Evaluation of local, high yielding and hybrid transplanted aman rice varieties for phenology, grain morphology and yield

An experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University during the period from June to December 2016 to evaluate local, high yielding and hybrid transplanted aman rice varieties for grain morphology and grain yield. The experiment was comprised of 15 transplanted aman (T. aman) rice varieties viz., high yielding varieties (HYV): BR11, BRRI dhan34, BRRI dhan38, BRRI dhan49, BRRI dhan52, BRRI dhan56, BRRI dhan62, Binadhan-7, Binadhan-12, Binadhan-13; local varieties: Balam, Kalizira, Nizersail, Bashiraj; and hybrid variety: Agro dhan-12. Duration of the phenological events such as date of emergence of seedlings, booting, heading, anthesis, physiological maturity and total growth duration was higher in local varieties compared to high yielding and hybrid. The lowest duration of these events were recorded in BRRI dhan62 and BRRI dhan56. The tallest plant was obtained from local variety Kalizira (167.27 cm) and the shortest one was obtained from HYV BRRI dhan56 (105.20 cm). Hybrid variety Agro dhan-12 possessed the highest number of effective tillers hill−1 (17.0) which was similar to HYV BRRI dhan49 (17.0) and the lowest number was recorded in HYV BRRI dhan38. Number of grains panicle−1 was the highest in hybrid variety Agro dhan-12 (235) and the lowest was present in local variety Balam. Thousand grain weight was highest at hybrid variety Agro dhan-12 (35 g) and the lowest one was observed in BRRI dhan34 (12.07 g). Grain yield was highest in hybrid variety Agro dhan-12 (6.50 t ha−1) which was similar to high yielding varieties BRRI dhan49 (6.0 t ha−1). In lower part of panicle, primary and secondary grain length (L), breadth (B), volume, L/B ratio was maximum in Binadhan-7 and Agro dhan-12. In middle part of the panicle, primary and secondary grain length, volume was found the maximum in Binadhan-7 and breadth was maximum in BR11, Agro dhan-12. Height was maximum in BRRI dhan56. In upper part of the panicle, primary and secondary grain length and volume was maximum in Binadhan-7 and breadth was maximum in Agro dhan-12 and height was maximum in BRRI dhan52.


Introduction
Rice (Oryza sativa L.) is the staple food for nearly half of the world's population as well as for 157.90 million people of Bangladesh (AIS, 2017). To feed the fast-increasing global population, the world's annual rice production must be increased to 760 million tons by the year 2020 (Kundu and Ladha, 1995). Rice production has to be increased annually by 1% to deliver sufficient rice for the ever-growing population of riceconsuming countries. Rice plays absolutely dominant role in Bangladesh agriculture as it covers 65% of total cropped area. Annual per capita consumption of rice in Bangladesh is the highest in the world (Nasiruddin, 1993). However, Bangladesh needs to increase the rice yield further in order to meet the growing demand. The National Commission of Agriculture projected that in order to remain self-sufficient, Bangladesh would need to produce 47 million tons of paddy (31.6 million tons of clean rice) by the year 2020, implying a required growth rate of production of 1.7% per year.
There are three rice growing seasons in Bangladesh namely aus, aman and boro. Aman is one of the main crops in Bangladesh. It is the second largest rice crop in the country in respect to the volume of grain yield and production. It is notable that the area coverage of aman is the largest as a single crop. The production of aman depends on the weather condition of the country. Average yield rate of aman for the year 2018-19 has been estimated to be 2.50 tons ha −1 which is 1.46% higher than that of the last year (BBS, 2020). This is quite lower compared to that of many other rice growing countries like China, Japan, Korea and USA where yields are 6.23, 6.79, 6.59 and 7.04 t ha −1 , respectively (FAO, 2004). There are different types of transplanted aman rice varieties such as local, inbred or high yielding and hybrid. To ensure the food security for the increasing population, the cropping area under rice cultivation could hardly be increased but 15-30% yield advantage could be obtained with the modern inbred rice varieties over conventional pure line varieties (Julfiquar et al., 2002;Yuan et al., 2005). The latter do not frequently exhibit higher yield (Yang et al., 2002;Horie et al., 2003;Nayak et al., 2003;Hejun et al., 2008;Abou Khalifa, 2009). Higher grain yield of hybrid rice is an intricate outcome of the genotype and environment interaction.
Now-a-days, different hybrid and high yielding rice varieties are available which have more yield potential than conventional local varieties. Rice grain dimensions, traditionally including length, breadth, and thickness, are the major breeding targets, as they affect yield and grain quality, and marketability (Huang et al., 2013). Grain size, shape (length-tobreadth ratio) have a direct implication on the commercial success of rice cultivars. Long and slender grains are generally preferred by the majority of consumers. Additionally, grain dimension is positively associated with grain weight and it is one of the most important factors determining yield potential of a rice cultivar (Xin et al., 1999;Yang et al., 2002;Zhang and Tang, 2004;Yongmei et al., 2007;Guo-qing, 2010). Therefore, proper knowledge on grain morphology of these hybrid varieties are required in order to gain insight in to their adaptability in the prevailing socioeconomic condition of Bangladesh.
The information is limited on varietal response more particularly in respect of grain morphology of the panicles. There is limited knowledge on grain architecture specially, the length, breadth, height, volume and length breadth ratio of local, high yielding and hybrid rice varieties. Grain characters of rice are considered as one of most important characters for varietal acceptance and rejection of rice by the farmers. These characters like length, shape, 1000-grain weight etc. are main important characters for classification of rice genotypes. Kato et al. (2007) have studied various grain characters like grain size, grain length, breadth, height, volume, length breadth ratio and shape of rice varieties (local, high yielding and hybrid) and reported that the these characters have direct effect on grain yield. Literature typically suggests that grain length, breadth, and height are the only determining factors of grain weight and grain quality (Sakamoto and Matsuoka, 2008). Under the above circumstances the present experiment was undertaken to examine the plant characters, grain morphology and yield of local, high yielding and hybrid T. aman rice varieties.

