PHENOTYPIC AND GENOTYPIC VARIABILITY STUDIES ON SOME RICE GENOTYPES IN LOW LAND ECOLOGY OF NIGERSTATE, NIGERIA

ABSTRACT

Variability has been known as a tool for any crop improvement programme. Yield improvement can be ascertained if there is enough variability existing in a population. Therefore, this study was conducted to asses morpho-agronomic variations in the lowland rice genotypes in an Alpha lattice design with three replications. The experiment was conducted at National Cereals Research Institute Badeggi and Edozhigi in 2017. Parameters such as Days to 50 % flowering, tiller number, panicle number, panicle length, panicle exertion, plant height, panicle weight and grain yield were collected. The result showed that there exists significant variability amongst the genotypes in all the parameters studied, except panicle weight. In all the yield components studied, the phenotypic coefficient was higher than the genotypic coefficient of variation. Days to 50 % flowering had high heritability (83.63). Association study revealed that positive correlation existed among some of the yield components and some of them were significant such as association between panicle number with panicle length (0.295*). Plant height (0.1506) had the highest direct contribution to the yield and the residual effect for the path analysis was a positive value (0.0291).  Principal component analysis partitioned the variability into eight principal components, days to 50 % flowering (0.61) contributed highest variability in the first principal component. Five major cluster groups were identified at cophenetic percentage of 0.578. This investigation therefore, recommends that FARO 15, FARO 17, FARO 24 and Waluye which out yielded the standard checks can be used for further rice improvement programmes.

CHAPTER ONE

1.0       INTRODUCTION

1.1      Background to the Study

Rice, Oryza sativa (2n = 24) belongs to the family poceae and sub family Oryzoidae and is consumed by more than fifty percent of the world’s population especially in developing countries. The third highest cereal produced is rice after wheat and maize (FAO, 2012). India has the largest area under rice cultivation in the world and ranks second in production (Anonymous, 2013). Rice is one of the significant cereal commodities for the world’s population.  (Lopez and Joseph, 2008).

It has shaped the culture, diets and economy of thousand of millions of peoples. For more than half of the humanity “rice is life”. Considering its important position, the United Nation designated year 2004 as the “International Year of rice. More than 430 million metric tonnes of rice consumed worldwide (USDA, 2008). Rice is a nutritional staple food providing 20 % of the calories and 15 % of proteins consumed by the world‘s population (Muhammad et al., 2015). On the other hand, rice is poor in nitrogenous substances with their  average composition being only in trace amounts. The fat content or lipids are only negligible and due to this reason it is considered as a complete food for eating.

Local  rice  production  in  Nigeria  has  now  reached  15  million  metric  tones  annually (Ahmad, 2017).  West Africa remains the hub of rice production in sub-Saharan Africa but the shortfall in rice production has increased significantly as consumption rises at a rate well above that of production growth. In 2006, paddy rice production in sub-Saharan Africa was estimated at 14.2million tonnes. Rice production in sub-Saharan Africa grew at 3.23% per annum from 1961 to 2005. This growth rate was higher than the yearly population growth rate of 2.90% during the same period (ARC, 2007).

Rice straw is used as cattle feed, it also used for thatching roof and in cottage industry for preparation of hats, mats, ropes, straw board and litter material. Rice husk is used as animal feed, paper making and as fuel source. Rice flour is rich in starch and is used for making  various  food  materials.  It  is  also  used  by  brewers  to  make  alcoholic  malt. Likewise, rice straw mixed with other materials is used to produce porcelain, glass and pottery. Rice straw is also used in manufacturing of paper pulp and livestock bedding. The rice bran is also an important source of  animal feed in many countries of the world (Muhammad et al., 2015). In husked rice, protein content ranges between 7 and 12 %. The use of nitrogen fertilizers increases the percentage content of some amino acids in rice.

Globally,  improving  quantity  and  quality  of  rice  grain  has  been  approached  to  solve several problems among the world population such as decreasing the number of hidden hunger and malnutrition (Burchi et al., 2011). However, a wide variation of grain morphological characteristics will be required as source of genetic materials in breeding for some specific traits as it would have effect on consumer’s acceptance in the end. According to Couch and Hittalmani ( 2018) The yields of rice are complex quantitative traits that involve multiple quantitative trait loci (QTLs), so it is not simple to improve them. Also, the crop environment varies depending on the season, year, location, and a specific area within the field. These variations lead to large fluctuations in crop yield. Therefore, breeders need to assess yield stability of crops in different environments to develop and launch a new variety. Recent advances in rice genomics have improved the understanding of individual QTL functions, thereby unraveling genotype-phenotype relationships and facilitating grain yield improvement (Ikeda et al., 2013).

1.2      Statement of the Research Problem

The populations in the major rice-consuming countries continue to grow at a rate of more than 1.5 % per year. According to various estimates, world rice production must increase at the rate of 2 million tonnes per year. To meet this challenge, rice varieties with higher yield potential and greater yield stability are needed.

Inadequate information generated from phenotyping these germplasms that can be used as basis to augment diversity in the genebank collections as well as baseline information for utilization in rice breeding programs. One of the most difficult tasks in carrying out a successful breeding programme is the choice of germplasm. In order to develop a variety with a set of desirable characteristics, rice breeders need to be sure that the source of germplasm  has  desirable  genetic  variability and  to  make  the  right  choice  of  parental material to be used in a breeding   programme breeders must clearly know the type of product to be developed.

1.3      Justification of the Study

Rice genotypes with wide genetic variability are essential to generate viable progenies. The major resource of plant breeders is the genetic variability in gene pool that is accessible to the crop of interest (Thottappily et al., 2016). Success of rice improvement programmes depends on the amount of genetic variability and the degree to which the desirable traits are heritable (Ravi et al., 2003). Hence assessment of genetic variability among genotypes becomes important in establishing relationships among different cultivars for the initiation of appropriate breeding procedures in crop improvement programmes. Hence, it becomes necessary to split over-all variability into its heritable and non heritable components with the help of certain genetic parameters, which may enable the breeders to plan a proper breeding programme. Therefore, the progress of a population mainly depends upon the amount and magnitude of genotypic variability present in the population. Information on genetic variability among growth as well as yield components in rice has been reported by many workers (Sivasubramanian and Madhava, 2010; Latif and Zamin 2010). The characterization of these genetic resources is a necessity not only for posterity, but also for utilization in different improvement programs such as br eeding for improved yield and tolerance to various stresses. The study of morpho-agronomic traits is the conventional way of evaluating genetic variability in crops (Bui and Nguyen, 2015).

1.4      Aim and Objectives of the Study

Aim

The aim of this study was to determine  the extent of phenotypic and genotypic variability among the rice genotypes.

Objectives

The objectives of this study were to:

i.         Determine extent of variability in some lowland rice genotypes.

ii.        Evaluate for growth, yield an yield components in lowland rice genotypes.

iii.       Determine direct and indirect contribution of each component to yield in lowland genotypes.

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