Pure Appl. Biol., 8(1): 698-705, March, 2019 http://dx.doi.org/10.19045/bspab.2019.80011 Published by Bolan Society for Pure and Applied Biology 698 Research Article Identification of traits for the improvement of grain yield in bread wheat under nitrogen stress and non- stress conditions Fahim Ullah Khan 1* , Fida Mohammad 2 , Manzoor Ahmad 3 , Muhammad Adil 1 , Naveed ur Rehman 1 and Arshad Iqbal 2 1. Department of Agriculture, Hazara University Mansehra-Pakistan 2. Department of Plant Breeding and Genetics, The University of Agriculture, Peshawar-Pakistan 3. Department of Agronomy, Bacha Khan University Charsadda-Pakistan *Corresponding author’s email: fahimbiotech@hu.edu.pk Citation Fahim Ullah Khan, Fida Mohammad, Manzoor Ahmad, Muhammad Adil, Naveed ur Rehman and Arshad Iqbal. Identification of traits for the improvement of grain yield in bread wheat under nitrogen stress and non-stress conditions. Pure and Applied Biology. Vol. 8, Issue 1, pp698-705. http://dx.doi.org/10.19045/bspab.2019.80011 Received: 19/11/2018 Revised: 11/01/2019 Accepted: 14/01/2019 Online First: 21/01/2019 Abstract Correlation, path coefficient and step-wise regression analyses were used to identify important traits that affect grain yield in bread wheat. Thirty bread wheat varieties were field tested under with (N + ) and without nitrogen (N 0 ) conditions at New Developmental Research Farm, The University of Agriculture, Peshawar-Pakistan. Experimental materials were planted in randomized complete block (RCB) design with three replications. Correlation analysis revealed significant positive association of grain yield with number of spikes m -2 , biological yield and harvest index under both production systems. For the 1000-grain weight, positive association was observed under N + condition only. Furthermore, path coefficient analysis confirmed the true relationship of harvest index, biological yield, number of spikes m -2 , and 1000-grain weight with grain yield in wheat. Similarly, step-wise regression analysis identified spikes m -2 , grains spike -1 , 1000-grain weight, harvest index and biological yield as important traits affecting grain yield in wheat under respective production system. Overall, on the basis of current statistical procedures spikes m -2 , grains spike -1 , 1000 grain weight, harvest index and biological yield needs due weightage in breeding program for further improvement in grain yield of bread wheat. Keywords: Biological Yield; Correlation; Path analysis; Step-wise regression Introduction Grain yield is a complex trait and is highly influenced by many genetic factors and environmental fluctuations. In plant breeding program, direct selection for yield as such could be misleading. A successful selection depends upon the information on the genetic variability and association of morphological and agronomic traits with grain yield reported by Kalimullah et al. [1]. Likewise, Khan et al. [2] explained that correlation analysis provides useful information about association among variables with economic yield. Generally, correlation measures the degree of association between two variables and is determined by genetic and environmental factors. The latter is mainly responsible for the correlation of traits with low heritability, such as grain yield. The genotypic correlation represents the genetic portion of the phenotypic correlation and is the only one of inheritable nature, and