Vergara - 1976 - Physiological and morphological adaptability of ri

PHYTUIRONS IN AGRICULTURAL RESEARCH
IN'TERAC'I'ING COMPONENTS OF CLIMATE:
SOh/[E EFFECTS OF NIGHT TEMPERATURE
Early experiments in the Pasadena phytotron led Went to suggest that many
plants are favored in their growth and development by night temperatures lower
than the daytime optimum. and by a diurnal cycle in temperature, which he
referred to as thermoperiodism. The Solanaceae provided several striking examples
of lower optimum night temperatures for grouith in tobacco and peppers.
tuberization in potatoes. and fruit set in tomatoes (Went, 1957). He showed that
yield of tomatoes could be limited by poor fruit set when night temperatures
were high. and that varieties differed considerably in their tolerance of high and
low night temperatures at this stage. Controlled environments in the Earhart
Laboratory xvere therefore used on a considerable scale to identify tomatoes
tolerant to high night temperature at fruit set (a Philippine cultivar. in fact) for
use in a plant breeding program. and to select progeny‘ for that characteristic,
leading to the production of new varieties for several areas in southeni USA.
Subsequent experiments in other phytotrtms have shown that, for many
plants. optimum night temperatures need not be lOWBT than those by day. and
that a diurnal change in temperature is not essential for maximum growth. No
evidence was found of a requirement for therrnoperiodicity during growth of
sugar cane (Glasziou et al.. 1965) or for tlovt-‘ering in peanuts (Wood. 1968).
Even with tobacco, Hopkinson (1967) could find no evidence of a need for
lovi-‘er night temperatures at any stage of growth in either USA or Australian
cultivars.
To some extent the need for cooler nights may depend on light intensity
during the day‘. being less pronounced when intensities are high and photosynthesis
less limiting to growth. Similarly. there can be strong interactions between
night temperature and day length. particularly in the control of tlovxering in
many crops. Tuberization in some potato eultivars may be indifferent to day
length at low night temperatures, but take place only on short day's when nights
are wann (Went. 1957). Likewise in some cultivars of cotton, such as Pima.
flowering is far more delayed on long days than on short days when night
temperature is high (Moraghan et al, 1968). At moderately high temperatures,
citrus will flower only on short day's. whereas at low temperatures it flowers in
all day lengths (Moss. 1969). In other short-day plants, however. floyvering may
be inhibited by cool nights. This is so with [R8 rice. for example (Owen. 1972).
thereby‘ limiting its use during winter in some subtropical areas such as northern
Australia.
Given the great variety of interactions between night temperature and day
length among crops. and the near impossibility’ of unravelling these in field
experiments. it is clear that ph_vtotrons can play a major role in clarifying the
nature of such bottlenecks to crop adaptation. and in reproducibly providing
critical conditions for the selection of plants insensitive to these bottlenecks, as
in the selection by plant breeders of the Campbell Soup Company; of new tomato
cultivars able to set abundant fruit in areas with high night temperatures.