
Rice, like wheat and maize, is one of the most important staple foods in the world, feeding more than 50% of the global population. Crop production needs to increase by 50% due to the rapid world population growth, which is projected to reach about 9.8 billion people by 2050 (Khush 2001; Khush 2003). However, recently, a dramatic decrease of rice consumption was observed in a few countries, such as Japan and Korea, despite being the staple food. In recent years, a growing interest has been observed in rice processing-oriented breeding programs that promote the improvement of glutinous rice for making rice cakes, and high amylose containing rice for making rice noodles in order to reverse the trend of the declining rice consumption.
Rice starch is composed of amylopectin and amylose molecules. The synthesis of endosperm amylose is controlled by the
The dull mutant was found to be a low amylose containing line based on the determination of amylose content in endosperm starch using the iodine amperometric ti-tration (Okuno 1976). Furthermore, following the report of a few low amylose varieties in Japan, such as cv. Aya and cv. Milky Queen (Kunihiro
Rice has been established as the model plant for monocots (Sasaki
Considering the fact that amylose content is directly related to the organoleptic qualities, more efforts to promote rice consumption have been made, focusing on rice varieties with low amylose content. The rice cultivars Baegjinju and Geunyang2 are low amylose containing varieties, released by Korean breeding programs (Hong
Rice lines with diverse levels of amylose content were cultivated in the experimental field of the National Institute of Crop Science (NICS), Department of Southern Area Crop Science, Rural Development Administration (RDA), Miryang, Korea (Table 1). The rice cultivars Shinseonchal for glutinous, LGC-soft, Milky Queen, Geunyang2, Baegjinju, Milyang320 were used for their low amylose content, Nampyeong and LGC1 as check varieties for common amylose content, and Milyang319, the pyramiding line carrying two dull genes derived from a cross between Milyang241 and LGC-soft. The rice lines were subjected to field and physicochemical studies. The seeds were sown on April 30 and transplanted on May 30, 2015 in summer season. The planting density was 22.2 m2 (15 cm × 30 cm), and plants were fertilized with N-P2O5-K2O (90–45–57 kg/ha).
Table 1 . List of rice lines used in the pedigree study for dull genes.
Rice lines | Starch properties | Gene designation | Origin of dull gene |
---|---|---|---|
Nampyeong | Normal | - | - |
Milky Queen | dull | Koshihikari mutant | |
LGC-soft | dull | NM391 | |
LGC1 | Normal | - | - |
Baegjinju | dull | - | Ilpumbyeo mutant |
Geunyang2 | dull | NM391, LGC soft | |
Milyang241 | dull | Milky Queen | |
Milyang320 | dull | Geunyang2 | |
Milyang319 | dull | Koshihikari mutant, NM391 | |
Shinseonchal | glutinous | - | - |
The rice cultivar Milyang319 carrying both
To investigate physicochemical properties of the genetic materials, amylose content was determined by the relative absorbency of starch-iodine color following the method of Juliano (1971) with slight modifications. In addition, the nitrogen content of rice grains was measured by Micro-Kjeldahl method (2300 Kjeltec Analyzer, Foss). The estimation of the protein content was done by multiplying grain nitrogen content value by 5.95, the nitrogen–protein conversion factor. A 1.4% KOH digestion, α-amylase (Megazyme kit: Mega-Calc Alpha-Amylase), and rapid viscosity analysis (RVA Super 4, Newport Scientific, Australia) were also studied. The texture of cooked rice was also measured (RHS 1A, Satake, Japan). Palatability characteristics of the rice samples were measured using a TOYO meter (MB-90A and MA-90B, Toyo Co.) to determine the glossiness of the cooked rice. The grain appearance of brown and milled rice was measured by single grain rice inspector (RN600, Kett. Co.).
Seven simple sequence repeat (SSR) markers tightly linked to
The Duncan’s multiple range test (DMRT) was used for multiple mean comparisons using the SAS statistical software (version 8.2; SAS Institute, Cary, NC).
The field performances of Milyang319 carrying two dull genes were evaluated in 2015. The heading date of Milyang319 observed on August 16 showed a similar record with Nampyeong, the mid–late maturing ecotype. Milyang319 recorded a culm length of 83 cm, and the average panicle length of 19 cm. Moreover, the average number of grains per panicle of Milyang319 (89) was similar to that of Nampyeong. The thousand grain weight (TGW) of brown rice was 22.2 g. The grain filling and brown rice ratio of Milyang319 were 80% and 81%, respectively. Furthermore, Milyang319 recorded a low yield value (4.54 mt/ha) of milled rice compared to the check variety, Nampyeong (5.03 mt/ha). Also, Milyang319 exhibited a susceptible phenotype to major field diseases and insect attacks (Table 2, 3).
Table 2 . Agronomic traits and disease and insect response of Milyang319.
