DEGREE OF ASSOCIATION AND CAUSE-EFFECT ANALYSIS FOR SPOT BLOTCH DISEASE RESISTANCE AND ANCILLARY CHARACTERS OF YIELD IN BARLEY (HORDEUM VULGARE L.) Kailash Chandra*, Ravindra Prasad, L.C. Prasad, Kuduka Madhukar, Rashmi Reddy and Padma Thakur Department of Genetics and Plant Breeding, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi-221 005 (U.P.), India. Abstract Ninety-six genotypes of Barley were tested under natural as well as epiphytotically created biotic stress condition for spot blotch disease caused by Bipolaris sorokiniana (Sacc.) Shoemaker at Agriculture Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi which is a hot spot for spot blotch. The objective of this experiment was to know the nature of the association between pairs of characters associated with disease-resistant in spot blotch and seed yield at the phenotypic level and thereby compare the direct and indirect effect of character under study. Phenotypic correlation revealed that under natural condition association estimates have shown AUDPC has a significant negative relationship with grain yield (r = -0.46) followed by thousand-grain weight (r = -0.233), days to maturity (-0.168). Whereas, under biotic stress condition also it has significant and negative relationship with important yield and yield attributing traits viz. grain yield g/plant (r = -0.65) followed by days to maturity (r = -0.43), thousand grain weight (r = -0.27), grain filling duration (r = -0.23) and spike number per plant (r = -0.23). Thus implies that indirect selection for these traits helps in the development of spot blotch resistant genotypes. From the path coefficient analysis based on correlations, it was observed that under natural conditions maximum direct negative effect on AUDPC was exhibited by grain yield per plant (-0.478). However, the direct positive effect on AUDPC was observed for grain filling duration (0.030) and plant height (0.120) while under biotic stress condition maximum direct negative effect on AUDPC was exhibited by grain yield per plant (-0.589) followed by days to maturity (-0.381). Therefore, the characters which show negative direct effect may play a significant role in the formation of selection criteria for breeding the resistant genotypes. Thus, direct selection for these traits in order to achieve yield improvement will be fruitful. Thus, these characters play an important role in the formation of selection criteria to enhance the resistance to spot blotch in Barley. The present investigation suggests that selection in Barley germplasm based on the degree of association and causes effect analysis will be effective in selecting superior plants for yield parameters and spot blotch resistance in isolating high yielding disease resistant genotype in Barley. Key words: Spot blotch, Bipolaris sorokiniana, Area under disease progress curve, correlation, path analysis. Introduction Barley (Hordeum vulgare L.) is one of the most important cereal crops in India and grown in about 100 countries worldwide (Prasad, 1992). During 2014, globally barley occupied the fourth rank amongst the cereal crops with 144.33 million ton production, after maize, rice and wheat (Kumar et al., 2014) and share about 7% of the global cereal production (Pal et al., 2012). It is frequently being described as the “most cosmopolitan of the crops” and also considered as “crop of marginal farmers” because of its low input requirement and better adaptability to harsh environments like drought, salinity, alkalinity and marginal lands (Kumar et al., 2014). However, in North-eastern plain zone barley crop is adversely threatened by leaf blight or spot blotch disease caused by Bipolaris sorokiniana pathogen. Many researchers have reported a range of yield loss in south Asia and India to be 19.6% and 15.5% respectively by Dubin & van Ginkal, 1991. Duveiller & Gilchrist, 1994 also reported 20 to 80% yield losses and if the infection is so much severe then up to 100% yield losses also Plant Archives Vol. 20 No. 1, 2020 pp. 1-8 e-ISSN:2581-6063 (online), ISSN:0972-5210 *Author for correspondence : E-mail: kailash5026@gmail.com