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Dilday, R.H., P. Nastasi, R.J. Smith, Jr., and K. Khodayari. 1990. Herbicide-tolerant germplasm in rice. p. 146-150. In: J. Janick and J.E. Simon (eds.), Advances in new crops. Timber Press, Portland, OR.

Herbicide-tolerant Germplasm in Rice

R.H. Dilday, P. Nastasi, R.J. Smith, Jr., and K. Khodayari

  6. Table 1
  7. Table 2
  8. Fig. 1


Red rice (Oryza sativa L.) and cultivars of white rice belong to the same genus and species (Hoagland and Paul 1978). Red rice is one of the most common and troublesome weeds of rice in the southern U.S., causing an estimated loss of $50 million dollars annually (Smith 1976). Red rice is a problem weed because it has a red pericarp or seed coat which is commercially unacceptable; reduces yield because it competes for light, nutrients, and space; tillers more profusely; increases lodging because of its weak straw; reduces milling yield because it requires more severe milling to remove the red pericarp; and shatters easily which makes it hard to eliminate from commercial fields (Dodson 1898; Nelson 1979; Smith 1981). Control of red rice in commercial rice fields is economically prohibitive and selective herbicides for control of red rice in rice are not available.

Strawhull and blackhull are the two principal types of red rice. Chemical control of red rice in commercial fields has not been achieved because of the similar biological and physiological properties of red and commercial rice. However, rice rotated with upland crops combined with effective herbicides will control red rice (Baker and Sonnier 1983; Smith 1976, 1979). Soybeans grown for two years and followed by rice the third year has reduced red rice infestations sufficiently for satisfactory rice production (Smith 1979). Alachlor, which is absorbed by germinating seeds, controls red rice in soybeans (Khodayari et al. 1987).

The development of rice cultivars which are tolerant to a herbicide that controls red rice would help control red rice in commercial rice. Intraspecific variation in tolerance to herbicides has occurred in crops such as barley (Hordeum vulgare L.) (Derscheid et al. 1952); oats (Avena sativa L.) (Smith and Buchholtz 1964, Williams 1953); corn (Zea mays L.) (Williams 1953, Wright and Rieck 1973, 1974); sorghum [Sorghum bicolor (L.) Monech] (Scifres and Bovey 1970); sugarcane (Saccharum officinarum L.) (Matherne and Millhollon 1973, Millhollon and Matherne 1968); soybeans [Glycine max (L.) Merr.] (Barrentine et al. 1982, Hays and Wax 1975, Wax et al. 1974, Williams 1953); potato (Solanum tuberosum L.) (Graf and Ogg 1976); and tomato (Lycopersicon esculentum Mill.) (Stephenson et al. 1976). Rice cultivars and advanced lines that are tolerant to molinate, an herbicide which controls barnyardgrass, have been identified (Richard and Baker 1979, Smith 1970).

The objectives of this study were to develop field and laboratory techniques for evaluating rice germplasm for resistance to alachlor and evaluate accessions from the rice portion of the USDA/ARS small grains germplasm collection for tolerance to alachlor.


Six experiments involving two concentrations of alachlor and 4,567 accessions from the rice portion of the USDA/ARS small grains collection were conducted from 1983 to 1985 near the Rice Research and Extension Center, Stuttgart, Arkansas. The tests were drill seeded (3 g of seed/m) in single row plots 1.23 m long with a 19 cm row spacing in two replications on June 1-2, 1983; June 10-12, 1984; and May 23-25, 1985. Prior to seeding, 4.58 and 6.88 kg ai/ha of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] was incorporated to a depth of 5 to 8 cm into a Crowley silt loam, a fine montmorillonite thermic Typic Albaqualf. Plant height and grain type were determined at maturity. Two replicated tests were conducted in 1986. Each test included 2 row plots 1.23 m long with each row being 19 cm apart and the tests were treated with 4.58 and 6.88 kg ai/ha of alachlor. The experimental design for this test was a randomized complete block with four replications. The total number of seedlings that emerged were determined 7, 14 and 21 days after seeding in each test.

The 4,567 rice accessions that were evaluated for tolerance to alachlor originated in 34 countries. Sixteen accessions that had a higher level of tolerance to alachlor than the others originated in Pakistan, India, Sierra Leone, Madagascar, Sri Lanka and Philippines. Furthermore, eight of the 16 accessions came from an area along the Pakistan and India border, three from the Philippines, two from Africa (Sierra Leone), two from Islands in the Indian Ocean (Madagascar and Sri Lanka), and one unknown (Table 1). The accessions included short, medium, and long grain types that produced plant heights ranging from 90 to 157 cm. Based on results from field trials and laboratory tests, the 16 accessions were evaluated further in the field in 1986. Seedling emergence was significantly greater for two accessions, 'IR 1317-152' and ' Jhona White Pak 83', than for the other 14 accessions or the two checks.

