Transgenic Bt Rice for Resistance to Stem Borer

Stem borer damage is a serious problem in rice, causing estimated losses of 10-30% of the total yield. Scirpophaga incertulas (yellow stem borer) and Chilo suppressalis (striped stem borer) are the major stem borers, and are widely distributed from Japan to India. Stem borer larvae start their attack by boring through the inner portion of the leaf sheath. The subsequent boring through the stem by caterpillars causes considerable damage, resulting in "deadheart" symptoms, and the affected tillers do not bear panicles. Panicles often emerge with empty grains, called "whiteheads" (Fig. 22.2a). Bacillus thuringiensis (Bt), the common soil bacterium, produces crystals containing insecticidal proteins. These toxins kill insects by binding to and creating pores in the midgut membranes. Bt toxins are highly specific and therefore are not toxic to beneficial insects, birds, and mammals, including humans.13 But, Bt toxins are insecticides and, like conventional chemical insecticides, insects may quickly adapt to them unless Bt plants are carefully designed and deployed. A greater assurance of durable resistance can be achieved if a Bt toxin is combined with a second unrelated type of toxin.14 Tissue-specific promoters, particularly the green-tissue specific

Table 22.1. Estimated yield losses by groups of constraints (kg ha-1) rice seasons

in the main

Region

Insects

Diseases

Drought

Soils

Other abiotic stresses

Others

China

92

88

n.a.

635

557

91

Eastern India

104

93

177

74

81

167 (weeds, lodging, birds

West Bengal

43

213

n.a.

n.a.

772

Southern India

215

137

44

72

7

87 (weeds, lodging, nutrients)

Bangladesh

135

111

172

27

106

22 (weeds)

Indonesia

399

24

n.a.

n.a.

n.a.

189 (rats)

Thailand

78

12

n.a.

n.a.

n.a.

5 (rats)

Nepal

810

560

210

150

10

150 (rats, weeds, lodging)

Philippines

250

198

n.a.

407

90 (variety, others)

Source: Herdt, 1996.2

Table 22.2. Insect control costs (US $ Table 22.3. Use (%) of pesticides by million) countries and regions

Crop

Control cost

Substitution value

Country

Percentage

Rice

1190

422

Japan

45.7

Cotton

1870

1161

Korea

27.9

Corn/maize

620

158

Europe USA

8.8 6.3

Fruits and

2465

Indonesia

India

5.9 2.5 1.3

vegetables Other

1965

Total

8110

2632

Latin America

0.9

Source: Krattiger, 1998.3

Africa

0.6

Table 22.4. Development and use of transgenic rice for biotic stresses

Rice

Method used

Genes transferred

Traits Reference

Japonica

Protoplast

npti I*

Resistant to kanamycin

21

Japonica

Protoplast (electroporation)

hpt*

Resistant to kanamycin

22

Indica

Protoplast (PEG)

hpt*

Resistant to kanamycin

17

Japonica

Protoplast (PEG)

nptII

Resistant to kanamycin

23

Indica (IR72) Protoplast (PEG)

bar*

Resistant to herbicide

24

Japonica

Protoplast (electroporation)

cp-stripe virus

Resistant to stripe virus

12

Japonica

Protoplast (electroporation)

Bt

Resistant to insects

25

Japonica

Agrobacterium

hpt*

Resistant to hygromycin

26

Indica

Protoplast (PEG)

chi11

Resistant to sheath blight

10

Japonica

Protoplast

cc

Resistant to insects

27

Japonica

Biolistic

Xa-21

Resistant to bacterial blight

28

Japonica

Biolistic

cpTi

Resistant to insects

29

Indica

Protoplast and biolistic

Bt/(DWR)

Resistant to stem borer

7

Japonica/ Indica

Agrobacterium

hpt*

Resistant to hygromycin

30

Japonica

Biolistic and protoplast

pinII

Resistant to insects

31

Indica

Biolistic

Bt

Resistant to stem borer

32

Indica/ Japonica

Biolistic and protoplast

early nodulin

Biological N2 fixation

33

Indica

Biolistic

Bt

Resistant to stem borer

6

Indica/ Japonica

Biolistic and protoplast

Bt Resistant to (tissue-specific) stem borer

5

Indica (IR72)

Biolistic

Xa-21

Resistant to bacterial blight

9

Indica

Biolistic

Bt ML for hybrid rice

Resistant to stem borer

8

Indica

Biolistic

PR genes

Resistant to sheath blight

11

*Used as selectable marker gene; ML, maintainer line; DWR, deepwater rice.

Table 22.5. Production of transgenic rice

for field testing

Cultivars

Methoda

Genesb

Plants in Southern+ greenhouse enzyme (total #) assay

Fertility status

(%)

Transgenic lines selected

IR72

B

Bt, chi, Xa-21

32

2G

6G

12

IR64

B, P

Bt, chi

2G

3

2G

1

CBII

P

Bt, chi

18GG

16G

8G

18

IR58

P, B

Bt, chi others

2lG

2

6G

1

IR51500

P, B, A

Bt, chi

6G

3

4G

2

Basmati 370

P, B

Bt, chi, others

72

16

2G

3

Basmati 122

P, B, A

Bt, chi

66

l8

3G

4

New plant others

B, P

Bt, chi, others

12G

66

3G

15

Maintainer line for hybrid rice

B, P

Bt, chi, others

14G

22

6G

12

MH63

B

Bt, chi

62

l6

7G

11

Vaidehi-1

B

Bt, chi

26

6

8G

2

aB, biolistic; P, protoplast-mediated; A, Agrobacterium bBt, encoding resistance for stem borer; chi, chitinase gene for sheath blight resistance cPlants chosen based on Southern, Western, and bioassay data promoter (PEPCP) used in Bt gene expression in rice, were allowed to express preferentially in green tissue and significantly reduced expression in grain. Thus, Bt rice plants with PEPCP or pith promoter, either alone or in combination, should provide a better strategy for providing rice plants with protection against insect pests, thus minimizing the expression of the CryIA(b) protein in seeds and other tissue.5

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