A major section of the world's population relies mostly on rice (Oryza sativa L.) as a source of sustenance. According to India's Annual Report 2020–21 (Anonymous 2022), rice has been grown on 43.79 million ha, producing 116.42 million t and yielding 2659 kg per hectare. On the other hand, rice is cultivated in the state of Bihar over an area of 3.30 million ha, producing 8.09 million ton with an average productivity of 2447 kg per hectare (Anonymous 2022). India is a leading producer and exporter of Basmati rice, which is renowned for its aroma, cooking and grain type. Aromatic rice comprised both Basmati and non-Basmati grain types, are highly priced due to their grain texture, specific pleasant aroma and other special qualities. The most common, ceremonial, and best-quality scented rice in Bihar is Katarni Rice, a traditional non-basmati variety. It is renowned for its flavor, palatability, and ability to produce Chura (beaten rice). It flowers between the end of October and the beginning of November, maturing in December. Its height ranges from 140 to 160 cm (Smriti et al. 2016). However, Katarni has a low yield of 25 to 30 Q/ha susceptible to lodging due to its tall stature (140–160 cm), vulnerable to pests and diseases and late maturing (155–160 days). The tall and week culm results in lodging at maturity and creates problems in mechanical harvesting. Semi-dwarf rice varieties can evade the damage due to their strong culm and short height (Berry et al. 2002). Due to photoperiod sensitivity, its flowering in Katarni is delayed considerably under long-day treatments (Kumar et al., 2018a) making it unfit for traditional rice-wheat cropping system.
The semi-dwarfing gene sd1 is one of the most crucial genes used in rice breeding and played a vital role in first green revolution during 1960s. Due of its recessive nature, the culm of sd1 gene containing plant is shorter and more resistant to lodging. The dominant allele of the sd1 gene, encodes gibberellin 20 oxidase-2 (GA20ox-2) and a deletion or substitution mutation in this gene renders the protein inactive. The bioactive growth hormone GA3, which regulate plant height, is therefore lacking in the plants (Spiemeyer et al. 2002). Increased levels of 2-acetyl-1-pyrroline (2AP) have been linked to the aroma of fragrant rice (Buttery et al. 1983; Lorieux et al. 1996; Widjaja et al. 1996; Yoshihashi 2002). The betaine aldehyde dehydrogenase (badh2) gene, which is a single recessive gene on chromosome 8, regulates the aroma in rice (Bradbury et al., 2005; Peng et al., 2018). As a result of badh2 enzyme activity, loss caused by inhibition, deletion, or mutation of the fgr gene, levels of 2-AP precursors rise and 2-AP accumulates to produce fragrance in aromatic rice (Shan et al. 2013; Chakraborty et al. 2016; van Quoc et al. 2023). In addition, the time of flowering or the heading date (HD) is thought to be an essential factor not only for the quantity but also for the quality of rice grain production in general and photosensitive rice varieties like the Katarni, in particular (Fan et al. 2005). According to Tamaki et al. (2007), the Hd3a locus has a significant role in flowering time and has been roughly mapped on chromosome 6 (Monna et al., 2002). Grain kernel length (KL) is an important agronomic and grain quality trait for breeding of rice (Oryza sativa L.), influencing seed weight and ultimately the crop yield (Luo et al. 2004). A QTL named GS3, located in the peri-centromeric region of chromosome 3 is reported to be responsible for 80–90% of the variation in kernel length. Later, the locus was also resolved as a minor QTL for grain width and thickness (Fan et al. 2006). It is crucial to generate lines with shorter plant height, early flowering, with desired quality traits through marker assisted backcross breeding (MABC). Microsatellites (SSRs) are essential tool for identifying the genetic diversity among rice accessions (Sajib et al., 2012; Ma et al., 2011). These markers are widely used in genetic diversity analysis, the creation of molecular maps, and gene mapping (Ma et al. 2011) as they are highly informative, primarily monolocus, codominant, easily analyzed, and cost-effective (Gracia et al. 2004). They are also capable of detecting high levels of allelic diversity. Incorporating semi-dwarf trait into rice has been effectively accomplished through a number of molecular breeding strategies without affecting fragrance (Rajpurohit et al., 2011).
Katarni rice was tagged with geographical indication (GI) in 2018 for its unique cooking qualities which is linked to its confined GI territory. For enhancing area beyond GI area under this covered rice genetic resource, yield barrier and late maturity problem has to be addressed without compromising the unique grain qualities, a marker-assisted Backcross breeding (MAB) program was started at Bihar Agricultural University by crossing Katarni with semi-dwarf rice types namely, Rajendra Sweta, BPT5204, and MTU7029 in order to shorten the height and maturity time. Further, through marker-assisted forward and backcross breeding approach, the generation was advanced (Vaibhav et al. 2019; Suvidha et al. 2020) to obtain the homogeneous population. It is necessary to characterize the advanced Katarni derived lines for distinctness both at molecular and morphological level with respect to parental source lines and confirming the presence of target genes. Functional markers for the target traits along with genome wide SSR markers were used in the present study to evaluate advanced breeding lines of Katarni and to assess the genetic diversity.