GENETIC IMPROVEMENT OF WHEAT YIELD POTENTIAL AND ADAPTATION IN CHINA - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 190

Table 6. Frequency (%) of Rht-B1b , Rht-D1b and Rht8 genes in Chinese cultivars in
various regions

Gene Zone I Zone II Zone III Zone V Total

Rht-B1b

22.9 27.6 45.0 9.1 24.5

Rht-D1b

34.3 60.3 20.0 39.4 45.5

Rht8

40.0 49.1 30.0 48.5 46.8

Numbers of cultivars tested in Zone I, II, III and V were 35, 116, 20 and 33, respectively.

U TILIZATION OF D WARFING G ENES

The improvement of grain yield and HI, largely due to a reduction in plant height ( r
between HI and plant height ranged from -0.59 to -0.88) (Table 5), are closely associated with
incorporation of dwarfing genes into the leading cultivars (Zhang et al., 2006; Zhou et al.,
2007a and b). Reduced height genes Rht-B1b , Rht-D1b and Rht 8 of 220 cultivars from four
main autumn-sown wheat regions in China were detected by molecular markers (Zhang et al.,
2006). They include landmark landraces, leading cultivars and core parents used in various
breeding programs from 1950s to the present, and introductions used both in production and
breeding, and therefore provide valuable information on varietal replacements and evolution
in diverse environments (Table 6). Overall, Rht-D1b and Rht 8 showed similar frequency in
Chinese wheats, with 45.5% and 46.8%, respectively. The presence of Rht-B1b is much
lower, with a frequency of 24.5%. However, notable difference was observed in various
regions. For example, Rht-B1b is quite high in Zone III with 45.0%, and it is only with 9.1%
in Zone V. Rht-D1b showed high frequency in Zone II, with 60.3%, while Rht 8 has high
frequency in Zones I, II, and V.
Twenty-one genotypes with only Rht 8 gene were presented in cultivars released before
1970s in Zone II or current cultivars in Zones I, III, and V. This is agreeable with general
observation that plant height is much shorter in Zone II in comparison with three other
regions (Zhuang, 2003). The distribution of both Rht-B1b and Rht-D1b genes shows a
regional pattern or close linked with various institutional breeding activities. Forty varieties
(six from Beijing, two from Hebei, five from Shandong, 19 from Henan, two from Shaanxi,
one from Anhui, one from Hubei, three from Sichuan, and one from Yunnan) contain both
Rht-D1b and Rht 8 genes. Twenty-eight genotypes (two from Beijing, five from Hebei, one
from Shandong, three from Henan, six from Shaanxi, five from Shanxi, four from Jiangsu,
one from Anhui, and one from Yunnan) have the combination of Rht-B1b and Rht 8 genes.
Only two Chinese varieties, i.e., CA9532 from Beijing and Shannong 1355 from Shandong
Province, and Suwon 86 from Korea carry both Rht-B1b and Rht-D1b . Zhoumai 11 from
Henan Province has three dwarfing genes, Rht-B1b, Rht-D1b, and Rht 8. This might give an
indication that combination of Rht-B1b or Rht-D1b with Rht 8 could meet the needs of wheat
production in most autumn-sown regions.
None of the above three dwarfing genes were identified in 30 genotypes, most of them
are tall landraces or cultivars released before 1970s, however, cultivars including Beijing 837,
Yuandong 9428, Jing 411, and Chuanmai 107 have plant height around 90-95cm, and
Henong 326 and Xinong 291 have plant height of about 85cm in Beijing. This indicates that