Yoshida - 1981 - Fundamentals of Rice Crop Science

238 FUNDAMENTALS OF RICE CROP SCIENCE
anthesis may cause high percentages of sterility.
f. Strong winds. Strong winds can cause sterility at flowering by desiccating the
plant, impair grain growth by causing mechanical damage to the grain surface,
and cause the crop to lodge. A hot, dry air called foehn frequently causes white
head, particularly when it occurs during panicle exsertion (Hitaka and Ozawa
1970). Strong winds from the coast often contain brackish water and cause
sterility.
g. Soil salinity. High salinity in the soil causes a high percentage of sterility.
h. Drought. Drought at flowering often causes high percentages of sterility in
rainfed lowland and upland rices.
7.3.4. Grain weight
Grain size is rigidly controlled by hull size. When a piece of vinyl film was placed
inside the palea and lemma at anthesis, grain filling proceeded normally but the
grain weight decreased from 22 mg (untreated) to 18 mg (treated) (Matsushima
1970).
Under most conditions, the 1,000-grain weight of field crops is a very stable
varietal character (see Table 2.11, Fig. 2.3, and Soga and Nozaki 1957). The CV
of 1,000-grain weight ranged from 2.2 to 4.4%, with a mean value of 3.3% for
data collected from 9 varieties for 19 years at Konosu, Japan. The mean CVs of
panicle number and yield were 12.4% and 14.1%, respectively (Matsushima
1970).
Heavy shading before heading changed the hull size and decreased 1,000-grain
weight from about 26 to 21 g (Matsushima 1970). As will be discussed later, CO 2
enrichment also affects the grain weight to some extent.
7.4. Frequency curve of individual grain weights of Koshiji-wase at
30 days after heading (drawn from data of Nakayama 1969).