Comparative Study on Rice Eating Quality with Parameters-Related Differences between Indica and Japonica Rice Subspecies  

Xiaoling Wang1* , Jianguo Lei1* , Chuanyuan Yu1 , Yulong Xiao1 , Zhiquan Wang1 , Zhibao Zhou2* , Mazhong Li1
1. Rice Research Institute, Jiangxi Academy of Agricultural Sciences, Nanchang, 330200, P.R.China
2. Tobacco Corporation of Guangchang County Branch , Fuzhou 344900, P.R.China
*The same contribution to this paper
Author    Correspondence author
Molecular Plant Breeding, 2013, Vol. 4, No. 19   doi: 10.5376/mpb.2013.04.0019
Received: 30 May, 2013    Accepted: 11 Jun., 2013    Published: 14 Jun., 2013
© 2013 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Wang et al., 2013, Comparative Study on Rice Eating Quality with Parameters-Related Differences between Indica and Japonica Rice Subspecies, Molecular Plant Breeding, Vol.4, No.19 150-156 (doi: 10.5376/mpb.2013.04.0019)

Abstract

This research aimed to explore the physicochemical mechanism of differences of eating quality between indica and japonica rice subspecies by testing the differences of their physical and chemical properties, including appearance quality, cooking quality, and eating quality. A total of 57 rice varieties, including  20 early season traditional indica, 13 late season traditional indica, 12 late season indica hybrid, and 12 japonica, were selected, and 21 parameters, including 4 grain parameters, 6 RVA characteristics parameters, 3 physicochemical parameters, 8 eating parameters, were tested, then the character values relating to eating quality, RVA characteristic spectrums and 6 step decision coefficient (R2) from parameters to eating quality were analyzed. The results indicated that variability of the physicochemical parameters was much bigger among indica rice (early season traditional indica, late season traditional indica and late season indica hybrid) than among japonica rice, and bigger these variability were basic the same in three groups of indica rice. The values of RVA feature (x5-x10) and variation coefficients were bigger among traditional indica rice (early and late season) than among late indica hybrid rice and japonica rice, and their coefficient of variation of taste value was also relatively bigger. Besides eight taste parameters, the hot paste viscosity and pasting temperature coming from late indica hybrid rice and the chalkiness rate coming from japonica rice were all the most reliable evaluation parameters to forecast eating quality of rice because of their more coefficient of association to taste. The curve graphs reflecting cp (Centipoise) value demonstrated respectively almost similar model from both late indica hybrid rice and japonica rice in cooking process, that was, the change of viscosity value tended to be consistent in cooking process respectively in two groups of rice, and it was very difficult to breed the rice varieties having bigger viscosity difference, However these curve graphs coming from traditional indica rice(early, late season) with bigger change range demonstrated their more genetic diversity.

Keywords
Indica rice; Japonica rice; Subspecies; Rice quality; RVA feature

Since the 1980s, the farmers in south of China were favorite to cultivate the hybrid indica rice which made a great contribution to China’s and even the world’s food security due to their higher yield. In recent years, with the improvement of people's living standard, the market share of indica rice (especially early indica hybrid rice) have been dropping because of poorer rice quality, yet the market share of japonica rice have been increasing year by year because of better rice taste quality. In south of China, some farmers began to cultivate japonica rice instead of indica rice in some regions of suitable condition. Beginning to explore and implement the project that japonica rice was planted in south accelerated to research differences of rice eating quality between indica and japonica subspecies

