Rice (Oryza sativa L.) is the most important food crop in the world, providing over 21per cent of the calorific needs of the world’s population and 76 per cent of the calorific intake of the population of South East (SE) Asia. In countries where rice is consumed, traits of grain quality dictate market value and have a pivotal role in the adoption of new varieties. So there is a growing demand for better quality rice like Jasmine and Basmati, especially the country like India. The growing demand for better quality rice is explained by higher household incomes and now consumers are offering to pay more for better quality rice (Fitzgerald et al., 2009).

 

            Quality traits for rice encompass physical appearance, milling quality and cooking quality which nowadays becoming more important for consumer point of view and the value of each trait varies according to local cuisine and culture. Cooking and eating quality is the easiness of cooking as well as textural properties of cooked rice that is springiness, stickiness, aroma and chewiness of cooked rice. These grain quality and cooking parameters are controlled by starch physicochemical properties of the rice and are measured by using Apparent Amylose Content (AAC), Gelatinization Temperature (GT) and Gel Consistency (GC).

 

            Breeding for improved grain quality is complex because many of the quality traits are phenotyped using subjective and expensive biochemical methods. Consequently, the scientific community mapped/cloned many quantitative trait loci (QTLs)/genes for various quality traits and developed molecular marker to facilitate selection for specific grain quality types. This has enabled the development of functional markers to facilitate the selection for this complex trait. Functional markers, especially those targeting mutations in the BADH2, waxy, alk and GS3 genes, are highly associated with aroma, AAC, GT and grain size, respectively; and thus effective for marker-assisted breeding. Different alleles can be combined through gene pyramiding to improve rice grain quality for various consumers. To be able to meet future needs, rice breeders must exploit modern marker technologies such as genomic selection (GS) to take care of the effects of both major and minor genes for grain quality as well as high yield, abiotic and biotic stress tolerance.

 

Myint et al. (2009) carried out 336experiment to improve fragrance and intermediate AC in Manawthukha, Basmati370 was used as a donor parent to introgress the Basmati alleles of genes conferring fragrance and intermediate AC into Manawthukha by Marker Assisted Backcrossing (MAB). Here four backcrosses and one selfing were carried out to transfer positive alleles of badh2 and Wx from Basmati into Manawthukha. Twelve BC4F2 selected lines that carried the homozygous Basmati alleles were planted in multi-location trials (four in Myanmar and one in Thailand) and examined for their agronomic performance and cooking quality. The seeds of the improved lines and their parents, harvested from Kamphaeng Saen, Kuaukse, Kyauktada and Latpatan, were investigated for fragrance and AC. All improved lines had fragrance and intermediate AC similar to the donor parent Basmati, whereas their agronomic performances were the same as the original Manawthukha. MAB accelerated the development of superior qualities in the genetic background of Manawthukha. The improved Manawthukha should be immediately useful for Myanmar farmers and will help farmers to increase their incomes.

 

Kimberly et al. (2018) used multi-parent advanced generation intercross (MAGIC) for association mapping of rice cooking and eating quality (CEQ). QTLs were identified for 10 physicochemical properties related to CEQ using 508 F6 MAGIC lines. The whole population and 8 founder lines were genotyped. All traits had high heritability estimates and showed a large genetic variation in the MAGIC population. Highly significant phenotypic correlations were present between traits. AC was significantly positively correlated with Peak Time (PKT), Trough Viscosity (TV), Final Viscosity (FV), Setback Viscosity (SBV), Peak time (PKT), and Retro-gradation (RT) but significantly negatively correlated with Gel Consistency (GC) and Breakdown Viscosity (BDV). 7 QTLs were identified for all traits. GBSSI locus was hosted closely to nine QTLs, it suggesting that GBSSI impacts the overall CEQ and these results confirmed that QTL mapping via association mapping using a MAGIC population is a powerful method in genetic analysis of complex traits. 

           

Since rice is eaten mainly by humans as whole grain in cooked form, its grain quality is extremely important. Breeding for these specific consumer demands can be challenging because grain quality is phenotyped using subjective, biochemical analyses that can be very expensive. Marker assisted selection is thus a very good option for breeding for grain quality. The sequencing of the rice genome over a decade ago has made it possible for researchers to identify genes for the various grain quality traits. Functional molecular markers have been developed that are highly efficient in selecting for grain size, aroma, AAC and GT parameters. These markers are increasingly being used for breeding for consumer-preferred grain qualities around the world. Modern genome-wide marker technologies which will take care of genes with small effect and allow breeders to simultaneously select for grain quality, yield and stress tolerance are recommended for future rice breeding work.

 

           

References:                                              

Fitzgerald, M. A., Mc Couch, R. S. and Hall, R. D., 2009, Not just a grain of rice: the quest for quality.         Trends in Plant Sci., 14(3): 1-7. 

 Kimberly, P. S., Guoyou, Ye. And Xiangqian, Z., 2018, QTL identification for cooking and eating       quality in indica rice using Multi-Parent Advanced Generation Intercross (MAGIC) population.             Front. Plant Sci. 9: 1-9.

Myint, Yi., Khin, T. N., Apichart, V., Witith, C. and Theerayut, T., 2009, Marker assisted backcross        breeding to improve cooking quality traits in Myanmar rice cultivar Manawthukha. Field crop      res., 113(1): 178-186.