Do semi-dwarfing genes affect growth in temperate cereals?Tobias Wojciechowski1, 2 Luke Ramsay1 Mike Gooding2 Peter Gregory1

1SCRI, Invergowrie, Dundee DD2 5DA. 2University of Reading.

The aim of the project is to characterise the

effect of semi-dwarfing and dwarfing genes on

root development and growth in barley and

wheat. Although reduced height genes (Rht)

are associated with yield reduction and

reduced early vigour, a few of the genes

compensate for the reduced biomass with an

increase in the harvest index or lodging

resistance. About 90% of the semi-dwarf

wheat cultivars grown currently contain

Rht-B1b (formerly Rht1) and Rht-D1b (formerly

Rht2) genes, which cause a moderate

reduction in final crop height of approximately

15%.

The reduced height phenotype is mainly

caused by reduced sensitivity to gibberellic

acid (GA) by an interruption of GA

biosynthesis or signal transduction. The

effect of Rht genes on stem development and

growth is well documented, but little is known

about their effects on root growth. Whether

and how Rht genes affect the root systems of

temperate cereals is not clear, and there are

conflicting reports about their effects on roots.

The question is: Do semi-dwarfing and

dwarfing genes affect root development and

growth in temperate cereals?

To address the question, several near

isogenic wheat lines (cv Mercia) were grown in

gel chambers and soil. The root systems of

these Rht lines were analysed with “Winrhizo”

and Winrhizotron”.

Conclusion

The following near isogenic lines in wheat showed significant

differences in their total root length from the wildtype: Rht-B1c,

Rht-D1c and Rht12. These genotypes had an increased total

root length when grown in a gel chamber for 10 days but a

shorter root system in the soil experiment after 26 days.

Future work will test if root growth is influenced by the growth

media or plant developmental stage. Expression studies of

orthologous genes in barley should help to answer the

question: how do these genes affect root growth?

Results

Method

Near isogenic lines of wheat (cv

Mercia) containing semi-dwarfing

genes (Rht-B1b, Rht-D1b, Rht-B1c,

Rht8, Rht-D1c, and Rht12) were

grown in gel chambers and in soil.

Weighed seeds were individually

surface sterilised, pre-germinated on

filter paper and two seedlings planted

in a gel chamber. The plants were

grown at 15˚C for 10 d. The number of

seminal root axes was counted and root length and diameter recorded by

scanning with “Winrhizotron” at 2 d intervals. At final harvest, the plants

were removed from the chambers and the dry weight of roots and shoots

measured.

Seeds with a defined seed mass (40mg ± 1mg) were pre-germinated for the

soil experiment. The seedlings of each genotype were grown in columns

containing soil at either 27% or 18.5% volumetric water content. The water

content of columns at 27% was kept constant while those at 18.5% were

allowed to dry. After 26 days the root systems were washed and scanned

with “Winrhizo” to measure total root length, average diameter and surface

area.

d

of

y

Wild

type

Rht-B

1b

Rht-D

1b

Rht -B

1cRht

8

Rht-D

1c

Rht 1

2

Gel chamber experiment Soil experiment

Figure 3 shows total root length for each

genotype at harvest (26 days). The genotypes

compared to wildtype with a least significant

difference (p < 0.05) are marked (*). The root

systems of

Rht-B1c,

Rht-D1c, Rht12

differ from

wildtype with

the total root

length

significantly

reduced.

Figure 1 shows the increase of

total root length with time (two

days intervals)

Wild

type

Rht-B

1b

Rht-D

1b

Rht -B

1cRht

8

Rht-D

1c

Rht 1

2

2500

2000

1500

1000

500

0

[cm]

Average total root length

WWild

tdtype

Rht-B

1b

Rht-D

1b

Rht -B

1cRht

8

RhRhtht-D

1c

Rht 1

21222

255500

200000

155500

100000

55500

0

[cm]

Average total root leng

Figure 3: total root length after 26 days with standard error of difference

< 0.05) are marked ( ). The root

t12

h

t

gth

0

10

20

30

40

50

[cm]

0

10

20

30

40

50

[cm]

0

10

20

30

40

50

[cm]

Total root length (day 10)

0

10

20

30

40

50

[cm]

Wild

type

Rht-B

1b

Rht-D

1b

Rht -B

1cRht

8

Rht-D

1c

Rht 1

20

110

220

330

440

50

[c ]

00

11011

220220

3303

4404

505

[c ][

0000

10111

220220220220

3303

440444

550555555

[c ][[[

Total root length (day 10)

00000000000000

101001000010101010101010

2202200220000220220220220220220220

33033030330303030330330330330330330330

4040040000440440440440440440440

55055050550505050550550550550550550550

[cm][cm][ ][cm][ ][ ][ ][cm][cm][cm][cm][cm][cm][cm]

Wild

Wild

tyyppe

Rht-B

1b

RRht-D

1b

Rht -B

1cRht

8

Rhtht-D-D

1c

RRRht 1

22

Figure 2: Total root length at day ten with standard error of difference

Figure 2 shows the total root length at final

harvest. The genotypes with least significant

differences (p < 0.05) are marked (*). The

genotypes (Rht-B1c, Rht-D1c, and Rht12)

showed significant increase in total root length

from the wildtype by 8 d.

4.939.8916.8

21.9930.1

4.6410.4818.5927.4836.6

4.719.61

15.9424.8134.1

5.7812.9320.3130.6142.2

4.3310.3917.1927.1736.4

4.329.82

17.1428.7639

4.9212.9721.1234.1344.5

1.3232.6553.9996.1167.9

2468

10

Day Wild

type

Rht-B

1b

Rht-D

1b

Rht -B

1c

Rht 8

Rht-D

1c

Rht 1

2

lsd (5

%)

4 934.939.9.8916.8

2121.9930.1 30

4 644.6410.4818.5927.4836.6

4 714.719.61

15.9424.8134.1

5 785.7812.9320.3130.6142.2

4 334.3310.3917.1927.1736.4

4 324.329.82

17.1428.7639

4.9224.9212.9721.1234.1344.5

1.322332.655553.999996.111667.9

2468

110

DDaay WWild

tdtype

Rht-B

1b

RRht-D

1b

Rht -B

1c

Rht 8

Rht-D

1D1cc

Rht 1

222

lslslsdsd (5

%%)

%)

Table 1: Total root length with time

The table highlights significant differences between

the genotypes over time. The data were adjusted

for the seed mass covariant, as the seed mass had

a significant effect on root growth (p < 0.01).

Figure 1: Total root length with time