Genetic parameter estimates and diversity studies of upland rice

Introduction

Rice (Oryza sativa L.) feeds over 50 percent of the world's population (Rasel et al., 2018). The crop is the staple food of Sierra Leone with an annual rice consumption estimated at 530,000 tons (Baggie et al., 2018). However, its production and productivity are far below the demand for rice resulting into high government expenditure on importation of about $144,078 annually (GoSL, 2017). The Global Hunger Index (GHI) of Sierra Leone is estimated at 38.3 scores, which falls within the 119 countries with highest GHI ranging from 35.0-49.9 scores (SLNSS, 2017). The low production and productivity of rice in many rice growing areas including Sierra Leone is partly due to the prevalence of low yielding varieties, declining soil fertility, and the influence by climate change involving changes in rainfall and temperature levels that impede its growth and yield (Li et el., 2015; Tripathi et al., 2016; Bebeley et al., 2021). Moreover, the dearth of well-articulated information on genetic parameter estimates and diversity studies of upland rice in Sierra Leone, limits the genetic improvement of the crop. The generation of adaptable varieties largely depends on the availability of desirable genetic variability for important traits (Pratap et al., 2014).

Rice germplasm is a rich reservoir of useful genes which researchers can rely on for expanding rice production (Singh et al., 2015). Rice contributes a minimum number of the large ex situ germplasm accessions in the world (Vanniarajan et al., 2012). Local varieties are well known as useful source of genetic diversity that could be utilized for the genetic improvement for yield and other desired traits (Vanniarajan et al., 2012; Bidhan, 2013; Singh et al., 2015). However, the agronomic performances of these varieties are often influenced by genetic, non-genetic and environmental factors (Rabara et al., 2014). 

Genetic variability is the basis of plant breeding because crop improvement depends on the amount and direction of genetic association of the traits in the base population (Tuhina-Khatun et al., 2015; Aditya and Bhartiya, 2013). Genetic variability provides a wide range of genotypes for selection of parents with desired complimentary traits to develop new varieties (Pandey et al., 2009). Useful genetic variability is essential in crop improvement for the efficient utilization of germplasm resources and related crop species (Banumathy et al., 2010). Development of elite varieties with desired agronomic traits requires the existence of genetic variability and genetic variability is the key component of breeding programs for broadening the gene pool (North, 2013). Selection is effective when a significant amount of variability exists among the breeding lines (Sumanth et al., 2017). The existing genetic variability in genotypes is measured using genotypic and phenotypic coefficient of variation which is used to partition genetic and environmental variances (Onyia et al., 2017).

 Estimates of the genetic parameters of quantitative traits, such as heritability and genetic advance, are important because they give an indication of the ability of a species to respond to selection and the potential of that species to evolve (Falconer and Mackay, 1996). Development of effective genetic evaluation and improvement programs requires knowledge of the genetic parameters for economic growth and reproduction traits. Heritability is used to assess the amount of genetic improvement that is transmitted to next generation (Dutta et al., 2013). Genetic advance denotes the degree of gain obtained in a character under a particular selection pressure (Ogunniyan, and Olakojo, 2014; Norman et al., 2021). Both heritability and genetic advance are more powerful in predicting genetic gain than using heritability estimates alone (Ogunbayo et al., 2014).

 A wide dissimilarity has been reported among and within rice landraces that necessitate future improvement (Singh et al., 2015). In Sierra Leone, dearth of knowledge exists on the extent of genetic diversities among upland rice as well as the genetic parameter estimates of relevant traits.

Landraces thrive well in their local environment and are known to harbor valuable genetic traits for rice improvement (Vanniaraja et al., 2012). Thus, a good understanding of genetic diversity is important for crop management, crop improvement, selection of parental lines for hybridization or recommendation for short term release, detection of genome structure, and transfer of desirable traits to other plants (Varshney et al., 2008; Sasaki, 2005). The selection decision of the germplasm determines the success of plant breeding program. The objectives of this study were (i) to determine genetic parameter estimates of upland rice genotypes; and (ii) to determine the extent of genetic diversity among rice genotypes using agro-morphological traits in Sierra Leone.