Promoting plant growth in a commercial rice cultivar by endophytic diazotrophic bacteria isolated from rice landraces

Population density of endophytic diazotrophic bacteria (EDB) was highest in the rice landrace root tissues at nursery stage. Indole-3-acetic acid (IAA) production (0.85–16.66 μg mL⁻¹) was found in 21 strains tested. More than 80 % (18 isolates) of the isolates solubilized phosphate, while only 28.57 % (six isolates) of selected strains produced siderophore. Seventy-one percent of tested isolates produced ammonia. The effects of EDB isolated from rice landraces on seed and on the growth of the commercial jasmine rice cultivar Khao Dawk Mali 105 were evaluated in greenhouse. Inoculation of all EDB on rice seeds significantly increased nitrogen content in roots (P = 0.05). The potentially useful isolates belonged to four different genera Burkholderia, Klebsiella, Novosphingobium and Sphingomonas. In vivo colonization of Burkholderia sp. SS5, Klebsiella sp. SS2, Novosphingobium sp. TR4 and Sphingomonas sp. PS5 was confirmed using the commercial rice cultivar Khao Dawk Mali 105 as a model host. The inoculated roots with ß-glucuronidase (GUS)-tagged bacteria exhibited a blue color, which was most intense at the tip of root hairs, root tips, germination point and leaf tips.