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Rice Breeding For Herbicide Resistance In Turkey

 1Halil Sürek, 2Necmi Beşer, 1Recep Kaya, 1Rasim Ünan

 

1)Trakya Agricultural Research Institute, Edirne, Turkey.

2)Trakya University, Havsa Vocational School, 22500 Havsa/Edirne, Turkey.

Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

 

              Abstract

                The objective of this study was  to develop IMI (Imidazolinone) group herbicide resistant rice varieties to control weedy rice (red rice) and the weeds gained resistance against conventional rice herbicides in rice fields. For this, the thirteen  cross combinations were done with a IMI resistant rice variety at Trakya Agricultural Research Institute in 2007. Using these crosses, some breeding activities carried out. As a results of these studies promising IMI resistant lines were developed and they were tested in the observation nurseries and the yield trials in 2012 and 2013. Also, a backcross program started in 2008,  eight backcross combinations were obtained, seven of them reached to BC6 and one to BC4 at the end of 2013.

                As a preliminary results, some promising IMI resistant rice lines selected in 2013, and they are being tested in the regional trials and demonstration experiment under farmer’s conditions  in 2014.  A few of them will be nominated for registration as commercial varieties in the end of  2014 crop season.

                 Key Words: Herbicide resistant, Imidazolinone herbicide, rice (Oryza sativa L.), rice breeding.

 

           INTRODUCTION    

           Rice domestication  emanated from the Asian continent specially China about 8000 year ago through selection of agronomically  desirable from wild Oryza Spp  (Khush, 1997). With human influence on the evolutionary process and the intermittent genetic introgression from wild relatives to the crop, weedy relatives of rice come into being. On the other hand, Sato (2000) mentioned that weedy rice differentiated from natural hybridization between cultivars or between perennial wild and domestic types.

            Weedy rice populations have been reported in many rice growing areas in the world where the crop is directly seeded. It is a serious problem in the temperate regions. In Asia, however, weedy rice is an emerging problem for example, weedy rice infestation were first reported in Malaysia in 1988, in the Philippines in 1990, and in Vietnam in 1994. They infest rice fields in almost all the rice-growing areas in south and southeast   Asia, Sri Lanka and the Philippines (Chauhan, 2013). Sato (2000) pointed out that the weedy rice strains were recognized as harmful weeds in lowland fields, particularly in direct-seeded habitats in Thailand, Malaysia, Vietnam, China, Korea,  and Japan. Also, it is a common weed in Bolivia, Chile, Colombia, Guyana, Brazil, United States, and Venezuela.

           Weedy rice is a superior competitor to crop cultivars due to early vigor, greater tillering, and greater height of  plats. It is a close relative of rice, and weedy rice is most easily recognized in the field at harvest by examination of panicle and grains. Most red rice biotypes are characterized by a red pericarp or outer covering, during processing, it reduces the quality of milled white rice, and shattering the grains before harvesting, it also reduces paddy yield. Burgos et al., (2008) estimated 274 US dollar loss per hectare due to red rice. Rice yield losses due to weedy rice depend on the amount of infestation, it caused rice yield loss by 50-60% with moderate infestation (15-20 weedy rice panicle m-2), 70-80% under high infestation (21-30 panicle m-2) (Chauhan, 2013). Volgsaroj (2000) reported yield losses ranging from 60% to 80% due to red rice infestation in Thailand. Kwon et al., (1991) determined reduction in head and total milled rice production, depending on duration of competition and red rice density, the reduction increased. On the other hand, Diarra et al., (1985) reported 22, 77, and 82 yield losses when the red rice densities 5, 108, and 215 plant/m-2, respectively. Fischer and Ramirez (1993) determined a very strong competition between cultivated rice an red rice plants, when 5 and 20 red rice plants/m-2  existed  in rice filed, the yield reduction was 40% and 60%, respectively. Twenty red rice plants/m-2  shattered only 35 seeds/m-2  before harvest, but contaminated harvested rice with about 1100 kg/ha of red rice grain.

           Weedy rice is a great problem in direct seeded area, if the rice is monoculturaly cultivated in the same areas without rotation for a long time, this situation makes the problem more serious. Weedy rice seeds can be dormant for a longer time, because of its shattering and dormancy traits, once a field is infested with red rice, the seed will remain viable and problematic for many years. Noldin et al., (2006) reported that the red rice seed longevity was greater with deeper burial. After  a year, there was no viable seed at 5 cm depth, however, at 25 cm depth, there were more persistent, its longevity continues more than three years. Since commercial rice and red rice so closely related, it is difficult to control red rice  with conventional herbicides without giving damage to the commercial rice crop.

