Evaluation of oriental tobacco (Nicotiana tabacum L.) genotypes using selection indices under the presence and absence of broomrape

Tobacco (Nicotiana tabacum L.) is one of the industrial plants and is important in the economy of many countries. Plant breeders are usually interested in modifing and breeding several traits simultaneously in their breeding programs. Index selection is the selection of several traits simultaneously based on a simple index. In order to construct and evaluate tobacco genotypes using selection indices, 92 oriental and water pipe’s tobacco genotypes were studied in terms of agro-biological traits using a randomized complete block design with three replications under normal (absence of broomrape) and presence of broomrape conditions during two successive years in Urmia Tobacco Research Centre. Selection indices including optimal selection (Smith-Hazel), Base (Brim), desired gain (Pesek-Baker) and Robinson were calculated based on all the studied traits (including: flowering date, plant height, number of leaves, leaf area, fresh and dry weights of leaf, fresh and dry weights of root, fresh and dry weights of aerial parts) for studied genotypes in both normal (absence of broomrape) and broomrape presence conditions. The results of the direct and correlated response of traits showed that the genotypes with more value for leaf area and fresh weight of leaf and aerial parts had potentially a higher performance. Selection based on Smith-Hazel and Brim indices which had the highest selection efficiency (DH) in both normal (absence of broomrape) and presence of broomrape, resulted in increasing the leaf area and fresh weight in normal conditions and leaf area and fresh weight of aerial parts in broomrape stress conditions. On the other hand, fresh weight of leaf and aerial parts were the traits with highest correlated response with dry weight of leaf, therefore, these two indices with the highest correlation with breeding value and with the highest relative efficiency of selection were presented as the best indices. Accordingly, genotype 24 (H.T.I) was introduced as the best genotype under normal (without broomrape stress) and broomrape stress conditions.