The need as indicated by stakeholders 

US growers produce an abundance of fresh fruits and vegetables, but deterioration of quality, storage disorders, decay and contamination with mycotoxins continue to cause considerable losses.  As a result, the fresh fruit and vegetable industries rely on numerous pre- and postharvest practices to ensure minimization of losses. Several key developments in production and storage technologies make this project highly relevant for the fruit and vegetable industries in North America.

Postharvest losses for fresh produce are severe and vary widely, depending upon the crop and handling conditions employed. Gustavsson et al. (2011) noted that global food losses are about 1.3 billion tons annually.  The FAO Sustainable Development Goal 12.3 aims, “by 2030, to halve per capita global food waste at the retail and consumer levels and reduce food losses along production and supply chains, including postharvest losses” (Fabi and English, 2019). Considering factors of climate change, a growing population reaching Malthusian limits, and less agricultural land being used to produce more food, new technologies, crops and decay management strategies are needed to increase food security and help slow food loss and waste.

Apples are a prime example of a commodity that is subject to significant losses during storage and transport. However, pre and postharvest rots caused by Colletotrichum (bitter rot) are significant problems for apple, citrus, blueberry and vegetables like tomato (Barad et al., 2017; Jurick II and Cox 2016; Liu et al., 2020). Postharvest rots of fresh fruits and vegetables not only reduce quality, but also limit their availability for consumption, and sometimes processed products can contain mycotoxins that harm human health. While postharvest fungicides are approved for use to control these pathogens on a limited number of these crops, concerns over maximum residue limits, antimicrobial resistance, and environmental impacts necessitate development of new tools and strategies to abate decay. New disorders in apple (skin wrinkling and leather blotch) appear to be more prevalent, as well as continued occurrence of others such as bitter pit and soft scald. The ability to identify conditions that lead to disorder development is dependent on a collaborative effort. 

More frequent and deleterious environmental stresses, particularly high heat, have impacted produce quality and caused losses in the storage and supply chain.  It is anticipated that this will increase losses due to poor quality and higher incidence of storage disorders. Preharvest growing conditions such as high temperature have increasingly become more stressful for plants, and this can have a deleterious effect on the postharvest outcome.  High temperatures during maturation can delay apple coloration and force growers to delay harvest, but with limitations for storage life. Grower use of reflective ground covers to address poor color can impact fruit maturity and postharvest conditions.  Unknown growing conditions are involved in the development of storage disorders, such as apple bitter pit.  Therefore, a coordinated effort is needed to identify the conditions that lead to greater incidence and our predictive capacity.

Fresh produce items are sold in a wide range of locations from local farmers’ markets and roadside stands to local and regional markets to school lunch programs and to export destinations. These locations place varying demands on the techniques and technologies necessary to extend postharvest quality while reducing losses during this value chain. The fresh produce industry also provides reliable and constant employment to significant numbers of U.S. and foreign workers.

Increased consumer expectations that fruits and vegetables are available year-round and often out of season have created changes in which cultivars are grown and have expanded the regions where fruits are produced. This has been coupled with the development of new cultivars with specific adaptations to regional climates outside traditional production regions. Blueberries, strawberries, cherries and peaches are examples of this phenomenon. New types of these traditional fruits such as crisp-fleshed blueberries and firm-fleshed peaches have expanded the potential for marketing highly perishable fruits. Where once only round and cherry tomatoes were available in supermarkets, nowadays typical produce sections sell a variety of tomato types including on-the-vine (aka cluster), grape, varietal, heirloom, Roma, and hydroponic-grown, by both conventional and by organic methods. A similar phenomenon has occurred with other types of vegetables such as Ripe bell peppers and cucumbers. Consumer interest in new types of fruits such as muscadine grapes and elderberries has increased but with relatively unknown postharvest needs. New cultivars of virtually every type of produce are continually being adopted that may have unknown issues.

