Rice is a staple food for more than half of the world’s population. Globally, more than 3.5 billion people directly depend on rice for at least 20% of their daily calorie intake (GRiSP 2013). Asia is the dominant rice consumer and accounts for 90% of its global consumption (Futakuchi et al. 2021). Before green revolution in 1960s, farmers mainly cultivated local landraces where yield potentiality was very low with some unexpected agronomic traits such as lodging tendency, low response to nitrogen fertilizer, low harvest index, and higher diseases infestation (Rahman et al. 2016). Across major rice producing countries of South Asia, green revolution started with the development of first semi-dwarf rice variety IR8 in the year of 1960 at International Rice Research Institute (IRRI), Philippines. This semi-dwarf rice had higher yield potential, higher harvest index, more responsive to nitrogenous fertilizer compared to local landraces of rice. Since then, IRRI developed rice varieties and advanced breeding lines have contributed greatly to boost up rice production around the world. At that time, the primary focus of rice breeding was shorter plant stature along with better agronomic characters and specific adaptability (Mackill and Khush 2018; Siddiq and Vemireddy 2021).

At present, Bangladesh holds fourth position in terms of rice production among all countries in the world and rice consumption acts as a source of more than 60% of the average caloric intake of the population (GRiSP 2013; Naher et al. 2014). In Bangladesh, rice breeding activities such as introduction, cultivar development and dissemination of those cultivars initiated through the establishment of Bangladesh Rice Research Institute (BRRI) in 1970. Rice cultivation of Bangladesh is characterized by three grow-ing seasons namely Aus, Aman, and Boro. Boro is consi-dered as dry season (from November to May) whereas Aman represents the wet season (from July to November) and Aus season is in between Boro and Aman season starting from April and extends to July (Pearson et al. 1999, Shelley et al. 2016; Afrin et al. 2020; Biswas et al. 2020; Ahmed et al. 2021). During the period of green revolution, IRRI developed rice variety IR20 appeared as first released variety of Bangladesh. It was released in 1970 as BR1 for cultivation in Bangladesh for both Boro and Aus season. The yield potentiality of BR1 was 5.5 t/ha in Boro and 4.0 t/ha in Aus season. Till now, BRRI has developed 99 modern inbred rice varieties for cultivation across different rice ecosystems (BRKB 2021). Among them, the cultivar BR11 is considered as most popular cultivar suitable for rainfed lowland area cultivated in Transplanted Aman (T. Aman) season. The popular rice variety BR11 was released in 1980. It is well accepted to the farmers due to its good cooking quality (amylose 26%), higher yield (6.0 t/ha) and attractive phenotype (plant height 115 cm, 145 days growth duration). Furthermore, it is weakly photosensitive in nature (Biswas et al. 2020). On the other hand, the rice variety BRRI dhan28 and BRRI dhan29 are most popular cultivar for irrigated ecosystem during Boro season (Iftekharuddaula et al. 2011; Kretzschmar et al. 2018). The cultivar BRRI dhan28 was released in 1994. Gradually it became popular to farmers because of its good grain quality such as high amylose content (28%), medium slender grain and high yield (6.0 t/ha) with comparatively shorter growth duration (140 days). Likewise, BRRI dhan29 was also released in 1994. It is well accepted to single Boro areas because of its high yield (7.5 t/ha) with comparatively longer growth duration (160 days). During dry season, the rice cultivar BRRI dhan28 occupies 23% rice growing areas whereas BRRI dhan29 occupies 28% areas (BRRI 2019). Taken together, they constitute more than 50% rice cultivation areas and significantly contribute to total rice production during Boro season.

Despite these achievements in developing popular cultivars, great challenges remain unexplored to boost up further efforts on genetic improvements of rice by acceler-ating rice breeding program. Recent climatic events have changed rice production scenario around the world. For example, old rice varieties have become susceptible to major diseases (such as blast) and often cause severe yield loss. In the future, higher genetic gain is required to meet the future challenges of crop improvement through accu-mulation of favorable alleles in the background of impor-tant popular rice varieties. Thus, future popular variety should possess resistance allele and other important agro-nomic traits. In this context, breeding history of some iconic rice varieties like IR64 of IRRI, Koshihikari of Japan, Basmati of India, and Jasmine rice of Thailand have been well documented to understand their importance in the rice breeding sectors (Kobayashi et al. 2018; Mackill and Khush 2018; Singh et al. 2018; Vanavichit et al. 2018). More importantly, their pedigree information indicated that new popular rice varieties of those countries have been evolved from the progenies or prenatal lineage of old mega rice cultivars.