Study location
This experiment was implemented at the Agronomy Field Laboratory of Bangladesh Agricultural University, Mymensingh during the transplanted aman season (June to December 2016). The experimental field is located at 24°43 10.3 N, 90°25 40.7 E at an elevation of 18 m above the sea level. It belongs to the Noncalcareous Dark Grey Floodplain Soil (Old Brahmaputra Alluvial Soil Tract) under the Old Brahmaputra Floodplain of Agro Ecological Zone-9. The experimental field was medium high land with loamy soil having pH value of 5.7. The area is under the subtropical climate. The experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications. The total numbers of unit plots were 45. The size of each unit plot was 10 m 2 (4 m × 2.5 m). The spaces between blocks and plots were 1 m and 0.75 m, respectively. The experimental plots were fertilized as per the recommendations for respective varieties. Intercultural operations were done properly. When 80-90% of the grains became golden yellow, the crops were considered to be matured. An area of 1 m 2 was selected in the middle portion of each plot to record the grain morphology and yield of grain. Grains were then sun dried at 14% moisture level and cleaned. Finally, grain yield plot −1 were recorded and converted to t ha −1 . Phenological events (booting, heading, anthesis, physiological maturity) recorded using the scale proposed by Zadoks et al. (1974). Grain morphology (length, breadth, height), volume and L/B ratio was recorded as a panicle was divided into three parts such as lower, middle and upper and grains belong to central axis in the lower part are called lower primary grains (LPGN) and grains produced from the primary rachis are called lower secondary grains (LSGN), are similarly middle primary grains (MPGN), middle secondary grains (MSGN) and upper primary grains (UPGN), upper secondary grains (USGN). An architectural view of rice panicle is shown in Fig. 1. Following this diagram, six grain categorized (LPGN, LSGN, MPGN, MSGN, UPGN and USGN) were counted and weighted for each variety. The individual grain weight of the varieties from a panicle of the lower primary secondary, middle primary, secondary grain and upper primary and sec-ondary grain length (cm) was taken with the help of the digital caliper in the Laboratory of Department of Agronomy, Bangladesh Agricultural University, Mymensingh. The collected data were analyzed using computer package program STATIX-10 and the mean differences were read judged by Duncan's Multiple Range Test (DMRT) (Gomez and Gomez, 1984).

Plant height
Kalizira produced the tallest plant height (167.27 cm) and the shortest plant height was obtained from BRRI dhan56 (105.20 cm) (Fig. 3a). These differences are mostly due to the genetic variation among the varieties. These results are in consistent to those of Khisha (2002), Mia (2003), and Anjuman (2012) who recorded variable plant height among varieties.