New cultivars typically have unknown postharvest needs that make their handling challenging. Small-scale operations oftentimes are at the forefront of testing and marketing new cultivars. However, the postharvest practices differ between large-scale operations with extended storage durations and small-scale operations with rapid marketing and brief periods of storage. Consequently, new cultivars initially tested for small-scale production may be unsuitable for large-scale production with concomitant stringent postharvest expectations of quality. Honeycrisp is a good example of an apple cultivar grown to satisfy demand, but with many storage issues. 

Techniques for season extension, most notably high tunnels, have also contributed to expanded production of fruits and vegetables for small-scale local markets, but with unknown impact on quality. In addition, production in protected culture such as high tunnels and greenhouses is increasing in the U.S. with simultaneous changes in cultivars and postharvest needs.  Therefore, it is essential that our growers, packers and shippers be provided with the latest postharvest information to thrive in this highly competitive arena.  Limited research on the postharvest needs has necessitated the need for multistate research to gain an understanding of how these new cultivars and growing environments contribute to preservation of quality and prevention of decay at the physiological, molecular, genomic and genetic levels.

Severe limitations in the availability of labor have forced the fruit and vegetable industry to investigate greater use of mechanical harvesting and to adopt cultivars that are better adapted to mechanization. Many fruits and vegetables ripen at uneven rates. Thus, to maintain quality during marketing, fruit and vegetables are spot-picked to ensure harvest at the optimum stage of maturity. However, mechanical harvesting often necessitates a once-over harvest that requires the crop to be at a uniform stage of maturity to maximize yield and overall quality.  Crops that can be mechanically harvested for the fresh market include blueberries, cranberries, leafy crops and root crops, and for processing markets include grapes, prunes, oranges, peaches, cherries, jalapeno peppers, tomatoes and olives. Research is needed to determine the impact of mechanical harvesting on consumer acceptability and shelf-life.

Continued demand for reduced reliance on chemicals and for organic fruit is accompanied by a requirement for compatible storage technologies. Improvements in the use of nonchemical approaches for preventing storage scald of apples called dynamic controlled atmosphere (DCA) storage comes with risks and additional need for how to apply this method to new cultivars.  Highly sophisticated and sometimes risky postharvest storage technologies can be used in place of synthetic chemical controls, but uncertainties of their efficacies for the many different cultivars remain. Consumer demand for reduced Minimum Residue Levels is a significant driving factor to develop novel tools to maintain quality, reduce losses and mitigate toxins. Postharvest chemical applications remain an important method of preventing decay, but new nonchemical approaches have been developed to meet the needs of organic markets, and to minimize losses of fruit during storage and transport. New approaches to preventing losses come with potential risks whereas, generally recognized as safe (GRAS) chemical alternatives that prevent decay are largely untested. Testing of reduced-risk materials such as essential oils has shown effectiveness for controlling decay in some fruits, but large-scale application and impact on eating quality are untested. A better understanding of relationships between postharvest physiology of fruits and their susceptibility to physiological disorders and decay pathogens is essential for developing improved control measures and reducing chemical use.

New postharvest technologies that extend postharvest storage and shelf life need additional testing to confirm efficacy and identify risks for the different cultivars and types of produce.  Elevated CO₂ storage for raspberry can extend shelf-life, but research is needed to pinpoint optimum levels for the many cultivars and regions where raspberries are grown. Physiological disorders can be affected positively or negatively by these new storage technologies. For example, superficial scald of apples is inhibited by 1-MCP, DPA, and DCA storage, while other disorders, especially carbon dioxide-related ones tend to be increased by 1-MCP. The adoption of the plant growth regulator 1- MCP has altered the risks of long-term storage. These practices have increased greatly, largely in response to the need to maintain quality during storage and marketing. New application methods for in-carton application of 1-MCP such as sachets and incorporation into films have the potential to improve storage of other types of produce, but with many unanswered questions regarding efficacy.  

