The impact of biological variation on postharvest behaviour of Belgian endive: The case of multiple stochastic variables

Data generated in postharvest research is often characterised by its large biological variation. This variation generally obscures the behaviour of interest, complicating both the statistical and conceptual interpretation of the data. This paper outlines a general model approach of how to account for the propagation of biological variation when analysing experimental postharvest data. Previous work on the case of a single stochastic variable was extended to the situation of two stochastic variables. The proposed technique was applied to experimental data on stem growth of Belgian endive. By explicitly using the information on biological variation, the number of model parameters to be estimated (only two) did not change while the fitness of the model to describe the experimental data was improved tremendously as compared to the traditional fitting of a model without stochastic variables.The model could describe the complex behaviour of a batch showing propagation of biological variation in stem length of Belgian endive as a function of time and temperature during postharvest storage. Differences between batches could not be related directly to either grower, harvest or culture type but probably depends on a complex interaction with preharvest factors.     

Time-related behaviour of phenotypic variation in Lotus corniculatus regenerants under field conditions

Summary Plants of Lotus corniculatus regenerated from single genotype-derived calli showed for several agronomic and morphological traits a variation similar to that present in the original population. Comparisons of the results obtained under field conditions during the 2nd and 3rd year from plant regeneration show: a) the maintenance of significant variance within callus-derived population for several traits examined; b) the total disappearance of minus variants indicating a time-related decrease of depressive in vitro effects.Research work supported by C.N.R., Italy-Special grant I.P.R.A.-Subproject 1. Paper n. 553.     

Phenological development in spring cereals: response to temperature and photoperiod under northern conditions

Phenological development of spring cereals was investigated using observations from several sites in Finland during the period 1970–1990. Different mathematical models which relate temperature to development rate were examined to predict the duration of phenological phases. A photoperiodic response of plant development before heading was also tested. For all phases the relationship between temperature and development was approximately linear. There was no significant response of plant development to photoperiod. This was explained by consistently long photoperiods in the observational material. Parameters for a linear model were derived from a regression analysis of mean development rate of each phase against mean temperature. However, a different response may occur under higher or lower temperatures or under shorter photoperiods than those experienced here.     

The efficacy of ultrasonic fumigation for disinfestation of storage facilities against postharvest pathogens

Inoculum of postharvest pathogens can accumulate inside storage rooms and contaminate new batches of fruit and vegetables, but this chain can be broken by disinfecting storage facilities between storage periods. Quaternary ammonium (QA) has been known for over 50 years as an efficient disinfectant against microorganisms, with wide applications in the food industry. The aim of this study was to determine the efficacy of didecyldimethylammonium chloride (Sporekill, designated here as QA^sk), against development of Botrytis cinerea after direct exposure or by ultrasonic fogging. Following direct exposure to a concentration of QA^sk below 5 mg L^?1, a population of 10⁴ conidia of B. cinerea was inactivated after 2 min; ultrasonic fogging with QA^sk at 500 mg L^?1 took 30 min to achieve consistent inactivation. Fumigation at 20 °C was considerably more effective than fumigation at 5 °C, and similar results were obtained for three other postharvest pathogens, Penicillium expansum, Colletotrichum gloeosporioides and Alternaria alternata. These results show that conidia of B. cinerea are highly sensitive to direct exposure to QA^sk, but that effective sanitation of a storage facility by ultrasonic fumigation requires a QA^sk concentration two orders of magnitude greater.     

Effects of gamma and UV-C irradiation on the postharvest control of papaya anthracnose