Number of total tillers hill −1
The tiller number of the varieties increased with the advancement of growth stages. But it was not consistent as reduced number of tillers hill −1 was observed at harvest in some of the varieties. Death of some tillers was the reason behind the reduction of effective tillers. Hybrid Agro dhan-12 showed the highest number of total tillers hill −1 (18.67) which was similar to high yielding variety BRRI dhan49 (18.67). On the other hand, minimum tillers hill −1 was found in case of inbred BRRI dhan38 (8.60). Bhowmick and Nayak (2000) reported similar trend of tillering habits with different varieties of rice.

Number of effective tillers hill −1
The highest number of effective tillers hill −1 was produced by hybrid variety Agro dhan-12 (17.0) which was similar to high yielding variety BRRI dhan49 (17.0). Among the local varieties Kalizira produced highest number of effective tillers hill −1 (11.13) and the lowest number was produced by hybrid variety BRRI dhan38 (7.73) (Fig. 3b). Among the local varieties Bashiraj produced the lowest tillers (9.33). These findings collaborated with those reported by BRRI (2000) who stated that effective tillers hill −1 varied with variety.

Number of non-effective tiller hill −1
The results showed that the highest number of noneffective tillers hill −1 was produced by Binadhan-7 (3.0), BRRI dhan52 produced the second highest number of non-effective tillers hill −1 (2.23) which was greater than hybrid Agro dhan-12 (2.20) ( Table 1). The lowest number of non-effective tillers hill −1 was produced by local Kalizira (0.53). Variable effect of the variety on number of non-effective tillers hill −1 was also reported by Islam (1995) who noticed that number of total tillers hill −1 differed among varieties.

Number of grains panicle −1
Hybrid variety Agro dhan-12 produced the highest number of grains panicle −1 (235) which was statistically similar to the inbred variety BRRI dhan49 (234.67) (Fig. 3c). Among the local varieties Kalizira showed the best performance (182.09) for grains panicle −1 . The results obtained by Bhowmick and Nayak (2000) and Patel (2000) were in agreement with the findings of present study.

Panicle length
The results showed that the longest panicle was produced by hybrid variety Agro dhan-12 (32.0 cm) which was identical with high yielding BRRI dhan49 (31.0 cm) (Fig. 3d). Among the local varieties Kalizira produced highest panicle length (26.04 cm) and lowest was observed in Nizersail (24.85 cm). These results were similar to Anjuman (2012) and Haque (2011) who reported that panicle length has significant relationship with variety.

Number of sterile grains panicle −1
The results showed that the highest number of sterile grains panicle −1 was observed in BRRI dhan34 (30.0) and the lowest number (7.34) was obtained from high yielding variety BR11 (Table 1). In general, all the local varieties in this study possess average (26.94) maximum sterile grains panicle −1 .

1000-grain weight
The highest 1000-grain weight (WTS) (35 g) was obtained from hybrid variety Agro dhan-12 (Fig. 3e) Kundu and Ladha (1995) who found that variety does not show any significant effect on WTS.

Grain yield
The results indicated that hybrid variety Agro dhan-12 produced (6.50 t ha −1 ) which was identical to high yielding variety BRRI dhan49 (6.0 t ha −1 ) and the second highest grain yield was produced by another high yielding variety BRRI dhan52 (5.83 t ha −1 ), Binadhan-7 (5.42 t ha −1 ) which was on an average 30-40% more than local varieties performance and hybrid Agro dhan-12 gave 15-20% more yield than high yielding varieties (Fig. 3f). The lowest grain yield was produced by Binadhan-13 (2.67 t ha −1 ). Among the local varieties, Nizersail produced the highest grain yield (3.76 t ha −1 ). The probable reason of the different grain yields due to the different yield parameters (number of tiller, number of grain panicle −1 , number of filled grains panicle −1 , 1000-grain weight etc.) influenced by the genetic make-up of the variety. Grain yield differences due to varieties were also reported by Saha (2013), Anjuman (2012) and Khisha (2002) who observed variable grain yield among varieties.

Straw yield
The result showed that Bashiraj produced the highest straw yield (7.63 t ha −1 ), which was statistically similar with another local variety Nizersail (7.62 t ha −1 ) ( Table 1). The lowest straw yield was obtained from high yielding BRRI dhan56 (5.42 t ha −1 ), which was statistically identical with BRRI dhan49 (5.46 t ha −1 ). The probable reason of the different straw yield due to the different yield parameters which was mainly influenced by the genetic make-up of the variety. The results were similar with Kirttania (2013) and Chowdhury et al. (1993) who found different straw yield among the varieties.

