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Genetic diversity in allelopathic rice accessions (Oryza sativa L.)

Hua-qin He1, Li-hua Shen, Yu-chun Guo, Jing-Yuan Wang and Wen-xiong Lin

1.College of Life Science, Fujian Agriculture and Forestry University, Fuzhou,China 350002,2. Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, China

Abstract

Random amplified polymorphic DNA (RAPD) markers were used to estimating genetic diversity among 57 allelopathic rice accessions (Oryza sativa L.). There were 59 polymorphic bands in the 85 RAPD loci within the tested accessions, and the percentage of polymorphic bands (PPB) was 69.4%. The result from the clustering analysis by Unweighted Pair Group Mathod Arithmetic Average (UMGMA) indicated that those accessions from the same geographical location were clustered into one group. It was also found that some rice accessions with higher allelopathic potential were clustered together, such as IAC25、IAC47and IAC120 implying that the genes conferring allelopathy in those rice accessions might be isolocus. However, some rice accessions with different allelopathic potential clustered into the same group performed lower level of generic polymorphism which was attributed to oriented selection for other traits in breeding program. This offers us a genetic pool for the selection of rice cultivars with high allelopathic ability.

Key Words

Allelopahic rice accessions; Oryza sativa L., Genetic diversity; RAPD

Introduction

Weeds are one of the most important causes of yields losses in rice. In the upland rice ecosystem, yield loss estimates from weed infestation have ranged from 30 to 100% (Luoise 2001). With the increasing of labor-cost increasing and the availability and efficacy of herbicide, herbicide use has increased exponentially in Asian rice production (Naylor 1996).Despite the overwhelming economic benefit, the heavy reliance on chemical herbicides is considered a potential threat to public health and to the environment (Jiwan and Gates,1994).Furthermore, the appearance of herbicides-resistance weeds is an increasing problem (Boutsalis and Powles,1995).These factors have prompted research into alternative means of weed control.( Motiul Quader et al,2001).

Allelopathy is defined as “direct or indirect (harmful or beneficial) effects of a plant, on another plant through the release of compounds that escapes into the environment”(Rice,1984).Three seasons of field experience finally led to the conclusion that allelopathy could explain 34% of the variation among cultivars in the ability to suppress weeds (Olofsdotter et al.1999).

Allelopathic potential has been identified in most major cereal crops (Lovett and Hoult,1995).Based on the selection for rice accessions , the assessment of genetic diversity became necessary when a significant level of intraaccession variability in allelopathic expression became evident ( Motiul Quader et al,2001).

Methods and Materials

Plant Materials

Fifty-seven rice accessions of Oryza sativa L. introduced from American, Korea, Brazil, China and the International Rice Research Institute (IRRI), were screened for allelopathic potential. Barnyardgrass (Echinochloa crus-galli L.)was used as a receiver plant.

Screening for allelopathic potential

The procedure was adapted from the relay seedling technique (Navarez and Olofedotter 1996). 0.5% water agar was used as growth medium after compared with Perlite (the data unpublished). The root length of barnyardgrass was recorded.

DNA extraction and RAPD analysis

All seeds were grown in Petri dishes containing 0.5% water agar under sterile conditions. Genomic DNA were extracted from duplicate samples from a single seedling by the method of Weining et al.(1994). The polymerase chain reaction (PCR) was performed in a 15μl reaction mixture containing 10ng template DNA,1.5μl 10buffer,200μmol/L dNTPs,1.5μl Taq DNA polymerase and 1ng 10-mer primer. Amplification program is :30s at 94 ;30s at 40 ;90s at 72 ;40 cycles, 10min at 72 then stored at 4。

Statistical Analysis

The root length of barnyardgrass was transferred into Inhibition Ratio (IR), i.e. IR=(1-TR/CK)100%, while TR represented the treatment,CK was the control.

Genetic data analyses were performed by using the computer package TFPMG 1.3(Miller et al.1997).The dendrograms was constructed by the unweighted pair group method (UPGMA)(Sneath and Sokal,1973).

Results

Screening for allelopathic potential

Of 57 accessions, 5 rice cultivars, such as Iguape Cateto, PI312777, Azucena, Taichung Native 1 and IAC25, demonstrated over 50% inhibition of barnyardgrass root growth. IRs of 12 cultivars ranged from 40% to 50%, that of 21 cultivars from 30% to 40%,13 cultivars from 20% to 30%, while IRs of 6 cultivars were less than 20%(Table 1). The distribution of allelopathic activity in rice accessions tested was normal(Fig 1).