IR 1317-152 is identified as PI 349393 in the rice portion of the USDA/ARS small grains collection that is maintained at Aberdeen, Idaho. IR 1317-152 originated at the International Rice Research Institute, Los Banos, Philippines and its identifying plant characteristics are: medium grain, semidwarf plant that requires between 100 to 110 days to develop from seedling emergence until 50% of the main tillers show panicles, culm or culm angle is open, panicle type is intermediate, hull completely covered with short hairs or pubescence, straw colored hull and sterile lemma, partly awned with long awns, light brown seed coat (bran/pericarp) color and lodging resistance is moderately strong. 'Jhona White Pak 83', identified as PI 385565 in the rice collection, originated in Pakistan and its identifying plant characteristics are: long grain, tall plant that requires between 90 to 100 days to develop from seedling emergence until 50% of the main tillers show panicles, culm or culm angle is open, panicle type is intermediate, hull completely covered with short hairs or pubescence, straw colored hull and sterile lemma, awns are absent, light brown seed coat, and lodging resistance is very weak. The definition of each plant characteristic is based on the IBPGR-IRRI Rice Advisory Committees report on "Descriptors for Rice Oryza sativa L." (IBPGR-IRRI Committee 1980).


In 1985 five seeds per accession from a total of 180 accessions and two checks, 'Lemont' and 'Lebonnet', were germinated in disposable petri dishes which contained Whatman's No. 1 filter paper, moistened with 3 ml of 2 and 3 ppmw of alachlor. The mesocotyl and coleoptile were measured after the petri dishes were placed in a temperature controlled germination chamber for seven days at 28°C. Abnormal or diseased seedlings were determined for percent germination but the mesocotyl and coleoptile lengths were not measured because of abnormal growth and development of these seedlings. Each seed was considered germinated when the mesocotyl-coleoptile developed to a length of 2 mm. The seedlings which produced leaves were washed in water and transplanted in herbicide-free soil in pots in the greenhouse for 3 weeks to observe their growth and development. In 1986, 16 of the most tolerant accessions and 2 checks (Lemont and Lebonnet) were evaluated in a germination chamber at 28°C for 7 days on Whatman's No. 1 filter paper, moistened with 3 ml of 0 (check), 0.1, 0.5,1.0, 3.0, 5.0, and 10.00 ppmw of alachlor. After 7 days the mesocotyl coleoptile, primary leaf, secondary roots, and radicle of each seedling were measured. Each laboratory test was replicated 6 times.

Alachlor is absorbed primarily through the mesocotyl and coleoptile tissue of the seedling and ultimately disrupts the development of the radicle, secondary roots, and primary leaves (Pillai et al. 1979). Furthermore, the elongation potential of the mesocotyl and coleoptile is heritable and varies according to the genetic constitution of the germplasm (Dilday et al. 1988). Inge and Loomis (1937) demonstrated that mesocotyl elongation is inhibited when the tip of the coleoptile is exposed to light. Also, the elongation of the mesocotyl and coleoptile is influenced by the depth of seeding (Fig. 1).

Results from the laboratory experiments demonstrated that the mesocotyl/coleoptile elongation was reduced by about 50% in 'Lemont', 'Lebonnet', and IR 1317-152 at 0.1 ppm (by weight); whereas, 1 0.0 ppm not inhibit mesocotyl/coleoptile elongation by 50% in Jhona White Pak 83 (Table 2). Secondary root development of the checks, Lemont and Lebonnet, did not occur even at the lowest concentration of 0.1 ppm. Secondary root development of Jhona White Pak 83 occurred up to 3.0 ppm. Furthermore, secondary root development of IR 1317-152 occurred at the highest concentration of 10.0 ppm. Primary leaf development was not initiated in either check at 0.1 ppm; however, it did occur at 0.1 and 0.5 ppm in Jhona White Pak 83. Primary leaf development continued to occur at the highest concentration (10.0 ppm) in IR 1317-152. The development of the radicle was reduced by 50% or more in the two check cultivars at the lowest concentration (0.1 ppm) of alachlor, however, a 50% or greater reduction in the development of the radicle did not occur until treated at the 0.5 ppm alachlor concentration for both tolerant germplasm accessions.


