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NE1018: Postharvest Biology of Fruit

Duration:
October 01, 2003 to September 30, 2008
Administrative Advisor(s):
Bradley Hillman (NJ.)
NIFA Reps:
D. Ramkishan Rao

Statement of Issue(s) and Justification:

Consumption of fruit contributes significantly to human health, and yet Americans fall far short of consuming the recommended servings. US consumers have access to moderately priced fruits of apparent good quality, the result of many years of effort by fruit breeders and postharvest specialists. Yet, consumers limit purchases with the primary complaint of insufficient quality and lack of flavor. Fruit producers often market fruit from cultivars with poor quality and flavor to maintain market share. The key to increasing consumer consumption of fresh fruits, without loss of grower income, lies in providing fruit with both superior flavor and shelf life.

Storage protocols of temperate fruits are cultivar- and sometimes region-specific, and must be optimized to reduce postharvest losses. Protocols are needed for each replacement cultivar on a regional level. The geographical composition of the team in this project provides a unique situation where responses of cultivars to a wide range of growing conditions can be studied. Such studies provide essential postharvest linkages to studies on productivity and other horticultural factors carried out in the NE183 Regional Project. New apple cultivars such as Honeycrisp have been widely planted in the US and a number of physiological and pathological disorders are limiting continued expansion and threatening the viability of the industry.

While the introduction of agrichemicals has contributed to considerable gains by fruit producers, negative effects of some chemicals on the environment and/or human health have caused increased concern (NAS, 1993). Globally, increased emphasis is being placed on production of high-quality food and fiber at low cost and with minimal deleterious effects on humans or the environment. The National Academy of Sciences has recommended that the U.S. Make research investments and policy changes that emphasize development of pesticides and application technologies that pose reduced health risks and are compatible with ecologically based pest management (NAS, 2000). The Academy further specified that the development and incorporation of new, safer chemistries into agriculture to maintain productivity while protecting human and environmental health must be based on sound fundamental and applied research, and decisions must be based on science. and they recommended expansion of the research effort in government, industry, and university laboratories.

The fruit industries are heavily reliant on postharvest chemicals to control decays, insects, and physiological disorders during storage. Kuchler et al. (1997) reported that 47 percent of detectable pesticide residues on apples were attributable to products such as diphenylamine (DPA), thiabendazole, and captan that are applied after harvest. Non-toxic alternatives are needed to better position our domestic producers for maintaining their global market share. New approaches are needed to minimize losses of fruit during storage and transport. A better understanding of relationships between postharvest physiology of fruits and their susceptibility to decay is essential for developing improved control measures.

Recent progress in understanding the biology and genetics of ethylene formation and its role in fruit softening will enable us to interfere with fruit softening at the genetic level. Recent developments of transformation vectors and protocols will permit the tailoring of ethylene suppression to individual apple cultivars for extended storage life and aroma formation. One of the targets for extended storage life is McIntosh, an apple cultivar that is produced in the largest quantities in the US, has appealing characteristics, but softens rapidly.

The presence of insects after harvest can interfere with international and domestic marketing of US fruit crops. Phytosanitary treatments must control the pests without damaging the fruit and be safe for the environment. Postharvest insect control often involves fumigation with methyl bromide or other fumigants. There is great interest to develop sustainable alternatives that are economically feasible. Alternative strategies are essential to maintain important export markets for US fruit crops and to compete effectively with foreign producers.

The discovery and commercialization of 1-methylcyclopropene (1-MCP) as a means of controlling fruit ripening, maintaining fruit quality in storage and reducing storage disorders has developed a critical area of research for this project. 1-MCP was approved for food use in July 2002 and used commercially on apples in several states. It has low toxicity, has negligible residues, and is effective at low concentrations. However, as with many new technologies, there are still many questions left to be answered on how it can best be used to ensure high fruit quality.

Thus the focus of our project is to evaluate the storage potential of new cultivars, make better use of existing storage technologies, and develop new, safer technologies, with a minimum use of chemicals. Underpinning this research, we have an active group that is investigating the metabolism of ripening and the biological causes of physiological disorders. Our emphasis has also shifted towards investigating the effects of postharvest handling on the nutritional and flavor quality of fruit because of their importance to consumers. Specialist skills within this multistate project will allow collaborative activity among regions, allowing greater advances in a shorter period of time. As in the past, the group will develop experimental protocols on various research topics that will be carried out in diverse geographical regions to explore the effects of environment on fruit response to various factors. In addition, members with more fundamental research skills will team with those with more applied knowledge to allow a greater understanding of the issues. Participation in this multistate project facilitates these important types of interactions that may not be available within the individuals institution. In some cases, storage facilities and equipment will be shared among members to increase efficiency and efficacy.

