Effect of Plant Growth Promoting Endophytic Bacteria Gluconacetobacter diazotrophicus, on Germination Attributes and Seedling Growth of Rice Varieties under In vitro Conditions

The production of rice mainly depends on nitrogen fertilizer. Extensive applications of chemical nitrogen fertilizer have adverse effects on plant health and the environment. The use of plant growth promoting microorganisms can increase the soil fertility and productivity of rice and also reduce the negative impact of chemical nitrogen fertilizer. Gluconacetobacter diazotrophicus PAL5 is a gram-negative endophytic bacterium that plays an important role in nitrogen fixation and plant growth promotion. The present investigation was to evaluate the effect of inoculation with G. diazotrophicus on seed germination indices of fifteen rice varieties (Oryza sativa L.) and seedling growth under in vitro conditions. Among the fifteen rice varieties inoculated with G. diazotrophicus, the highest increase in germination indices was observed in five varieties, viz. BPT5204, TN1, ISM, IR64, and Dhan53, which showed an increase in germination percentage (4.26-10%), Mean germination time (3.8-5.8%), germination speed 10.5- 26.8%), synchronization index (22.74-43.60%), standard deviation of germination rate (2.10-9.70%) and coefficient of variance of germination (11.80-18.36%) in comparison with the control on agar medium after 5 days. Furthermore, inoculation resulted in a significant increase in growth parameters (viz., root length, shoot length, root dry weight, shoot dry weight, seedling vigour index- I and seedling vigour index- II) over uninoculated control seeds in five rice varieties in comparison with the remaining rice varieties. The results thus reveal endophytic G. diazotrophicus not only increased the germination percentage but also enhanced the seedling growth parameters of rice varieties while eliciting a genotype-specific response in rice genotype.