1) Hokkaido National Agric. Exp. Station, Hitsujigaoka, Sapporo, 004 Japan
2) Research Institute for Bioresources, Okayama University, Kurashiki, 710 Japan
Eleven isogenic pairs differing in grain size were derived from a cross, Shin 2 x Fusayoshi, by selecting heterozygotes in each of F2 to F9 generations. Cool weather at the young microspore stage is known to be critical in causing infertility. The isogenic pairs were subjected to a 12 deg C treatment for three to five days at this stage.
Lines with larger grain had larger anthers than their counterparts with smaller grain. Their anthers were 1.31 times in length and 1.4 times in volume as large as, and contained 1.61 times as many pollen grains as those of small-grained counterparts. They also showed a lower rate of pollen degeneration after a chilling treatment at 12 deg C than the small-grained lines (Table 1).
For evaluating cold torelance of different lines, fertility index is used which is given by
sin-1SQRT(% fertility in chilled plot) (Satake 1986). _______________________________________ sin-1SQRT(% fertility in control)The small-grained isogenic lines had an appreciable cold tolerance, their mean index reaching 67% (Table 2). But their large-grained counterparts showed much higher tolerance as shown by an index of 92%, which was higher than that of most tolerant variety, Hayayuki.
The high tolerance of large-grained lines is due to their large number of
pollen grains per anther and low rate of pollen degeneration after chilling
as
compared with their small-grained counterparts. Varietal comparison has
shown that cold-tolerant varieties are characterized by many pollen grains
and low degeneration rates after chilling (Satake 1986). The Lk-f gene, for
long grain derived from Fusayoshi, affects various agronomic characters
(Takeda et al. 1987). It also seems to affect the traits conferring cold
tolerance.
References
Satake, T., 1986. Anther length as indicator to estimate chilling tolerance
at the booting stage in rice plants. In B. Napompeth and S. Subhadrabandhu
(eds.), New Frontiers in Breeding Researches, p. 221-228. Kesetsart
University, Bangkok.
Takeda, K., K. Saito, K. Yamazaki and T. Mikami, 1987. Environmental
response of yielding capacity in isogenic lines for grain size of rice. Jpn.
J. Breed. 37: 309-317. (Japanese/English)
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Character Small Large Ratio
(Large/small)
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Anther,
Length (mm) 2.04 2.68 1.31
Breadth (mm) 0.447 0.462 1.03
Volume (mm3) 0.409 0.573 1.40
Pollen grain,
Number/anther 978 1573 1.61
Diameter (micron) 48.9 49.1 1.00
Pollen degeneration(%),
Control(26/20 deg)6a
16.8 15.6 0.93
Chilled(12 degC)3 daysb
39.6 30.1 0.76
Chilled(12 degC)5 daysc
56.6 31.6 0.56
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a-Mean for 11 lines
b-Mean for 5 lines
c-Mean for 4 lines
Table 2. Fertility index and pollen number per anther in isogenic pairs and
other Japonica varieties after chilling treatment
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Fertility index(%) Pollen number/anthera
Line/variety Chilled: % of control
==================== =======================
3 days 5 days Control 3 days 5 days
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Large grain 92 64 1573 85 79
Small grain 67 33 978 72 50
Hayayuki 82 1036 81
Kitaake 74 1177 77
Somewake 70 1655 80
Norin 20 49 820 52
Reimei 47 699 59
Toyohikari 38 647 47
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a-Anther length was reduced to 90 to 96% after chilling treatment.