Harvest index
The highest harvest index (HI) (41.06%) was observed in BRRI dhan34 which was statistically at par with Binadhan-7 (39.89%), BRRI dhan56 (39.39%), and hybrid Agro dhan-12 (34.41%) (  The major structures of the panicle are the base, axis, primary and secondary branches, pedicel, rudimentary glumes, and the spikelets. The panicle axis extends from the panicle base to the apex; it has 8-10 nodes at 2-to 4-cm intervals from which primary branches develop. Secondary branches develop from the primary branches. Pedicels develop from the nodes of the primary and secondary branches.

Grain number
The highest lower primary grain was observed in local variety Kalizira (24.1) and the lowest primary grain was found high yielding variety Binadhan13 (11.75) and the highest lower secondary grain was observed in high yielding variety BRRI dhan62 variety (27.50) and the lowest secondary was counted in Binadhan-13 (12.50) ( Table 2).

Middle part of the panicle
In middle part of the panicle, the highest primary grain number was counted in local variety Kalizira (20.83) and lowest primary grain was counted in local variety Bashiraj (10.50). In middle part of the panicle, the highest secondary grain number was counted in high yielding variety BRRI dhan49 (44.66) and lowest secondary grain was present in Binadhan-13 (17.0).

Upper part of the panicle
The highest upper primary grain was counted in high yielding variety BRRI dhan49 (15.83) and the lowest upper primary grain was present in high yielding

Lower part of the panicle
The highest individual primary mean grain weight was recorded in Binadhan-12 (22.17 mg) and lowest individual mean grain weight was observed in high yielding variety BRRI dhan38 (16.48 mg) ( Table 3). The highest individual lower secondary grain weight was recorded in high yielding variety BRRI dhan56 and hybrid variety Agro dhan-12 (19.93 mg). The lowest grain weight was found in local variety Kalizira (12.24 mg).

Middle part of the panicle
The highest individual middle primary grain weight was recorded in local variety Bashiraj (20.67 mg) and was identical to hybrid variety Agro dhan-12 (19.98 mg). The lowest grain weight was found in inbred variety BR11 (15.15 mg). The highest individual middle secondary grain weight was calculated in local variety Balam (20.84 mg) and the lowest grain weight was calculated ininbred variety Binadhan-12 (14.59 mg).

Upper part of the panicle
The highest individual upper primary grain weight was recorded in high yielding variety BRRI dhan34 (21.29 mg) and the lowest primary individual grain weight was calculated in local variety Kalizira (17.27 mg). The highest individual upper secondary grain weight was recorded in high yielding variety Binadhan-7 (20.83 mg).

Lower part of the panicle
The highest primary length of grain was measured in high yielding variety Binadhan-7 (9.37 mm) and was identical to hybrid variety Agro dhan-12 (9.07 mm). The lowest primary length was measured in Binadhan-13 (5.13 mm) ( Table 4). The highest primary breadth of grain was measured in hybrid variety Agro dhan-12 (1.89 mm) and the lowest primary breadth was measured in Balam (1.69 mm). The highest primary height of grain was measured in high yielding variety BRRI dhan56 (2.56 mm), lowest primary height was measured in BRRI dhan34 (1.67 mm). The highest lower primary volume of the grain was measured in high yielding variety Binadhan-7 (21.95 mm 3 ) and was identical to hybrid Agro dhan-12 (20.19 mm 3 ) and the lowest primary volume was measured in BRRI dhan34 (5.76 mm 3 ). The highest lower primary L/B ratio of the grain was measured in high yielding variety Binadhan-7 and lowest primary L/B ratio was measured in .
The highest secondary length of grain was measured in high yielding variety Binadhan-7 (9.25 mm). The second highest secondary grain length was measured in hybrid variety Agro dhan-12 and the lowest secondary length was measured in high yielding variety BRRI dhan38 (5.57 mm) and identical to local variety Kalizira (5.91 mm). The highest primary breadth of   ** ** ** ** ** ** ** ** ** ** LPL = lower primary length, LPB = lower primary breadth, LPH = lower primary height, LPV = lower primary volume, LPR = lower primary ratio, LSL = lower secondary length, LSB = lower secondary breadth, LSH = lower secondary height, LSV = lower secondary volume, and LSR = lower secondary ratio   62 mm). The highest lower secondary volume of the grain was measured in high yielding variety Binadhan-7 (21.32 mm 3 ) and the second highest volume of lower secondary grain was measured in hybrid Agro dhan-12 (19.71 mm 3 ). The lowest volume of lower secondary grain was measured in inbred variety BRRI dhan34 (5.61 mm 3 ). The highest lower secondary L/B ratio of the grain was measured in high yielding variety Binadhan-7 (5.09) and the L/B ratio of lower secondary grain in hybrid Agro dhan-12 (4.60).