Anthracnose is the main postharvest disease in papaya fruit. Today, there is considerable interest on alternative methods of control to promote resistance against pathogens and supplement or replace the use of fungicides. The goal of this work was to evaluate the effects of gamma and UV-C irradiation on Colletotrichum gloeosporioides, the causal agent of anthracnose. Mycelial growth, sporulation, and conidial germination were evaluated in vitro after fungal exposition to different irradiation doses. In the in vivo assays, ‘Golden’ papaya fruit were inoculated through subcuticular injections of a conidial suspension or mycelium discs. Next, fruit were submitted to different irradiation doses (0, 0.12, 0.25, 0.5, 0.75, and 1 kGy), using Co⁶⁰ as source, or UV-C (0, 0.2, 0.4, 0.84, 1.3, and 2.4 kJ m⁻²). To check the possibility of resistance induction by irradiation, papayas were also inoculated 24, 48, or 72 h after the treatments. The fruit were stored at 25 °C/80% RH for 7 days and evaluated for incidence and rot severity. The results showed that the 0.75 and 1 kGy doses inhibited conidial germination and mycelial growth in vitro. All doses increased fungal sporulation. The 0.75 and 1 kGy doses reduced anthracnose incidence and severity, but did not reduce them when the fruit were inoculated after irradiation. All UV-C doses inhibited conidial germination and those higher than 0.84 kJ m⁻² inhibited mycelial growth. The 0.4, 0.84, and 1.3 kJ m⁻² UV-C doses reduced fungal sporulation in vitro. There was no effect of UV-C doses and time intervals between treatment and inoculation on anthracnose control and fungal sporulation in fruit lesions. Moreover, all UV-C doses caused scald on the fruit. Thus, gamma irradiation can contribute for the reduction of postharvest losses caused by anthracnose and reduce the use or doses of fungicides on disease control.     

Determination of the genetic variation in the effect of temperature and daylength on bolting of Brassica campestris L.

Summary Effects of temperature and daylength on the bolting of a number of B. campestris accessions were investigated both in the open and in the IVT phytotron. From the results it was concluded that low temperature and genotype are the predominant factors with respect to bolting. Daylength has rather limited influence. One cultivar bolted more than 12 weeks earlier at 10 and 14°C than at 18°C. On the other hand some cultivars did not require vernalization at all.At 14°C and short daylength, depending on genotype, the period of time between sowing and 50% bolting ranged from 8 to 30 weeks. At this temperature the stimulating effect of long day (24 h), depending again on the genotype, ranged from 0 to 4 weeks. The genotypes most resistant to bolting appeared to be the stubble turnips (B. campestris ssp. rapa).In terms of seed(ling) vernalization at 5°C the cold requirement ranged from 0 to more than 3 weeks, depending on the genotype. The required vernalization periods at 5°C can be used as a criterion in screening for resistance to bolting.     

Ultralow oxygen treatment for postharvest control of western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), on iceberg lettuce: I. Effects of temperature, time, and oxygen level on insect mortality and lettuce quality

Ultralow oxygen (ULO) treatments with different oxygen levels, treatment times, and temperatures were studied to determine effects on western flower thrips mortality and postharvest quality of iceberg lettuce. Thrips mortality increased with reduced oxygen level and increased treatment time and temperature. At 0.003% oxygen, over 99.6% mortality rates of thrips were achieved in three ULO treatments of 2, 3, and 4 d at 10, 5, and 1 °C, respectively. No treatments caused injury to lettuce surface leaves and there was no reduction in visual quality for treated lettuce. However, about 9–33% of lettuce heads sustained injury to heartleaves. The 2 d ULO treatment with 0.003% oxygen had the lowest injury rate to heartleaves and the injury increased with increased treatment duration. The amount of injured leaves was small (<2 g per head). There were also some variations among the lettuce cultivars in susceptibility to heartleaf injury by ULO treatments. Four out of eight cultivars tested tolerated the 2 d ULO treatment at 10 °C without any injury. Therefore, ULO treatment has potential to be developed as an alternative postharvest treatment for western flower thrips on iceberg lettuce.     

