The experiment was conducted at Plant Systematics Laboratory of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh, during the month of May to June 2017, to evaluate the effect of different seed sizes on germination, vigour as well as seedling growth in three Sesbania species viz.
S. bispinosa, S. cannabina and S. sesban. Seeds were collected from the previous year plants raised on Field Laboratory of the Department of Crop Botany, Bangladesh Agricultural University and harvested seeds were stored in a polythene bag. Seeds were graded, based on length, into three categories viz. small (3.1–3.5 mm; 16.4g 1000-seed–1), medium (3.6–4.0 mm; 16.8g 1000-seed–1) and large (4.1–4.5 mm; 17.2g 1000-seed–1) which were measured with digital slide callipers from each species. After seed size grading,
200 seeds in each size were weighed with digital electric balance. Healthy seeds were used as experimental materials. The treatments were arranged in a completely randomized design having four replications. In a Petri dish, 50 seeds from each group were sown in the mixture of sand: soil: compost in 1:1:1 ratio. Desired soil moisture was maintained using water up to ten days. The seedlings emergence was considered just after coming out of cotyledons above the soil surface (Mishra et al., 2014). For the judgment of growth and dry weight, 10 randomly selected seedlings from each replication were harvested from each Petri dish. Shoot length, root length, base diameter, length & width of cotyledons and length & width of leaf were measured using a ruler scale and digital slide callipers. Fresh & dry weights of seedling were measured by electric digital balance at ten days of age. Fresh samples were oven dried at 72±2 0C for 72 hrs. The cumulative germination (CG) percentage of seeds was counted daily up to 10 days. The CG percentage of seeds was calculated by the following formula (Bewley and Black, 1994).
% CG = (∑n / N) × 100
Where n is the number of seeds germinated at each day and N is the total number of seeds sown.
Vigour index (VI) was considered based on the mean shoot and root length; multiplied by the percentage of seed germination on 10th day/final day (Shreelalitha et al., 2015).
VI= (Mean shoot length + Mean root length) × Germination percentage
The collected data were analyzed by using Statistix 10 software, arithmetic mean, standard deviation, the coefficient of variation of seeds and seedlings attributes of three Sesbania species were compared with Duncan’s new Multiple Range Test (DMRT) at 5% probability. Matrix correlation and the relative contribution of seed and seedling parameters were done through Principal Component Analysis using the “R” software program.