Food security of South Asian countries like Bangladesh solely depends on rice. Sustainable rice production is required against major abiotic stress drought, salinity, submergence and stagnant flood tolerant (Brammer et al. 2010). To boost up secured rice production, old rice varieties originated from both favorable and abiotic stress tolerance environment could lay foundation of new improved rice varieties through the pace of cyclic breeding. Moreover, rice markets of Bangladesh have experienced a dramatic shift from medium bold grain to long slender grain (Khatun et al. 2019). In recent studies, it was found that the majority of the abiotic stress tolerant accessions predominately originated from Bangladesh centered narrow geographic region (Rahman and Zhang 2018). In addressing sustainable crop production, further genetic improvement combined with improved management practices might be a key factor in adapting new cropping systems against climate change (Atlin et al. 2017; Bailey-Serres et al. 2019). In this context, breeding history of important popular varieties and their important progenies could help us in understanding the nature of parent selection, important progeny development and subsequent use in future crop improvement program.

Furthermore, private-sector breeding approaches have been introduced and practiced to public research organi-zations in Asia such as the International Rice Research Institute and Bangladesh Rice Research Institute (Collard et al. 2017; Cobb et al. 2019; Kato et al. 2019). These approaches include elite by elite crossing, rapid generation advance, earlier multi-location trials, high selection pressure, an increased use of genome wide molecular markers, and using variety product profiles to replace old rice varieties. Such review could help breeders and relevant policy makers to design and execute modern breeding approaches to accelerate genetic gain in rice breeding programs. In this review, we mainly discussed the pedigree-based breeding history of BR11, BRRI dhan28, BRRI dhan29 as well as their important agronomic traits, grain qualities and molecular characteristics in a suitable pattern.

Breeding history of popular cultivar BR11

Characteristics of BR11

In Bangladesh, the rice variety BR11 is termed as most popular T. Aman cultivar. It was released in 1980. The main features of this cultivar include medium bold grain, high amylose content (26.0%), longer maturity period (145 days), and high yield (6.0 t/ha). In 1980s, breeding program at BRRI mainly focused on combining different quan-titative and qualitative traits desired by farmers which includes high yield, resistance to biotic and abiotic stresses, improved grain quality. Segregating progenies were evaluated in pedigree nurseries for selection and advancement.

Development of popular cultivar BR11

The pedigree of BR11 is BR52-87-1-HR88. The cross combination between two IRRI varieties IR20 and IR5 produced BR11. Here, IR20 was used as female parent whereas IR5 was selected as male parent or pollen parent.

On the other hand, the pedigree of BR4 and BR10 are BR51-91-6 and BR51-46-5-HR65, respectively. These two lines developed from the cross combination between IR20 and IR5-114-3-1. This information indicates that both BR4 and BR10 have been originated from the same parental combination like popular cultivar BR11. The variety BR4 and BR10 were released in 1975 and 1980, respectively. BR4 has medium bold grain, high amylose content (25.0%), longer growth duration (145 days), and high yield (5.0 t/ha). In contrast, BR10 has similar agronomic cha-racters along with comparatively higher yield (6.0 t/ha). Although BR4 and BR10 have common parentage but BR10 has higher yield potentiality in comparison with BR4. In fact, IRRI developed IR20 was noted for its good cooking quality (intermediate amylose), as well as having some tolerance to salinity, bacterial leaf blight, and blast. IR5 was also high yielding rice variety, and moderately resistant to blast (Khush 2005). Actually, the cross com-bination of IR20 and IR5 led to develop three rice varieties BR4, BR10 and BR11 (Fig. 1).

Figure 1. Breeding history and pedigree tree of BR11 and its relatives.

