Inheritance of kernel elongation in F2 rice populations crossed between Indian rice basmati 370 and selected Malaysian rice varieties

*Nur Suraya, A., Asmah, A., Mohamad Bahagia, A.G., Mohamad, O., Noorshilawati, A.A. and Shamsiah, A. Faculty of Plantation and Agrotechnology, Universiti Teknologi MARA, 77300 Merlimau, Melaka, Malaysia Rice and Industrial Crop Research Centre, MARDI Seberang Perai, 13200 Kepala Batas, Penang, Malaysia Department of Crop Science, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia Faculty of Plantation and Agrotechnology, Universiti Teknologi MARA, 26400 Bandar Jengka, Pahang, Malaysia


Introduction
Rice or its scientific name Oryza sativa belonging to the Poaceae family and is well-known as the main staple food for most of the world's populations (Savitha and Ushakumari, 2016). To meet the growing rice demand, researchers have undertaken numerous studies to produce new varieties to improve existing rice varieties. Among the studies that have been done is the production of high-quality rice (Cheng et al., 2017), high yield varieties (Nirmaladevi et al., 2015), agronomic traits improvements (Seth et al., 2018), resistant to pest and disease such as blast (Mehta et al., 2019), brown planthopper (BPH) (Mohamad Bahagia et al., 2011) and adaptation to diverse environmental conditions. Presently, due to changes in lifestyle, eating habits, income, and health concerns, consumers preferred highquality rice with special attributes such as pleasant fragrant, long-grain, intermediate amylose, low glycemic index, and so on (Nirmaladevi et al., 2015). Consumers usually classify rice quality based on the grain appearance, size, and shape of the grain, behaviour upon cooking, taste, tenderness, and flavour of cooked rice (Nadaf et al., 2016). Verma et al. (2015) suggested that rice quality can be grouped based on physical, chemical, cooking, and nutritional quality. Physical properties include kernel size, shape, milling recovery, degree of milling, grain appearance (Dela Cruz and Khush, 2000), kernel length, kernel breadth, and kernel length/breadth ratio (Reddy et al., 2012) while physicochemical properties refer to amylose content, gel consistency and gelatinize temperature (Chemutai et al., 2016).
Grain elongation which was determined through cooked kernel is the most important quality traits which differentiate the highly valued aromatic rice from the other rice types (Golam et al., 2010). However, the preferences for grain size and shape varied within different cultures and regions (Suwannaporn et al., 2008). Some cultures prefer short and bold grains, while others prefer medium and long slender grains. For example, people in Asia preferred on cooking and eating rice that is determined by the properties of starch that makes up to 90% of milled rice (Nadaf et al., 2016) while in Japan, short-grain with sticky texture is preferred by Japanese for making sushi (Suwannaporn et al., 2008).
The character of grain elongation is a major component of the grain quality which can be found in Basmati rice types. The world price for Basmati rice showed the highest value in the year 2008 at USD1,077/ metric ton (FAO, 2012). Basmati rice is important in economics of India, Pakistan and Thailand and also preferred by people in India, Pakistan and the Middle East (Shahzadi et al., 2018). In Malaysia, there is an increasing demand for quality rice in domestic markets. Nowadays, Malaysia has released more than 40 rice varieties including aromatic rice such as MRQ50, MRQ74, MRQ76 and MRQ88. Most of the released varieties have special characteristics such as high yield and resistance to pest and disease (Jamal et al., 2014) and so on. However, some of the aromatic rice in Malaysian reported has undesirable agronomic characters such as low yield and susceptible to pest and disease (Golam et al., 2011). Introducing other speciality rice varieties under the Malaysian climate may not be very suitable because some growth of the speciality rice may be influenced by the changes in the environmental conditions thus would result in low yields. Besides that, crop improvement in rice depends on the magnitude of genetic variability and the extent to which the desirable genes are heritable (Savitha and Ushakumari, 2014). Moreover, grain size and shape are also among the main important quality trait considered by breeders before releasing new varieties (Shamim et al., 2017). Both private and government industries are always working together to ensure a continuous supply of high-quality rice for farmer use although sometimes they have to face problems related to unpredictable weather conditions which may reduce the quality seed supplied (Mohd Shukor et al., 2018). Cheng et al. (2014) stated that the development of rice is quite challenging without considering grain quality improvement especially to meet preferences of wealthier consumers living in well-developed countries. To meet consumer and industry preferences as well as market demand, improving milling, cooking, eating and processing qualities is crucial in quality rice breeding instead of yield performance (Nirmaladevi et al., 2015). Therefore, an investigation has been conducted to observe the segregation pattern of cooked kernel elongation in F 2 generation of six Basmati rice crosses. The information gathered from this study is beneficial for future rice quality improvement and varietal development as well as to ensure the Malaysians achieve a 100% target of rice self-sufficiency level (SSL).

Source of plant materials
The study on thirteen rice genotypes comprised of seven varieties viz. Basmati 370, MR219, Mahsuri Mutant, Mahsuri Mutant 98, MRQ50, MRQ74, MRQ76 and six F 2 rice generation has been conducted at the Malaysian Agricultural Research and Development Institute (MARDI). Two hundred plant representing F 2 generation of each cross were analyzed to evaluate segregation pattern of grain elongation in the cooked kernel.

