ABSTRACT
CONTENTS 8.1 Introduction ........................................................................................................................ 160 8.2 Unifying Physiological Concept of Disorder Development ........................................ 161
8.2.1 Ethylene-Related Response.................................................................................... 161 8.2.2 Oxidative Response ................................................................................................ 163 8.2.3 Defense against Oxidative Response ................................................................... 164 8.2.4 Enzymatic Browning .............................................................................................. 164
8.3 Disorders Occurring in Air Storage that Are Alleviated or Aggravated by CA=MA............................................................................................... 165 8.3.1 Low-Temperature or Chilling Injury ................................................................... 165
8.3.1.1 Symptoms of Chilling Injury ................................................................... 165 8.3.1.2 Effect of CA=MA ....................................................................................... 166 8.3.1.3 Physiological Background........................................................................ 167 8.3.1.4 Superficial or Storage Scald ..................................................................... 168
8.3.2 Ethylene Injury ........................................................................................................ 169 8.3.3 Senescence-Related Disorders ............................................................................... 169
8.3.3.1 Internal Browning in Apple and Pear.................................................... 170 8.3.3.2 Flesh Bleeding in Peach ............................................................................ 171 8.3.3.3 Pericarp Browning..................................................................................... 171
8.3.4 Pitting Disorders in Apple and Pear.................................................................... 172 8.3.5 Other Disorders....................................................................................................... 172
8.4 Disorders Not Known to Occur or Rarely Occur in Air Storage and Induced by CA=MA .................................................................................................. 173 8.4.1 Blocking Ripening-Related Quality Changes ..................................................... 173 8.4.2 Cortical Browning in Apple and Pear ................................................................. 173 8.4.3 Carbon Dioxide Injury ........................................................................................... 175 8.4.4 Skin Disorders ......................................................................................................... 176 8.4.5 Other Disorders....................................................................................................... 176
8.5 Methods to Avoid CA=MA-Related Disorders ............................................................. 176 8.5.1 Preharvest Factors and Maturity .......................................................................... 176 8.5.2 Chlorophyll .............................................................................................................. 177 8.5.3 Acclimation .............................................................................................................. 177 8.5.4 General Adaptation Syndrome............................................................................. 177 8.5.5 Antioxidant Application ........................................................................................ 178
8.5.6 1-MCP Treatment.................................................................................................... 178 8.5.7 Dynamic Control Atmosphere.............................................................................. 179
8.6 Conclusions and Future Research Needs....................................................................... 179 References.................................................................................................................................... 180
Controlled and modified atmosphere storage of fruits and vegetables is employed to maintain the highest level of fruit and vegetable quality for relatively long periods of time by slowing down the respiration-related processes of senescence, and by providing environments unfavorable for pathogen or insect survival (low O2 and=or high CO2 at low, but above-freezing temperatures) (Prange and DeLong, 2006). Generally speaking, the capacity for controlled atmosphere (CA) or modified atmosphere (MA) storage gives unprecedented advantages to food-producing nations in securing long-term food supply for regional and national populations, supplier-controlled export options, and a level of food quality that is historically unparalleled. In light of these major advantages, CA and MA technologies are industry standards in developed countries that grow crops suitably stored in these environments. With MA in particular, crops can be sealed in the MA packaging immediately following harvest, shipped to ports of destination, and be ready for sale without significant loss of quality. Hence, MA (and in some cases, CA) technology is not necessarily confined to a singular site for the duration of the established storage atmosphere. While the benefits of crop storage in CA and MA environments are many, a major
concern does exist for the potential loss of crop quality and related economic revenue through the development of storage disorders, which are defined as areas of tissue degradation not directly caused by insects, diseases, or mechanical damage. At least five categories of physiological disorders exist, and are related to (1) nutrition, (2) temperature (usually low), (3) respiration, (4) senescence, and (5) miscellaneous (Wills et al., 2007). Each of these disorder types can be alleviated, exacerbated, or induced by CA or MA environments. Thus, it is imperative for storage physiologists generally, and storage operators specifically, to be familiar with the potential for disorder development in those crops being managed over the duration of CA or MA storage. An additional problem is that symptom description can be very similar for different physiological disorders and it is often very difficult to distinguish amongst them. It is one thing to identify the symptoms but agreement on what the disorder is and identifying the underlying mechanism based on the symptoms can be difficult, especially when working with a disorder that may vary amongst different cultivars or different species. The sensitivity to many disorders is determined by cultivar and=or preharvest condi-
tions, which include genetic factors, cultural practices, and climatic factors (Watkins and Rao, 2003). Cultural practices and their influence on disorder development have been studied extensively and include rootstock, soil management, nutrition, training and pruning practices, crop load, application of growth regulators, and final product size (Emongor et al., 1994; Ferguson et al., 1999; Kruger and Truter, 2003). Climatic factors such as temperature, solar irradiance, and soil and water characteristics play an important role in the regional propensities for disorder development and in season-to-season variation within a particular region (Ferguson et al., 1999; Lau, 1998; Park et al., 1997; Paull and Reyes, 1996; Thomai et al., 1998). For some species (specifically apples, pears, peaches, and nectarines) and some of their disorders, cultivar sensitivity may be well
known, as well as the cultural and climatic circumstances that increase this sensitivity. For other species and disorders, this is still speculative. The identification of disorder symptoms is often difficult because some disorders
occur simultaneous and thus show a multitude of symptoms (e.g., superficial scald and internal breakdown, watercore, and internal breakdown). Also, the terminology used to describe symptom expression is not standardized across all growing regions. Along with the problem of correct symptom diagnosis is the need to know the preharvest and storage conditions (e.g., temperature, atmosphere, duration) that exacerbate disorder expression. This knowledge is helpful for correct disorder identification and for possible amelioration. For specific symptom description as well as the storage temperatures and duration associated with specific disorders for individual horticultural crops, several good references are the USDA Agriculture Handbook Number 66 (Gross et al., 2004), the postharvest produce fact sheets (UC Davis, 2008), the apple disorder guide (Jones et al., 2007), and AAFC publication 1737=E (Meheriuk et al., 1994). Generally speaking, there are at least three levels of investigation when attempting
to understand the development of postharvest physiological disorders: (1) identification of the preharvest conditions that predispose a fruit or vegetable towards disorder development; (2) identification of symptoms and the physiological processes that alleviate or exacerbate symptoms; and (3) research to determine the underlying mechanisms, the initiating process, and the first triggering events. Much of the emphasis in this chapter will be on these last two levels, emphasizing disorders that are (1) alleviated or exacerbated and (2) induced by CA and MA environments.