When BR11 was released in 1980 for the rainfed lowland area of Bangladesh, its stable yield (6.5 ton/ha) made it the most popular variety of T. Aman season in Bangladesh. Additionally, it was moderately resistant to tungro disease and tolerant to yellow stem borer. Because of its popularity among the farmers, it was widely used as a parent and standard check for basic studies by many researchers.

Among three rice growing seasons of Bangladesh, Aman is characterized by diverse rice growing areas including favourable rainfed lowland with wide range of drought, salinity, submergence and tidal flood-prone areas. These diverse rice growing environments led to develop area specific rice variety development in the T. Aman season. For this reason, rice breeders have attempted to retain the agronomic traits of BR11 among newly developed breeding lines.

Important progenies of BR11

In later decades, IR20 derived rice varieties BR11, BR4, and BR10 were extensively used as parents in the rice breeding program of Bangladesh. They also produced considerable amount of rice varieties with special agronomic characters such as photosensitivity, earliness, tidal flood tolerance. For instance, the popular photosensitive variety BR22 was developed from the cross combination between BR10 and another local photosensitive rice variety Nizershail. Another rice variety BR23 has been developed from BR4 (Fig. 1). The variety BR22 and BR23 became very popular photosensitive rice variety in delayed plantation after recession of flood water. Actually, they are widely grown in flood prone areas as an option to minimize grain yield in delayed planting (Biswas et al. 2020).

Furthermore, two important T. Aman rice varieties BRRI dhan31 and BRRI dhan52 were developed in the back-ground of BR11. The availability of genome-wide mole-cular markers for marker assisted selection enabled the transfer of important traits into popular varieties like BR11 through marker assisted backcrossing (Collard and Mackill 2008). The rice submergence tolerance gene SUB1 was introduced by marker assisted backcrossing into BR11 along with several other popular varieties of major rice growing areas (Septiningsih et al. 2009; Iftekharuddaula et al. 2011). The cross between BR11 and CR146-7027-224 led to develop BRRI dhan57 which is noted for long slender grain with drought avoidance character for its shorter maturity period (100-105 days) in T. Aman season (Fig. 1).

The rice variety BRRI dhan44 is an excellent example of a tidal flood tolerant variety. It was developed directly from a cross between two improved cultivars BR10 and BRRI dhan31 under same pedigree tree. Again, cross between BRRI dhan44 and one IRRI line IR75862 produced two rice varieties namely BRRI dhan76 and BRRI dhan77 with improved tidal flood tolerance and better agronomic characters (Fig. 1).

Above pedigree history clearly indicates that IR20 derived three rice cultivars BR4, BR10 and BR11 acted as key parents in developing most of the T. Aman rice varieties of Bangladesh. As a whole, two IRRI developed rice varieties IR20 and IR5 had contributed greatly in developing better rice varieties and subsequent progenies in Bangladesh. Thus, the pedigree information revealed that IR20 and IR5 laid foundation in development of modern T. Aman rice varieties of Bangladesh in terms of producing three BRRI varieties BR4, BR10, and BR11.

Key features of BR11 group and its progenies

A total of eight rice varieties namely BR22, BR23, BRRI dhan31, BRRI dhan44, BRRI dhan52, BRRI dhan57, BRRI dhan76, and BRRI dhan77 have been developed from BR11 group. In this group, all developed progenies were selected as T. Aman cultivar and they were released between 1988-2016. Among the progenies of BR11, there was considerable variation in plant height, growth duration and yield. It ranged from 115-140 for plant height, 140-163 days for growth duration, 5.0-5.5 t/ha for yield. It is important to note that no progeny surpassed the grain yield of its founder parent BR11 (Table 1).

Table 1 . Agronomic characters and release year of improved rice varieties developed from popular cultivar BR11 group.

Variety name	Season	PHa (cm)	GDb (days)	YLDc (t/ha)	Release year	Group	Remarks	Reference
BR11	T. Aman	115	145	6.0	1980			BRRI, 2020
BR22	T. Aman	125	150	5.0	1988	BR11	Photosensitive
BR23	T. Aman	120	150	5.5	1988	BR11	Photosensitive
BRRI dhan31	T. Aman	115	140	5.0	1994	BR11	Stagnant flood tolerant
BRRI dhan44	T. Aman	130	145	5.5	2005	BR11	Tidal submergence
BRRI dhan52	T. Aman	116	155	5.0	2010	BR11	Submergence tolerance
BRRI dhan76	T. Aman	140	163	5.0	2016	BR11	Tidal submergence
BRRI dhan77	T. Aman	140	155	5.0	2016	BR11	Tidal submergence

^aPH: plant height, ^bGD: growth duration or maturity days, ^cYLD: grain yield.