Growers increasingly rely on predictive tools and rapid tests to determine storage potential and relative susceptibility to postharvest losses.  Low-cost, rapid tests that measure postharvest characteristics and predict storage life or potential losses will allow growers to segregate high-risk produce and make informed decisions regarding storage duration. Peel analysis and the “passive” tests for predicting bitter pit in apples are examples of industry use of tests that were developed through collaborative research. Additional research is needed to understand how regional variation will impact application of these predictive tools.  Recent advances in understanding how loss of xylem function leads to bitter pit can be combined with these predictive tests to improve grower ability to prevent severe cases of this disorder.  Water loss, an important cause for quality loss in several fruits and vegetables can be measured using a low cost, nondestructive sealed chamber.  Wide scale testing is needed for its commercial application. Other predictive or rapid tests currently in development include rancidity in walnuts, surface moisture measurement on leafy vegetables for preventing decay and measuring aroma volatiles to predict chilling injury in peaches.  Knowing the status of produce going into storage is critical and can extend shelf life by a few days for highly perishable fruits and vegetables such as asparagus.  Storage and marketing practices such as “first in first out” logistics lead to losses because they do not consider the physiological maturity or any adverse preharvest and harvest conditions (high temperatures, poor cooling to remove field heat) that compromise shelf-life in different batches of harvested fruit and vegetables.  

Members of the NE1836 have collaborated to address the multiple disorders of apple cultivars that create complex storage requirements with the added need for predictive tools. In addition, recent advances in understanding the causes of disorders, mycotoxin abatement, and prevention will require multi-year testing and refinement in the many regions where they are now grown, and a coordinated effort to speed up real-world application of these new tools.

Expanding our knowledge on the harvest and storage of these specialty crops is critical to ongoing success in maintaining product quality of the fresh fruit and vegetable industries.  Sharing of knowledge, especially about application of new technologies, increases the probability of successful outcomes. The project involves postharvest scientists in the different geographical regions of the US and Canada, nearly all with extension/outreach responsibilities, thereby providing a powerful platform for development and extension of this knowledge.  

Research in this project will focus on these and other needs under the following objectives:

1. Enhance and/or adapt current handling, storage and postharvest practices/technologies to ensure high-quality products to increase their acceptability by consumers.  


2. Expand and translate fundamental plant biology to develop new storage technologies and plant materials that will enhance human nutrition and energy-efficient postharvest systems.


3. Advance our fundamental knowledge of host-pathogen-microbe interactions to maintain high-quality fruits and vegetables while reducing food loss and waste.

Importance of the Work 

Previous and current versions of this project (NE103, NE1018, NE1036, NE1336, NE1836) have made major contributions to the fresh fruit industry. These include industry adoption of innovative applied methods developed by the group, and basic research on postharvest problems such as bitter pit in apple, and chilling injury (CI) in pome and stone fruits. The efforts of this project have led to more effective control measures and new knowledge of the genetic and biochemical causes of the disorders and diseases. Other environmental impacts during fruit growth, especially elevated temperature and solar irradiation, are major contributors to annual postharvest losses in major production regions. By necessity, our collective work continues to assess the fundamental basis of these losses and to identify novel solutions to mitigate them in a changing regulatory environment. Nonchemical and reduced risk chemical methods of preventing losses have been studied/developed to extend storage life of highly perishable fruits such as berries. Studies on apples have continued to be a major focus with an emphasis on newly emerging problems such as increased CO₂ injury in storage and the ability to predict disorders that cause major losses for producers. 1-Methylcyclopropene (1-MCP), an ethylene action and ripening inhibitor has been used to maintain quality in storage of apple and is now being used for several other fruits and vegetables. New methods of application can potentially expand the use of the compound for the benefit of small-scale producers.  

This multistate project was traditionally focused on fruits, but with research on vegetables being conducted concurrently.  Research on vegetable storage practices is just as important and will benefit from the collective abilities of the group.  

Technical Feasibility of the Research and Advantages for Doing the Work as a Multistate Effort 

A goal of this group is to actively collaborate and exchange results from different systems to find solutions and to develop methods for rapid implementation to maintain industry profitability. We can accomplish this by conducting applied research in conjunction with a strong basic program while seeking to understand fruit/vegetable and pathogen physiology and biochemistry, particularly concerning responses to genetic differences among cultivars, and responses to technologies such as 1-MCP and modified/controlled atmosphere storage regimes. Many years have gone into selection of apple cultivars that maintain quality during long storage durations, but this type of coordinated effort is also needed to identify cultivars of other fruits and vegetables that may be better suited to the rigors of storage and marketing.  The researchers in this project have diverse skill sets that span several scientific fields and have an established track record for collaboration on projects across North America. 