Designation | DHz)1 (days) | CL2 (cm) | 3 (cm) | NP4 | NGP5 | GFR6 (%) | GW7 | HR8 (%) | GY9 (mt/ha) | Index of GY(%) |
---|---|---|---|---|---|---|---|---|---|---|
Milyang319 | 8.16y) | 83 | 19 | 15 | 89 | 80.0 | 22.2 | 81.0 | 4.54 | 90 |
Nampyeong | 8.17 | 77 | 18 | 15 | 87 | 86.7 | 21.8 | 81.9 | 5.03 | 100 |
z)1DH: Days to headings, 2CL: Culm length, 3PL: Panicle length, 4NP: Number of panicles per hill, 5NGP: Number of grain per panicle, 6GFR: Grain filling ratio, 7GW: Thousand grain weight in brown rice, 8HR: Husking recovery percentage of brown rice per rough rice, 9GY: Grain yield in metric tons per ha.
y)No significant difference was observed between Milyang319 and Nampyeong.
Table 3 . Disease and insect response of ‘Milyang319’.
Designation | Diseasez) | Bphy) | ||
---|---|---|---|---|
Blast | BB | RSV | ||
Milyang319 | S | S | S | S |
Nampyeong | M | S | R | S |
z)Blast: Leaf blast under field test, BB: Bacterial blight, race: K1, K2, K3, K3a, RSV: Rice stripe virus.
y)Bph: Brown plant hopper.
The rice cultivar Milyang319 that carries
The primers W1 and W2 amplified 741 bp bands size of
The physicochemical properties, such as amylose and protein contents, alkali digestion of eight rice lines are shown in Table 4. The recorded amylose content of Milyang319 (9.0%) carrying two dull genes was similar to that of the glutinous rice Shinseonchal (8.6%), whereas the donor lines of Milyang319 had 15.7% (Milky-Queen) and 14.5% (LGC-soft). The low amylose containing rice lines, Baegjinju and Geunyang2, harboring a single dull gene recorded about 12.2 to 14.1% amylose contents, respectively. Interestingly, in 1.4% KOH digestion value, Milyang319 showed a high value of 6.0, which was similar to that observed in the glutinous rice Shinseonchal, while in Nampyeong and other single dull gene lines, the recorded values ranged from 5.0 to 5.5. In addition, Milyang319 had the lowest protein content (4.7%) compared to other rice lines. In palatability characteristics of the rice samples, the value of glossiness of the cooked rice were not much different among the dull lines.
Table 4 . The physicochemical properties of eight rice lines.
Lines | Protein (%) | Amylose (%) | 1.4% KOH (1-7) | α-amylase (Units/g) | Palatability (Toyo value) |
---|---|---|---|---|---|
Nampyeong | 5.5b z) | 21.6b | 5.5 | 0.0336c | 78.2a |
Milky-Queen | 5.1c | 15.7c | 5.0 | 0.0223f | 78.6a |
LGC-soft | 5.6b | 14.5d | 5.5 | 0.0379b | 72.6bc |
LGC1 | 5.0c | 22.9a | 6.5 | 0.0249e | 64.4d |
Baegjinju | 5.4b | 12.2f | 5.5 | 0.0343c | 73.6b |
Geunyang2 | 6.2a | 14.1e | 5.5 | 0.0566a | 71.1c |
Milyang319 | 4.7c | 9.0g | 6.0 | 0.0290d | 73.9b |
Shinseonchal | 5.5b | 8.6h | 6.0 | 0.0348c | 65.2d |
z)Significant difference between varieties at the 5% probability level by DMRT.
Except Nampyeong, the whole (normal) grain ratio of brown and milled rice were obscure among the lines due to the white hazy endosperm appearance that falls between opaque white translucent in dull and glutinous rice grains (Table 5). Compared to the values recorded in rice lines carrying a single dull gene, the break-down of Milyang319 was as low as 92.1 and other characters of Milyang319, such as final viscosity and set back were more closed to the one observed in the glutinous rice Shinseonchal rather than single dull gene lines in rapid viscosity analysis (RVA) study (Table 5). The texture of cooked rice of Milyang319 showed the lowest hardness value, while the balance (stickiness/hardness) was as high as 0.20, similar to Baegjinju and Shinseonchal. In springiness, however, there was significant difference between the lines, the difference was not much high as shown in hardness and stickiness (Table 6).
Table 5 . The grain appearance of brown and milled rice in eight lines.
