Character Association Studies in Various Brassica napus Genotypes under Drought Stress

Abstract

Increased aridity and desertification are one of the most threatening setbacks to present day agriculture throughout the globe. Pakistan, being a sub-tropical country, is on the verge of an overwhelmingly increased rate of desertification. Therefore, it needs abrupt interventions to ensure food security. Brassica napus, being an integral part of indigenous edible oil production in Pakistan, needs some serious interventions for its adaptability under rain-fed agro-ecological conditions. Therefore, the present investigation was carried out to screen drought tolerant B. napus genotypes. For that purpose, ten B. napus accessions (Shiralle, DGL, Cyclone, Punjab Sarsoon, Cone-1, Cone-2, Rainbow, Dunkled, Zn-R-8, and Zn-M-6) were screened out for their relative tolerance to drought stress both in in-vitro and in-vivo conditions. An in-vitro experiment was carried out by following a completely randomized design (CRD) with three replications. Polyethylene glycol (PEG) solution with various concentrations (T1 = 2.5 % and T2 = 5 %) was applied to induce drought conditions and was compared with the control treatment (To = normal). Data were recorded for seedling length, root length, number of secondary roots, fresh seedling weight, and dry seedling weight. Results of ANOVA elucidated that all varieties showed significant responses in accordance with all studied characters except root length. Correlation analysis revealed that seedling length exhibits a high positive correlation with dry shoot weight followed by that root length under drought conditions; while path analysis revealed maximum positive direct effects of dry shoot weight under drought conditions (both in T1 and T2). An in-vivo experiment was also conducted by following a randomized complete block design (RCBD) under split plot arrangement. Data were recorded on the following parameters; days to 50% emergence, plant height, leaf area, silique length, number of silique plant, number of seed/siliques, seed yield/plant and 1000-seed weight. Results of the in-vivo experiment based on correlation analysis revealed that plant height exhibits the highest positive correlation with 1000 seed weight followed by the number of seeds per silique. Path analysis revealed that seeds per silique showed maximum direct contribution in the seed yield per plant of all of the evaluated varieties under both drought treatments (T1 and T2). Among all of the evaluated varieties, varieties named “Cone-2” and “Zn-M-6” showed the highest performance under both drought and control conditions. Therefore, these genotypes are recommended for cultivation in arid agro-ecological zones of Pakistan.