Study on Physical-Chemical Characters and Heritability for Yield Components in Rice ( Oryza sativa L.)

. Present study was performed to analysis both physical and chemical properties of rice germplasm and heritability for yield components in combinations. A total of 44 lines/varieties obtained from Cuu Long Rice Research Institute genebank, and 30 F 1 generation combinations were evaluated. The results showed that the rice line IR79008-B-11-B-B-1 showed overall good physical characters (head rice, grain length, grain width, chalkiness). In terms of chemical characteristics, three varieties IR75499-73-1-B, OM6162, and OM4900 were found to have good amylose content, gel consistency, protein content, gelatinization temperature, and aroma. A very notable finding was that the cross between OM6162/SwarnaSub1 that low amylose content (20.2%), high gel consistency (78.2 mm), high protein content (8.1%), appropriate gelatinization temperature (scale 5), low chalkiness (level 0), high heritability (0.9) for grain yield trait/cluster, and (0.84) for the number of panicles/cluster. Moreover these characters consist of plant height, panicle length, number of panicles/cluster, number of filled grains/panicle, number of unfilled/panicle, and grain yield/ cluster showed moderate to high heritability of mean for combination OM6162/SwarnaSub1. The results suggest that the grain yield trait/cluster and the number of panicles/cluster are important yield contributing traits to rice breeders for selecting ideal combinations for higher yield and quality of next generations.


Introduction
Rice is an important staple food for more than half of the world's population, especially in developing countries. For thousands of years, the culture, economy and history of many countries and regions in the world have been profoundly shaped by this plant. In Vietnam, currently, one of the most important objectives of rice production is to develop new varieties, which have high quality and highly adapt to climate change. Research strategy in rice breeding is creating of rice varieties with desired traits including long grain, low amylose content (< 20%), less chalkiness, aroma, short growth duration (90-100 days), and stable tolerance to both biotic and abiotic stresses.
Grain quality in rice plays an important role in acceptance by consumers as the second most important factor behind high yield in objectives of rice breeding [1][2][3]. Furthermore, it determines the market price of rice [4]. Therefore, evaluation of rice quality involving chemical compositions, cooking quality, gelatinization temperature and physical properties of rice is essential [5]. The quality of rice into three groups consisting of (1) physical characteristics including moisture content, shape, size, whiteness, translucency, chalkiness, head rice, broken rice, brewers, green kernels and yellow kernels; (2) chemical characteristics including amylose content, protein content, gel consistency, expansion level of cooked rice, water absorption, and cooking time; (3) the sensory aspects of cooked rice including color, aroma, hardness, stickiness, and consistency [6]. The three key components determining cooking and eating are amylose content, gelatinization temperature and gel consistency. The chemical characteristics include the amylose content (AC), gelatinization temperature (GT), gel consistency (GC), protein content (PC) and aroma which are directly related to cooking and eating quality [7].
Beside quality of rice, a quantitative trait rice yield is a complex character of any crop. The success of a breeding program depends on the availability on genetic variability in the subjected to selection [8]. Genetic variability for agronomic traits is key component of breeding programmes for broadening the gene pool of rice [9]. Yield potential of rice can be improved with different strategies [10]. Breeding strategy in rice depends on degree of associated characters as well as its magnitude and nature of variation [11]. Commonly, plant breeders select for yield components which indirectly increase yield [9]. Moreover, heritability of traits is essential for selection based improvement as it indicates the extent of transmissibility of a character into generations [12]. Therefore, the main objective of this study were (1) to evaluate the quality levels of physical and chemical characteristics of rice germplasms in order to improve quality rice cultivars, in which several beneficial traits should be combined; and ( 2) to estimate the heritability of yield and yield components of F4 generation.

