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Materials and methods
In addition to the dwarfing tetraploid wheat landrace
Aiganfanmai, native to Shaaxi, China, the tall tetraploid wheat
landrace Fenzhilanmai native to Sichuan, China and the hexaploid
wheat variety, Tom Thumb were used as the cheek materials in the
investigation of reaction to GA respectively. All the materials were
obtained from Triticeae Research Institute, Sichuan Agricultural
University, China. Aiganfanmai was crossed with Fenzhilanmai. Some
F1 hybrids were selfed to obtain F2 seeds, the
others-were crossed with Aiganfanmai to obtain BC1 seeds
in the 1996-1997 cultivated season. The seeds of the two parents, the
F1 and the F2 were sowed in the experiment
field at the same day. Plants were kept 10 cm apart. All the seeds of
each population were randomly planted with aids of label for
identification. The backcross test was carried out in the 1997-1998
cultivated season by sowing the BC1 (F1 x
Aiganfanmai) seeds in the field. Every internode length of the main
stem was investigated at harvest. The length of all the internodes
but the first one was recorded as the modified plant height.
The GA reaction test of seedlings was carried out on 45 unselected
seeds from Aiganfanmai and Tom Thumb. Seeds were placed in petri
dishes, moistened with running water for 1 day at 18-20C then grown
for 2 days at 2C to ensure even germination. Half the germinated
seeds were treated with 0.15 mM GA, and the other half were
continuously grown in running water. After a further 6 days at
18-20oC with 12 hour light-12 hour dark period, the length
of coleoptile and the first leaf were measured.
Results
Like other wheat plants, Aiganfanmai possessed seven internodes.
Measurements indicate that all the internodes of Aiganfanmai were
statistically shorter than those of the tall landrace, Fenzhilanmai
except the first one (Table 1). The length
of the first internode was mainly determined by the deepness of the
seeds in soil. To some extent, the deeper the seeds were in soil, the
longer the first internodes of stem were. This contributed to the
non-correlation between the plant heights and the length of the first
internode in 1996-1997 season (r=0.203, p=0.059). In addition, spike
length of Aiganfanmai was 9.2 + or - 0.5 cm, which was obviously
shorter than that of Fenzhilanmai (14.4 + or - 0.08 cm, p <
0.001). According to the previous report (Goud and Sridevi 1988), the
spike length has its own genetic basis other than the Rht
genes. So, the term plant height in this paper was designated to
represent the total length of internodes from the second to the
seventh, which was different from the term final plant height that
included the length of both stem and spike in previous
literature.
Aiganfamnai has been planted in our experiment field since 1993. The
mean of plant height of Aiganfanmai varied considerably depending on
the supply of water and artificial fertilizers in different
cultivated seasons. However, the dwarf landrace Aiganfanmai was
always very much shorter than the tall landrace Fenzhilanmai in the
same season (Table 2). So, the dwarf trait
of Aiganfanmai should have its genetic basis.
The mean plant height of the F1 progeny (Aiganfanmai x
Fenzhilanmai) is much higher than that of Aiganfanmai, and more close
to that of Fenzhilanmai (Fig. 1). This result
indicates that the dwarf trait of Aiganfanmai is recessive. The
F2 population segregated into dwarf and tall plants
(Fig. 1). According to the plant height
distributions we can arbitrate that the plants shorter than 106 cm
are dwarf and those higher than 110 cm are tall in F2
Population. Thus, the F2 population comprised 85 dwarf
plants (about 22.6 %) and 292 tall plants (about 77.4%).
Chi2 analysis showed that the segregation of dwarf and
tall plants in F2 population fitted to the ratio of 1 : 3
very well (chic2=1 .083, p=0.298). To confirm
monohybrid segregation further, backcross test was carried out in
1997-1998 season. BC1 (F1 x Aiganfanmai)
population segregated into 84 dwarfs (shorter than 100cm) and 74
talls (higher than 112cm). The segregation ratio fitted to the
expected 1 : 1 very well (chic2=0.513,
p=0.481). Thus, it is evident that the dwarf trait of Aiganfanmai is
conditioned by one gene.
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