Agriculture Reference
In-Depth Information
Table 11. Frequencies (%) of photoperiod insensitive allele Ppd-D1a in landraces and
improved cultivars from different zones
Zone
I
II
III
IV
V
VI
VII
VIII
X
Total
Landrace
18.2
32.8
58.2
54.5
59.1
na
na
5.3
na
38.6
Improved
cultivar
89.5
96.1
98.0
na
98.3
36.0
87.5
87.9
78.1
90.6
Subtotal
48.5
71.2
69.2
54.5
87.8
36.0
87.5
43.7
78.1
66.0
na = not available.
The frequency of the Ppd-D1a in 263 improved cultivars released in Zones I and II
(94.7%) was three fold that among 211 landraces (27.5%). The frequency of Ppd-D1a also
increased markedly from landraces (58.3%) to improved cultivars (98.2%) in Zones III and V.
For Zones VI, VII and VIII, the frequency of Ppd-D1a in improved cultivars was 71.9%.
Generally, the frequency of the Ppd-D1a in landraces (38.6%) was much lower than in
improved cultivars (90.6%), a consequence of the introduction of Ppd-D1a to improve
cultivar adaptation to various environments.
Among landraces in the autumn-sown wheat zones, the frequencies of Ppd-D1a in Zones
I to V were 18.2%, 32.8%, 58.2%, 54.5%, and 59.1%, respectively. The frequency of Ppd-
D1a was comparably lower (5.3%) in landraces from Zone VIII, a spring-sown spring wheat
area. This indicated that the presence of Ppd-D1a in landraces gradually increased from north
to south in the five autumn-sown wheat zones (I, II, III, IV and V). Among improved
cultivars, those in Zones II, III and V located in the middle and southern parts of China had
high frequencies of Ppd-D1a , ranging from 96.1% to 98.3%, followed by Zones I (89.5%),
VII (87.5%), VIII (87.9%), and X (78.1%), and the lowest frequency was observed in Zone
VI (36.0%). This again showed the increasing frequency of Ppd-D1a in improved cultivars
from north to south.
Detailed analysis indicated that all current cultivars with early maturity in Zones I, II, III,
IV, VII, and VIII carry the Ppd-D1a where early maturity is needed to avoid sprouting
damage and to allow optimal sowing of maize after wheat. Zone VI is a high latitude
environment, thus cultivars are expected to have a certain level of photoperiod sensitivity (He
et al. 2001). Nine improved cultivars from Heilongjiang had the Ppd-D1a as expected since
strong photoperiod sensitivity is required in high latitude environment. In Zone X, seven
improved cultivars identified with Ppd-D1b were developed and grown in Xinjiang, and were
expected to have photoperiod sensitivity.
C HALLENGES FOR I MPROVING W HEAT G RAIN Y IELD
IN THE F UTURE
Due to utilization of dwarfing genes, the 1B/1R translocation, and dominant vernalization
and photoperiod genes for early maturity, improvement of wheat grain yield in China has
achieved significant since 1949. However, breeding for high yield potential still remains the
first priority, since the Chinese population increase by more than 1% annually and arable land
diminishes by 1% (He et al., 2001). The future challenge of wheat breeding in China is to
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