Members of the group have the ability and expertise to study physiological, biochemical, and genetic/genomic basis of quality and development of storage disorders as well as fungal and bacterial pathology. Combined efforts have led to finding the causes of browning disorders in apple, quality loss and decay in blueberry and to predict or prevent such problems. Recent research has combined applied and basic approaches to identify underlying causes and potential solutions for such issues as apple bitter pit disorder, senescence associated genes (SAGS) in broccoli and lettuce, and changes in texture, peel elasticity and weight loss that predict shelf life in 60 blueberry cultivars. Furthermore, research that is based in many regions of the US and Canada contributes to the thorough study of many storage disorders that are impacted by local growing conditions so that cultural practices and storage conditions can be designed for regional needs.  The broad geographical distribution of the team in this project provides a unique opportunity by which responses of fruits and vegetables to a wide range of growing conditions can be studied and the difficulties posed by the intrinsic variability of a fruit and vegetable crop can be overcome. 

Members of the NE1836 have access to state-of-the-art facilities to conduct sensory and consumer testing.  Integration of sensory testing into postharvest research is needed to determine how production and storage practices impact consumer preferences since technical measurements do not encompass the full human experience of quality. The combination of new cultivars and changes in pre- and postharvest practices can influence consumer acceptance.  

As in the past, the current NE1836 members work as a research and extension team to solve industry problems and to provide rapid dissemination of research results that is greatly enhanced by the organization of a multistate project. The strong connections with producers that many members possess is a strength that ensures research is relevant and addresses the most pressing issues they face. The multistate project combines the respective strengths of each member for coordinated effort to investigate postharvest problems and to find much needed solutions to the specialty crop producers, both regionally and nationally.  

Impact 

The accomplishments of the NE1836 project include thorough postharvest evaluation of commercially important and emerging fruit cultivars, development of methodologies that enhance storage life, quality, and flavor and elucidation of mechanisms involved in flavor and storage disorder development in fruits. An example of impact resulting from our continued collaboration is the testing and development of a predictive test for bitter pit disorder for the Honeycrisp apple in various regions of the U.S. and Canada. This and other tests will allow producers to segregate at-risk produce to prevent their loss in storage.  The collaborative efforts of the NE1836 program have also generated key information that has provided solutions to storage of apples including the development of storage regimes that address CO₂ sensitivity in CA storage. Continued and wide-scale industry use of previous recommendations has been important for the economic success of Honeycrisp producers in the northeastern US. Successful transfer of information to researchers and industries is well integrated within the project and has been done via peer-reviewed publications, grower meetings, trade publications and websites. 

Most members of this project have strong extension/outreach programs associated with their research, and they have been successful at guiding practices of fruit growers. The North American apple industry, for instance, has directly and demonstrably benefitted from our research and extension efforts and now employs a protocol for dynamic CA storage for apples with reduced reliance on postharvest chemicals. NE1836 members have worked with the National Mango Board (NMB) to develop the handling practices such as for harvest maturity, temperature management, ripening and transport that are recommended to that industry. The same is true for many other crops such as stone fruits, strawberries, and tomatoes. The primary goals of our new project are to increase competitiveness for domestic fruit and vegetable production and preserve 'fresh-picked' sensory and nutritional quality, which in turn will increase the availability of locally grown and highly perishable fruit. The large increase in new cultivars has the potential to increase availability of highly perishable produce in the market, but this will depend on research that leads to cultivar selection that is appropriate to commercial harvesting practices and storage.  The overall impact of this project will be to improve the long-range health of the American populace via greater consumption of fresh fruits and vegetables, and to increase farm profitability at all levels of scale.

Annual reports are available on the NIMSS project website: NE1836: Improving Quality and Reducing Losses in Specialty Fruit Crops through Storage Technologies – NIMSS