In recent years, the world has shown considerable concerns about environmental degradation accompanied by urban expansion. In terms of size, Bogura is equivalent to most of the major cities in Bangladesh, yet no thermal and ecological assessment has ever been conducted here. This study uses multitemporal Landsat satellite images between 2001 and 2020 to investigate the thermal and ecological conditions of Bogura Sadar (sub-district). Land surface temperature (LST) is obtained from Landsat images using the widely used radiative transfer equation. The thermal and ecological conditions are evaluated by computing urban heat island (UHI) and urban thermal field variance index (UTFVI) from LST data. The influence of vegetation, built-area, water-body, and bare soil on LST are examined using land cover indices through pixel-level multivariate linear regression analysis. According to the findings of this sub-district-scale (urban and rural areas) study, the mean LST has increased by 0.62 °C in the last 20 years. As per local administrative-wise findings, LST has increased in most areas, regardless of their urban or rural function. The difference between the urban area and the rest of the surroundings was significant (1.74 °C) in 2020. In 2001, UHI affected area was 5.65 km 2 , which expanded to 8.84 km 2 in 2020. Thermal and ecological conditions are worse in urban areas than its surrounding areas. The regression models of the LST and land cover indices could explain more than half (R 2 : 0.66 to 0.73) of LST variation over the years. Land cover could explain the LST in 2020 to the least extent implying that anthropogenic activities have greater influence than earlier. Land cover could explain less than half of the LST variation in the urban area.
The experiment was conducted to observe the callus induction ability of Brassica species. Plantlets were regenerated from cotyledon and stem explants of Brassica napus, Brassica campestris and Brassica juncea through direct organogenesis. The experiments were conducted in a Completely Randomized Design (CRD) with 4 replications. The highest frequency of callus formation was recorded in MS containing 2.0 mgl -1 BAP, 0.5 mgl -1 NAA and 2.0 mgl -1 AgNO 3 in both stem and cotyledon explants. Among these explants, stem was found to be better responsive in callus induction than cotyledon. Among the genotypes used, BINA Sarisha-4 induced the highest percentage (100.00%) of callus from stem explants which was followed by BINA Sarisha-5 (100.00%) and Sampad (83.35%). On the other hand, BINA Sarisha-4 induced callus from 91.67% cotyledon explants, followed by BINA Sarisha-5 (75.00%) and Sampad (66.67%). Similarly, the highest percentage of shoot regeneration (58.34%) from stem explants of BINA Sarisha-4 was observed in MS medium supplemented with combination of hormone and silver nitrate concentrations. The highest percentage of root induction was 66.67 and 58.33% in plantlets derived from stem and cotyledon explants, respectively in ½ MS medium supplemented with 2.0 mgl -1 IBA and 0.5 mgl -1 of NAA. The highest survival rate was found after acclimatization of plants derived from stem (77.78%) and cotyledon (64.28%) explants of BINA Sarisha-4 in pot and 64.33 and 55.55%, respectively in field.
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