Japonica and indica rice are two subspecies of cultivated rice with a strong population structure within the wild progenitors. While a large number of polymorphism markers between them were discovered successfully, the conclusive evidence was not provided about hypotheses for both a single origin and independent origins of rice, which were previously proposed and were about their origin and evolution (Wan et al., 2004; Zhang et al., 2007; Ge et al., 2011). Some conclusions that japonica rice experienced more bumpy domestication process, so the indica rice had more genetic diversity (Gao et al., 2008) and a large amount of genomic DNA including domestication-related genes could be detected only in indica rice (Yang et al., 2012), were consensus in academia. Some reports showed study progress about eating quality of rice, such as, the gel consistency test for eating quality of rice was opened firstly (Cagampang et al.,1973); Quantitative trait loci associating with rice eating quality traits were researched gradually by using a population of recombinant inbred lines derived from a cross between two temperate japonica cultivars and two indica cultivars (Lanceras et al., 2000; Wang et al., 2007; Kwon et al., 2011); The genetic basis for the effect of characteristics on the eating quality of cooked rice were studied respectively also by using the chromosome segment substitution line population (Wan et al., 2004; Liu et al., 2011); since 2009, a large number of molecular markers (STSs, SNPs and SSRs) had been used to evaluate eating quality difference among japonic species(Lestari et al., 2009; Sun et al., 2011). As for a single character, Tian et al (2009) believed that allelic diversities in rice starch biosynthesis leaded to a diverse array of rice eating and cooking qualities; Gao et al (2011) proved ALK as the key gene for gelatinization temperature by transgenic technology. Considering all the previous studies were confined within one subspecies and no study had been reported on the differences of eating quality between indica and japonica subspecies. In our study, we found out various kinds of key parameters impacting differences of eating quality in various groups rice and their physiological mechanisms.
1 Results
1.1 Data characteristics
The taste value of early season traditional indica, late season traditional indica, late season indica hybrid and japonica rice were respectively: 57.7, 73.5, 70.2, 81.2, and their coefficient of variation were small (Table 1). The results revealed the deviation range of eating quality in four rice groups would be not too big. The parameters with big coefficient of variation separately are chalkiness rate, breakdown value, setback value, amylose content of early season traditional indica, and chalkiness rate, breakdown value, setback value of late season traditional indica and late season indica hybrid, and setback value of japonica rice, that explained the indica rice (early season traditional indica, late season traditional indica and late season indica hybrid) showed significantly more difference than japonica rice in physical and chemical properties, and the parameters with observably difference were basically the same. The coefficients of variation in the chalkiness rate from late season traditional indica and from early season traditional indica were essential difference, but the former quantity was far lower than the latter that. Amylose content of early season traditional indica showed bigger difference. The values of RVA characteristic (x5~x10) and coefficient of variation from traditional indica rice (early, late season) were bigger than that from late indica hybrid rice and japonica rice, and their coefficients of variation of taste value were also relatively bigger. Setback value was as a very important index to evaluate palate value of rice hardness from hot to cold, and their values in this index were all big for four groups of rice varieties, accompanying the value of traditional indica (early, late) rice the biggest. All of upper results explained the difference of taste value in traditional indica rice was bigger than in indica hybrid and japonica due to their wider genetic diversity.


Table 1 The character statistics of rice in four ecological region
1.2 Determination coefficient
The values of 6 step determination coefficient (R2) from parameters to taste value can forecast contribution of parameters to taste value. The seven parameters (x14~x20) relating taste value contributed to taste value the biggest than others 13 parameters (x1~x13) (Table 2). In late indica traditional rice varieties, the values were most obvious, and in japonica rice, the values were relatively smaller, which explained the method, GB/T15682-1995, was more accurate in evaluating taste quality of indica than in japonica, especially in late indica traditional rice the best. Besides taste parameters, hot paste viscosity and pasting temperature from late indica hybrid rice and chalkiness rate from japonica rice contributed to taste value also considerable, that explained the three parameters had bigger prediction to their respective taste quality. They were only three parameters found only in the two groups of rice varieties beyond taste parameters, which could forecast more reliability rice taste quality.


Table 2 6 step determination coefficient of parameters to taste value in four groups rice varieties
 
1.3 RVA characteristic spectrum
The curve graphs reflecting cp (Centipoise) value demonstrated almost similar model from late indica hybrid rice, and from japonica rice in cooking process (Figure 1 C; Figure 1 D), that was, the viscosity change tended to be consistent in cooking process respectively in the two groups of rice varieties, and it was very difficult to breed the rice varieties with very big viscosity difference. However, the same curve graphs from traditional (early, late) indica rice demonstrated bigger change range (Figure 1 A; Figure 1 B), which reflected differences of the cp value in cooking process that the highest viscosity value and inflection point of time were all very big from different traditional indica rice varieties. Above conclusions illustrated the traditional indica rice varieties (early, late) with more genetic diversity in cooking viscosity character, and having more chance to improve viscosity quality in breeding progress. From these results it was summarized that the difference size of coefficient of variation of the viscosity value in four groups of rice was coincident with that supplied in Table 1. The information showed further the traditional indica rice with more genetic diversity, and later season indica hybrid and japonica rice with simpler genetic background, The right Y axis is the temperature. The left Y is the temperature-related viscosity (cp). The X axis is time in RVA process for each Fig.