The two tolerant germplasm accessions responded differently to alachlor which suggests that the tolerance is due to separate genetic mechanisms. For example, the mesocotyl-coleoptile development of the two cultivars and IR 1317-152 was similar when grown in alachlor; whereas, there was no significant difference in mesocotyl/coleoptile development of Jhona White Pak 83 to alachlor at the 0.1 and 0.5 ppmw concentration. Conversely, the leaf and secondary root development of IR 1317-152 was more tolerant to alachlor when compared with Jhona White Pak 83. The development of the radical of the two tolerant germplasm accessions grew similarly in alachlor. This suggests that pyramiding of tolerant genes from different germplasm sources such as IR 1317-152 and Jhona White Pak 83 could increase the overall level of germplasm tolerance to alachlor.

Red rice causes an estimated loss of $50 million dollars annually in commercial rice in the southern U.S. because there is not an economical method of controlling red rice in commercial rice. The concept of developing and utilizing herbicide-tolerant cultivars in a red rice control program could be a very practical approach for control of this weed.


Table 1. Origin, plant height, grain type, and number of emerged seedling/m of 16 germplasm accession and two cultivar checks that varied in tolerance to alachlor (4.58 kg/ha).

Germplasm identification Country of origin Plant height (cm) Grain typez No. emerged seedlings/m
ARC 10311 India 157 M 9.0ay
IR-1317-152 Philippines 91 M 8.5a
Jhona White Pak 83 Pakistan 146 L 8.2a
ARC 10105 India 155 M 4.4b
IR-1317-386 Philippines 90 M 4.0bc
PI 433811 Sierra Leone 119 MX 3.5bcd
Early Prolific Sel 388 Unknown 109 M 3.5bcd
PI 461222 Sierra Leone 115 MX 3.2cd
IR-527-1-57 Philippines 93 M 3.1cd
Coarse Pak 76S Pakistan 142 M 2.5de
Jhona Sufaio Pak 67 Pakistan 123 L 1.8ef
Madagascar 1300 Madagascar 144 S 1.6ef
BG 34-8-Ceylon SRI Lanka 102 S 1.6ef
ARC 10757 India 133 L 1.5ef
Siah Nakidar Pak 195 Pakistan 131 L 1.4f
ARC 10583 India 168 M 1.2f
LMNT U.S. 85 L 0g
LBNT U.S. 109 L .0g
zM = Medium grain; MX = Mixed grain; L = Long grain; S = Short grain.
yMean separation by Duncan's multiple range test, 5% level of probability

Table 2. Response of 2 cultivars without tolerance and 2 germplasm accessions with tolerance to Alachlor.
Alachlor rate (ppmw) Lemont Lebonnet IR-1317-152 Jhona White Pak 83z
Mesocotyl/Coleoptile length (cm)
0 1.1a 1.7a 1.9a 0.8ab
0.1 0.6bc 0.8b 1.0b 0.9a
0.5 0.4cd 0.6bc 1.0b 0.8ab
1.0 0.4cd 0.4cd 0.8bc 0.6b
3.0 0.4cd 0.4cd 0.8bc 0.6b
5.0 0.4cd 0.4cd 0.7c 0.6b
10.0 0.3d 0.2d 0.7c 0.5b
Length of secondary root(cm)
0 0.4 1.2 0.7a 1.0a
0.1 0.0 0.0 0.7a 0.6b
0.5 0.0 0.0 0.3b 0.2c
1.0 0.0 0.0 0.4b 0.1c
3.0 0.0 0.0 0.4b 0.0
5.0 0.0 0.0 0.2c 0.0
10.0 0.0 0.0 0.2c 0.0
Length of primary leaf(cm)
0 1.1 2.3 3.2a 1.6a
0.1 0.0 0.0 0.4b 1.6a
0.5 0.0 0.0 0.2bc 0.2b
1.0 0.0 0.0 0.2bc 0.0
3.0 0.0 0.0 0.1c 0.0
5.0 0.0 0.0 0.1C 0.0
10.0 0.0 0.0 0.1C 0.0
Radicle length (cm)
0 3.6a 4.9a 3.7a 5.4a
0.1 1.8b 1.7b 3.2a 5.2a
0.5 1.1c 1.4b 1.7b 1.2bc
1.0 0.9c 1.2bc 1.3bc 1.7b
3.0 1.1c 0.7cd 1.3bc 1.3bc
5.0 0.8cd 0.8cd 0.8c 1.5bc
10.0 0.3d 0.5d 0.8c 1.0c
zMeans separation in columns by Duncan's multiple range test, 5% level of probability.

Fig. 1. Schematic of rice seedlings showing the major seedling components and demonstrating how seeding depth influences mesocotyl/coleoptile elongation.

Last update August 26, 1997 by aw