Milling and Aromatic Quality Traits of Rice (Oryza sativa L.) Landraces of Nepal
Abstract
Milling and aromatic quality are two of the most economically important post-harvest attributes that determine the market value and consumer acceptance of rice (Oryza sativa L.). This study evaluated six milling quality traits and grain aroma in 30 rice landraces along with 3 released check varieties of Nepal. Milling quality was assessed in a completely randomized design (CRD) with three replications following the IRRI Rice Knowledge Bank protocol, while grain aroma was scored using the standard 1.7% KOH sensory method on a 1-4 intensity scale by a panel of evaluators. Analysis of variance revealed significant genotypic differences for all studied milling quality traits. Head rice recovery, the most economically valuable milling trait, ranged from 50.07% (Ramkumar-3) to 75.05% (NGRC02829), with NGRC02829 emerging as the best milling-quality genotype. The KOH aroma test classified the 33 genotypes into four groups: 8 non-aromatic, 21 slightly aromatic, 3 moderately aromatic, and 1 strongly aromatic (Kalo Nuniya, mean score 3.50 ± 0.84), a genotype independently documented as an aromatic Nepalese landrace. A Kruskal-Wallis test confirmed significant genotypic variation in aroma intensity (H = 66.84, df = 32, p < 0.001), corroborated by a complementary one-way ANOVA (F = 3.10, p < 0.001), although inter-panelist agreement was low (Fleiss' κ = 0.05), reflecting the well-documented subjectivity of sensory-based aroma scoring. Hierarchical cluster analysis based on the combined milling and aroma trait profile grouped the genotypes into four clusters, separating a superior-milling cluster (headed by NGRC02829) from a poor-milling cluster, and showed that the strongly aromatic landrace Kalo Nuniya did not belong to the best-milling group. Overall, the study identifies landraces with superior milling recovery and distinct aroma expression that represent valuable breeding material for improving the grain quality of Nepalese rice.
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Introduction
Rice (Oryza sativa L.) is the staple food crop of Nepal, meeting approximately half of the population's daily caloric requirement and occupying a central place in the country's agricultural economy [1], [2]. Nepal is regarded as one of the centers of rice diversity, harboring thousands of indigenous landraces that have evolved under diverse agro-ecological conditions ranging from the lowland Terai to the high-altitude Himalayan valleys [3], [4]. Beyond their adaptive value, these landraces harbor considerable variation in grain quality attributes such as aroma, cooking behavior, texture, and milling characteristics that are increasingly valued by both producers and consumers [5], [6].
Rice quality is a multifaceted trait combining subjective and objective components, of which grain length, breadth, length-breadth ratio, milling recovery, and aroma are among the key physical and sensory parameters that determine market value and consumer preference [7]. Milling quality specifically reflects the ability of the grain to withstand the de-husking and polishing processes without excessive breakage, and is commercially expressed through brown rice recovery, milling recovery, head rice recovery, broken rice percentage, and dockage percentage [8]. Head rice recovery is considered the single most economically important milling trait because intact, unbroken kernels command a substantially higher market price than broken rice [9].
Aroma is likewise a premium grain-quality trait; aromatic rice types such as Basmati and Jasmine command a considerable price premium in both domestic and export markets [10]. Grain aroma in rice is primarily governed by 2-acetyl-1-pyrroline (2-AP), and the loss-of-function badh2 allele responsible for its accumulation segregates widely among South Asian landraces. Although gas chromatography and molecular markers allow precise aroma quantification, the alkaline (KOH) sensory test remains the most widely used, low-cost, and rapid screening method for aroma detection in breeding programs and germplasm surveys [11].
Despite the wide genetic base of Nepalese rice landraces, scientific information on their milling and aromatic quality remains scarce, which limits their utilization in quality-oriented breeding programs [6], [12]. With Nepal importing substantial quantities of fine and aromatic rice every year, characterizing local landraces for milling and aroma quality is essential to identify superior genetic resources for varietal improvement and import substitution. The present study was therefore undertaken with the objective of evaluating the milling quality traits and grain aroma of 30 Nepalese rice landraces along with 3 released check varieties, in order to identify genotypes of superior milling and aromatic quality that could serve as valuable parental material in future rice breeding programs.
Conclusion
This study demonstrated significant genotypic variation in both milling quality and grain aroma among 30 Nepalese rice landraces and 3 released check varieties. NGRC02829 emerged as a superior landrace for head rice recovery and milling strength, while Nirwan Dhan and Simtari Dhan exhibited the highest brown rice recovery. The KOH aroma test identified Kalo Nuniya as a strongly aromatic landrace, along with Sano Damauli and Ramkumar-3 as moderately aromatic, representing valuable genetic resources for aromatic rice breeding in Nepal. Hierarchical cluster analysis combining all quality traits further grouped the 33 genotypes into four distinct clusters, distinguishing a superior-milling group (Cluster I) from a poor-milling group (Cluster III), and revealed that the strongly aromatic landrace Kalo Nuniya did not co-occur with the best-milling cluster, pointing to the need for targeted crossing to combine both traits.
References
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