           In order to control red rice, Clearfield technology developed in the United States. It allows the control of red rice (Lincombe, 2004). This technology provides to use imidazolinone herbicides in rice production. The varietal resistance is as a result of induced mutations that were selected for this resistance. The genetic resistance in these mutations has been incorporated into agronomically viable varieties by conventional plant breeding techniques.

            Lincombe (2004) IMI resistant rice developed by Dr Timothy Croughan at the Louisiana  State University,  Agricultural Rice Research Station in 1993 as ethyl methyl sulfonate induced mutation.   Using this source, the first IMI varieties CL 121 and CL 141 were released in 1999 and then CL 161 released in 2000. Linscombe (2010) reported that the Clearfield technology was first used on a limited areas in 2002 in United States. This area steadily increased through the years and Clearfield rice was grown on more than 60% of the rice area in the southern United States. This technology is also used in some shout  American countries such as Costa Rica, Columbia , and Brazil and European countries such as Italy, Spain, Greece, and Bulgaria.  Imidazolinone-tolerant technology  is not used only in rice crop (Oryza sativa L.), it is also used in the other crops such as maize (Zea mays  L.), wheat (Triticum eastivum L.), oil seed rape (Brassica naspus L.), and sunflower (Helianthus annus L.)  (Tan et al., 2005).

           Imidazolinone herbicides provide  a useful tool to control red rice and some weeds are resistant to conventional rice herbicides.  Meins et al., (2003) applied imazamox from the 3- to 4- leaf up to panicle initiation, it provided excellent control of red rice population.  Chin et al., (2007) used imazapic, imazapyr, imazapic+imazapyr and the result revealed that common weeds observed  in the experiment field including Echinochloa cruss-galli, Leptochloa chinensis, Cyperus iria, Cyperus difformis, Ludwigia octovalvis and especially weedy rice (Oryza sativa) were controlled successfully by herbicides in Vietnam. On the other hand, in  both conventional and reduced tillage systems conditions, 70 g ai/ha Imazethapyr applied  by Levy (2004) at preemergence and postemergence  stages, controlled red rice (Oryza sativa L.), barnyardgrass  [Echinochloa cruss-galli (L) Beauv.], Amazon sprangletop [Leptochloa panicoides  (Persl) Hitchc.]i and rice flatsedge (Cyperus irina L.) 87 to 99%, respectively.

           Rice have been cultivated under continuous flooding irrigation systems  for a long time in Turkey. The amount of water needed for rice irrigation depending on length of irrigation period and soil structure   changes between  1500 and 2000 mm. Therefore, rice crop needs too much water, because of water shortage, rice growing area is very limited in Turkey.  In addition, rice still is a very profitable crop in Turkey, thus, the farmers are very willing to grow rice, therefore, the rice is monoculturaly cultivated without rotation for a long time. On the other hand, after mechanization of rice cultivation or developing high yielding varieties, short plant height varieties have poor competition ability with red rice, are widely grown in Turkey. These situations aggravate the red rice problem, these conditions cause weed problems as well and the weed populations increase year by year in the rice fields. Also, some weed species or weed varieties are getting resistant to conventional rice herbicides in the last years. Thus, new alternative tools are needed for weed control. Imidazolinone group herbicides could be a new alternative to control herbicide resistant weeds.

           The objective of this study was  to develop IMI (Imidazolinone) group herbicide resistant rice varieties to control weedy rice (red rice) and the weeds gained resistance against conventional rice herbicides in the rice fields.

 

           MATERIAL AND METHOD

           Material

           An IMI resistant variety which has resistant  gene against Imidazolinone group herbicide, used in this study as resistance source. This variety was crossed with commercial varieties  such as Osmancık-97, Durağan, Halilbey, Ece, Kıral, Neğiş, Krasnodarsky-424, Edirne, Şumnu, and Gönen in Trakya Agricultural Research Institute. In 2007. Thirteen cross combinations were conducted (see in table-1). Seven of them  were also used for backcross breeding in 2008. The commercial varieties were used as recurrent parent in backcross combination. 

Table 1. The cross combination conducted in 2007.