Breeding history of popular cultivar BRRI dhan28

Characteristics of BRRI dhan28

In Bangladesh, BRRI dhan28 is considered as one of the most popular Boro rice varieties in terms of yield, maturity days and good grain quality. It was released in 1994. The main features of BRRI dhan28 include medium slender grain, high amylose content (28.0%), shorter maturity days (140 days) and high yield (6.0 t/ha).

Development of popular cultivar BRRI dhan28

The rice variety BRRI dhan28 was developed from the cross between IR28 and Purbachi (Fig. 2). In 1980s, the pedigree number IR2061 was most important cross of IRRI which was made from the combination of three breeding lines IR833, IR1561, IR24 and one wild rice Oryza nivara. From this cross, three varieties IR28, IR29, and IR34 were developed by IRRI and they were well adaptable across major rice growing countries. Additionally, advanced lines developed from that cross also contributed to rice breeding in developing high yielding varieties (Khush and Virk 2005). IR28 was released as a rice variety in numerous rice producing regions of Asia and Africa including Bangladesh, Cameroon, China, Egypt, Gambia, India, Indonesia, Iran, Mauritania, Myanmar, Philippines and Togo.

Figure 2. Breeding history and pedigree tree of BRRI dhan28 and its relatives.

In Bangladesh IR28 was directly released as a variety in 1977 with the designation BR6. Aside from that, IR29 was released as a rice variety in China and Philippines. IR34 was released as a rice variety in India, Indonesia, Madagascar, Myanmar, Philippines, and Tanzania.

However, one advanced line namely IR2061-465-4-5-5 from the same pedigree tree of IR28, IR29 and IR34 produced world’s most adaptable popular rice variety IR64 in combination with the IRRI line IR5657-33-2-1 (Khush and Virk. 2005; Mackill and Khush 2018). IR64 is a indica rice variety with semi-dwarf nature and short growth duration which has good resistance to brown plant hopper and green leaf hopper (Cohen et al. 1997; Khush 2005). It has an excellent resistance to blast disease (Roumen 1992; Bastiaans and Roumen 1993; Grand et al. 2012). IR64 was not directly released as a variety in Bangladesh due to Tungro susceptibility. But it was used as a parent in developing modern rice variety for Boro season. To sum up, above pedigree history clearly indicates that BRRI dhan28 and IR64 have been originated from the same pedigree lineages of IR28, IR29 and IR34 (Fig. 2).

Important Progenies of BRRI dhan28

Among three rice growing seasons of Bangladesh, Boro is characterized by irrigated rice ecosystem including low lying haor areas where rice is cultivated in dry season. Here irrigation is provided to establish and maintain crop growth throughout the cropping period. In these areas, BRRI dhan28 has become more popular due to earliness, cooking quality, and high yield. Although BRRI dhan28 has a tendency of lodging during maturity period but it gives satisfactory yield at farm level. The stable yield of BRRI dhan28 across irrigated rice areas has become the standard yield potentiality for short duration rice varieties of Boro season. Thus, BRRI dhan28 has been extensively used as a standard short duration check for basic studies by many rice researchers.

The pedigree history indicated that two rice varieties BRRI dhan63 and BRRI dhan81 were developed from the cross combination between Amol-3 and BRRI dhan28 where BRRI dhan28 was used as a male parent. Recently, BRRI dhan28 showed greater compatibility with wild rice Oryza rufipogon. BRRI dhan96 have been developed from backcross breeding where the cross combination was BRRI dhan28 and Oryza rufipogon (Accession no. IRGC103404). BRRI dhan28 was backcrossed two times to recover the background of BRRI dhan28 for better agronomic and grain quality traits. The greater yield advantage of newly developed varieties suggested that wild rice have potentiality of introducing yield attributed traits in modern Bangladeshi rice variety (BRRI 2019).

