Screening, Characterization and Improvement of Nutrient Rich Okra Variety for Resistance to Yellow Vein Mosaic Virus

Abstract

Okra [Abelmoschus esculentus (L.) Moench], is an important highly nutritive vegetable crop cultivated throughout the world. But the main constraint of okra production in Bangladesh is the viral disease caused by Yellow Vein Mosaic Virus (YVMV), which is spread by an insect vector namely white fly (Bemisia tabaci). The loss in marketable yield has been estimated at 50-94 % depending upon the stage of crop growth at which the infection occurs. Although several local and commercial high yielding varieties are available, their pathogen resistance potentials are not enough for our local climatic condition. Moreover, the knowledge about the biochemical and nutritional composition of different varieties of okra cultivated in Bangladesh is very limited. Therefore, the aim of the study was to develop a nutrient rich and YVMV resistant high yielding okra variety. This study was undertaken to-evaluate the field performance of 10 varieties of okra against YVMV disease incidence, compare their nutritional, phytochemical and medicinal values and genetic improvement of nutrient rich variety through induced mutation technology for resistance to YVMV, molecular characterization of the YVMV resistant mutant lines by the development of molecular markers such as RAPD and SSR, identify the high yielding and YVMV resistant gene in mutant okra lines and finally the mutant lines are further re-investigated to analyse the nutritional (qualitative and quantitative) properties and cytotoxic level to confirm the higher nutrient content (nutrient rich establishment) subject to health issue. Ten varieties of okra e.g. Shamol Bangla (SB), Mahira Cross (MC), Orka Anamika Local (OAL), Shomy Hybrid (SH), Orka Anamika India (OAI), Shabuj Shathi (SS), Iron Bhendi (IB), BARI-1 (B1), Kolatia Bhendi (KB) and Dherosh Chamak (DC) were cultivated under the open field condition and premature pods were extracted using methanol as solvent. Qualitative and quantitative analyses of extracted phytochemicals were done using standard procedures. In vitro antioxidant activity of extracted phytochemicals was assayed by employing several methods. Cytotoxicity study of the extracts was performed using brine shrimp lethality bioassay. Several in vitro assay models were employed to investigate the medicinal properties of the extracts. Another way, okra premature pod extracts were prepared using water as solvent. Biochemical and nutritional analysis of aqueous extracts were performed using standard procedures. Screened nutrient rich variety was used for mutation-breeding to develop YVMV resistant mutant okra lines. Seeds were treated with Sodium Azide (NaN3) at concentrations of 1, 2, 3, 4 and 5 mM for chemical mutagenesis, sown under open field condition without any pesticide application and subsequent generations with YVMV resistance were screened starting from Mutant generation-1 (M1) to Mutant generation-6 (M6). Molecular characterization of nutrient rich and YVMV resistant mutant okra lines was performed by using RAPD and SSR markers. Genomic DNA (gDNA) of 7 mutant okra lines was extracted and purified by modified CTAB method, then amplified by PCR; RAPD and SSR bands were analyzed. Data were used for construction of phylogenetic tree by Dendrogram using UPGMA with Jaccard index of bioinformatics…………………