Cross No

Pedigree

Cross Combination

1

2007020-TR2500

Osmancık-97 x IMI Variety

2

2007041-TR2521

IMI Variety x Durağan

3

2007043-TR2523

IMI Variety x Halilbey

4

2007044-TR2524

IMI Variety x Ece

5

2007045-TR2525

IMI Variety x Kıral

6

2007046-TR2526

IMI Variety x Neğiş

7

2007047-TR2527

IMI Variety x Osmancık-92

8

2007048-TR2528

IMI Variety x Krasnodarky-424

9

2007049-TR2529

IMI Variety x Kızıltan

10

2007050-TR2530

IMI Variety x Edirne

11

2007051-TR2531

IMI Variety x Şumnu

12

2007074-TR2554

Halilbey x IMI Variety

13

2007134-TR2614

Gönen x IMI Variety

 

Table.1 The backcross combination started in 2008.

Cross No

Pedigree

Cross Combination

1

2007020-TR2500

Osmancık-97 x IMI Variety

2

2007043-TR2523

IMI Variety x Halilbey

3

2007044-TR2524

IMI Variety x Ece

4

2007046-TR2526

IMI Variety x Neğiş

5

2007047-TR2527

IMI Variety x Osmancık-92

6

2007049-TR2529

IMI Variety x Kızıltan

7

2007074-TR2554

Halilbey x IMI Variety

 

           Method

           The single cross was conducted to create segregating population. The modified bulk selection method was practiced for selection. For this, F2 was planted and harvested as bulk and F3 was planted as bulk and harvested as single plant selection. Afterward, the pedigree selection method was practiced. The selection continued until obtaining  the pure lines to F6-F7 generation.  

           After selecting the pure lines, they were tested in observation nursery, preliminary yield and yield trial, respectively.

Observation nurseries were seeded in dry conditions as row planting. Each plot was 5 m long and consisted of  four rows, spaced  25 cm apart.

           The yield trails were conducted with randomised complete block experiment design with three replications at Trakya Agricultural Research Institute. The seed rate was 450 seeds m-2 and fertilize dose was N180P60 kg ha-2 for the experiments. The plot size was 3x5= 15 m-2 at planting and it was 2,5x4,5= 11,25 m-2 for preliminary yield trial, and it was 4x5= 20 m-2 at planting and 3,5x4,5= 15,75 m-2 at harvesting for yield trials, respectively. The planting was done into standing water broadcasting by hand.

           The observations were recorded for flowering and maturity days, plant height and panicle length, the number of panicle per squarmetter, spikelet sterility, grain shattering, lodging, paddy yield, 1000 grain weight of rice and milled grains, head and total milled rice yield.

           Backcross Breeding

           As mentioned above  a backcross program started in 2008. The commercial varieties used as recurrent parent in backcross combination  and the backcrossing continued until BC6           

           Herbicide Application 

           Imidazolinone group herbicides, imazamox was used in this study, 40 g imazamox ha-2 was applied at 3-4 leaf stages as first postmergence  application and 80 g imazamox ha-2 herbicide applied as second application after 40-45 days of planting to avoid the late emerging red rice and weeds. After imazamox application the plants did not have resistant gene died, and then selection and backcrossing practiced on remaining alive plants. 

 

           RESULTS AND DISCUSSION

           Conducting an herbicide resistant rice breeding program between 2007 and 2013, some herbicide resistant promising lines obtained and they tested in the yield trials in 2012 and 2013. Also, some of them were evaluated in the  observation nurseries . However, some data related to yield trials and backcross studies will be given in this paper.

           The analysis of variance revealed high significant difference   among the genotypes for rice yield in the experiments conducted in 2012 and 2013 (Table-3 and table-4). Most of IMI lines had higher rice yield than conventional varieties, Osmancık-97 and Edirne. Also, some of them have higher yield potential than the IMI variety, the source of resistant gene used in this breeding program.

 

           Table .3 The paddy yields of preliminary yield trial conducted   in 2013.

Entry No.