Ripeness stage at harvest influences postharvest life of cranberry fruit: physiological and anatomical explanations

We investigated the relationship between postharvest life of cranberry (Vaccinium macrocarpon Ait. cv. Stevens) fruit and ripeness stage at harvest. Wet harvested, mature fruit were sorted into four ripeness stages and rated for quality after 4 and 7 weeks of cold storage at 3 °C. In addition, CO₂ and ethylene production as well as anthocyanin content were measured. After 7 weeks of storage, the marketable fruit among dark-red, light-red, blush, and white were 82, 74, 63, and 44%, respectively. The ethylene production was nearly the same for all the ripeness stages. However, white, blush, and light-red fruit had significantly higher respiration rates than dark-red fruit. We also found that cuticle thickness was significantly higher for red fruit as compared to other ripeness stages. There were stomata present at the calyx end of the fruit, which became impregnated with wax in red fruit. Furthermore, a compact cell layer in the calyx opening accumulated anthocyanins in red fruit only. Our studies suggest that red fruit have longer postharvest life, possibly because (i) red fruit have lower respiration rates, (ii) thicker cuticle and wax accumulation (especially at the calyx end) on these fruit may retard the entry of microorganisms into the fruit during wet harvest and may mitigate mechanical injury by harvesting equipment.     

The effect of CO2 and 1-methylcyclopropene on the regulation of postharvest senescence of mint,Mentha longifolia L.

The regulatory effects of 5 kPa CO₂ and of the ethylene action inhibitor, 1-methylcyclopropene (1-MCP) at 0.5 μmol/l on the senescence of harvested mint, Mentha longifolia L. were assessed. Visual parameters of senescence including yellowing, browning, decay and leaf abscission were recorded and scored on scales linking the onset and progression of senescence to marketability. The effects of plant age on the rate of postharvest senescence and on the efficacy of the CO₂ and 1-MCP treatments were also investigated. All experiments were repeated with and without the presence of exogenous ethylene. Two experimental formats were used, with 6 days storage at room temperature representing local market conditions, and 6 days cold storage at 1.5 °C followed by 4 days at room temperature representing export market conditions. Sprigs from old plants were no longer of marketable quality after 6 days storage at room temperature. Exogenous ethylene accelerated the onset of senescence causing unacceptably high rates of leaf abscission. Raised levels of CO₂ in a controlled atmosphere system were found to be more effective in inhibiting senescence without the presence of exogenous ethylene than pre-treatment with 1-MCP, and no additive effect was found. However in the presence of exogenous ethylene, a combined treatment with 1-MCP together with raised CO₂ levels resulted in a significant additive effect in nullifying the ethylene-induced leaf abscission. Respiration rates as measured by CO₂ production, and ethylene production, were recorded throughout all experiments. While CO₂ levels were not affected by any experimental treatment, ethylene production was elevated in mint sprigs exposed to an initial dose of gaseous 1-MCP, and was further increased under a combined treatment of 1-MCP together with 5 kPa CO₂. However in the presence of exogenous ethylene, CO₂ strongly suppressed the 1-MCP induced ethylene production.     

The effect of temperature on pollen production in carnations

Summary For breeding carnations the supply of good pollen may be a problem. For this reason the effect of temperature on pollen production in carnations was studied.In phytotron experiments a temperature of 23°C proved to be the optimum.     

Molecular sleuthing: The invader Cynodon case

DNA amplification fingerprinting (DAF) was used to characterize different Cynodon dactylon (L.) Pers. cultivars and accessions and evaluate the genetic diversity among them. DAF analyses of some well known cultivars used in South Africa, i.e. Sahara, Tifway, Tifgreen, Harrismith, Royal Blue, Silverton Blue, Elliott, Tifdwarf, Gulf Green, Magennis, Klip, Florida, Oval, Bayview, Bermuda, X Kweek, Natal Kweek and Tifton 78, as well as 23 unknown Cynodon specimens were done. The unknown Cynodon specimens represent invaders of cultivated lands, with considerable morphological variation. The results were used to determine the genetic distances between the cultivars and unknown accessions, to identify the unknown specimens and to determine the phylogenetic affinities between the cultivars and accessions. The results obtained from the genetic distance matrices confirmed the results obtained from the phylogenetic analyses. In this study DAF analyses was successfully used to distinguish between different C. dactylon cultivars and accessions and could be used to trace the current weed back to its introduction area. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic variation and comparative analysis of thrips resistance in glandless and glanded cotton under field conditions

