Callogenesis and embryogenesis are integral parts of many tissue culture procedures for genetic manipulation in rice. However, the efficiency of both processes is largely dependent on the media constituent especially the plant growth regulators (PGRs) due to the genotype-dependent nature of in vitro culture protocols. Therefore, this study investigates the effect of two PGRs; 2, 4-dichlorophenoxyacetic acid (2, 4-D) and kinetin (Kin) on callus growth and somatic embryogenesis of an important Malaysian rice cultivar (Oryza sativa L. cv. MARDI Siraj 297). Mature rice seeds explants were inoculated in Murashige & Skoog (MS) medium supplemented with different combinations of 2, 4-D (0 to 3.5 mg/L) and Kin (0 to 0.5 mg/L) to induce callogenesis. Parameters for callus growth such as fresh weight (FW), callus induction frequency (CIF), embryogenic callus frequency (ECF), regeneration frequency (RF), number of plantlets per callus (PPC), callus texture and callus color were observed after 35 days of inoculation. The results show that the maximum callus growth was achieved in MS medium supplemented with combination of 2.0 mg/L 2, 4-D and 0.2 mg/L Kin, represented by the highest FW (211 mg), CIF (95%), ECF (90%), RF (100%) and PPC (22 plantlets); along with friable callus texture. Low concentration of 2, 4-D (0 to 0.5 mg/L) in the presence or absence of Kin promotes root growth instead of callus, while high concentrations (above 3.0 mg/L) retard the callus formation. The embryogenic calli from this optimized PGRs combination were successfully formed shoots in MS medium supplemented with 2 mg/L BAP and 1 mg/L NAA, followed by rooting in PGRs-free MS medium. This finding provides an efficient protocol for callogenesis and somatic embryogenesis of MARDI Siraj 297, since this is the first published report regarding somatic embryogenesis induction of this cultivar.

Malaysia is currently experiencing the same scenario as other countries, as the majority of consumers have shifted their preferences from locally produced rice to imported rice. This has resulted in a significant influx of imported rice into the domestic markets. Food security in the long term cannot be achieved by depending on imported food. Therefore, countries must make an effort to develop high-quality rice to meet the demand of customers. The study aimed to evaluate the grain physical traits and physicochemical properties of 30 Malaysian rice landraces to optimize the use of rice landraces in breeding programs. The grain physical traits were evaluated according to grain size, grain shape, and kernel elongation. Meanwhile, the physicochemical properties were determined by amylose content, alkali spreading value, and gel consistency. The grain length ranged from 4.14 to 8.16 mm and the grain width varied between 1.76 and 2.81 mm. The grain shapes were categorized into three types: medium, long and slender, and bold. Most of the rice landraces exhibited a low amylose content ranging from 16.07 to 19.83, while intermediate amylose content ranged from 20.00 to 23.80. The alkali spreading value showed that most of the rice landraces require an intermediate cooking time. The gel consistency exhibited a wide range, varying from soft to hard. The gel consistency exhibited the highest phenotypic and genotypic coefficient of variance, with values of 42.44% and 41.88%, respectively. Most of the studied traits except for kernel elongation were identified as having high heritability and high genetic advance as a percentage of the mean. A dendrogram effectively revealed the genetic relationships among Malaysian rice landraces by generating three distinct clusters. Cluster Ⅰ was primarily composed of glutinous rice landraces with a low to very low amylose content and exhibited the highest mean values for gel consistency and kernel elongation. Cluster Ⅱ consisted of 13 rice landraces that had the highest mean value for milled grain length and grain shape. Cluster Ⅲ was composed of rice landraces and control rice cultivars, and they exhibited the highest mean values for alkali spreading value, amylose content, and milled grain width. Bokilong, Kolomintuhon, Silou, Tutumoh, and Bidor in Cluster Ⅲ exhibited comparable physicochemical properties and cooking quality traits as the control rice cultivars. The findings of this study are important for identifying potential donors for breeding programs focused on developing high-quality or specialty rice cultivars.