Table 1: IRs of rice alleloapthy on the root of barnyardgrass*

No

Rice accession

Origin

IR (%)

No

Rice accession

Origin

IR (%)

1

Iguape Cateto

Brazil

58.41.6

30

Chaoerzhan

China

33.36.3

2

PI312777

America

56.82..3

31

Sanyizhaozhan

China

32.76.7

3

Azucena

The Philippines

53.91.4

32

Wab56-125

Ivory Coast

32.54.1

4

Taichung Native 1

Taiwan

50.28.9

33

Polha Murcha

Brazil

32.06.6

5

IAC25

Brazil

50.04.7

34

Qisanzhan

China

31.87.5

6

AU257

Bangladesh

48.40.6

35

Dourado Pecoce

Brazil

31.83.5

7

Red Rice5

China

48.26.8

36

Bala

India

31.66.7

8

Batatais

Brazil

47.55.2

37

Arroz de campos

Cuba

30.77.9

9

IAC120

Brazil

46.77.4

38

Shuangzhan 2

China

30.47.5

10

Co39

India

45.22.6

39

Fengaizhan

China

29.15.8

11

IAC47

Brazil

45.17.5

40

IR721413

The Philippines

28.94.7

12

IR72417-3R-8-2

The Philippines

44.513.2

41

Qidaizhan

China

28.98.8

13

Yehuazhan

China

43.65.9

42

IR73384

The Philippines

27.79.4

14

IR70617

The Philippines

43.26.7

43

IR64

The Philippines

27.75.3

15

Jingyouzhan

China

41.18.6

44

Xinsimiao

China

27.31.3

16

IAC164

Brazil

41.16.9

45

Daishuzhan

China

27.04.3

17

Mafeng 1

China

40.910.1

46

Qingxiangzhan

China

26.86.1

18

189Taizhong 189

China

39.38.6

47

IR62266-42-6-2

The Philippines

25.94.0

19

Dinorado

The Philippines

39.32.2

48

IR65907-116-1-B

The Philippines

24.19.1

20

Vandana

Colombia

38.25.6

49

Moroberekan

Guinea

23.26.6

21

IAC165

Brazil

37.51.1

50

IR60080-46A

The Philippines

21.44.1

22

IR56

The Philippines

36.64.7

51

IR72412

The Philippines

20.27.8

23

Shuangmeizhan

China

36.46.4

52

Zhengyou 1

China

19.51.9

24

IR70651

The Philippines

35.72.4

53

IR55423-01

The Philippines

18.42.5

25

IR36

The Philippines

34.54.3

54

Pratao Precoce

Brazil

18.22.6

26

Dee Geo Woo Gen

Taiwan

34.33.8

55

Aisanruzhan

China

17.74.6

27

Muxiang 25

China

34.13.1

56

Dular

America

14.12.1

28

IR73382

The Philippines

33.92.8

57

Lemont

America

10.93.2

29

IR71331

The Philippines

33.39.4

CK

   

0.0

*CK, Control= Echinochloa crusgalli L. grown alone

Fig.1(Left) The distribution proportion of rice accessions in different interval of IR value

Fig.2 (Right) The cluster analysis on allelopathic rice as determined by UPGMA from RAPD

Genetic diversity in 57 accessions

12 primers were selected from a previous study on the basis of polymorphisms revealed in 5 rice accessions. The primers were used to detect the polymorphism of 57 rice accessions (Figure 3). The total of 85 bands were scorable, of which 59 were polymorphic, and the percentage of polymorphic bands(PPB) was 69.4%.

Fig.3 DNA fragment amplified by primer 1409

Clustering

From GD=0.1875, 57 rice accessions were grouped into eight main group(Fig.2). The first group was composed of 31 cultivars, of which 14 were from Mainland China, 13 from the Philippines, 2 from Taiwan, 1 from American and 1 from India. In this group, 8 cultivars showed over 40% of inhibitory effect on the root of baryardgrass. The sixth group included 6 accessions introduced from Brazil. Three cultivars, IAC25(5), IAC47(11) and IAC120(9), which all showed high allelopathic potential on barnyardgrass, were clustered together. Another three cultivars, Iguape Cateto(1), Dourado Pecoce(35) and Pratao Precoce(54) were grouped into one subgroup, performing that the inhibition ratio (IR) were 58.4%, 31.8% and 18.2% respectively.

Discussion

In this study, the genetic polymorphism of allelopathic rice detected by RAPD approach indicated that those accessions from the same geographical location were clustered into one group. It was also found that some rice accessions with higher allelopathic potential were clustered together, implying that the genes conferring allelopathy in those rice accessions might be isolocus. However, some rice accessions with different allelopathic potential clustered into the same group, such as Iguape Cateto(1), Dourado Pecoce(35) and Pratao Precoce(54) , performed lower level of generic polymorphism which was attributed to oriented selection for other traits in breeding program. Bustos et al (1998) have successfully used RAPD markers to investigate the genetic diversity within and among wild populations of species of the genus Hordeum (Poaceae). With careful screening and replication, M.Quader et al (2001) observed high level of intraaccession genetic diversity (4-24%) in accessions of Triticum Speltoides by using RAPD.

Acknowledgements

This work was supported by grants (30200170, 2003F012) from National Natural Science Foundation of China, and The key Scientific Technological Program of Fujian Province, China.

Reference

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