Plant materials:
Rice germplasms were used in this study, including 44 lines/varieties in the genebank of Cuu Long Delta Rice Research Institute (CLDRRI).
The experiment was conducted in 2015 -2016 dry season at Cuu long Delta Rice Research Institute, Viet Nam. After 15 days old seedling, each variety were transplanted with one plant per hill in Randomized Block Design with three replications. The row-to-row and plant-to-plant spaces of 20 cm x 15 cm were maintained. Ten-day after transplanting, the drainage through drain taps was set up; without provide the water until flowering. The fertilizer was applied at rate 100-40-30 kg N-P 2 O 5 -K 2 O ha −1 for dry season and 80-40-30 kg N-P 2 O 5 -K 2 O ha −1 for wet season. After harvesting the seeds of each line/variety were dried using solar heat to obtain 14% moisture content, and then dehulled for evaluation of the grain quality in three replications.
The hybrid materials were screened in the field and used for making crosses. Total F 1 seeds of 30 combinations were made by a single cross. The data for amylose content (AC), gel consistency (GC), protein content (PC), gelatinization temperature (GT), and aroma are main major traits for the first step to select combinations.
Developing the population F 1 and production of F 2 seeds then selecting F 2 , F 2 generations from 30 combinations during 2015 dry season to 2016 wet season at Cuu Long Delta Rice Research Institute, Viet Nam. F 2 generation was grown and selected separations for generating the F 3 generation, and F 3 plants were selected. F 3 lines were planted to continue to evaluate for the F 4 generation. For the performance test agronomic characteristics such as plant height, panicle length, number of panicle/cluster, number of filled grain/panicle, number of unfilled grain/panicle, and grain yield/cluster (g) were investigated.

Evaluation of physical characteristics:
Brown rice (BR) and milled rice (MR) ratios were measured by a standard dehusker [13]. Head rice (HR) was tested by using a hundred grams of dehusked rice grains that had no visible breakage. The percentages of HR and broken rice were then calculated [13]. Chalk index was determined by placing ten dehusked rice grains on a light box and visually identifying the chalkiness of each grain. The chalkiness percentage of each rice line/variety is an average of ten values from ten grains. The following levels were used for classifying endosperm chalkiness of milled rice including level 0 (no chalkiness), level 1 (less than 10% chalkiness), level 5 (10 -20% chalkiness), and level 9 (more 68 ILNS Volume 57 than 20% chalkiness) [13]. The grain size, one of the important characteristics was measured in length (mm) and width (mm) of grain.
Gel consistency (GC): Milled rice samples (10 grains) were ground into a fine powder in the Wig-L Bug grinder. Consistency is measured by the length in a test tube of the cold gel held horizontally for 1h after heating in 0.2 N potassium hydroxide (KOH) (2 mL) and categorized as soft (61 -100 mm), medium (41 -60 mm), and hard (26 -40mm) [15].
Gelatinization temperature (GT): GT is estimated by the extent of alkali spreading, according to [15]. Ten milled rice grains were placed in a Petri dish, and then 10 mL of 1.7% KOH was added. The sample was placed in an incubator at 25 o C for 24h. The degree of spreading is measured using a 7-point scale as follows: 1 (grain not affected), 2 (grain swollen), 3 (grain swollen, collar incomplete and narrow), 4 (grain swollen, collar complete and wide), 5 (grain split or segmented, collar complete and wide), 6 (grain dispersed, merging with collar), and 7 (grain completely dispersed and intermingled). The scale includes 1-2: high (74. 5 - Aroma: Ten leaves of rice were cut into 5 mm long pieces, and then put into a capped test tube. A volume of 5 ml of 1.7 % KOH solution was added and incubated at 50 o C for 10 min. Five panelists were asked to classify the samples as either aromatic or non-aromatic by their own smell. Aroma classification is defined as score 0 (no aroma), score 1 (slight aroma), score 2 (moderate aroma), and score 3 (strong aroma) [16].

Data analysis:
All measurements were conducted in triplicates. An analysis of variance (ANOVA) for all data was performed using the SAS 9.1 software. Broad -sense heritability (h 2 ) was calculated was the ratio of the genotypic variance to the phenotypic variance using the formula according to Allard [17]: h 2 = σ 2 g/σ 2 p Where h 2 = broad -sense heritability, σ 2 g = genotypic variance and /σ 2 p = phenotypic variance.

