Vergara - 1976 - Physiological and morphological adaptability of ri

14 (ZLIh-L-XTE ant: RICE
essential that the operative factor be identified. In field experiments this may
require experimentation and analysis of heroic proportions, with little certainty
of success. but experiments under controlled environments may readily clarify
the problem.
As an example. let us consider the effects of radiation and temperature on
grain filling in cereals. For most cereals. grain growth is largely dependent on
concurrent photosynthesis rather than on reserves stored earlier in the life cycle,
so that environmental influences on the rate and duration of grain growth are
major determinants of the extent to which final yield approaches the potential
yield determined earlier in the life cycle.
Although photosynthesis in wheat plants and crops responds to increasing
light intensity up to levels approaching full sunlight. the rate of grain growth
does not increase in a parallel manner. being unaffected by incident radiation
except at extremely low daily inputs (Fig. l). At higher radiation levels. therefore.
the rate of grain growth is presumably not limited by the rate of photosynthesis.
but by the capacity for carbohydrate transport to the grain or starch
synthesis in it. Temperature influences the rate of grain growth to some extent.
but not markedly’. Consequently‘, the duration of grain growth becomes a major
determinant of yield. Field experiments in Engiand and Mexico indicated a
curvilinear relation between incident radiation and the duration of grain filling,
Growth rate t mq-qroirW-dny" l
2O
'
I’
v I
V v0'
15- 9
I‘
'°'v
zmsa:
OSunmnrqrown
Ivlimerquwn
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05»-
QT t 1 1 1
O 5O DO I50 200 250
Daily radiation
(cot - cm'2- any“ t
l. Effect of incident visible radiation on the rate of
growth of wheat grains at 2l"»‘l6“‘C. under artificial light
( I) or in glasshouses during winter (I) or summer (I )
(Solield. Evans. and Wardlaw: I974).