In this review, pedigree history indicated that BRRI dhan28 and IR64 were developed from same parental lineage. Thus, IR64 might have greater potentiality in developing Bangladeshi rice cultivars. In line with this, IR64 has remarkable role in developing important rice varieties of Bangladesh. For example, BRRI dhan36 was developed from the cross combination between IR64 and IR35293-125-3-2-3 while BRRI dhan55 produced from IR64 and wild rice Oryza rufipogon. In this context, BRRI dhan36 and BRRI dhan55 were progenitors of IR64. BRRI dhan36 showed moderately cold tolerance at seedling stage when treated with cold water in greenhouse condition (Khatun et al. 2016). The rice variety BRRI dhan55 was released in 2014 and it was recommended for cultivation in both Aus, and Boro. Due to low amylose content (22.0%), it was not popular among rice consumers of Bangladesh. Later, BRRI dhan67 was developed using one IR64 progenitor variety BRRI dhan36 as a background parent. However, BRRI dhan67 is the most salt tolerant rice variety in Boro season with yield potentiality of 3.0-6.0 t/ha depending on the salinity level. In recent adaptive field trials, it has been found that BRRI dhan67 has moderately cold tolerance at both seedling and reproductive stage.

The lines derived from IR2061 combinations acted as common parent in developing IR64 and BRRI dhan28. The pedigree information indicates that same ancestors of IR64 laid foundation in the development of popular rice variety BRRI dhan28 and subsequent rice varieties BRRI dhan36, BRRI dhan55, BRRI dhan63, BRRI dhan67, BRRI dhan81, and BRRI dhan96.

Key features of BRRI dhan28 group and its progenies

The popular cultivar BRRI dhan28 was released in 1994. A total of six rice varieties namely BRRI dhan36, BRRI dhan55, BRRI dhan63, BRRI dhan67, BRRI dhan81, and BRRI dhan96 have been developed from BRRI dhan28 group (Table 2). In this group, all developed rice varieties were Boro cultivar and released between 1998-2020. Aside from that, there was considerable variation in plant height, growth duration and yield. It ranged from 86-100 for plant height, 140-146 days for growth duration, 5.0-7.0 t/ha for yield. Except BRRI dhan36, most of the developed rice varieties surpassed the grain yield of its founder parent BRRI dhan28.

Table 2 . Agronomic characters and release year of improved rice varieties developed from BRRI dhan28 group.

Variety	Season	PHa (cm)	GDb (days)	YLDc (t/ha)	Release year	Group	Reference
BRRI dhan28	Boro	90	140	6.0	1994		BRRI, 2020
BRRI dhan36	Boro	90	140	5.0	1998	BRRI dhan28
BRRI dhan55	Boro	100	145	7.0	2011	BRRI dhan28
BRRI dhan63	Boro	86	146	6.5	2014	BRRI dhan28
BRRI dhan67	Boro	100	145	6.0	2014	BRRI dhan28
BRRI dhan81	Boro	100	143	6.5	2017	BRRI dhan28
BRRI dhan96	Boro	87	145	7.0	2020	BRRI dhan28

^aPH: plant height, ^bGD: growth duration or maturity days, ^cYLD: grain yield.

Breeding history of popular cultivar BRRI dhan29

Characteristics of BRRI dhan29

The rice variety BRRI dhan29 is one of the most popular Boro rice varieties. It was released in 1994 for cultivation in favorable Boro ecosystem of Bangladesh. The main features of this rice variety include longer growth duration (160 days), high amylose content (29.4%) and high yield (7.5 t/ha).

Development of popular cultivar BRRI dhan29

The pedigree-based breeding history indicated that cross combination of IR5 and IR20 made foundation of Boro rice varieties in terms of developing BR4 and BR10 (Fig. 3). In 1980s, BG90-2 was very renowned high yielding variety across major rice producing countries. It was released as a rice variety in India, China, and Sri-lanka. The rice variety BRRI dhan29 was developed from the cross combination BG90-2 and BR10, where T. Aman variety BR10 was used as a male parent.

Figure 3. Breeding history and pedigree tree of BRRI dhan29 and its relatives.

