Genetic analysis of some quality traits in three rice cultivars

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Extra long/long grain and slender rice, which has aroma, is highly valued in many areas of the world including Ghana. Information on the inheritance of aroma and grain quantitative traits (length, width and length: width ratio/shape) will facilitate the development of such varieties. Reciprocal crosses were made amongst a non-aromatic, extra long and slender rice variety IDSA 85 and two aromatic varieties JASMINE 85 (J85) and NERICA / (N I) to study the inheritance of aroma and to understand the gene action of the grain quantitative traits in these nec cultivars. Inheritance of spikelet fertility was also studied because of low seed set in F1 hybrids. Leaf tissue from the parental cultivars and of backcross, F1 and F2 progenies were placed in 0.3 mol L’ KOH and rated for strength of aroma. Heritability estimates and F2 frequency distribution curves were obtained for the grain quantitative traits. Plants were grouped into a low fertility and a normal fertility groups based on the fertility range of the less fertile parent. Lack of leaf aroma in all non-aromatic/aromatic F1 plants as well as the hackcross to the non-aromatic parent indicated that aroma is a recessive trait. H segregation ratios of 1: 3 (aromatic: non-aromatic) indicated that a single recessive gene each controls aroma in NERICA 1 and JASMINE 85. A testcross (IDSA 85/Nl//Nl) ratio of 1:1 confirmed that aroma in NERICA I is under the control of a single recessive gene. The F1 leaves of the Nl/J85 crosses as well as its reciprocal were all aromatic revealing that the aroma genes in the two cultivars are allelic. Broad sense heritability estimates for the cross were 0.5 I . (1.50 and (1.50 for grain length, width and shape respectively that for the IDSA 85/NI cross were 0.31. 0.75 and 0.38 respectively. Narrow sense heritabilities were 0.11. 0.25 and 0.15 for grain length. width and shape (length: idth ratio) respectively for the IDSA 85/NI cross. Heritability estimates as well as F frequency distribution of grain length, width and shape indicated the presence of additive and non- additive effects in the control of the three traits. The inheritance of grain length and grain shape were either predominantly additive or dominant depending on the cross; that for grain width was predominantly additive for the two crosses made in this study. Transgressive segregation towards the shorter parent was observed for grain length, width and shape. The F, of the two crosses made in this study was found to have into 9 low fertility plants: 7 normal fertility plants. This indicates that spikelet fertility in both crosses displayed duplicate recessive epistasis. It is recommended that pedigree (using a large F2 population) or backcross method of breeding be used to introduce aroma into non-aromatic cultivars. Also aroma genes should be mapped and marker assisted selection be used to facilitate the rice breeding programme in Ghana. Recurrent selection or dialled selective mating could also he used to improve rice grain quantitativc traits. To overcome the fertility harrier that is normally experienced in rice hybridization it is recommended that wide compatibility varieties which produce normal fertility hybrids when crossed with a wide range of varieties are used; also another culture techniques and “embryo rescue’ should he exploited fully.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of Master of Science degree, 2004