Related, Current, and Previous Work:

Past NE-103 projects have investigated relationships between storage quality and preharvest factors which are known to markedly affect postharvest performance (Bramlage, 1993). Through studies on the mineral nutrition of apple fruit, we have improved our understanding of the mechanisms of calcium (Ca) action (Burmeister and Dilley, 1993; Conway and Sams, 1987; Picchioni et al., 1998; Whitaker et al., 1997) and developed prophylactic measures to treat fruit both pre- and post-harvest (Bramlage, 1993; Conway et al., 1994; Roy et al., 1996). Due in part to the efforts of the NE-103 project, the problem of Ca-related disorders is no longer of much commercial significance in North America. Research on the effect of plant growth regulators such as aminoethoxyvinylglycine (AVG) and ethephon, as well as nutritional and other harvest management factors has continued (Clayton et al., 2002; Stover et al., 2003; Wang and Dilley, 2001; Wargo et al., 2003). In addition, much has been learned about the effects of growing conditions on storage quality, but while we have identified major effects of such conditions on the ability of fruit to withstand postharvest treatments such as low O2 (Lau et al., 1998) and high CO2 (Burmeister and Dilley, 1995; Watkins et al., 1997), the reasons for this variation are not yet understood. An understanding of this variation is essential, especially for growing regions such as the northeastern US, which experience wide yearly variations in climate. These variations in climate are critical as it can be argued that the limitations to utilization of new technologies and cultural tools lies less with the performance of that technology than with the variable responses of fruit to it. For instance, fruit cultivars vary markedly in their response to, and tolerance of, low 02 (Gran and Beaudry, 1993; Park et al., 1993), high C02 (Burmeister and Dilley, 1995; Fernandez-Trujillo et al., 2001; Watkins et al., 1997), and other postharvest treatments (Watkins et al., 2000). Apparently, responses of cultivars to many postharvest treatments are affected by growing environment (Bramlage et al., 1977; Lau et al., 1998). Cultivars also vary widely in susceptibility to storage disorders such as superficial scald, soft scald, low temperature breakdown and senescent breakdown (Barden and Bramlage, 1994a, b; Barden and Greene, 1997; Wolk et al., 1998) and postharvest factors need to be taken in to account in selection of new cultivars for North American apple industries.

The development of new cultivars for the North American fruit industries has become key to economic success. Information on the storability of a range of fruits has been produced by NE103 (Agar et al., 1999; Clayton et al., 2003; Cliff et al., 1998; El-Shiekh et al., 2002; Grant et al., 1996; Kupferman, 2002a,b,c,d; Kupferman and Gutzwiler, 2002; Lau and Lane, 1998; Reed, 2002; Volz et al., 1998; Watkins et al 2003). One of the most planted apple cultivars in the last few years has been Honeycrisp, a Minnesota-bred apple that has unique flavor and texture characteristics. However, the incidence of disorders has caused concern within the industry. A trial involving five stations was set up in 1999 and 2000 to investigate the effects of growing locations and storage temperature on soft scald incidence in Honeycrisp apples and the results published (Tong et al., 2003). This research has provided the initial information required for planning of future work.

Small fruits, such as cherries, blackberry, raspberry, strawberry, and blueberry, have a high cash value as both U-pick and shipping acreages, and offer an additional income source to apple and small acreage producers. New blackberry cultivars are of excellent shipping quality (Perkins-Veazie et al., 1994; 1996; 1997; 1999a,b; 2000). A new type of blueberry, the southern highbush, has a multiple species background and has been found to have adaptability in northern states. The quality of this type is widely variable, depending on cultivar (Perkins-Veazie et al., 1996).

Members of the NE-103 group have been leaders in the development of information on the effects of 1-MCP, an ethylene action and ripening inhibitor, on fruit crops. Overviews of 1-MCP use on horticultural crops have been published by our members (Blankenship and Dole, 2003; Prange and DeLong, 2003; Watkins, 2002). Of the temperate fruits, apple, pear, apricot, peach, plum, strawberry, and persimmon respond to 1-MCP applications to various extents. The data suggest that among these fruits, apple has the most consistently beneficial response.

In apples, 1-MCP has been found to be generally effective for delaying ripening in most cultivars, with the response saturating at approximately 1 LL-1 (Fan et al., 1999a; Rupasinghe et al., 2000b). Some cultivars, however, such as McIntosh and Law Rome required higher concentrations for full response (Watkins et al., 2000). The 1-MCP treatment duration needed to provide maximal response was found to be dependent on temperature, and cultivars may differ in the minimum time needed to gain maximal benefit (DeEll et al., 2002).

1-MCP has been shown to reduce storage scald on apples (DeEll et al., 2002; Rupasinghe et al., 2000a). In Granny Smith apples 1-MCP suppressed -farnesene, reduced the amount of its oxidation products, conjugated trienes and 6-methyl-5-hepten-2-one, and reduced scald (Fan et al., 1999b). Superficial scald was also suppressed in Delicious and Law Rome apples along with a reduction in -farnesene and conjugated trienols (Watkins et al., 2000). 1-MCP reduced 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity and respiration rate in apples, resulting in a 72% reduction in -farnesene (Rupasinghe et al., 2000a, 2001). Physiological responses of apple to 1-MCP include reduced respiration and ethylene production (Fan and Mattheis 1999; Fan et al., 1999a,b; Jiang and Joyce, 2002; Lurie et al., 2002), and aroma volatile synthesis (Fan and Mattheis, 1999a, 2001; Lurie et al., 2002; Rupasinghe et al., 2000b).