Important progenies of BRRI dhan29

Among three rice growing seasons of Bangladesh, Boro is characterized by irrigated rice ecosystem including low lying haor areas where rice is cultivated in dry season. In these areas, BRRI dhan29 has become more popular due to high yield (more than 7.5 t/ha) associated with higher number of tillers and comparatively longer growth duration in Boro season. The stable yield of BRRI dhan29 across irrigated rice areas has become the standard yield potentiality for long duration rice varieties. Thus, BRRI dhan29 has been extensively used as a standard long duration check for basic studies by many rice researchers.

Till now, seven rice varieties namely BRRI dhan58, BRRI dhan68, BRRI dhan74, BRRI dhan84, BRRI dhan87, BRRI dhan88, and BRRI dhan89 have been developed using BRRI dhan29 as a background parent. In this context, BRRI dhan58 and BRRI dhan88 have been made from the lines generated from somacolonal study (Aditya and Baker 2006). The cross combination of BRRI dhan29 and one IRRI line IR68144 produced three varieties BRRI dhan68, BRRI dhan74, BRRI dhan84. However, BRRI dhan74 and BRRI dhan84 zinc enriched Boro variety released in the year 2015, and 2017, respectively. Recently, BRRI dhan29 also showed greater compatibility with wild rice Oryza rufipogon. Two rice varieties BRRI dhan87 and BRRI dhan89 have been developed from backcross breeding where cross combination was BRRI dhan29 and Oryza rufipogon (Acc no. IRGC103404). The rice variety BRRI dhan29 was backcrossed two times to recover the important agronomic traits of BRRI dhan29. Furthermore, the yield advantage of these two rice varieties suggested that wild rice have greater potentiality for introducing yield attributed traits in modern Bangladeshi rice variety (BRRI 2018). Aside from that, BRRI dhan29 is also used as a model rice variety for introgression of important agronomic and grain quality traits. For instance, BRRI dhan29 was used as developing near isogenic lines of Golden rice, GR2-E BRRI dhan29 Golden Rice where transgenic lines showed acceptable performance as golden rice (Biswas et al. 2021).

The rice variety BR4 was developed from the cross combination of two IRRI varieties IR20 and IR5. It was released in 1975 for T. Aman season. Later, the rice variety BRRI dhan30 was developed using BR4 as background parent. It was released in 1994 for T. Aman season. The main features of this cultivar include medium slender grain with high amylose content (26.7%). Although BRRI dhan30 is a T. Aman cultivar, it showed greater compatibility in developing Boro cultivar. For example, BRRI dhan30 in combination with one IRRI line IR67684B produced BRRI dhan50. It was released as a variety in 2008 as Boro variety and popularly known as Banglamoti. Because it has long slender grain with mild aroma. In recent times, the grain qualities like BRRI dhan50 is considered as Banglamoti grade and it is highly rated for standard grain quality in the rice market of Bangladesh because of high price and wide acceptance by consumers.

Taken together, above pedigree information indicates that two IRRI varieties IR20 and IR5 also laid foundation in development of modern Boro rice in Bangladesh in terms of producing BR4, BR10 and their important progenies.

Key features of BRRI dhan29 group and its progenies

The popular cultivar BRRI dhan29 was released in 1994. Since then, a total of seven rice varieties namely BRRI dhan30, BRRI dhan50, BRRI dhan58, BRRI dhan68, BRRI dhan74, BRRI dhan84, BRRI dhan87, BRRI dhan88, and BRRI dhan89 have been developed from BRRI dhan29 pedigree group (Table 3). In this group, most of the rice varieties belongs to Boro and Aman season and they were released between 1994 to 2018. For agronomic traits, there were considerable variation in plant height, maturity days and yield. It ranged from 82-122 for plant height, 127-145 days for growth duration in Aman, 141-156 days for growth duration in Boro, 5.0-6.5 t/ha for yield in Aman, and 6.5-8.0 t/ha for yield in Boro. Among the rice varieties of BRRI dhan29 group, two rice cultivars BRRI dhan87 and BRRI dhan89 have out yielded other existing rice varieties developed from this group.

Table 3 . Agronomic characters and release year of improved rice varieties developed from BRRI dhan29 group.

