20

        Itsuro Takamure¹ , Mei-chu Hong² and Toshiro Kinoshita¹

          1) Plant Breeding Institute, Faculty of Agriculture, Hokkaido University, Sapporo, 060 Japan
           2) Taichung District Agricultural Improvement Station, Tatsuen Hsiang, Changhua, Taiwan, O.R.C.

    Variation in grain size is important for rice breeding. Several major genes for large and small grains are already reported such as Lk-f (Takeda and Saito 1980), lk-i (Takamure 1994) and Mi (Takeda and Saito 1977).
    In this report, two kinds of spontaneous mutants (N-179, N-182) possessing long grains were found in a breeding material, Nagayama 77402 at Kamikawa Agricultural Experiment Station. One of them, N-179 is characterized by long grain with low seed setting and reduced spikelet number. In the F₂ and F₃ populations from the cross, N-179 X A-58 (normal grain), segregants for
normal and long grains based on a single recessive gene were found and the gene was tentatively designated as lk-l(t) (Table 1). Further, allelism tests indicated that /k:-/(t) is non-allelic to Lk-f and lk-i, respectively.
    N-182 is another mutant for long grain and accompanied with reduced panicle and spikelet numbers. In the crosses between ws-5 (normal grain) and N-182, the F₂ and F₃analyses indicated the segregation for an incomplete dominant gene, designated as Lk-2(t) (Table 1). Non-allelic relation of Lk-2(t) to Lk-f was also demonstrated. It was found that Lk-2 (t) is linked with sp belonging to chromosome 11, with a recombination value of 19% in coupling phase.
    Independent relations and additive genie effects on spikelet length were recognized between lk-l(t) and Lk-f, and between lk-l (t) and Mi, respectively (Tables 2 and 3).
    According to the combinations of various genes for grain size, it is possible to enlarge the variability of grain characters in rice.

Table 1. F₂ segregations and mean values of F₂ genotypes for grain size, F₂genotypes were
estimated from progeny tests in F₃ lines
Cross: N-179XA-58

Table 2. Mean spikelet length and width in the nine genotypes of F₂ plants estimated
from F₃ progeny tests in the cross, N-179X Fusayoshi, showing the independent relation
between lk-l (t) and Lk-f (Fusayoshi long grain)

Table 3. Mean spikelet length and width in the nine genotypes of F₂
plants estimated from F₃progeny tests in the cross, N-179 X H-343,
showing independent relation between lk-1(t) and Mi (Minute)

Takamure, I., 1994. Genetic studies on several mutants related to morphological and physiological characters in
        rice. Mem. Fac. Agr. Hokkaido Univ. 19: 151-202. (in Japanese with English summary)
Takeda, K. and K. Saito, 1977. The inheritance and character expression of the minute gene derived from a
        rice genetic tester "Minute". Bull. Fac. Agr. Hirosaki Univ. 27: 1-29. (in Japanese with English summary)
Takeda, K. and K. Saito, 1980. Major genes controlling grain size of rice. Japan. J. Breed. 30: 280-283. (in
        Japanese)

Estimated genotype in F2 plants	Goodness of fit
Estimated genotype in F2 plants	++	+lk-1(t)	lk-l(t)lk-1(t)	Total	X²(1:2:1)	P
No. of F3 lines	17	46	13	76	3.79	0.1-0.2
Spikelet length	6.78 ± 0.90 .a) (100).b)	6.82±0.27 (101)	7.45 ± 0.25 (110)
Spikelet width	3.28 ± 0.08 (100)	3.28±0.11 (100)	3.35±0.13 (102)
Cross: ws-5XN-182
Estimated genotype in F2 plants	Goodness of fit
Estimated genotype in F2 plants	Lk-2(t)Lk-2(t)	Lk-2(t) +	++	Total	X²(1:2:1)	P
No. of f3 lines	23	43	16	82	1.39	0.4-0.5
Spikelet length	7.14±0.17 (110)	6.94±0.24 (107)	6.47 ± 0.17 (100)
Spikelet width	3.55±0.10 (106)	3.55±0.10 (106)	3.35±0.12 (100)

Estimated genotype in F₂plants		No. of F₃, lines	Spikelet length	Spikelet width
++	++	7	6.73 ± 0.15.a)	3.51±0.10
			(100)"'	(100)
++	+lk-l(t)	13	6.87±0.17	3.51+0.12
			(102)	(100)
+ +	lk-1(t) lk-l(t)	4	7.46 ± 0.14	3.59±0.11
			(111)	(102)
Lk-fr	+ +	17	7.55+0.24	3.59 +- 0.13
			(112)	(102)
Lk-f+	+lk-l(t)	20	7.60 ± 0.17	3.63±0.11
			(113)	Lk-f+

Lk-f+	lk-1(t) lk-l(t)	6	8.27 ± 0.22	3.65 ± 0.17
			(123)	(104)
Lk-fLk-f	+ +	2	8.09±0.21	3.79±0.16
			(120)	(108)
Lk-fLk-f	+lk-l(t)	6	8.24 ± 0.26	3.71± 0.22
			(122)	(106)
Lk-fLk-f	1k-1(t) lk-I(t)	4	8.92±0.21	3.70±0.04
			(133)	(105)
	Total	79

Estimated genotype in F₂ plants		No. of F₃, lines	Spikelet length	Spikelet width
Mi Mi	++	4	4.51±0.10 .a)	3.47 ± 0.04
			( 74).b)	( 93)
Mi Mi	+ lk-1(t)	6	4.57 ± 0.12	3.41±0.15
			( 75)	( 92)
Mi Mi	lk-I(t) lk-l(t)	3	5.38±0.23	3.40±0.17
			( 89)	( 91)
Mi Mi	++	15	5.08 ± 0.15	3.50 ± 0.09
			( 84)	( 94)
Mi +	+ lk-l(t)	23	5.21+0.25	3.54±0.08
			( 86)	( 95)
Mi +	/k-/(t) lk-/(t)	10	5.93 ± 0.17	3.61±0.10
			( 98)	( 97)
++	++	4	6.06 ± 0.28	3.72±0.11
			(100)	(100)
++	+lk-l(t)	14	6.17±0.27	3.57 ± 0.10
			(102)	( 96)
++	lk-l(t) lk-I(t)	3	6.93 ± 0.09	3.55±0.17
			(114)	( 95)
	Total	82