Advancing maturity and ripeness of tree fruit decreases the effect of 1-MCP (Mir et al., 2001; Watkins et al., 2000). The reason for this is not entirely clear; ripening of some climacteric fruits such as tomato can be arrested at any stage of development (Hoeberichts et al., 2002). The degree to which stage of ripening of different pome and stone fruit cultivars influences 1-MCP responsiveness is not known. 1-MCP may be useful for determining the fundamental basis for the irreversibility of some features of ripening.

Some instances of a negative influence on quality have been reported in apple, although the occurrence of damage has been variable. A marked delay in the de-greening of Fuji and Redchief Delicious apples (Fan and Mattheis, 1999b; Mir et al., 2001) has the potential to reduce fruit quality, especially for cultivars typically sold with yellow background color. Of greater concern are preliminary reports of enhanced sensitivity of some cultivars to CO2 injury brought about by 1-MCP treatment (DeEll, 2001).

The NE-103 group has made major contributions to the study of superficial scald control for apples and pears. Chill unit accumulation prior to harvest has been tested as a predictor of scald susceptibility (Bramlage and Weis 1997; Ma et al., 2000; Weis et al., 1998). The ability to predict scald susceptibility would allow storage operators to forgo chemical applications or expensive storage methods when the risk of scald development was very low. Low O2 CA storage has been extensively studied as a means to control scald (Chen and Varga, 1997; Wang and Dilley, 2000a, 1999; Wang et al., 1997) and a collaborative project was conducted at several member stations (Lau et al., 1998). The results have shown that this technique cannot be used in all growing regions because of varying effectiveness in controlling scald and intolerance to the low O2 atmosphere in fruit from some regions. Chlorophyll fluorescence was developed to detect the lowest acceptable O2 concentration in storage (Prange et al., 2002) allowing better use of low O2 for scald control (Prange et al., 2002b; 2003). Further testing is necessary before this method can be adopted. Other approaches for scald control have included use of ethanol (Wang et al., 1997;) high CO2 shock (Fernandez-Trujillo et al., 2001), intermittent warming (Alwan and Watkins, 1999; Watkins et al., 2000) and hypobaric storage (Wang and Dilley, 2000b).

Developing alternative strategies for decay control has been a high priority for the group. The two most common pathogens contributing to postharvest decays of fruit crops are Botrytis cinerea and Penicillium expansum. These pathogens have been controlled by applying fungicides either before or immediately after harvest, but control with fungicides has become less effective as many pathogens have developed resistance to the most common postharvest fungicides. Alternative approaches evaluated for controlling postharvest decays have included biological controls (Zhou et al, 2003), heat treatments (Palou et al., 2001; Wszelaki and Mitcham 2003), adjusting N2, Ca or B levels (Rosenberger, 1999; Chardonnet et al., 2000; Fallahi et al., 1997;), or combinations of these treatments (Conway et al., 1999; Janisiewicz et al., 1999; Klein et al., 1998; Leverentz et al., 2000; Wszelaki and Mitcham, 2003). Exposure of fruit to various volatiles have all provided some suppression of fungi (Chu et al., 1999, 2001; Sholberg et al., 2000; Simpson et al, 2003; Song et al, 1998; Zhou et al., 2000).. Regulation of osmotic pressure and 2-nonanone have proven useful for controlling these pathogens in fresh-packed apple slices (Chardonnet et al., 2001, 2002; Leepipattanawit et al., 1997).

Sanitation measures that reduce inoculum levels on fruit and in packing facilities can reduce losses due to postharvest decays. Rosenberger (2001) has reported that P. expansum recycles on field bins and is present at high concentrations in packinghouse air. Proven sanitation measures include chlorination of water flumes (Spotts and Peters, 1980), use of chlorine dioxide (Roberts et al., 1994; Spotts and Peters, 1980), hydrogen peroxide, peracetic acid (Baldry et al., 1983), and ozone (Spotts et al., 1992). Many of the sanitation measures involve the use of reducing agents that can either injure fruit or are incompatible with antioxidant treatments such as DPA. Continued research is needed to identify cost-effective sequences for application of sanitizers, fungicides, and other postharvest treatments that are safe for the crop, applicators, and consumers.

Some of the alternative strategies that have been explored for postharvest insect control include natural fumigants, surfactants, heat treatments with water, air or radio frequency energy, and controlled atmosphere treatments. Fumigation with acetaldehyde has been demonstrated to have insecticidal activity; however, its use with fruit crops is limited by the rapid absorbance and metabolism of the fumigant by fruits and phytotoxicity to green tissues (Simpson et al., 2003). Surfactants have been shown to be quite effective against surface pests such as mites, thrips and aphids (Tipping et al., 2002), but additional work on fruit tolerance is needed. Controlled atmosphere treatments, especially elevated CO2 atmospheres, have shown promise for postharvest insect control in some crops (Zhou and Mitcham, 1998); however, fruit tolerance is limited and treatments must be developed for each specific insect. Increases in our knowledge of how CA affects insects will help to speed the development of effective treatments (Zhou et al., 2000, 2001). Postharvest heat treatments using radio frequency energy have been developed for walnut (Wang et al., 2001) and additional treatments are under development for sweet cherry, avocado, and other subtropical fruit.