Middle part of the panicle
The highest middle primary length of grain was measured in high yielding variety Binadhan-7 (9.36 mm) and hybrid variety Agro dhan-12 (8.64 mm) and the lowest primary length was measured in BRRI dhan38 (5.51 mm) ( Table 5). The highest primary breadth of grain was measured in high yielding varieties Binadhan-12 (1.89 mm) and the lowest primary breadth was measured BRRI dhan34 (1.22 mm). The highest primary height of grain was measured in high yielding variety BRRI dhan56 (2.61 mm) and the lowest primary height was measured in BRRI dhan34 (1.67 mm). The highest middle primary volume of the grain was measured in high yielding vari-ety Binadhan-7 (21.60 mm 3 ) and the second highest middle primary volume of the grain was measured in hybrid variety Agro dhan-12 (19.27 mm 3 ) and the lowest primary volume was measured in BRRI dhan34 (6.16 mm 3 ). The highest secondary length of grain was measured in high yielding variety Binadhan-7 (9.12 mm) and hybrid variety Agro dhan-12 (8.53 mm) and the lowest secondary length was measured in high yielding variety BRRI dhan38 (5.57 mm). The highest secondary breadth of grain was measured in inbred BRRI dhan52 (1.88 mm). The lowest secondary breadth was measured in high yielding variety BRRI dhan34 (1.21 mm). The highest primary height of grain was measured in high yielding variety BRRI dhan56 (2.56 mm). The highest middle secondary volume of the grain was measured in high yielding variety Binadhan-7 (21.08 mm 3 )) and the lowest secondary volume was measured in BRRI dhan34 (5.75 mm 3 ). The highest lower primary L/B ratio of the grain was measured in high yielding variety Binadhan-7 (4.97) and hybrid Agro dhan-12 (4.65) and the lowest secondary L/B ratio was measured in high yielding BRRI dhan38 (3.13). There is a great relations of grain dimensions (length, breadth, height, volume) with yield exacerbate. If the breeder can amplify lower, middle, upper part of grain it will be a revolution for yield increasement.

Upper part of the panicle
The highest upper primary length of grain was measured in high yielding variety Binadhan-7 (9.19 mm) and lowest primary length was measured in Binadhan-13 (5.57 mm) ( Table 6). The highest primary breadth of grain was measured in high yielding variety BRRI dhan52 (1.89 mm) and the lowest primary breadth was measured BRRI dhan34 (1.17 mm). The highest primary height of grain was measured in high yielding variety BRRI dhan56 (2.56 mm) and the lowest primary height was measured in BRRI dhan34 (1.65 mm). The highest upper primary volume of the grain was measured in high yielding variety Binadhan-7 (20.78 mm 3 ) and the lowest upper volume was measured in BRRI dhan34 (5.71 mm 3 ).
The highest upper primary L/B ratio of the grain was measured in high yielding variety Binadhan-7 (5.09) and the lowest primary L/B ratio was measured in high yielding BRRI dhan38 (3.25). The highest upper secondary length of grain was measured in high yielding variety Binadhan-7 (9.38 mm) and hybrid variety Agro dhan-12 (8.78) and the lowest secondary length was measured in Binadhan-13 (5.42 mm). The highest upper secondary breadth of grain was measured in high yielding variety Binadhan-12 (1.89 mm) and hybrid variety Agro dhan-12 (1.88 mm) and the lowest upper secondary breadth was measured in BRRI dhan34 (1.19 mm). The highest secondary height of grain was measured in high yielding variety BRRI dhan56 (2.52 mm) and the lowest primary height was measured in BRRI dhan34 (1.68 mm). The highest upper secondary volume of the grain was measured in high yielding variety Binadhan-7 (21.92 mm 3 ) and the lowest upper secondary volume was measured in BRRI dhan34 (5.94 mm 3 ). The highest upper secondary L/B ratio of the grain was measured in high yielding variety Binadhan-7 (5.07) and hybrid Agro dhan12 (4.66) and the lowest secondary L/B ratio was measured in high yielding BRRI dhan38 (3.15).

Conclusion
The present study suggests that the Agro dhan-12, Binadhan-7, BRRI dhan49, BRRI dhan52, BRRI dhan56 varieties under this study may preferable to obtain better grain quality and yield under AEZ-9 in Aman season. But studies at different agro-ecological zones are needed to arrive at a definite conclusion.