Summary Three species of Tacca J. R. & G. Forst., namely T. plantaginea, T. chantrieri and T. integrifolia, were investigated cytogenetically and at the molecular level to solve their taxonomic rank. The diploid chromosome number 2n=28 was found in T. plantaginea and T. integrifolia whereas 2n=22 was found in T. chantrieri. This is probably the first report on the diploid chromosome number of T. plantaginea and T. chantrieri around the world. The three species differed in respect of centromeric formulae such as 22m+6sm in T. plantaginea, 18m+4sm in T. chantrieri and 28m in T. integrifolia. In addition to regular 2n=22 chromosomes, four to eight small chromosomes were found in some cells of T. chantrieri suggesting the probable occurrence of B-chromosome. In T. integrifolia, a pair of satellites was found on the short arm, one in each member of pair VI, after orcein and CMA staining but not in DAPI, revealing the GC-rich nature. A wide range of CMA-and DAPI-positive bands was found in the metaphase chromosomes of the three species. DAPIfluoresced chromosomes were frequent in these three species. Six primer combinations were applied for RAPD analysis in the three species of Tacca to find out their genomic relationship. The three species showed some unique bands useful as markers for each species. Conventional and fluorescent karyotype together with RAPD fingerprinting indicated that T. integrifolia is distantly related to T. plantaginea and T. chantrieri. Therefore, the compilation of the above cytological and molecular information will be very useful for authentic identification of the three Tacca species. This genetic information will help in the proper conservation of and to make patent for the three threatened Tacca species found in Bangladesh.

Phytoplanktons, also called microalgae, are microscopic photosynthetic living organisms that generally found in aquatic environments. Although they are considered as the most important primary producers and bioindicators of aquatic ecosystems, there was no previous report found for Barishal City about these tiny organisms. Consequently, the present study selected 10 freshwater reservoirs from the city to investigate phytoplankton communities and listed 110 taxa under 4 phyla, 7 classes, 18 orders, 24 families and 49 genera. The distribution of Chlorophytes was abundant relatively in terms of species number (45 taxa) followed by Euglenophytes, Chlorophytes and Cyanophytes in this area. Only Euglenaceae possessed one-third of the total species of this report. Among all stations, the highest number of taxa was recorded from station 2 and according to nine biodiversity indices, the station 2 and 9 showed comparatively good results. All of the recorded taxa were previously mentioned by different authors from Bangladesh.

Impacts of climate change on phytoplankton species are very focusing issues nowadays. This research explored the probable impacts of different pH (pH 5.90 to 9.10) and salinity (0.60 to 3.0 ppt) concentrations on freshwater phytoplankton Chlorella vulgaris, Euglena granulata and Scenedesmus quadricauda. The initial community composition was 4:2:1 for the three taxa, which changed to 6:3:1, 6:2:1, 6:3.5:1 and 9:4:1 in pH 5.90, pH 9.10 and salinity 2.20 and 3.0 ppt respectively. E. granulata showed more tolerance in a wide range of pH (pH 5.90 to 8.30) based on growth rate studies. The other two species showed growth rates reduction gradually in changes with pH and salinity concentrations. Conspicuous changes of total biomass were seen in pH 5.90 and 9.10, and salinity 2.20 and 3.0 ppt conditions. Moreover, significant changes in cell morphology were found in pH 9.10 and 3.0 ppt salinity. The authors concluded that as group, the Chlorophytes were more susceptible than the diatom in these variable pH and salinity conditions, while S. quadricauda was comparatively more vulnerable as a single species.

The river Kirtankhola has great importance in southern part of Bangladesh due to its necessity in transportations, municipal and agricultural purposes. But the ecological status and impacts of water quality on phytoplankton diversity were undiscovered. To cover the maximum area of the river, water samples were collected from the 6 locations (ST) covering about 13 km. Some parameters were measured immediately after sampling by portable devices and others done in laboratory following standard methods. The overall quality of the water was found good according to water quality guidelines of World Health Organization, although the water of port area showed comparatively high SO42- and CO3- values which attracts attention for future monitoring. ST 6 showed comparatively more alkaline water (pH 8.45) along with highest EC, TDS, NO3-, NH4+ and DIP values. Besides, 53 phytoplankton taxa belonging to Cyanophyceae (6), Chlorophyceae (10), Euglenophyceae (12) and Bacillariophyceae (25) were identified from the river. Scenedesmus acuminatus was found commonly in five stations except ST 1, whereas Euglena chlamydophora (ST 1), Gomphonema olivaceum (ST 3) and Cymbella parva (ST 5) found rarely. Highest diversity was counted in ST 6. Moreover, Chlorophyceae and Bacillariophyceae have positive correlation with several physical parameters, whereas Cyanophyceae negatively correlated. Euglenophyceae has both negative and positive correlations with some physico-chemical parameters. However, this was first attempt to measure diversity of primary producers and their correlations with water quality of Kirtankhola River.

This study used different supporting media (poly-styrene sheet, sand, and gravel) during outdoor hydroponic farming of onion within a natural environment setup. Domestic onion variety Taherpuri was taken as a model onion plant. As for performance parameters, plant height, number and length of leaf, length of root, bulb weight, number of bulblet, and chlorophyll contents were recorded. The number of produced leaves was almost same, although the length of leaf and root was found to have variations in these three supporting media. The yield (weight of bulb and number of bulblet) performance was slightly higher in polystyrene sheets (7.74 g and 3 bulblets per plant) than in the others. Chlorophyll-a, Chlorophyll-b, and total chlorophylls were comparatively higher in polystyrene sheets, 0.530, 0.764, and 1.294 mg/g respectively. Other growth parameters also showed better results in the case of polystyrene sheets. Finally, the results suggested that the polystyrene sheet as a hydroponic floating bed is suitable for outdoor hydroponics for onion cultivation.