Numerous studies have suggested that the phytochemical content and corresponding antioxidant activity of fruits and vegetables contribute to their protective effect against chronic and degenerative diseases (Heinonen et al., 1998; Record et al., 2001). Phytochemicals that exhibit antioxidative activity include phenolic compounds, nitrogenous compounds, and tocopherols, carotenoids and ascorbic acids. The antioxidants present in fruits and vegetables exhibit anticarcinogenic and antimutagenic activity (Weisburger, 1999). Feeding studies by Jacobs et al.(2003) have demonstrated that consumption of sweet cherries has anti-inflamatory and anti-gout effects in humans. Perkins-Veazie and Collins (2001) indicated the various health benefits of various small fruits; however, postharvest handling can influence these health benefits. Studies indicate that antioxidants or total antioxidant activity in small fruits may be adversely affected when CO2 concentrations in storage exceed 10% (Holcroft and Kader,1992; Perkins-Veazie and Collins, 2002; and Gunes et al., 2002).

To increase consumption of healthy fruit, the eating quality must be improved. For apples, texture is a very important quality component. There is considerable cultivar variability in firmness at harvest (DeEll et al., 2001) and the effect of temperature and ethylene on apple softening during storage (Johnston et al., 2002) or the effects of orchard and storage conditions on apple texture vary with the cultivar (Johnson, 2000). We may be able to exploit this genetic variability to study the molecular and physiological mechanisms controlling maintenance of fruit texture (Tong, et al., 1999), as well as the effects of environmental conditions on the eating quality of fruit.

Great variability exists in the quality of apples at the time of packing (Kupferman, unpublished). Quality standards can be set by the apple producers to screen out inferior fruit if parameters of acceptability have been determined. Various researchers have worked with consumer and sensory panels to describe how people react to apples of various quality (Allan-Wojtas 2003; Boulton 1997; Harker et al., 2003; MacFie 1993; Andani 2001). Using information from these studies, researchers are evaluating how consumers evaluate edible and visual quality of apples.

Fundamental information relating to various aspects of fruit physiology and biochemistry is developed by some members of the Technical Committee and then used by other members to guide their more applied research. This type of collaboration is one of the most beneficial aspects of this Multistate Project. Research by group members has contributed substantial information about the control of fruit ripening by ethylene and cell wall-derived oligosaccharides (Sisler and Blankenship, 1993, 1996; Melotto et al., 1994, respectively). It has also utilized biochemical and molecular techniques to characterize CO2 impacts on strawberry gene expression (Watkins, unpublished) that may reflect more general CA impacts on ripening processes. Several laboratories have examined aspects of cell wall metabolism that are important in the control of ripening-related fruit softening (Wu et al., 1993). NE-103 researchers have also examined factors that influence a fruit's ability to resist infection by postharvest pathogens. Research on one fruit protein (the poygalacturonase inhibitor protein, PGIP) studied in labs in Beltsville and Davis may lead to reductions in the use of fungicidal chemicals while reducing fruit decay (Powell et al., 2001). Methods have been developed to study ripening-related cell wall metabolism and texture change in tomato fruit tissue explants. This will enable more efficient, targeted genetic manipulations designed to provide better management of fruit softening and improved texture properties of processed fruit.

A collaborative group has focused on the metabolic pathways that are invgolved in the synthesis of aroma volatiles that are crucial to the development of organoleptic quality (Mattheis et al., 1992a, b, Mattheis et al., 1995). The techniques and information from those studies were used to examine the relationship of harvest maturity (Mattheis et al., 1991a) and fruit storage conditions (Mattheis et al. 1991b, 1995, 1997, Fellman et al., 1993a, b) to aroma development. The relationship of stressful CA conditions and aroma development has been described for strawberry (Fernadez-Trujillo et al., 1999; Peleyo et al., 2003). Genes involved in fatty acid synthesis, linked to aroma development in ripening and senescing apples, have been described. This work intersects with studies of related aroma volatile synthetic pathways by Mattheis and Fellman. Continuing work with polygalacturonase-inhibiting protein [PGIP] is designed to understand details of its contribution to fruit resistance to fungi, Very recent results suggest that PGIP may also help to ameliorate the damage caused by insect feeding. Work on apples indicates that growth of different fungi on fruit may cause tissue pH changes that either support or repress the growth of the food-bourne human pathogen Listeria monocytogenes on the fruit. This study could pave the way to biological methods for control of this and other human pathogens (Chardonnet et al. 2002). Effects of other fungi on tissue pH may also influence the ability of fruit fungal pathogens to macerate host tissues.

A hypothesis (Purvis 2002) linking chilling injury and production of active O2 species (AOS, superoxide radicals etc.) is being tested that may help to explain the beneficial effect of DPA treatments in reducing scald. The farnesene synthase gene has been cloned and its expression during fruit storage was followed. Two additional genes involved in farnesene synthesis, hmg1 and hmg2, have been identified. Examinations of contributions of antioxidant gene expression to scald reduction are ongoing [Kochhar et al., in press].