Figure 1 The RVA characteristic spectrum
2 Discussion
In genetic relationship, some viewpoints, such as Asia’s culture rice originated from China (Ding, 1957), and the south of China was at least one of origin centers of traditional cultivated rice (Ganet al., 2002), were consensus in academia. There was dispute in study on evolution of subspecies, although many conclusions about study of indica and japonica rice were acquired. The genes which transcribed product to affect taste quality of rice wound inevitably be changed form indica to japonica for their different experience of genetic differentiation over 400,000 years. The characters including amylose content, gel consistency and gelatinization temperature determined the taste and cooking quality of rice, and related to each others (Tian et al., 2009). Gel consistency and alkali digestion value were the most important factors to affect eating quality of rice (Wu et al., 2003), but theirs function mechanism were not clear. This research also showed that the difference of eating quality of rice couldn't be judged from a single agronomic parameter because eating quality was a complex comprehensive character. The molecular mechanism of quality difference between subspecies might also be explained, if the key molecules or key mechanism on subspecies evolution had been breakthrough.
In habitat differences aspect, the habitat environment of cultivated indica and japonica was different, due to their taming progress in different environment (Yu et al., 2011), The characters of indica rice include grain slender, hull hair shorter and bulk raw, leaf curved and long, plant type looser. They were suitable for cultivation in low altitude, low elevation, humid and hot region, japonica rice with opposite them. In China, japonica varieties were planted as late season rice in the double season rice region of the middle and lower of the Yangtze river, or as single season rice in the north of the Yellow River of china. When japonica rice was planted in the south, the taste quality of rice had generally less advantage than in the north, following reasons that on September, higher temperature and bigger difference of temperature between day and night in the north, during this stage of grain filling, japonica rice might produce less chalkiness and more product in the north than in the south. Chalkiness which affected directly the amylose content, finals viscosity and setback value (Liu et al., 2009) was an important index of rice quality. Setback value was also a very important index to evaluate palate value of rice hardness from hot to cold process. The values of setback in early season traditional indica, late season traditional indica, late season indica hybrid and japonica rice were respectively: 948,376, 23.2 and 58.4, which explained traditional indica (early, later season) with more difference and genetic diversity in hardness character. To late season indica hybrid, chosen genes from their parents had been confined in comparatively narrow range by reason of their experience of more than 30 years quality (yield, resistance) breeding.
3 Material and Methods
3.1 Rice materials
Four groups of rice varieties were used in this study, the first group consisting of 20 early season traditional indica rice; the second groups consisting of 13 late season common indica rice; the third groups consisting of 12 late indica hybrid rice; the fourth groups from 12 japonic rice, coded: T1-T12. All of these rice varieties were planted and harvested repeated twice in farm field of Jiangxi Academy of Agricultural Sciences in 2010 and 2011.
3.2 Investigation of rice grain
Investigation data according to the Agricultural Industry Standard “Measuring Rice Method” (NY147-88); 20 grains of head milled rice were selected randomly from every varieties. The values of grain long (x1), grain width (x2), the length-width ratio (x3) by the digital display vernier caliper and the chalkiness rate (x4) on the projection glass plate were measured.
3.3 Scanning of RVA value
Grains were firstly dehulled by traditional dehulling machine, and then grinded into powder using homemade whirlwind machine in the China National Rice Research Institute, passing 100 mesh, 3.00g fine rice powder of each sample were divided out. All kinds of RVA character values were measured by the Swedish production viscosity rapid tester (RVA) (type: Newport Scientific pty Ltd. RVA-TecMaster) with two replications. A total of six parameter values were recorded: peak viscosity (x5), hot paste viscosity (x6), breakdown value (x7), final viscosity (x8), setback value (x9) and paste temperature (x10).
3.4 Measurment of physical and chemical properties
Measuring of physical and chemical properties was conductedat the Union Lab of Rice Quality and Nutrition in the China National Rice Research Institute-the International Rice Research Institution. Three parameters: gel consistency (x11), amylose content (x12) and pasting temperature(x13) were acquired according to Standard GB/T17981-1999 and GB/T15683-1995.
3.5 Tasting of eating value
Taste value (y/x21) and relish value (x20) were obtained according to approved standard method by the State Dureau of Technical Supervision of the Ministry of Agriculture “1995-08-17 GB/T15682-1995”, taste value connecting to smell value(x14), colour lustre value (x15), exterior value (x16), viscous (x17), elastic (x18), hardness (x19) (palatability) and relish value, as a composite value.
3.6 Statistical analysis
The data was analyzed statistically by biological software Excel2003, SPSS18.0 and SAS9.0.
Acknowledgements
Test working of this study was finished at the Union Lab of Rice Quality and Nutrition in the China National Rice Research Institute-the International Rice Research Institute, getting some teacher's genial help, Appreciation goes to them.
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