RJ. zhang1, S. ming1, C.W. Xu1, L.S. yang1, Y.S. bai1, C.Q. sun2 and X.K. wanc2
2) China Agricultural University, Beijing, 100094 China
Twelve parents (Table 1) were crossed according to NC II design and thirty-two F hybrids were obtained. The F1 s, their parents, and CK Shanyou 63 were grown in Hefei in midseason in 1995, in three replications of a randomized block design. Twelve parents were classified by Cheng's index (classification index of Indica and Japonica rice. Cheng 1993). Eight characters, i.e., days to heading, plant height, panicle length, number of effective tillers, number of grains per panicle, seed set, 1000-grain weight and grain yield per plant were observed in F1 s and parents.
The effects of female, male and their interaction on hybrids were estimated in terms of % variance. As shown in Table 2, the male effect was greater than female and interaction effects in all characters except for 1000-grain weight in which female effect was greater than the sum of male and interaction effect. Therefore, characters carried by R-line (male parent) was extremely important in breeding of Japonica Two-line hybrid rice.
Relative heterosis (RH) and standard heterosis (SH) were also estimated (Table 3). Positive crosses outnumbered negative crosses in all characters for RH, while only in three characters for SH. It was found that degree of heterosis remarkably diferred among crosses. In number of grains per panicle, heterosis ranged from -1.1% to 107.9% with a mean 33.5% in RH, and from -17.1% to 82.7% with a mean 23.1% in SH. In grain yield, SH
Table 1. Cheng's index and specific property of parents | ||
Parents | Cheng's index1) | Specific property2) |
4008s | 22(J) | WCV PGMS |
8087s | 21(J) | PGMS |
7001s | 21(J) | PGMS |
80-4B | 22(J) | B-line |
Cbao | 19(J) | R-line |
HP121 | 16 (J') | WCV R-line |
HP214 | 15 (J?) | WCV R-line |
PA64 | 4(I) | WCV R-line |
LH422 | 16 (J?) | WCV R-line |
YHIOI | 14 (J?) | WCV |
02428 | 20 (J) | WCV |
Neken 1 | 22(J) | WGV |
2) WCV: wide compatible variety, PGMS: photoperiod sensitive genie male sterile, B-line: maintainer, R-line: restorer.
Table 3. Comparison of degree of heterosis among different cross groups | |||||||||||||
Characters | Relative heterosis1) | Average of RH | Standard heterosis2) | Average of SH | |||||||||
P3) | N4) | A5) | J X J | J X J? | J X I | P | N | A | J X J | J X J? | J X I | ||
Days to heading | 30 | 2 | 8.8 | 5.1 | 7.3 | 22.6 | 32 | 0 | 10.2 | 7.4 | 9.4 | 22.3 | |
Plant height | 32 | 0 | 30.1 | 21.3 | 33.9 | 41.8 | 8 | 24 | -6.0 | -7.9 | -5.7 | -1.1 | |
Panicle length | 32 | 0 | 15.1 | 11.7 | 14.0 | 30.3 | 2 | 30 | -11.9 | -16.1 | -10.8 | -4.1 | |
Effective tillers | 22 | 10 | 9.1 | 1.8 | 9.7 | 28.4 | 17 | 15 | 4.0 | -0.3 | 0.1 | 32.7 | |
Grains per panicle | 31 | 1 | 33.5 | 22.7 | 33.6 | 65.2 | 28 | 4 | 23.1 | 6.0 | 36.3 | 21.8 | |
Seed set | 3 | 29 | -7.4 | -5.4 | -8.4 | -9.9 | |||||||
1000-grain weight | 0 | 32 | -16.0 | -15.7 | -15.8 | -17.5 | |||||||
Grain yield | 12 | 20 | -2.4 | -17.0 | 3.5 | 18.0 |
5) A: Average of all crosses.
36 Rice Genetics Newsletter Vol. 14
Fig. 1. Relationship between relative heterosis (RH) and the difference in Cheng's index between
Next, heterosis was compared among three cross-combination groups; J x J, J x F, and J x 1. In general, heterosis showed an order of J x J < J x J' <J x I, indicating that remotely related parents showed high degree of heterosis as expected. The differences in Cheng's index between the two parents were significantly correlated with respective RH (r = 0.52-0.72). The cases with number of effective tillers and number of grains per panicle are shown in Fig. 1. In SH, however, number of grains per panicle showed J x J < J x J' > J x I, suggesting that a large number of grains per panicle which is one of the important yielding components is expected in J x J ' crosses. But seed set and 1000-grain weight showed a trend of J x J > J x J ' > J x 1. The above results suggest that J x J ' cross may contribute to increase number of spikelets per panicle but all spikelets are not always fully filled.
Japonica PGMS line 4008s, Indica R-line PA64 and Japonica-like WCV YH101 had higher G.C.A. (general combining ability) value of grain yield. Hybrids with high S.C.A. (special combining ability) value of grain yield were 80-4B/YH101, 80-4B/02428 and 4008s/HP214. The difference in Cheng's index between the two parents had very little effect on S.C.A. values of seven characters, correlation coefficients ranging from -0.02 to 0.10 except for effective tillers (-0.36).
Cheng Kan-Sheng, 1993. Discrimination of Indica and Japonica subspecies in Asian cultivated rice. Yunnan