Variety	Season	PHa (cm)	GDb (days)	YLDc (t/ha)	Release year	Group	Reference
BRRI dhan29	Boro	95	160	7.5	1994		BRRI, 2020
BRRI dhan30	T. Aman	120	145	5.0	1994	BRRI dhan29
BRRI dhan50	Boro	82	155	6.0	2008	BRRI dhan29
BRRI dhan58	Boro	100	150	7.2	2012	BRRI dhan29
BRRI dhan68	Boro	97	149	7.3	2014	BRRI dhan29
BRRI dhan74	Boro	95	147	7.1	2015	BRRI dhan29
BRRI dhan84	Boro	96	141	6.5	2017	BRRI dhan29
BRRI dhan87	T. Aman	122	127	6.5	2018	BRRI dhan29
BRRI dhan88	Boro	96	142	7.0	2018	BRRI dhan29
BRRI dhan89	Boro	106	156	8.0	2018	BRRI dhan29

^aPH: plant height, ^bGD: growth duration or maturity days, ^cYLD: grain yield.

Grain quality traits of BR11, BRRI dhan28 and BRRI dhan29

In recent times, consumer preferences have changed for grain quality, nutrition and taste. Thus, improved grain characters with higher yield have become a major concern for rice breeding. In line with this, product profiles have been made using most popular rice cultivars as a benchmark variety to replace old popular rice varieties (J Cobb et al. 2019). The grain quality traits of three popular rice varieties BR11, BRRI dhan28 and BRRI dhan29 have been listed (Table 4). In case of grain quality parameters, there was remarkable differences among these rice cultivars. The percent of milling outturn, percent of head rice recovery, and chalkiness was almost same for those cultivars as they are basic grain quality traits accepted by Bangladeshi consumers. But grain size and shape showed distinct variation. It was medium bold for both BR11 & BRRI dhan29, and medium slender for BRRI dhan28. All these rice varieties had high amylose content. The cultivar BRRI dhan28 and BRRI dhan29 had higher content of zinc compared to BR11. Glycemic index was 65.0 for BRRI dhan28 and 61.0 for BRRI dhan29.

Table 4 . Grain profiles of three popular rice varieties BR11, BRRI dhan28, and BRRI dhan29.

Grain quality parameters	BR11	BRRI dhan28	BRRI dhan29	References
Milling outturn (%)	72	71	71
Head rice recovery (%)	66	68	65	BRRI, 2016
Chalkiness	Translucent	Translucent	Translucent
Paddy length (mm)	7.9	9.2	8.7
Paddy breadth (mm)	3.0	2.3	2.7
Milled rice length (mm)	5.0	6	6
Milled rice breadth (mm)	2.6	1.8	2.1
L/B ratio	1.9	3.3	2.9
Size and shape	Medium bold	Medium slender	Medium bold
1,000-grain weight (gram)	24.7	22.2	21.5
Amylose content (%)	26	26.4	26.5
Protein content (%)	8.2	8.5	7.5
Cooking time (minutes)	17	16.5	17.4
Elongation ratio	1.4	1.5	1.3
Imbibition ratio	3.6	4.3	4.4
Zn (ppm)	9.5	15.2	16
Fe (ppm)	6.2	8.2	7.8
Glycemic Index (GI)a	-	65.0	61.0	Shozib et al. 2017

^aParboiled milled rice was used to measure GI.

Genetic information and favorable alleles of BR11, BRRI dhan28 and BRRI dhan29

In recent times, trait-based SNP genotyping has paved the way of identifying important stress tolerance and grain quality traits in the breeding population. IRRI based geno-typing service laboratories offers deployment of more than 100 validated SNP markers for 25 identified QTLs/genes (IRRI, https://isl.irri.org/services/genotyping/trait-based- genotyping.). Genotyping of three rice varieties BR11, BRRI dhan28, and BRRI dhan29 revealed that numerous important genes are already present in these rice varieties (Table 5). This genetic information indicates that these rice varieties possess important alleles or genes for anaerobic germination tolerance, drought tolerance, blast resistance, bacterial blight resistance and some grain quality traits like low chalk and high amylose content.

Table 5 . Genetic information related to presence of different favorable alleles in the background of three rice varieties BR11, BRRI dhan28, and BRRI dhan29.