Research on stress related to CA storage is examining transient gene expression responses to low O2. Pyruvate decarboxylase, but not alcohol dehydrogenase, increases in dAnjou pears in response to damaging levels of low O2 well before fruit damage occurs. The impact of CA on ethylene production may be linked to the observation that CO2 activates ACC-oxidase through bicarbonate activation, with binding at the arginine-175 residue (Dilley et al., 2001).A gene encoding phospholipase D alpha, involved in membrane degradation and fruit senescence, has been cloned and used to develop transgenic tomato plants. These combinations of fundamental studies are providing crucial information needed to understand the development of stress disorders in fruits and suggesting ways to solve them. The work also provides useful biochemical and molecular markers for use in more applied studies.

Ethylene production is critically important to the maturation and ripening processes in climacteric fruit, whether or not the fruit are stored. Intensive research has identified key characteristics of ACC synthase and oxidase (Dilley-et al., 1995; Fan et al., 1996; Gorny and Kader, 1996b; Poneleit and Dilley, 1993; Rosenfeld et al., 1996; Wilson et al., 1993a,b) and an ELISA system for detection of ACC oxidase has been developed (Dilley et al., 1996). Molecular genetic down-regulation of ACC synthase gene expression in apples suppresses fruit softening and provides useful fruit material for further ripening studies.

Objectives

  1. To evaluate postharvest requirements of new and existing fruit varieties
  2. To develop sustainable controls for physiological disorders, diseases and pests
  3. To develop recommendations for the beneficial use of essentially safe postharvest chemicals, such as 1-MCP, on fruit to assure high quality and wholesomeness
  4. To expand knowledge of the influence of cultivar, production practices, and postharvest handling on the nutritional and eating quality of fruit.
  5. To expand fundamental knowledge of fruit biology required for development of improved and new technologies for maintenance and enhancement of fruit quality.

Methods:


Objective 1:

We will evaluate postharvest requirements of new and existing fruit cultivars that are optimally suited to regional climate and marketing demands. 1. Postharvest evaluations of apple cultivars in the NE-183 regional project. In the NE-183 project, 48 new cultivars and selections are planted (1995, 1999) in controlled field trials in over 15 sites across the US. As a major collaborative and interdependent work plan under this objective, we provide a continuum in evaluation of these fruit extending from the field through the storage period and into retail sales, where the consumer is directly affected. Five stations (MA, MI, ME, NC, and NY-I) are evaluating cultivars from various NE-183 sites within their region. Eight cultivars have been selected as part of the current project from the 1995 plantings, and each station is assessing at least two of these under air and CA storage conditions. The present protocol involves tests of moderate O2 levels (2.5%) and no CO2 at non-chilling temperatures (3oC) to define the storability of the cultivars. Evaluation of cultivars from the 1995 plantings will continue for 2 further seasons and will be summarized for publication. Then cultivars from the 1999 plantings will be selected in collaboration with researchers in the NE-183 project. Each station is utilizing the same standard protocols for evaluating maturity and storability of new cultivars. Cultivars that are currently part of the NE-103 cultivar trials will also be evaluated to determine if they differ significantly in their susceptibility to infection by P. expansum (NY-HV) using both wound inoculations and stem inoculations. Cultivar susceptibility to stem infections is expected to differ significantly whereas differences in susceptibility following wound inoculation may be minimal..

2. Evaluation of existing fruit cultivars in order to establish optimal handling and storage conditions. Here, we address specific quality issues limiting the storability of commercial cultivars. As the knowledge base expands, information obtained here is expected to integrate with knowledge derived from the other objectives in this proposal.

Most of the team focus will be on Honeycrisp apples (MA; ME; MI; MN; NS: NY-HV; NY-I). We will investigate the relationships among preharvest treatments, maturity, storage temperature and postharvest treatments on incidence of disorders. Fruit will be given preharvest treatments including calcium sprays, ethephon and AVG treatments, harvested at different maturity stages and stored at temperatures ranging from 0 to 3oC (MI; MN; NS; NY-HV; NY-I, ONT). The effect of delays at non-chilling temperatures before cold storage on storage disorders will be tested (NY-I; MA; MI; NS, ONT). Also, Honeycrisp progeny will be assessed for soft scald susceptibility (MN; NY-I, ONT). Similar work with the apple cultivar Ambrosia (BC, WA).

Several investigators on this project are working with small fruit. New cherry cultivars from the breeding program of Agriculture Canada in Summerland B.C. will be tested in WA and BC. Postharvest quality and shelf life of southern, northern, and rabbiteye selections of blueberries will be evaluated from university blueberry breeding programs using trial plots in Arkansas (CA; OK). In addition, the performance of Ozark Blue blueberries will be compared in Ark. and Calif. Additional benefits to be realized from progress under this research objective lie in the close coordination with efforts under Objectives 2, 3, 4 and 5. Examination of many different cultivars will facilitate comparative studies of disorder mechanisms, volatiles associated with disorders, molecular biology, and mechanisms of ripening and softening.

