APPLICATION OF MELATONIN AND BIOCHAR FOR SUSTAINABLE IMPROVEMENT OF DROUGHT TOLERANCE IN RAPESEED AND MUSTARD GENOTYPES

Abstract

Brassica oilseeds (rapeseed and mustard) are the major source of vegetable oil and becoming increasingly popular among consumers for its sensory and nutritional properties. Reduction of the yield of Brassica due to drought stress has been reported. Besides, many investigations have stated that melatonin and biochar can improve drought tolerance of crop plants. But their specific role on plant drought tolerance especially, in rapeseed and mustards genotypes are poorly understood in Bangladesh. Therefore, the present investigation was conducted with aimed to evaluate the enhancing role of melatonin and biochar for assessing the drought tolerance of rapeseed and mustard genotypes for photosynthetic pigments, physiochemical and yield traits. The experiment was conducted at the research field and laboratory of the Department of Crop Physiology and Ecology, Hajee Mohammad Danesh Science and Technology University, Dinajpur, Bangladesh during November 2022 to March 2023. The experiment was carried out in two factors split plot design with three replications. Factor A (main plot treatment) consisted five sets of growing conditions such as i) Well water (T1, Control, Provide two irrigations), ii) Rainfed (T2, No irrigation will be applied), iii) Rainfed + Melatonin @ 100 µM (T3), iv) Rainfed + Biochar @ 1 kg DM m-2 (T4) and v) Rainfed + Melatonin @ 100 µM + Biochar @ 1 kg DM m-2 (T5); whereas factor B (sub-plot treatment) comprised of three mustard genotypes viz. i) BARI Sarisha-16 from Brassica juncea group (Mustard), ii) BARI Sarisha-17 from Brassica campestris group (Rapeseed) and iii) BARI Sarisha-18 from Brassica napus group (Rapeseed). From the results, it was observed that drought stress plot (T2) showed lower performance in respect of yield and yield contributing traits, various water relations and physiological attribute compared to well water (T1, control) condition. When the drought stressed plots treated with exogenous melatonin (T3) and biochar (T4) alone, gave somewhat better outputs compared to drought (T2) environments. Overall, yield and yield contributing parameters such as plant height (cm), branches number plant-1, and leaf area plant-1 (cm2), number of siliqua plant-1, number of seed siliqua-1, siliqua length (cm), test weight, yield plant-1, and yield plot1 were greater in T5 treatments (Rainfed + Melatonin @ 100 µM + Biochar @ 1 kg DM m-2). Soil moisture content, relative leaf water content and canopy temperature depression greatly enhanced due to combine application of melatonin and biochar (T5) under drought condition compared to melatonin (T3) and biochar (T4) alone. Photosynthetic pigments chlorophyll a (Ca), chlorophyll b (Cb), total chlorophyll (Ca+b) and total carotenoids (Cx+c) were enhanced due to combine application of melatonin and biochar (T5) under drought condition but proline content reduces as compared to drought (T2), melatonin (T3) and biochar (T4) treatments alone. Overall, it was determined that the combined application of melatonin and biochar (T5) to mustard and rapeseed genotypes significantly ameliorating the state of drought stress.