Favorable allele/genes	Variety name			Major function
	BR11	BRRI dhan28	BRRI dhan29
AG1	+	‒	‒	Anaerobic germination tolerance
AG3	+	+	‒	Anaerobic germination tolerance
DTY3.2	+	‒	‒	Drought tolerance
DTY12.1	+	+	+	Drought tolerance
Pi54	+	‒	‒	Blast resistance
Pi-ta	‒	+	‒	Blast resistance
Pi25 (Pid3)	+	+	+	Blast resistance
Pid2	+	+	+	Blast resistance
Xa4	‒	+	‒	Bacterial blight resistance
Xa26	‒	+	‒	Bacterial blight resistance
Sweet13	+	+	‒	Bacterial blight resistance
Chalk5	+	+	+	Low chalkiness in grain
Waxy	Wx(a)	Wx(a)	Wx(a)	High amylose content

‘+’ refers to present and ‘‒’ refers to absent in the rice variety.

Present adaptation status of BR11, BRRI dhan28, and BRRI dhan29

From recent adaptation data of BRRI developed rice varieties, we observed considerably higher adaptation rate of BR11, BRRI dhan28, and BRRI dhan29 across rice ecosystems of Bangladesh (BRRI 2019). Till now, BRRI has developed 45 T. Aman rice varieties. They had more than 70% adaptation in Aman season (Fig. 4a). Most of the T. Aman cultivars are area-specific based on growth duration, yield and nature of ecosystem such as favorable, flood-prone, salinity, submergence etc. In T. Aman or wet season, the cultivar BR11 occupies 11% rice growing area of Bangladesh (Fig. 4a). On the other hand, BRRI has developed 46 Boro rice varieties which are cultivated across irrigated rice ecosystem in Boro season or dry season. Like T. Aman, Boro rice varieties have more than 70% adaptation in Boro or dry season (Fig. 4b). The rice cultivar BRRI dhan28 and BRRI dhan29 occupies 23% and 28 % rice growing areas, respectively. In total, these two cultivars constitute more than 50% area in Boro which contributes greatly in Boro rice production of Bangladesh (Fig. 4b).

Figure 4. Adaptation of BRRI varieties in T. Aman and Boro season in 2016-17 including comparison of BRRI developed T. Aman rice varieties with BR11 (a). Boro varieties included BRRI dhan28, BRRI dhan29 compared to adaptation of BRRI developed Boro rice varieties (b).

This brief review attempts to document the value and contribution of two IRRI cultivars (IR20 and IR64) in developing three popular rice cultivars (BR11, BRRI dhan28, and BRRI dhan29) through rice breeding programs of Bangladesh. Gradually these popular rice varieties are being replaced in most of the rice production areas by new rice varieties with higher yield potentiality and acceptable grain quality traits. Rice breeding is a continual process and all varieties are expected to be replaced by improved varieties over time. However, BRRI dhan28 and BRRI dhan29 are still popular among rice farmers, particularly in low lying haor areas. The development of high-quality popular varieties like BR11, BRRI dhan28, and BRRI dhan29 is still remain a challenge to rice breeders. In general, new rice varieties that aim to replace those old varieties must offer a clear advantage in terms of yield and grain quality to secure better price at farm level. For this reason, development of rice cultivars with high yield, better grain qualities, tolerance to major biotic and abiotic stresses are most urgent breeding objective. Therefore, improving our understanding on the genetic basis of old popular rice varieties along with their important progenies, major agronomic traits, and grain characteristics will be more important than ever before.

The authors declare that they have no conflict of interest.

We greatly acknowledge Wazifa Afrin from BRRI for making constructive comments on the initial draft. We are also thankful to Mr. Shariful Islam and Mr. Shobuj Kumar Dutta of Plant Breeding Division, BRRI for their technical help in collecting secondary data of BRRI developed inbred rice varieties.

Not applicable.

MME Ahmed and S Afrin prepared the draft manuscript. MME Ahmed analyzed the pedigree information and prepared the figures; A Biswas and S Afrin collected all agronomic characters and grain quality traits to prepare the tables and draft results. A Biswas and S Afrin made critical reviews and improved the text. All authors had read and approved the final version of the submitted manuscript.