Objective 2:

Three avenues of investigation will be undertaken with goals of developing control or management strategies for storage disorders (scald in apples and pears and bitter pit in apples), postharvest decay, and insect pests. The focus will be to develop techniques that minimize impacts on the environment, have the potential to reduce chemical residues on fruit, and/or provide consumer acceptable alternatives. Effects will be coordinated such that one control strategy does not preclude use of another, and combinations of strategies will also be explored for a systems approach. 1. Physiological disorders.

Promising strategies for controlling superficial scald on apples will be integrated with traditional protocols and subjected to a system evaluation. The criteria for evaluation will be ease of transition, profitability, and sustainability of the strategies (WA). Mathematical prediction models for determining when apple fruit are susceptible to scald will be refined and tested (MA, ONT). Studies optimizing ULO storage for control of storage scald utilizing chlorophyll fluorescence to achieve the lowest possible O2 concentration will continue (NS). Studies with transformed Gala and McIntosh apples that have been genetically engineered with antisense constructs to down-regulate softening of apples during storage will continue. Fruit from transformed trees will be compared with control fruit of the same cultivar to determine shelf life and effects of the transformation on susceptibility to scald and decay (NY-G).

2. Decay control

Sanitation measures for reducing populations of P. expansum in apple storages and packinghouses will be evaluated. Biocides (quaternary ammonia compounds, chlorine compounds, and peroxides) will be compared (NY-HV). Fungicidal vapors developed by various NE-103 participants will be evaluated for effectiveness in simulated commercial settings, and cost-effective materials will be tested in commercial packinghouses to determine if night-time fogging can be used to reduce levels of airborne spores in packinghouses (NY-HV). The new biocide, hydrogen dioxide, will be evaluated for compatibility with DPA and for effectiveness in controlling P. expansum inoculum in postharvest drench tanks. This product and other products that have activity against P. expansum will be evaluated to determine if they can be safely used (no phytotoxicity) with some of the promising new cultivars in the NE-183 plantings (NY-HV).

Alternative controls such as modified atmosphere storage and UV light will be evaluated for effectiveness in maintaining or increasing shelf life of blackberries, blueberries and muscadine grapes (OK). Fruit will be analyzed for total phenolics, total anthocyanins, and ORAC, compounds that indicate a response to UV-C light.

3. Insect control

The tolerance of table grapes and other fruit to insecticidal ethyl formate treatments will be determined by laboratory tests. Combinations of SO2 fumigation followed by ethyl formate fumigation will be tested. LD99 values for mortality will be developed for economically important arthropod pests. We will further explore the use of silicone surfactants to control surface insects on fruit crops to remove phytosanitary barriers to trade (CA). Radio frequency heating will be explored as an alternative to methyl bromide for postharvest insect control in nuts, tropical fruit, and sweet cherries. Product tolerance will be tested with various heating rates and the effect of temperature and exposure time determined. Arthropod mortality will be confirmed (CA).

Objective 3

The effectiveness of 1-MCP on controlling fruit ripening differs with application method, environment, cultivar, and species. As we improve our understanding of how to optimize use of this potent new growth regulator, we also need to understand its limitations and, in some circumstances, when it may actually compromise fruit quality.

1. Apple cultivar responses to 1-MCP

Our focus will be on evaluating how cultivar and postharvest handling affect the continued commercial implementation of this product, with a primary emphasis on apples of importance to the NE. Many of these apples lose firmness quickly in storage and at retail and could benefit greatly by the effective use of 1-MCP. The influence of different environmental and cultural conditions under which individual cultivars are grown will be evaluated by replicating efficacy trials across the U.S. and Canada (CA, BC, MA, MI, NY-I, NC, ONT, PA).

Cultivar responsiveness to 1-MCP will be measured as a function of the application of preharvest growth regulators such as AVG, fruit maturity, storage atmosphere and temperature, storage duration and post-storage holding conditions. Evaluations will include fruit textural properties, fruit color, and the incidence of decay and disorders. Special emphasis will be placed on describing the influence of 1-MCP on CO2-induced pitting and tissue browning in susceptible cultivars. Chlorophyll florescence will be tested as a method to determine when 1-MCP effects have dissipated in storage.

There are several states that have excellent controlled atmosphere storage facilities (BC, MI, NY, ONT, PA), while other states have limited CA resources. Fruit will be sent to the better facilities for CA studies. Not all cultivars are available in all states or are only available in limited quantities. Select states will concentrate on certain cultivars, to enable us to obtain a larger database of fruit responses for North America.

2. Development of application protocols for small farms

In most fruit production areas in North America and especially in the NE, small farms and integrated farm markets constitute an important component of the tree-fruit industrys production and sales. Application technologies for 1-MCP have thus far only been evaluated with large production and storage facilities in mind. There is a need to serve the smaller production and retail facilities. Systems for 1-MCP application, such as refrigerated trailers and small cold rooms suitable for small farmers to use profitably will be evaluated (MA, NC).