Physico-chemical characteristics of parental materials
Physical characters: Evaluation of targets grain quality parent materials under drought tress were significantly for the physical -chemical characters. In this study, physical traits were evaluated consisting of characters described in Table 1.
The percentage of BR ranged 75.6 to 88%, the lowest was recorded in the line IR78966-B-16-B-B-B and the highest was WAB340-B-B-2-H2. Most of the remaining varieties had the BR percentage higher than 80%.
The percentage of BR ranged 75.6 to 88%, the lowest was recorded in the line  The highest GC was found in IR78933-B-24-B-B-2 (100 mm) and the lowest was WAB176-42-HB (42.8 mm). There were 28 lines/varieties belonging to the categories soft rice, 19 lines/varieties belonging to medium. The gelatinization temperature (GT) is the temperature at which the starch granule begins to swell irreversibly in hot water with a simultaneous loss of crystalline. In this study, the GT scales had a large variation among lines/varieties which ranged from scale 1 to 7. The results demonstrated that the line IR79008-B-11-B-B-1 was the best in term of good physical characteristics, such as head rice, grain length, grain width, and chalkiness. The three lines/varieties that came out on top of the chemical characteristics were IR75499-73-1-B, OM6162, and OM4900. Identifying those lines that exhibit the best characteristics will be useful for improving the quality of future rice breeding programs. This will be helpful in assessing the varietal characters for selecting parents.

Grain quality characteristics of combinations
The grain quality traits of F 1 generation of 30 hybrid combinations were evaluated, shown in Table 3

Selecting line of F 3 generation and production F 4 seeds:
In lines selected generation with combinations were recorded in Table 4. Therefore, selection was 10 combinations recorded on phenotypic and relatively good yield and growth duration less than 100 days. The F 3 generation recorded through individual selection from many crosses reached segregation with many different shape, include grain shape and color of grain hulls. Result through the F 3 generation were recorded with 282 of selected lines were in planting to continue to evaluate for planting the F 4 generation from 10 combinations. Table 4 OM6162/ SwarnaSub1 250 1200 55 Selecting line of F 4 generation: F 4 generations was continued to grow and select to evaluate recorded. Total 8 combinations were selected relatively high yields. Two combinations IR75499-29-2-B//IR64Sub1 and IR78937-B-3-BB-3/IR64Sub1 generating seeds with beard should continue to be removed. In the F 4 generation was grown with 8 combinations recorded (Table 5). Table 5. Selection individual of the F3, F4 No. Combinations  medium (153,19). Trait number of unfilled/panicle in combination OM6162/SwarnaSub1 which showed that significant highest (63), lowest (5) and medium (18.5).

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Analysis of genetic parameters for grain yield trait and yield components is presented in Table  6. Significant heritability (h 2 ) of high yield, panicle length, number of unfilled grain/panicles and plant height at P<0.01 was 0.98; 0.74; 0.56; and 0.5, respectively by IR75499-29-2-B//IR64Sub1. The highest heritability was noticed in grain yield trait/cluster. Medium to significant heritability at P<0.05 was observed in number of filled grain/panicle trait.
The high heritability was observed in all most of the traits of combination OM6162/SwarnaSub1 at significant P<0.01. The heritability estimates observed for traits ranged from 0.4 to 0.9. High heritability observed for panicle length, number of panicles/cluster, number of filled grains/panicle, number of unfilled/ panicle, and grain yield/cluster. The final resultant of yield components was grain yield/ cluster. Combination OM6162/SwarnaSub1 attained statistically the highest grain yield/cluster (120 g) whereas combination IR75499-29-2-B//IR64 Sub1 (42.12 g), lowest (10.58 g), and medium (26.5 g).

