Abstract
Dhaincha (Sesbania spp.), an underutilized multipurpose crop, is used as green manure, fodder, ethno-medicine, firewood and other agro-forestry systems, in spite of this, dhaincha genetic resources of Bangladesh are not well characterized. Experiments were conducted at Field and Plant Systematics Labs of the Department of Crop Botany, Bangladesh Agricultural University, Mymensingh to characterize indigenous dhaincha genetic resources and to utilize them for the improvement of soil nutrient status. Seeds of 106 accessions were collected from 10 Agro-ecological Zones of Bangladesh and sown in 4.0 x 2.5 m plot for each accession with three replications. Seed emergence, germination and vigor indices were counted. Biomass yield was recorded at 10 days interval from 10 to 60 days after sowing (DAS) from each accession. Quantitative and qualitative descriptors e.g., growth habit, plant height, stem and leaf surfaces and color, base diameter, branch number, inter-node length and number, etc. of 10 randomly selected plants from each accession were studied at 60 DAS. Floral characters i.e., size and color of standard, wing and keel, stamen, carpel, ovary and pollen grains was measured. The multivariate analyses viz. Agglomerative hierarchical clustering (AHC), Principal component analysis (PCA) and Non-metric multi dimensional scaling (NMDS), were conducted based on the 38 quantitative descriptors. Six accessions selected, based on biomass yield, were grown at different plant densities, sowing dates and nitrogen doses to optimize plant density, sowing date as well as the nitrogen dose. With the optimum sowing date, plant density and fertilizer dose the six promising accessions were grown in the next year and incorporated into soil at 60 DAS to evaluate their effects on soil nutrient status. Among the dhaincha accessions, seeds of 5 accessions exhibited 100% germination, 80-99% in 78 accessions and <80% in 23 accessions. While higher vigor index (>1400) showed 17 accessions followed by 72 accessions (1000-1400) and another 17 accessions (<1000). Biomass yield varied significantly among the accessions and it ranged from 10.41-33.51 gplant1 at 60 DAS. Multivariate analyses (AHC and PCA) revealed that 106 accessions belong to four species viz. S. bispinosa (90), S. cannabina (9), S. sesban (6) and the known check foreign species S. rostrata (1 accession). The number of leaflet pair leaf1 was 25-30 in S. sesban, 33-35 in S. cannabina and 38-48 in S. bispinosa. Flowering time in S. sesban was July to August and both in S. bispinosa and S. cannabina was August to September. Standard was larger in size (21 × 21 mm2) in S. sesban followed by S. cannabina (13 x 13 mm2) and S. bispinosa (12 × 11 mm2) while wing size was about 20 × 6 mm2, 13 × 5 mm2 and 12 x 5 mm2 in S. sesban, S. cannabina and S. bispinosa, respectively. Keel size was 18 × 8 mm S. sesban followed by that (13 × 6 mm2) in S. cannabina. A dichotomous key based on studied agro-morphological descriptors was made for identification of Sesbania species. Accession #05, 28, 71, 77, 81 and 109 selected for further experiments. Among the sowing dates, planting densities and fertilizer doses, 30 April, 240 plants m-2 and 20 kgha-1 N were emerged as best treatments. Among six dhaincha accessions, the accession #71 was found better in terms of yield and yield contributing descriptors. The highest biomass yield was produced by accession #71 (16.49 t ha-1) and the lowest by accession #81 (8.92 t ha-1). Moreover, the accession #71 contained maximum ash percentage (12.98) and crude protein percentage (18.44) contents and released utmost organic matter percentage (2.38), total N percentage (0.14), available P (7.98 ppm) and exchangeable K (0.24 meq. /100g) and it was found at 50 days after incorporation of dhaincha in soil. However, accession #28 lead to release high S in soil. Among the selected accessions (#05, 28, 71, 77, 81 and 109), the accession #71 performed better in all aspects and, therefore, may be recommended to release as a cultivar.