A. alternata latent infection at the calyx end, middle part and stem end of the fruit peel was 40%, 24% and 42.8%, respectively, at harvest time.     

采后处理对菠萝营养成分的影响

贮藏期间,杀菌剂处理可以推迟采后菠萝可溶性糖含量的减少,而对可滴定酸含量没有明显的影响。采后贮前加热４０℃２４ｈ处理的菠萝,其可溶性糖、可滴定酸等营养成分的变化与对照果实没有明显差异。与对照果实相比较,ＧＡ３处理果实除可溶性糖含量下降明显减少之外,可滴定酸和抗坏血酸含量显著增加。     

Silencing of SlPL,which encodes a pectate lyase in tomato,confers enhanced fruit firmness,prolonged shelf‐life and reduced susceptibility to grey mould

Pectate lyase genes have been documented as excellent candidates for improvement of fruit firmness. However, implementation of pectate lyase in regulating fruit postharvest deterioration has not been fully explored. In this report, 22 individual pectate lyase genes in tomato were identified, and one pectate lyase gene SlPL (Solyc03g111690) showed dominant expression during fruit maturation. RNA interference of SlPL resulted in enhanced fruit firmness and changes in pericarp cells. More importantly, the SlPL‐RNAi fruit demonstrated greater antirotting and pathogen‐resisting ability. Compared to wild‐type, SlPL‐RNAi fruit had higher levels of cellulose and hemicellulose, whereas the level of water‐soluble pectin was lower. Consistent with this, the activities of peroxidase, superoxide dismutase and catalase were higher in SlPL‐RNAi fruit, and the malondialdehyde concentration was lower. RNA‐Seq results showed large amounts of differentially expressed genes involved in hormone signalling, cell wall modification, oxidative stress and pathogen resistance. Collectively, these data demonstrate that pectate lyase plays an important role in both fruit softening and pathogen resistance. This may advance knowledge of postharvest fruit preservation in tomato and other fleshy fruit.     

Response of barley grains to the interactive e.ect of salinity and salicylic acid

Effect of grain soaking presowing in 1 mM salicylic acid (SA) and NaCl (0, 50, 100, 150 and 200 mM) on barley (Hordeum vulgare cv Gerbel) was studied. Increasing of NaCl level reduced the germination percentage, the growth parameters (fresh and dry weight), potassium, calcium, phosphorus and insoluble sugars content in both shoots and roots of 15-day old seedlings. Leaf relative water content (RWC) and the photosynthetic pigments (Chl a, b and carotenoids) contents also decreased with increasing NaCl concentration. On the other hand, Na, soluble sugars, soluble proteins, free amino acids including proline content and lipid peroxidation level and peroxidase activity were increased in the two plant organs with increasing of NaCl level. Electrolyte leakage from plant leaves was found to increase with salinity level. SA-pretreatment increased the RWC, fresh and dry weights, water, photosynthetic pigments, insolube saccharides, phosphorus content and peroxidase activity in the stressed seedlings. On the contrary, Na⁺, soluble proteins content, lipid peroxidation level, electrolyte leakage were markedly reduced under salt stress with SA than without. Under stress conditions, SA-pretreated plants exhibited less Ca²⁺ and more accumulation of K⁺, and soluble sugars in roots at the expense of these contents in the plant shoots. Exogenous application (Grain soaking presowing) of SA appeared to induce preadaptive response to salt stress leading to promoting protective reactions to the photosynthetic pigments and maintain the membranes integrity in barley plants, which reflected in improving the plant growth.