Sample preparation
About 135 g of paddy at moisture content 13-14% were weighed using an analytical balance. Then, it was passed through Satake Rice Dehusker (Satake Co. Ltd. Tokyo, Japan) for milling process and after that were polished using Satake Rice Polisher (Satake Co. Ltd. Tokyo, Japan) to obtain milled rice. Unbroken polished rice grains were used for grain quality evaluation (Bhattacharya, 2011).

Determination of elongation ratio in F 2 rice population
Randomly, 200 pieces of head rice from each cross were selected and individually measured its length and width using Mitoyo Digital Caliper. The length/width ratio was recorded and classified based on the Standard Rice Evaluation System described by IRRI (2002) for comparisons of physical properties. The kernel elongation ratio of F 2 seeds was determined according to the procedures described by Sood and Siddiq (1980) with some minor modification.

Statistical analysis
The data were analysed by analysis of variance (ANOVA) using SPSS software version 23. Mean comparisons were made using Duncan New Multiple eISSN: 2550-2166 © 2020 The Authors. Published by Rynnye Lyan Resources FULL PAPER Range Test (DNMRT) and means were statistically significant when P<0.05. Frequency distribution was calculated from the data recorded and the chi-square analysis for elongation ratio among F 2 populations was calculated at 95% of a confidence interval. Table 1 presents the physical characteristics of parental lines and Table 2 shows the mean and range of kernel elongation of parental lines and six rice crosses used in the study. Among all varieties, Basmati 370 exhibited the best in grain length (7.05 mm) and grain length after cooked (14.07 mm). Four types of Malaysian rice genotypes consist of three aromatic rice MRQ50, MRQ74, MRQ76 and non-aromatic rice MRQ219 showed grain length more than 6.61 mm which is considered as long-grain while Mahsuri Mutant and Mahsuri Mutant 98 showed grain lengths of 6.31 mm and 6.22 mm respectively which indicated medium in size. The elongation ratio (ER) in all rice genotypes consist of aromatic and non-aromatic rice ranged from 1.68 to 2.00. The highest ER was found in Basmati 370 with a value 2.00 and length to width ratio (LBAC) with a value 3.72. The lowest ER was found in Mahsuri Mutant 98 and MRQ74 with value 1.68 respectively. A study conducted by Srivastava and Jaiswal (2013) also reported high ER in Basmati 370 (1.90) with LBAC ratio value 3.7 and they concluded that Basmati rice types exhibited excellent grain and physico-quality characteristics after cooking. Rosniyana et al. (2010) found that Maswangi rice or MRQ74 showed ER value of 1.67 and they stated that ER of rice below than two showed that the rice did not elongate during cooking.

Results and discussion
Among all crosses, B70/MM showed the highest ER (2.12) while the lowest ER was found in cross B370/219 (1.96). A study conducted by Golam et al. (2004) showed that Mahsuri mutant possessed the highest mean ER (2.14) as compared to Mahsuri (1.7) and 9192 (1.92). However, the hybridisation between Mahsuri Mutant with Mahsuri and 9192 produced F 2 generation with the mean elongation ratio more than two. The Mendelian ratio of six crosses was presented in Table 3. The results indicated that segregation pattern in grain elongation present and absent in F 2 is 3:1. The chi-square value in all crosses lesser than critical chi-square value at a degree of freedom one.
The study indicated that Basmati 370 exhibits its special features compared to other rice genotypes even though it is planted in the Malaysian environment. Rice grain elongation typically influenced by the environmental conditions, especially during ripening. The temperature of 25°C at day time and 21°C at night during ripening stage has been found to have a favourable effect in the aroma as well as kernel elongation where the maximum elongation in matured grains was reported at this temperature (Singh et al., 2000). Nevertheless, Golam et al. (2010) found that two global popular aromatic rice, E11 and Garib possess its normal aromatic and kernel elongation ratio even planting in Malaysian environment and this may be due to the presence of the dominant gene in these two traits. Basmati 370 was recognized as traditional rice and its special characteristics become the benchmark in  (Bradshaw, 2016). Besides quality traits, the consideration towards various characteristics contributed to yield performances are also very important in selecting high yield promising variety (Nur Suraya et al., 2018). The mechanism of the specific varieties also needs to be fully understood to achieve the breeding objective. Besides that, to meet sustainable manner in rice production, the collaboration between breeders and governments is needed to meet consumer preferences in the twenty-first century (Hanafiah et al., 2020).

Conclusion
The study had provided beneficial knowledge and information on the characteristics of F 2 populations that can be used for future rice improvement programs. Among the crosses, it can be concluded that the characteristics of long and slender grain found in parents Basmati 370, MRQ50, MRQ74, MR219, and Mahsuri Mutant showed that they can be used as parental lines in producing rice with long grain. The progenies of each crosses can be further evaluated to understand the mechanism of heritability  Table 3. The segregation in F 2 populations of six crosses.
Note: The data were subjected to chi square goodness of fit test against the Mendelian ratio 3:1.