Variety Name

Rice Yield (ton/ha)

17

2007051-TR2531-1-1-1

9,94 a

15

2007047-TR2527-2-3-1

9,91 ab

12

2007134-TR2614-3-1-2

9,57 abc

16

2007047-TR2527-2-3-3-2

9, 53abcd

9

2007050-TR2530-4-1-1

9,48 abcd

11

2007050-TR2530-4-1-2

9,23 abcd

3

2007041-TR2521-5-3-1

9,01 abcde

4

2007043-TR2523-3-1-1

8,91 abcde

2

2007020-TR2500-6-1-1

8,87 abcde

18

2007074-TR2554-3-3-1

8,73   bcde

6

2007044-TR2524-4-1-1

8,67     cde

1

Osmancık-97  (Check)

8,61     cde

5

2007043-TR2523-6-1-1

8,54     cdef

13

2007044-TR2524-1-2-1

8,48     cdef

8

2007046-TR2526-7-1-1

8,43     cdef

7

2007044-TR2524-4-4-1

8,36     cdef

14

2007044-TR2524-3-3-2-1

8,35       def

10

IMI Variety  (Check)

8,32       def

19

2007134-TR2614-3-1-1

7,85         ef

20

Edirne  (Check)

7,37           f

 

   CV (%) = 8,30                               LSD (%5)= 1,21

 

                 Table .4 The paddy yields  of yield trials conducted  in 2012 and 2013.

Entry No.

Variety Name

Rice Yield (ton/ha)

Yield Range

2013

2012

Average

13

2007051-TR2531-1-3

8,77 a

7,53

8,15

2

11

2007074-TR2554-2-2-1

8,46 ab

8,01

8,24

1

9

2007047-TR2527-2-1-2

8,31 abc

7,11

7,71

4

8

2007046-TR2526-2-1-1

8,03 abcd

6,14

7,08

12

3

2007041-TR2521-1-2-1

8,01 abcd

7,33

7,67

5

7

IMI Variety (Check)

7,95 abcde

7,26

7,61

6

2

2007020-TR2500-1-2-1

7,94 abcde

7,53

7,73

3

12

2007046-TR2526-2-2

7,91 abcde

6,64

7,28

8

4

2007043-TR2523-1-3-1

7,85 abcdef

6,75

7,30

7

1

Osmancık-97  (Check)   

7,70 bcdef

6,64

7,17

11

5

2007043-TR2523-3-1-1

7,41 cdef

7,14

7,27

9

6

2007044-TR2524-1-2-2

7,38 def

7,04

7,21

10

10

2007051-TR2531-3-1-1

7,03 ef

5,48

6,25

14

14

Edirne  (Check)

6,93 f

5,71

6,32

13

 

CV (%)= 7,08

LSD (%)= 0,93

 

 

The some agronomic and technological traits of IMI lines and check varieties were given in table-5 and 6. As it is seen in the tables, the characteristics of IMI lines are similar to the traits of conventional popular rice varieties, Osmancık-97 and Edirne at the moment in Turkey. Thus, their agronomic and technological traits can be accepted by the Turkish rice famers and consumers.

 

Table.5 The some  agronomic characteristics of lines or varieties tested in the yield trial in 2013. 

Entry

No

                                                                            

 

Variety Name

 

Days to Flower

 

Days to Maturity

Plant

Height

(cm)

Panicle Length

(cm)

Panicle Number M-2

Grain Shattering (%)

Spikelet Sterility (%)

 

Lodging

(1-9)

       

1-

Osmancık-97  (Check)

88

126

98,7

13,7

289

1

5,2

5

2-

2007020-TR2500-1-2-1

90

129

101,0

16,1

357

1

8,0

1

3-

2007041-TR2521-1-2-1

91

137

94,7

14,1

326

2

15,9

1

4-

2007043-TR2523-1-3-1

90

130

108,1

16,8

371

8

17,1

3

5-

2007043-TR2523-3-1-1

93

136

87,3

17,9

477

8

17,8

1

6-

2007044-TR2524-1-2-2

89

126

81,1

15,7

437

1

11,2

1

7-

IMI Variety  (Check)

102

144

83,1

19,6

513

4

21,9

1

8-

2007046-TR2526-2-1-1

96

140

107,5

18,1

330

1

11,4

1

9-

2007047-TR2527-2-1-2

87

126

96,7

16,4

399

1

10,8

3

10-

2007051-TR2531-3-1-1

92

126

93,3

16,7

403

1

9,1

1

11-

2007074-TR2554-2-2-1

93

137

99,5

15,5

361

2

13,9

1

12-

2007046-TR2526-2-2

97

140

110,4

19,3

369

1

5,7

3

13-

2007051-TR2531-1-3

95

140

110,7

15,4

381

2

12,4

3

14-

Edirne  (Check)

89

126

105,9

16,8

340

1

7,2

3

 

Table.6 The some  technological  characteristics of lines or varieties tested in the  yield trial  in 2013

 

