[131] but for a wide variety of other products such as CI-sensitive Australian oranges [132] and zucchini
squash [133].
D. Anomalous Chilling Injuries
Although the basic principles described above apply to a very wide range of CI-sensitive crops, there
are other forms of low-temperature injury. Apples are susceptible to a wide range of temperature-re-
lated storage diseases that constitute a field of study outside this discussion, with one exception. Ap-
ples grown in North America generally tolerate storage temperatures close to freezing point (1–2°C).
Apples, even of the same variety, grown in Britain or Northern Europe cannot tolerate such low tem-
peratures, however, and formerly this disadvantage sharply limited their marketing season. Thus “con-
trolled atmosphere” (CA) storage (then called “gas storage”) was developed in England in the early
1930s. Initially, CA relied on raising carbon dioxide levels to suppress the respiratory climacteric. Later
practice favors lowering oxygen to just above a level that would induce anaerobiosis [134]. Such CA
storage has made possible the year-round marketing of apples. I have seen no explanation of why ap-
ples from the two sides of the Atlantic should respond so differently to storage temperatures, but the
effect is real. Similar differences in response to temperature exist for other products from widely
dispersed growing areas. For example, Valencia oranges grown in California and Australia are suscep-
tible to chilling injury during long-term storage and shipment, whereas those from Florida and Brazil
are not.
Potatoes are subject to an important temperature-related storage disorder that can be very costly for
manufacturers of such products as potato chips and frozen ready-to-cook french fries. At temperatures be-
low about 5°C, potatoes undergo reversible starch-sugar hydrolysis, which causes potato products to
darken when the sugar caramelizes upon exposure to high cooking temperatures. Such discolored prod-
ucts are discounted or are unsalable. If chilled potatoes are held at room temperature for several days,
however, the reverse (condensation) reaction will convert the sugar back to starch.
Another anomalous postharvest “chilling” hazard is physical and pathological rather than physio-
logical. Some products, such as leafy vegetables, celery, and peaches, benefit from “hydro cooling” in re-
frigerated water. A marked exception is the tomato, which should never be immersed in water cooler than
product temperature. The skin of the tomato is virtually impervious; gas exchange is through the porous
stem scar. (A drop of molten wax on the stem scar of a green tomato will turn it into a self-contained “con-
trolled atmosphere storage unit,” thereby greatly delaying ripening.) When a warm tomato is immersed
in cool water, contraction of its internal atmosphere draws nonsterile water in through the porous stem
scar, with consequent greatly increased decay hazard [135]. The same problem obviously is possible with
other products.
IV. GLOBAL TEMPERATURE CHANGES
Since this chapter was first written, consideration of global temperature changes has become an interna-
tional concern of quite extraordinary magnitude. Despite objections from many reputable scientists, both
individually [136] and collectively [137], this has generated a popular media-driven controversy with
consequent proposals for economically disastrous measures to reduce emissions of CO 2 in order to main-
tain the status quo antefor worldwide temperatures [138,139].
Apart from the notable disregard for scientific findings in many fields of endeavor, this is hubris in
the classical Greek sense of arrogance that would challenge the gods.
Nearly a century ago, Svante Arrhenius showed that CO 2 is a “greenhouse gas” that transmits short-
wave radiation but impedes long-wave (heat) radiation. However, any possibly deleterious effects on
global temperatures from mankind’s generation of CO 2 are very minor in comparison with the sun’s dom-
inant effects, short term through sunspots [140–143] and longer term due to irregularities in its axis
[144,145]. Added to which is a gradual, but inexorable, change in the tilt of earth’s own axis [146] and
the precession of the equinoxes that so puzzled ancient astronomers [147].
Moreover, the climatic influence of the sun involves other variables, some as obvious as solar flares
[148,149], others as arcane as very minor irregularities in its orbit that mathematical astronomers are only
now beginning to explain.
TEMPERATURE IN THE PHYSIOLOGY OF CROP PLANTS 29