Effect of Two Bacterial Isolates on Selected Improved Rice Varieties Under In Vitro and Greenhouse Condition

Sri Lankan rice cultivation has been heavily dependent on the large-scale use of inorganic fertilizers since the introduction of new improved rice varieties to farmers in the 1960s. Excessive use of chemical fertilizers is adverse on human health and the environment. Plant growth-promoting bacteria are recognized as an eco-friendly approach to replace inorganic fertilizer. However, there are a few numbers of reports on efficient biofertilizers for Sri Lankan conditions. Therefore, the objective of this study was to determine the effect of two selected local bacterial isolates (I-I and I-II) under in vitro and greenhouse condition, on commonly grown improved rice varieties in the low country of Sri Lanka. The experiment was carried out in a Completely Randomized Design with three replicates. Bacterial isolates (106 colony forming units / millilitre) were inoculated on 2-day old sterile rice seedlings. Sri Lankan improved rice variety Bg 300 inoculated with I-I and I-II reported significant low number of days to flowering (DF) as 74 ±0 and 75±0.11 in contrast to that of control plants (79 ±0.16) and both isolates I-I and I-II significantly increased root length as 10 ±0.4, and 12±0.03 cm respectively, over control plants (7 ±0.2 cm) under in vitro condition. Above experiment was extended under greenhouse condition with three improved rice varieties of Bg 300, Bg 379/2 and At 308 in Faculty of Agriculture, University of Ruhuna, Mapalana, Sri Lanka (in ecological zone WL2 of Low Country Wet Zone) and with Bg 300 in Beliatta, Sri Lanka (in ecological zone IL1b of Low Country Intermediate Zone) under greenhouse condition with four replicates. The bacteria inoculated plants of Bg 379/2 reported significantly lower number of DF of 112.5±0.86 and 114±0.28 in contrast to that of control plants (118.5±1.22). The plants of Bg 300 and Bg 379/2 with I-I, produced the highest number of grains per first panicle (GP) as 134±7.35 and 157±11.2 respectively over those of the control plants of Bg 300 and Bg 379/2 (105.75±6.98 and 132±2.94 respectively). Bacteria inoculation did not affect DF and GP in rice variety At 308 indicating the different responses of variety on inoculation in the experiment at WL2. Bacterial isolate I-I inoculated plants showed significantly higher GP in contrast to control in greenhouse at IL1b. There is a potential for tested bacteria to be developed as a biofertilizer through subsequent field experiments in the future.