Discussion
Grain quality in rice is determined by the factors as grain appearance, nutritional value, cooking and eating quality [18]. The head rice recovery is the main factor effecting milling quality. In this study, most lines/varieties had more than 50% of HR recovery. However, previous studies showed that the HR should have a value of at least 70% [19]. In fact, rice grains in this study were evaluated under drought condition, so the HR average was lower. HR levels depend on different factors, such as grain type, chalkiness, environment during dry conditions, variety, and cultural practices [19,20]. The grain size is an important quality in rice trade with different preferences among consumers [21. The grain size was controlled by genetic traits [22]. Also, grain size is bred at the level of early generation, and the long grain type is generally preferred in Mekong Delta. The size and shape were stable varietal properties that could be used to identify a variety [23]. The most acceptable grain length is around 6 mm [24]. The shapes of milled rice, in terms of length -width ratio are slender > 3.0, medium (2.1 -3.0), bold (1.1 -2.0), and round (1.1) [25]. Based on the classification, rice materials could be defined as medium to long grain. Since the grain length and width of rice are of importance to those involved in the rice industry, these characteristics are seriously considered in the breeding of new varieties [26]. Thus, grain size is the first criteria of rice quality that researchers need to concentrate in the development of new varieties.
The chalkiness is influenced by both genetic and environment factors, as temperature immediately after flowering and other factors, such as soil fertility and water management [27] and drought stress during ripening and blast disease [28]. Most of the lines/varieties had low chalkiness from level 0 to 1. The line/varieties having minimum level of the chalkiness can be used as donors for breeding varieties of quality rice from the commercial point of view. Amylose content (AC) is one of the most important characteristics for cooking and processing practices [29]. Commonly, consumers like rice with intermediate AC ranged between 20 to 25% [30]. Gelatinization temperature (GT) is another important quality to determining the cooking quality of rice. GT is not associated with other grain traits except amylose content [25]. In this study, there were large variations of GT among lines/varieties. The nutritional values of rice depend on the total of protein.
High protein content equates with higher nutritive value. A wide range of protein content (4.5 -15.9%) was found among 2,674 rice varieties [31]. The aromatic level in rice is one of the other important traits in breeding and may cause high demand in the market [32]. Total of 114 different volatile compounds that are responsible for rice fragrance [33]. The biochemical basis of aroma was identified as 2-acetyl-1-pyrroline [34] which stands out as the main fragrance compound in both jasmine and basmati varieties.
The chalkiness is influenced by both genetic and environment factors [27]. If selection non-chalky is made only in the late generations (F6 -F7), it is difficult to eliminate. Therefore, selection of non-chalky grain should be made in an earlier generation in rice breeding programs.
In order to evaluate the association among characteristics is an important factor, particularly yield to determine the direction of selection and number of traits to be considered of rice yield. Heritability provides better genetic advance for selecting plant material regarding these traits. The highest heritability was noticed for grain yield trait/cluster both of two combinations. Results showed that high heritability for the number of spikelets per panicle, 1000 grain weigh and nuber of the panicles per plant [35]. In this study, high heritability observed in combination OM6162/SwarnaSub1 0.74 for panicle length, 0.84 for number of panicles/cluster, 0.7 for number of filled grains/panicle, 0.76 for number of unfilled/panicle, and 0.9 for grain yield/cluster. Previous study also reported that high heritability 41.74% for number of panicles per plant [36]. Results of high heritability and genetic advance of grain yield/plant are also in accordance with those reported by [37][38][39]. Heritability serves as a good index for transmission of traits from one generation to next and it should be considered in terms of selection concept [40]. Since high heritability do not always indicate high genetic gain, heritability with genetic advance considered together should be used in breeding [41].
These characters consist of plant height, panicle length, number of panicles/cluster, number of filled grains/panicle, number of unfilled/panicle, and grain yield/cluster showed moderate to high heritability of mean for combination OM6162/SwarnaSub1. Most of above traits have resulted that highest heritability was noticed for grain yield trait/cluster, and the number of panicles/cluster. Therefore, the results suggest that the grain yield trait/cluster and the number of panicles/cluster are important yield contributing traits and selection based on these characters would be most effective for rice breeding.