3. Development of optimized application protocols for non-apple fruit  pear, strawberries, blueberries, raspberries, apricots, peaches, and melons

The appropriate use of 1-MCP to enhance postharvest quality of pears, which tend to be significantly more variable in their response to 1-MCP than apple and must fully soften before consumption, will be developed. Pear response appears to be more highly dependent on fruit maturity at the time of application than apple and at high concentrations of 1-MCP, failure to ripen may result. Protocols will be developed using variations in 1-MCP concentrations and storage conditions to minimize unwanted effects on pear (CA, ONT, OR). Additional information will be collected on the benefits of 1-MCP for strawberries, blueberries, and raspberries (CA) and on peaches and melons (NC). Variability due to cultivar will be evaluated.

4. Aroma suppression and recovery in apple:

It is recognized that 1-MCP will suppress aroma volatile formation, but the impact of this suppression on volatile production during the marketing period and in response to variations in storage conditions has not been fully explored. We will investigate the effect of 1-MCP, alone or in conjunction with low O2 on the ability of apple fruit to produce characteristic aroma volatiles during the marketing period (MD, MI). The time needed for recovery of aroma biosynthesis following storage of various durations will be described for a limited number of cultivars that differ in their volatile profiles.

5. Superficial scald suppression in apple and pear:

The suppression of superficial scald in apple and pear fruit by 1-MCP has been documented, but suppression is typically not complete. The opportunity exists to couple 1-MCP use with alternative scald control technologies, such as low initial O2 stress and storage at non-chilling temperatures to improve its scald-control efficacy and reduce the use of ethoxyquin and DPA (MA, USDA/MD, MD, MI, NY-I). Postharvest chemical use in apples was documented in 2002 (MI). An additional survey will be conducted in 2006 to determine the effect of 1-MCP use by the apple industry.

Objective 4

The Technical Committee is supporting a multi-investigator approach in antioxidant evaluation of fruits. The extremely expensive and cross-discipline interactions (medicine, nutrition, horticulture, biochemistry, molecular biology) necessary to accomplish sensory evaluation and improvement, antioxidant, anti cell proliferative, and human clinical trial evaluations, preclude duplication of research efforts at multiple sites. These include sensory evaluation and genetic mapping of apple cultivars (WA, NZ, MN), variation in antioxidant content of small fruits in response to cultivar and postharvest treatments (NY-I, OK), and human health benefits of fruit (CA). Collaborative efforts among US and international researchers are ongoing within these projects. To effectively promote the consumption of fruits and to compete effectively for consumers dollars, the eating quality and nutritional value of the fruit that we market must be improved.

Apple quality. Consumer evaluation of the edible quality of fruit is invaluable in providing a product that consumers will purchase repeatedly. Intense descriptive analysis, preference mapping, and consumer evaluation are commonly done on new food products developed by large food processing companies. A collaborative effort among several labs (WA, OR, NZ) is assessing how consumers evaluate edible quality, using preference mapping, a powerful tool to describe how people view a specific product such as apples. These methods can be used to evaluate how firm an apple should be or a minimum level of flavor volatiles a fruit should have to appeal to a certain group of consumers (Hoehn 2003.).

Genetic control of apple texture (crispness) will be studied by identifying genes that are expressed in freshly-harvested apple fruit but not in stored fruit using a PCR-based technique (MN). The expression of these genes in different apple cultivars will also be determined. The function of such genes will be determined by silencing or increasing their expression in apple fruit, and determining changes in fruit phenotype. New cultivars that result from this work will be evaluated by other members of the Technical Committee for overall quality. Fruit antioxidants and human health. The effects of cultivar and postharvest treatment on antioxidant and antiproliferation activities of extracts from different strawberry cultivars will be explored (NY-I). Phenolic compounds, including free and bound flavonoids and anthocyanins will be measured. Total antioxidants and antiproliferative activities of strawberry extracts will also be determined.

Blueberry and blackberry cultivars will be evaluated for total phenolic and anthocyanin content (OK). A collaborative project between UCDavis and USDA ARS,OK will determine sensory, physical, and antioxidant quality of blueberries grown in two diverse climates. Representative samples will be subjected to storage studies and blueberries grown in Arkansas and California will be sent to Lane, OK for antioxidant analysis, with sensory analysis conducted by UCDavis.

The magnitude of, and reasons for, variation in concentrations of ascorbic acid, carotenoids, and flavonoids as well as total antioxidant activity of fruits, such as date, pear, pomegranate, and sweet cherry, will be determined (CA). The influence of genotype, maturity and ripeness stage at harvest, and storage conditions and duration will be investigated. Collaboration with human nutritionists for evaluation of the health benefits of eating sweet cherries will be continued as preliminary studies indicated that cherries have anti-inflammatory and anti-gout effects on humans.

Objective 5

Fruit ripening-related biology

Texture. Studies of fruit cell wall metabolism in relationship to tissue softening and the generation of active oligosaccharide signals (PDOs) will use tomatoes with genetically altered production of wall-metabolizing enzymes, biochemical and (perhaps) genomic searches for previously undescribed fruit enzymes, and extraction and characterization of endogenous PDOs and testing of their potential biological activities on fruit pericarp explants. [CA]

Flavor/Aroma generation. Work on apple fruit ester synthesis will continue with the focus on ATF genes and enzyme activity [WA]. Work to improve raspberry aroma will focus on ketone generation, through examination of the activity of a purified benzalacetone synthase (BLS) that is a member of the aromatic polyketide synthase (PKS) enzyme family. Work on the genome-wide cloning of the PKS genes has begun with the ultimate goal of cloning, expressing and characterizing the BLS gene and producing transgenic raspberries to test for modified aroma quality [NY-G,]. Studies examining the reasons that flavor-life of fruits is shorter than their appearance-life will focus on (1) the relationships between sugar, acid, phenolic, and volatile components and overall sensory perception in a number of fruit, and (2) ester synthetic pathway activity and ethylene responses in apple fruit lines that have been engineered to have reduced ethylene biosynthetic capacity [CA].

