Agriculture Reference
In-Depth Information
from Zones III and V (>94%) headed before 109 days, the rests were released before 1960.
The frequency of early heading genotypes increased gradually from north to south in the
autumn-sown regions. In Zones VI, VII and VIII, all 68 cultivars tested in the greenhouse
headed within 109 days. In Zone X, the frequency of early heading genotypes was 51.9%.
Therefore, it was concluded that spring cultivars in China are more frequent in the high
latitude regions (spring sowing) and in the low latitude area with warm winters (autumn
sowing). Winter cultivars are frequently present in the middle latitude area with relatively
cold winter (autumn sowing).
The 92 late heading (winter) cultivars all carried recessive alleles at the four vernalization
loci. Different combinations and proportions of vernalizaion alleles were found in other 172
early heading (spring) cultivars (Table 10). Single dominant alleles were observed for the
Vrn-A1
(11.0%),
Vrn-B1
(6.4%) or
Vrn-D1
(41.9%). We observed two gene combinations
including
Vrn-A1 / Vrn-B1
(20.9%),
Vrn-A1 / Vrn-D1
(4.6%) and
Vrn-B1 / Vrn-D1
(7.6%);
and three dominant allele combinations including
Vrn-A1Vrn-B1Vrn-D1
(6.4%), and
Vrn-
A1Vrn-B1Vrn-B3
(0.6%). In addition, one very early heading cultivar (Liaochun 10) carried
all four dominant alleles (
Vrn-A1Vrn-B1Vrn-D1Vrn-B3
).
The relationships between vernalization genotypes and heading times in diverse regions
are different (Table 10). In summary, the earliest cultivars were those carrying three to four
dominant alleles, including the rare
Vrn-B3
allele (average 30 to 31 days to heading),
followed by the one, two or three gene combinations, including
Vrn-A1
but not
Vrn-B3
(average 38 days to heading). Cultivars carrying the
Vrn-B1
/
Vrn-D1
allelle combination
headed approximately 42 days after sowing, whereas those carrying only the
Vrn-B1
(average
47 days) or
Vrn-D1
(average 54 days) were among the latest spring cultivars. On the basis of
these data, the strength of the dominant spring
Vrn-1
alleles can be ranked as
Vrn-A1
>
Vrn-
B1
>
Vrn-D1
.
Vrn-B3
resulted in the earliest heading times in combination with other
dominant
Vrn1
alleles.
D
ISTRIBUTION OF
P
HOTOPERIOD
G
ENES
The
Ppd-D1a
allele for photoperiod insensitivity is generally considered the most potent,
followed by
Ppd-B1a
and
Ppd-A1a
(Scarth and Law, 1984). A total of 926 Chinese wheat
landraces (438) and improved cultivars (488) collected from nine wheat growing zones were
tested for their genotypes at the
Ppd-D1
locus using allele-specific markers (Yang et al.,
2008). The overall frequency of the dominant
Ppd-D1a
allele in Chinese wheats was 66.0%,
but frequencies varied across regions (Table 11). The highest frequency was found in Zones
V (87.8%) and VII (87.5%), followed by Zones I (48.5%), II (71.2%), III (69.2%), IV
(54.5%) and X (78.1%), the lowest was in Zones VI (36.0%) and VIII (43.7%). Among the
four autumn-sown wheat zones where both landraces and improved cultivars were tested in
this study, the frequency of
Ppd-D1a
in the Northern China Plain (Zone I) was much lower
than that in the middle (Zone II) and southern parts (Zones III and V).
Search WWH ::
Custom Search