Glandless cotton can be grown for cottonseed free of toxic gossypol to be used as food and feed for non-ruminant animals. However, one of the most important limiting factors preventing its commercial production is its higher insect damage than conventional glanded cotton. Thrips is the one of the most important insect pests in the early growing season that may cause yield losses. In this study, 28, 29, 26, and 2 glandless cotton lines were compared with glanded control Acala 1517-08 and other glanded lines for resistance to the Western flower thrips, Frankliniella occidentalis (Pergande) in four replicated field tests each containing 32 genotypes. In the same field, 28 glanded commercial cultivars and 78 glanded breeding lines were compared with Acala 1517-08 and Acala 1517-99 in three other tests with 32 genotypes each. The experimental layouts allowed a comprehensive comparative analysis of thrips resistance within and between glandless and glanded cotton. Overall, glandless cotton had similar or lower thrips damages than glanded cotton, indicating that the glandless trait may serve as a genetic factor for suppressing thrips damage. As compared with Acala 1517-08 which represented one of the most thrips resistant genotypes among glanded cotton tested, glandless Acala GLS and many selections from glandless germplasm were more resistant, while some were similar to Acala 1517-08, indicating that genetic factors other than the glandless trait also affect thrips resistance in cotton. The estimates for broad-sense heritability for thrips resistance were moderate, indicating that thrips resistance is selectable. This is corroborated by the identification of many thrips resistant lines from a cross between Acala 1517-08 and Acala GLS. This study has laid a foundation for a more detailed study using most resistant lines with desirable agronomic traits in multiple environments.     

Evaluation of the use of sulfur dioxide to reduce postharvest losses on dark and green figs

Postharvest diseases limit the storage period and market life of fresh figs (Ficus carica L.). The objective of this work was to determine the effect of sulfur dioxide (SO₂) applied by fumigation and/or by dual release SO₂ generating pads on postharvest decay and quality retention of ‘Black Mission’ and ‘Brown Turkey’ (dark skin), and ‘Kadota’ and ‘Sierra’ (green skin) figs. A protocol for the computer-controlled application of gaseous SO₂ has been developed which allows the application of very low specific concentration × time products of SO₂ and simultaneous monitoring of the application progress. In vitro tests with important fungal, yeast and bacterial postharvest pathogens plated on Petri dishes and exposed to a SO₂ concentration × time product (C × t) of 100 (μL/L) h at different temperatures showed fewer survived at 20 °C than at 0 °C. Therefore, fumigations were carried out at 20 °C in the rest of the experiments. The evaluation of different SO₂ concentration × time products showed that a product of 25 (μL/L) h provided the best compromise between decay control and fruit injury. The performance of SO₂ fumigations on warm or cold fruit, its combination with SO₂ generating pads, and the use of repeated fumigations during cold storage were also evaluated. All the SO₂ treatments tested reduced the percentage of decay, extending the market life of fresh figs. However, in some cases, the use of SO₂ generating pads increased the incidence of skin bleaching. Fumigation of warm fruit at 25 (μL/L) h of SO₂ reduced populations of Alternaria and Rhizopus spp. growing on the fig surface. The treatment was more effective against Rhizopus spp. than against Alternaria spp. Contamination of fruit by Botrytis spp. and Penicillium spp. was also reduced by SO₂. In conclusion, results showed that SO₂ can be a potential tool to control postharvest rots and therefore increase the market life of fresh figs.     

枫香种子生物学特性的研究进展

枫香材用、观赏价值较高，是很有潜力的造林绿化树种。本文论述了枫香种子的结实、果实和种子成熟、采集、加工、贮藏萌发特性，树枫香种子生产、苗木培育具有指导意义。     

A comparative study of the cytological and reproductive behaviour of wheat and triticale subjected to two temperature regimes