Fruit color development. Fruit color often represents both visual quality and nutritional quality and includes both carotenoid and phenolic compounds. Carotenoid profiling will be done on red, yellow, orange and white-fleshed watermelons and profiling of phenolics in blackberries, muscadines, and Autumn Olive will begin [OK]. The impact of postharvest manipulations on color enhancement in strawberry will also be examined [ONT-G].

Ethylene biosynthesis. The detailed characterization of ACC oxidase catalytic properties will continue [MI]. Work on genes involved in ethylene synthesis and perception and responses of apple fruits after low O2 and/or 1-MCP treatment will continue [MD].

Senescence- and ripening-related gene expression. The rate of ripening in tomato fruits with anti-sense phospholipase D-alpha (PLD) genes will be studied. Ripening and senescence characteristics will be assessed in whole fruit and in fresh-cut fruit slices [USDA-MD]. Studies on the biochemical responses of apple fruit to elevated CO2 will continue [NY-I].

Fruit disorder-related biology

The fundamental focus on fruit disorders in this project will continue to be on the biochemistry of scald development (WA-P, USDA-MD, MD, ONT). Because the disorder appears to be linked to AOS generation in apple skin and AOS may perturb ethylene perception and subsequent responses, spin-trapping will be used to characterize the specific organic O2 species that accumulate [WA-P]. Work on the cloning and characterization of key genes for apple fruit α-farnesene synthesis will continue with a focus on HMG2 and HMG3. (encoding hydroxymethylglutaryl-CoA reductase [HMGR] isozymes) and the ethylene-responsive promoter of HMG3. The work will use specific primers to isolate full-length sequences from an apple peel library and then attempt their expression in E. coli to get protein for analysis of the enzyme [USDA-MD]. Additional work on HMGR genes will occur in a cooperating lab (MD).

Pest defense-related biology

Studies of polygalacturonase inhibitor protein (PGIP) contributions to pathogen defense will utilize tomato lines engineered to have unusually low or high endogenous PGIP contents. Work will determine whether the production of biologically active oligosaccharides is part of the mechanism of PGIPs enhancement of resistance to B. cinerea. Studies to determine whether PGIP interactions with the PGs in insect saliva may lead to a reduction in insect feeding damage will be intensified at the biochemical and molecular genetic levels. [CA].

Measurement of Progress and Results:

Outputs:
Outcomes or projected Impacts:
Milestones:

(2004): Evaluations of compatibility of hydrogen dioxide and DPA will be completed. If compatible, this combination will be adopted commercially.

(2005): Complete evaluations of post harvest requirements for new cultivars from the 1995 NE183 apple plantings. Complete evaluations of blackberry and blueberry selections and storage system trials. Usefulness of controlled atmosphere on muscadine grape shelflife will be finalized. Complete studies on methods for reducing airborne inoculum of P. expansum in apple packinghouses. Complete research developing ethyl formate for insect control in table grapes. Provide information to the industry on the performance of the various blueberry cultivars.

(2006): Complete investigations on strategies to avoid development of soft scald and bitter pit, and maximize quality of Honeycrisp apples. Complete evaluations of variation in response to 1-MCP between apple cultivars of common cultivars and 1995 NE-183 planting. Evaluation of sweet cherries in clinical trials as an anti-inflammatory and anti-gout agent Gene expression data from different apple germplasm will be used to develop markers for crispness, Information on consumer evaluation of apple quality from preference maps and possibly difference testing

(2008): Complete evaluations of post harvest requirements for new apple cultivars from the 1999 NE183 plantings. Determination of shifts in postharvest chemical use in the apple storage industry as a consequence of the integration of 1-MCP as a cultural tool. Complete evaluations of variation in response to 1-MCP between apple cultivars in the1999 NE-183 planting.

Projected Participation:

Include a completed Appendix E form

Outreach Plan:

Results of this research will be made available through several means: Refereed publications, conference papers and proceedings, project reports, on-line sources (web), and industry reports. Several participants have partial extension appointments and therefore will develop outreach materials through fact sheets and other extension publications.

Organization and Governance:

One person at each participating agency is designated, with approval of the agency director, as a voting member of the Technical Committee. Other persons at agencies are encouraged to participate as non-voting members. The Chair, Chair-Elect, Secretary, and Administrative Advisor will conduct the activities of the multistate project between annual meetings. Any member can be an officer, not only the official voting representatives. The officers are elected every second year by voting members and serve a two year term. A succession of officers from Secretary to Chair-Elect to Chair is the norm, but may vary depending on circumstances.

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