Yoshida - 1981 - Fundamentals of Rice Crop Science

54 FUNDAMENTALS OF RICE CROP SCIENCE
1.44. Examination of a young panicle by removing leaf sheaths
(adapted from Hoshikawa 1975).
b. Length of young panicle. The young panicle can be seen with the naked eye
for the first time at the early stage of differentiation of the secondary rachisbranches.
The panicle at that time is about 0.5–0.9 mm long. Table 1.14 shows the
relationship between panicle length and developmental stage. A panicle that has
grown 1.0 mm, has already entered the spikelet differentiation stage.
The young panicle is usually examined in the following way. Starting at about
30 days before the estimated heading date, several large tillers from 2 or 3
average-sized hills are cut from the plant’s base every 3 days. Since the leaf
sheaths envelop the culm very firmly, a sewing needle is used to split and strip the
sheaths one by one (Fig. 1.44). The flag leaf, recognized as a little white cone,
should be stripped off carefully with the tip of the needle. Inside is the young
panicle. At the 1-mm panicle stage (panicle initiation), the young panicle has
white hairs and is easily distinguished from a leaf. A magnifying glass makes the
examination easier.
The difference between the initiation of panicle primordia and the agronomic
panicle initiation stage is about 7–10 days.
c. Distance between the auricles of the frag leaf and the penultimate leaf. The
distance between the flag leaf auricle and the penultimate leaf (2nd leaf) auricle
provides a useful means by which to identify the reduction division stage, one of
the stages most vulnerable to environmental stresses.
When the flag leaf auricle has emerged from the sheath of the penultimate leaf
and is located above the penultimate leaf auricle, the distance is given a plus ( + )
sign. When the flag leaf auricle is positioned at the same height as that of the