 

Entry No

Variety Name

Rice Grain 1000 Grain Weight

(g)

Milled Grain 1000 Grain Weight

(g)

Rice Grain

      Milled Grain

Milled Yield

 

 

Appearance of Milled Grain

Length (mm)

Width (mm)

Lenth (mm)

Width (mm)

Total Milled

Head Rice

1

Osmancık-97  (Check)

32,4

24,4

8,6

3,2

6,1

2,9

73,9

64,3

Translucent

2

2007020-TR2500-1-2-1

31,7

23,3

9,5

3,0

6,7

2,5

72,7

66,5

Translucent

3

2007041-TR2521-1-2-1

26,0

19,7

7,6

2,9

5,6

2,6

72,8

64,5

Translucent

4

2007043-TR2523-1-3-1

25,7

19,3

9,0

2,5

6,7

2,3

73,9

63,9

Translucent

5

2007043-TR2523-3-1-1

26,8

20,2

8,8

2,5

7,0

2,4

73,5

57,8

Translucent

6

2007044-TR2524-1-2-2

30,6

22,1

9,0

2,9

6,4

2,6

72,7

61,3

Translucent

7

Clierfield  (Check)

23,8

18,1

9,0

2,5

6,7

2,2

73,4

65,3

Translucent

 

 

8

2007046-TR2526-2-1-1

37,0

27,7

 

 

9,4

 

 

3,2

 

 

7,2

 

 

2,8

 

 

70,2

 

 

48,7

Translucent with white belly

9

2007047-TR2527-2-1-2

28,2

20,8

8,9

2,9

6,2

2,5

74,5

55,9

Translucent

10

2007051-TR2531-3-1-1

22,8

16,8

8,7

3,1

2,7

2,5

71,7

62,2

Translucent

11

2007074-TR2554-2-2-1

28,1

21,1

8,7

3,2

6,3

2,6

72,2

64,3

Translucent

 

 

12

2007046-TR2526-2-2

33,0

24,7

 

 

9,1

 

 

3,3

 

 

6,5

 

 

2,7

 

 

72,7

 

 

62,8

Translucent with white centre

13

2007051-TR2531-1-3

24,4

18,9

8,3

2,9

6,0

2,6

72,4

63,9

Translucent

14

Edirne  (Check)

40,0

30,0

9,3

3,6

7,1

3,1

73,3

55,9

Translucent

 

           Backcross Breeding

           Backcross breeding to develop IMI resistant variety started in 2008 and it continued until BC6 generation  in 2013. This work finished in 2013 and the selection will be carried out in BC6F1 populations in  2014. The backcross combination reached to BC6 generation given in table-7.

  

Table. 7 The backcross generation in the end of 2013 crop season.

Pedigree

 Cross Combination

Backcross level reached in 2013.

2011147-TR3086

Osmancık-97x IMI Variety

BC6

2011149-TR3088

IMI Variety x Halilbey

BC6

2011150-TR3089

IMI Variety x Ece

BC6

2011151-TR3090

IMI Variety x Neğiş

BC6

2011152-TR3091

MI Variety x Osmancık-97

BC6

2011153-TR3092

IMI Variety x Kızıltan

BC6

2011154-TR3093

Halilbey x IMI Variety

BC6

           

At the same time, some single plants were selected in BC5F1 generations in 2013 (see table-8)  and they were planted in the experiment field as BC5F2 in 2014 rice growing season. The selection will be continued in these populations as well. 

 

         Table. 8 The backcross combination in BC5F1 generation and selected plants in 2013.

No

Pedigree

Backcross Combination

Generation

The number of selected plants

1

2011147-TR3086

Osmancık-97 x IMI Variety

BC5F1

6

2

2011149-TR3088

IMI Variety x  Halilbey

BC5F1

10

3

2011150-TR3089

IMI Variety x  Ece

BC5F1

4

4

2011151-TR3090

IMI Variety x  Neğiş

BC5F1

9

5

2011152-TR3091

IMI Variety x  Osmancık-97

BC5F1

7

6

2011153-TR3092

IMI Variety x Kızıltan

BC5F1

12

7

2011154-TR3093

Halilbey  x IMI Variety

BC5F1

11

Total

 

 

 

65

 

            Introducing  the IMI varieties to the Turkish farmers will take time, because, it is a new technology for the farmers, the Turkish rice farmers are very conservative in terms of changing technology.  Similar situation occurred in the United States, the IMI resistant varieties were first  used  on a limited areas in 2002 in this country, however, this area steadily increased through the years and IMI rice varieties were grown on more than 60% of the rice area in the southern United States.

