Plant growth promoting bacteria make differences in plant growth by different mechanisms which can be mediated by direct or indirect methods. Nowadays these bacteria can be used as natural bio fertilizers instead of synthetic fertilizers and dramatically reduce the environmental hazards. Root colonizing bacteria have the ability to increase the seed germination rate, growth of plant and yield of crops. Therefore present study was performed in order to find out the effect of one of the soil borne gram (-) ve , chemoorganotrophic , facultative anaerobic bacteria Serratia marcescens on seed germination of some selected healthy plant seeds varieties , Vigna mungo (black gram) , Vigna radiata(green gram) , Vigna uniculata (long bean) , Hibiscus esculentus (lady’s finger),Cucurbita maxima (pumpkin), Capsicum annum(chilli) and Solanum melongena (brinjal), which were collected from Agrarian service center ,Thirunelvely, Jaffna, Srilanka. Twelve surface sterilized seeds were placed into X ×107 cells/mL concentration of 75 mL bacterial suspension and soaked for overnight separately then seeds were transferred to sterile petridishes which containing sterile moistened filter paper and kept in dark at room temperature for 3-5 days, where sterile distilled water was used as control. By using above method, this study was also carried out for various soaking time intervals, (0,2,4 and 6 hours) and for different bacterial concentrations( X ×107cells/mL - X ×102cells/mL). Finally the mean length of developed germ tube was measured separately and the results were subjected to analysis of variance (ANOVA) and Tukey test at p=0.05 using statistical software minitab (version16). The analysis showed that the growth of C.annum and V.radiata were not affected by S.marcescens while the growth of V.mungo, H.esculentus , C.maxima and S.melongena were promoted by the bacterium. Unfortunately the germination of V.uniculata was suppressed by the bacterium for overnight soaking. Moreover, long bean, brinjal, black gram and lady’s finger exhibited optimum growth rate at 2 hours soaking period whereas, the development of germ tube for chilli revealed maximum rate at 4 hours soaking time. The concentration of bacteria at X ×103cells/mL and X ×104cells/mL were found as the optimum for the better growth of pumpkin and green gram respectively. Rest of the tested seeds exhibited highest growth activity at X ×10 2 cells/mL concentration. Therefore it was concluded that the bacterial activity on seed germination varied among the seed varieties, soaking time period and inoculum concentration. Hence, this study reveals the primary platform for the practical benefits of employing S.marcescens for a sustainable farming system.