Summary A comparison was made of the meiotic stability and reproductive behaviour ofTriticale hexaploide cv. Rosner andT. aestivum cv. Pitic in response to two temperature regimes (15° and 30°C) imposed continuously from premeiosis to maturity. Mean frequencies of MI open bivalents, univalents, and lagging chromosomes at AI were significantly higher in Rosner than in Pitic. Such irregularity would appear to arise from the asynchronous disjunction of chromosomes between Metaphase I and Anaphase I, resulting in meiotic disturbances and a high frequency of abnormal microspores. Despite such abnormalities, floret fertility was equivalent to that observed in Pitic, and the proportion of aneuploids recovered in the progeny, although greater than expected in wheat, was much lower than would be predicted. It is suggested that there is a strong certation effect in the transmission of aneuploid microspores and that the irregularities observed during microsporogenesis do not apply directly to megasporogenesis.No appreciable effect of temperature on meiotic chromosome behaviour during microsporogenesis was observed in either wheat or Triticale. In Triticale, high temperatures (30°C) substantially reduced spikelet fertility, and in contrast, low temperature (15°C) increased the frequency of aneuploids.Contribution No 232, Department of Plant Science, University of Manitoba, Winnipeg 19, Manitoba, Canada     

Influence of fumigation with high concentrations of ozone gas on postharvest gray mold and fungicide residues on table grapes

To control postharvest decay, table grapes are commercially fumigated with sulfur dioxide. We evaluated ozone (O₃) fumigation with up to 10,000 μL L^?1 of ozone for up to 2 h to control postharvest gray mold of table grapes caused by Botrytis cinerea. Fumigation for 1 h with 2500 or 5000 μL L^?1 of ozone were equal in effectiveness. Both treatments reduced postharvest gray mold among inoculated ‘Thompson Seedless’ grapes by approximately 50% when the grapes were examined after storage for 7 d at 15 °C following fumigation. In a similar experiment, ‘Redglobe’ grapes were stored for 28 d at 0.5 °C following fumigation for 1 h with 2500 or 5000 μL L^?1 of ozone. Both treatments were equal in effectiveness, but inferior to fumigation with 10,000 μL L^?1. Ozone was effective when grapes were inoculated and incubated at 15 °C up to 24 h before fumigation. The cluster rachis sustained minor injuries in some tests, but berries were never harmed. Ozone was applied in three combinations of time and ozone concentration (10,000 μL L^?1 for 30 min, 5000 μL L^?1 for 1 h, and 2500 μL L^?1 for 2 h) where each had a constant concentration × time product (c × t) of 5000 μL L^?1 × h. The effectiveness of each combination was similar. The incidence of gray mold was reduced by approximately 50% among naturally inoculated, organically grown ‘Autumn Seedless’ and ‘Black Seedless’ table grapes, and by 65% among ‘Redglobe’ table grapes, when they were fumigated with 5000 μL L^?1 ozone for 60 min in a commercial ozone chamber and stored for 6 weeks at 0.5 °C. Residues of fenhexamid, cyprodinil, pyrimethanil, and pyraclostrobin were reduced by 68.5, 75.4, 83.7, and 100.0%, respectively, after a single fumigation of table grapes with 10,000 μL L^?1 ozone for 1 h. Residues of iprodione and boscalid were not significantly reduced. Ozone is unlikely to replace sulfur dioxide treatments in conventional grape production unless its efficacy is improved, but it could be an acceptable technology to use with grapes marketed under “organic” classification, where the use of SO₂ is prohibited, or if SO₂ use were to be discontinued.     

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.     

Effect of salicylic acid treatment on alleviating postharvest chilling injury of ‘Qingnai’ plum fruit

The effects of salicylic acid (SA) treatment on chilling injury, disease incidence, electrolyte leakage, malondialdehyde (MDA) content, respiration rate and ethylene production, polyphenol oxidase (PPO) and peroxidase (POD) activities, and polyamine (PA) content of ‘Qingnai’ plum fruit were examined. Chilling injury, disease incidence, electrolyte leakage, MDA content, respiration and ethylene production of control fruit increased after about 15-30 days cold storage. Chilling injury promoted PPO and POD activities which were associated with fruit flesh browning. Accompanied by a polyamine content increase, chilling injury was positively correlated with putrescine and spermine contents in control fruit. Suppression of chilling injury by SA was associated with reducing leakage, MDA content, delayed activities of PPO and POD, and enhanced PA accumulation. SA treatment delayed the onset of the climacteric peak of respiration, and also inhibited respiration and ethylene production. The results suggest that SA treatment may be used commercially to control chilling injury in ‘Qingnai’ plum fruit during cold storage.