            The promising IMI lines may be registered as commercial varieties in a few years, after then, the farmers will be able to use them to control red rice. Using this technology, they do not control only red rice but also they can have chance to control some other weeds emerging in the rice fields such as Echinochloa Spp, Leptochloa Spp., and Cyperus Spp.  etc. Similarly Meins et al., (2003) excellently controlled red rice using imazamox. On the other hand, Chin et al., (2007) controlled Echinochloa cruss-galli, Leptochloa chinensis, Cyperus iria, Cyperus difformis, Ludwigia octovalvis, and weedy rice with imidazolinone herbicide in Vietnam. Also similar results reported by Levy (2004).

 

            CONCULUSION

            The herbicide resistant rice breeding program started in Trakya Agricultural Resaerch Institute in Turkey in 2008. Since then, the breeding works have been continued. At the moment, some herbicide resistant promising lines were developed. Also, some IMI resistant backcross population developed. Using these material, IMI herbicide resistant varieties may be  registered in the near future, and then, they can be used to control red rice and some weeds in the rice fields in Turkey. Thus, an alternative tool to control the weeds will be given to the rice farmers.

 

           Acknowledgement    

           Financial support have been partially provided by TÜBİTAK (The Scientific And Technological  Research Council of Turkey (Project No. 113O106) since  the first day of January 2013.


            LITERATURE

        Burgos NR, Norsworthy JK, Scott RC, Smith K (2008) Red rice (Oryza sativa) status after 5 years of imidazolinone-resistant rice technology in Arkansas. Weed Technollogy 22(1): 200-208.

          Chauhan, B.S., 2013. Management Strategies for weedy rice in Asia. IRRI, Los Banos, Philippines.

         Chin DV, Thien TC, Bi HH, Nhiem NT (2007) Study on weed and weedy rice control by ımidazolinone herbicides in clearfield paddy grown by imi-tolerance indica rice variety. Omonrice 15:63-67.

          Diarra ARJ, Smith RJ, Taibert RE, (1985)  Growth and morphological characteristics of red rice (Oryza sativa) biotypes. Weed Sci  33 (5): 644-649.

          Fischer AJ,  Ramirez A (1993) Red rice (Oryza sativa) competition studies for management decisions. Int. J. Pest Management. 39 (2):133-138.

          Khush GS (1997) Origin, dispersal cultivation and variation of rice. Plant. Molecular Biology  35:25-34..

          Kwon SL, Smith RJ, Talbert RE (1991) Interference of red rice (Oryza sativa L.) densities in rice (Oryza sativa L.). Weed Sci 39 (4): 169-174.

        Levy RJ (2004) Imıdazolinone-Tolerant Rice: Weed Control, Crop Response, and Environmental Impact. Dissertation for Doctor of Philosophy. Louisiana State University.  66 pages.

        Linscombe S., 2004. The development an introgression of clearfield technology into commercial rice production. In: proceeding of conferance  (Eds A Ferrero, F Vidotto). Torino, Italy 13-15 September, 2004  pp. 348-352.

           Linscombe S (2010) Clearfield technology clears out red rice. Rice Today  9 (4):44-45).

           Meins KB, Scott RC, Dillon TW, Pearrow ND (2003) Tolerance of Clearfield rice to imazamox. AAES Research Series 517 pp:132-136.

           Noldin JA, Chandler JM, McCauley GN, (2006) Seed longevity of red rice ecotypes buried in soil. Planta Daninha Viçosa-MG 24(4):611-620.      

           Sato Y (2000) Origine and evolution of wild, weedy, and cultivated rice. In: Proceedings of Wild and Weedy Rice in Rice Ecosystems in Asia (Eds BB  Baki, DV Chin, M. Mortimer) IRRI, Los Banos, Philippines. pp.7-15.

          Tan S, Evans RR, Dahmer ML, Singh BK,  Shanar DL, (2005) Imidazolinone-tolerant crops: history, current status and future. Pest management Sci 61 (3): 246-257.

        Vongsaroj P (2000) Wild and weedy rice in Thailand. In: Proceedings of Wild and Weedy Rice in Rice Ecosystems in Asia (Eds BB  Baki, DV Chin, M. Mortimer) IRRI, Los Banos, Philippines. pp. 55-57.