Yoshida - 1981 - Fundamentals of Rice Crop Science

206 FUNDAMENTALS OF RICE CROP SCIENCE
The growth efficiency indicates how much of the substrate is converted into the
constituents of new tissues. It follows that (1 - GE) is consumed for respiration to
produce the energy required for the biosynthesis of new tissues.
When germination occurs in darkness, seedling growth depends entirely on the
seed reserve. The growth efficiency can be calculated for such growth:
GE =
W 2 – W 1 –
GR
–
GR
S 1 – S 2 S 1 – S 2 D S
(5.15)
where W 1 and W 2 and S 1 and S 2 are the dry weights of seedlings and seeds at time t 1
and t 2 , respectively.
The growth rate is strongly affected by temperature but growth efficiency
remains about 56–58% for all 3 temperatures (Table 5.3). In other words, about
60% of the substrate is used for seedling constituents and about 40% is consumed
by respiration. Similar experiments have been conducted for different plant
species and are well documented (Penning de Vries 1972). The relative yields of
germinating seeds for 9 species range from 0.48 g/g for Vigna sesquipedalis to
0.96 g/g for groundnut. The growth efficiency or relative yield varies with the
chemical composition of seeds and of newly formed tissues because the energy
content is different among constituents such as carbohydrates, proteins, and lipids.
The concept of growth efficiency is applied to growing plants until maturity, and to
the growth of individual organs such as leaves or panicles (Yamaguchi 1978).
Some important findings from these studies may be summarized:
• When active vegetative growth is taking place, growth efficiency is high,
centering around 60–65%.
• Growth efficiency drops sharply after the milky stage of ripening.
• The growth efficiency of panicles is high (65–75%).
Respiration may be conveniently divided into respiration necessary for growth
and that for maintenance (this will be discussed in more detail in the succeeding
section). Thus, equation 5.14 can be rewritten as:
GE =
GR = GR
GR + R GR + Rg + Rm
(5.16)
Table 5.3. Effect of temperature on the growth efficiency of
Peta seedings germinated in the dark.
a
Temperature Wt of seedlings b Growth efficiency
(°C) (mg/plant) (%)
21
26
32
4.5
8.3
10.6
56
58
57
a Tanaka and Yamaguchi (1968). b At the end of 10-day growth.