RESEARCH ARTICLE AGBIR Vol.38 No.5 September 2022 1 Department of Plant Sciences, Haramaya University, Dire Dawa, Ethiopia; 2 Department of Crop Improvement, University of Ghana, College of Basic and Applied Sciences, Legon, Accra, Ghana Correspondence: Dosho BM, Department of Plant Sciences, Haramaya University, Dire Dawa, Ethiopia, E-mail: bdosho@wacci.ug.edu.gh Received: 01-Jul-2022, Manuscript No. AGBIR-22-68263; Editor assigned: 05-Jul-2022, Pre QC No. AGBIR-22-68263 (PQ); Reviewed: 19-Jul-2022, QC No. AGBIR-22-68263; Revised: 26-Jul-2022, Manuscript No. AGBIR-22-68263 (R); Published: 02-Aug-2022, DOI:10.35248/0970-1907.22.38.345-351 This open-access article is distributed under the terms of the Creative Commons Attribution Non-Commercial License (CC BY-NC) (http:// creativecommons.org/licenses/by-nc/4.0/), which permits reuse, distribution and reproduction of the article, provided that the original work is properly cited and the reuse is restricted to noncommercial purposes. For commercial reuse, contact reprints@pulsus.com 345 of additive gene action in kernel modification. General combining ability for kernel virtuousness and kernel hardness was positively correlated with an accumulation of dominant kernel modifiers but due to the complex genetic control of kernel modification and lack of reliable molecular markers linked to endosperm modifier genes, the effective approach is to physically screen the kernels using a ‘light box’ for identification of promising QPM genotypes with desirable kernel modification scores [6]. Also, since the QPM germplasm has to now compete with the normal-endosperm maize, information regarding combining ability of the QPM inbred lines coupled with important characters such as kernel modification scores, tryptophan, protein and protein quality index under low and optimum soil nitrogen environments is required for breeders to utilize this germplasm more effectively in the breeding programmes [6]. Because of the laboratory cost in lysine and tryptophan concentration analysis in the maize kernel endosperm, reports on effects of stress and non- stress soil nitrogen for the lysine, tryptophan, protein, and kernel endosperm modification as well as combining ability effects of QPM inbred lines are limited in Ethiopia. Objectives of this study were to (i) determine the combining abilities of QPM inbred lines for kernel modification score, tryptophan and protein contents, and (ii) determine reciprocal effects on quality traits and grain yield. MATERIALS AND METHODS Planting materials The 121 genotypes developed from complete diallel crosses of 11 QPM inbred lines with five checks were used for this study. For endosperm modification scores and tryptophan analysis, two plants for F 1 hybrids were sib-mated to have F 2 grains for all 126 genotypes. The sib-mated F 2 grains were shelled and a uniform size of 100 seeds for each genotype from each plot was taken for endosperm modification scores and tryptophan analysis both under low and optimum N environments. Combining ability study of QMM inbred lines for endosperm modi fcaton score and tryptophan content under low and optmum soil ni trogen environments Bedassa M. Dosho 1,2* , B.E. Ife 2 , I.K. Asante 2 , E.Y Danquah 2 , Habtamu Zeleke 1 inheritance were controlled by both additive and non-additive gene action. Inbred lines TL156579, TL156583, and VL05128 had good potential for endosperm modification score and inbred lines TL147078 and VL05128 had good potential for tryptophan, protein and protein quality index under low N environment. Under optimum N environment, parental lines TL156579, TL156583 and VL05128 had good potential for endosperm modification whereas parental lines TL156591 had good potential for tryptophan and protein concentration in grain and quality index. Hybrids TL155932 x VL05128 TL148288 x TL147078, TL155932 x TL156612, TL156612 x VL05128 and TL156579 x TL156591 had significant differences between F 1 hybrids and their F 1 reciprocals for grain yield under low N environment. Under both low and optimum N environments, the importance of reciprocal effects was also identified for endosperm modification score, tryptophan, protein, and quality index. Key Words: Protein quality index; Reciprocal effects; Tryptophan; Endosperm Dosho BM, Ifie BE, Asante IK, et al. Combining ability study of QMM inbred lines for endosperm modification score and tryptophan content under low and optimum soil nitrogen environments. AGBIR.2022; 38(5):345-350. The nutritional benefit of quality protein maize is more demonstrated on children who live under nutritional insecurity and also children suffering from a severe disease (Kwashiorkor) which is due to protein deficiency. To determine the effects of soil nitrogen on combining ability of tryptophan, endosperm modification score, protein and protein Quality Index (QI), 121 genotypes with five checks were sib-mated to generate F 2 grains under low and optimum N environments. Hereafter 100 grains of each F 2 generation were used for endosperm modification scores and tryptophan and protein concentration analysis in maize kernel endosperm. The results of the study indicated contribution of General Combining Ability (GCA), Specific Combining Ability (SCA) and reciprocal effects were important for all measured traits under both environments indicating quality traits INTRODUCTION M aize is deficient in lysine, methionine and tryptophan relative to the dietary needs of monogastric animals including humans. Deficiencies in these amino acids result in poor utilization of maize protein. In humans feed, these deficiencies are corrected by dietary supplementation with other protein sources or synthetic amino acids, but this adds to the cost of the diet [1] especially for farmers in Sub-Saharan Africa countries. In mature maize kernel, high concentration of protein is found in the endosperm and the germ. The maize kernel endosperm contains a high protein in quantity but low in quality, while the germ maize kernel contains a low level of protein in quantity with high in quality. However, the major portion of the maize kernel comprises of endosperm and contributes as much as 80% of the total grain protein [2]. The deficiencies of essential amino acids in maize kernel endosperm are due to the major seed storage proteins, the zeins. The levels of essential amino acids tryptophan and lysine in the maize kernel endosperm are altered by mutation opaque-2 due to a reduced content of zeins [3]. However, kernels carrying these mutations tend to have a number of pleiotropic effects that reduce their agronomic adaptability (soft kernel endosperm, which makes them susceptible to mechanical damage). Under stress and non-stress environments, both quantity and quality of maize endosperm protein are altered due to genetic variability of the crop and severity of the stress. Mosisa et al., [4] reported that under low N, the protein, tryptophan and lysine concentration in the grain endosperm of both non-QPM and QPM maize genotypes were low. A recent study revealed that Protein Quality-Index (PQI) was higher under low N environments than optimum N environments due to the concentration of QPM maize grain protein, which was more sensitive to low N than optimum N environments. The percentage of tryptophan in the QPM maize kernel was higher under low N environment than non-QPM maize kernel grown under optimum N environments [5]. Endosperm modification is quantitatively inherited with greater importance