Lines | Grain quality of brown rice (mass %) | Grain quality of milled rice (mass %) | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Whole | Cracked | Immature | Damaged | Colored | Dead | Normal | Chalky | Broken | Damaged | Cracked | Objectionable seeds | ||
Nampyeong | 68.5a z) | 11.9d | 15.6e | 3.0c | 0.4ab | 0.5bcd | 83.9a | 3.0g | 2.8d | 0.4d | 7.3d | 2.7b | |
Milky Queen | 33.0c | 40.5a | 17.7e | 8.5b | 0.2b | 0.1cd | 33.0c | 22.5e | 18.3a | 1.7c | 24.4b | 0.0c | |
LGC soft | 32.7c | 14.7c | 47.6d | 4.1c | 0.8a | 0.1cd | 35.5c | 39.0d | 10.1b | 3.2b | 12.1c | 0.1c | |
LGC1 | 47.6b | 32.6b | 15.3e | 3.8c | 0.4ab | 0.2cd | 44.1b | 9.5f | 10.9b | 1.7c | 33.7a | 0.0c | |
Baegjinju | 4.0ef | 1.4fg | 83.3a | 9.7b | 0.5ab | 1.1bcd | 0.4e | 78.8b | 17.2a | 3.2b | 0.4e | 0.0c | |
Geunyang2 | 27.0d | 6.4e | 61.3c | 4.7c | 0.5ab | 0.0d | 26.3d | 61.7c | 6.3c | 3.2b | 2.5e | 0.0c | |
Milyang319 | 7.0e | 1.6f | 77.1b | 13.3a | 0.2b | 0.7bc | 0.8e | 87.6a | 9.3bc | 1.5c | 0.5e | 0.2c | |
Shinseon-chal | 2.5f | 0.1g | 85.2a | 8.5b | 0.4ab | 3.2a | 0.1e | 75.4b | 6.1c | 4.7a | 0.0e | 13.6a |
z)Significantly different between varieties at the 5% probability level by DMRT.
Table 6 . The texture of cooked rice and Rapid viscosity analysis (RVA) of starch in eight rice lines.
Lines | Texture | Rapid viscosity analysis (RVA) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Hardness (g/cm) | Stickiness | Balance (Stick./Hard.) | Springness | Peak 1 | Trough 1 | Breakdown | Final Visc. | Setback | Pasting Temp | Peak Time | ||
Nampyeong | 4.45b z) | 0.60b | 0.13c | 0.72d | 219.6b | 154.7a | 64.9c | 251.8a | 32.2a | 70.9ab | 6.5a | |
Milky Queen | 4.06c | 0.60a | 0.15b | 0.70bcd | 300.3a | 127.8a | 172.5a | 177.8c | ‒122.5d | 71.3a | 5.6c | |
LGC soft | 3.42d | 0.50ab | 0.15b | 0.69d | 215.1b | 64.0cd | 151.1a | 103.4d | ‒111.7d | 70.3ab | 5.2d | |
LGC1 | 5.09a | 0.42b | 0.08c | 0.71abcd | 240.5b | 126.2b | 114.3b | 228.8b | ‒11.7b | 69.9bc | 6.0b | |
Baegjinju | 3.00e | 0.58a | 0.19a | 0.72ab | 164.2c | 58.1d | 106.1b | 89.8e | ‒74.4c | 69.4c | 5.2d | |
Geunyag2 | 3.58d | 0.58a | 0.16b | 0.71abcd | 215.9b | 65.2c | 150.7a | 105.9d | ‒110.1d | 69.5c | 5.3d | |
Milyang319 | 2.41f | 0.48ab | 0.20a | 0.72abc | 121.3d | 29.3e | 92.1b | 50.8f | ‒70.5c | 67.0d | 3.8e | |
Shinseonchal | 3.09e | 0.62a | 0.20a | 0.73a | 72.0e | 30.5e | 41.5c | 38.6g | ‒33.4b | 68.9c | 3.4f |
z)Significantly different between varieties at the 5% probability level by DMRT.
Developing diverse endosperm starch, particularly for angiosperm species, such as rice, is essential not only for consumption but also for processing raw materials that would give an added-value and beneficial outcomes for the consumers and the market. Gluten-free cereal-based products of rice become more popular with a more concerns on health (Gallaghera
Previously, a few rice varieties containing low amylose level, developed through mutations and conventional breeding strategies, were released in Japan and Korea (Sato
The confirmation of
The endosperm is a triploid tissue having one dose of paternal alleles and two doses of the maternal alleles. Previous studies reported the dosage effects of amylose content in rice endosperm. In general, amylose content increases with the increase in gene dosage, however not in a linear way (Okuno 1978; Kumar and Khush 1986). Owing to the above, with three low amylose content doses in endosperm, the level of Wx protein producing higher amylose may not be high causing glutinous like amylose content in Milyang319.
Milyang319 showed a high alkali digestion value of 6.0 as glutinous rice of Shinseonchal in 1.4% KOH digestion. In addition, protein and palatability were not clearly classified between rice lines (Table 4). Moreover, the grain appearance compared to normal grain, glutinous, and in low amylose content rice showed a high immature and chalky scores of brown and milled rice due to the opacity in the endosperm (Table 5). The rapid viscosity analysis revealed that Milyang319 recorded the lowest hardness score of 2.41 among the cooked rice, and a similar pattern with the glutinous rice, compared to the single dull gene rice (Table 6). Thus, it was shown that the Milyang319, which harbors
The waxy rice was derived from diverse cross combinations. The results revealed that the studied agronomically important traits and physicochemical properties of Milyang319, which carries both
This work was supported by the Rural Development Administration (Project title: Development of functional rice variety for fusion and complex of valuable characteristics, Project No.: PJ01428202), Republic of Korea.
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