ISOLATION AND CHARACTERIZATION OF RHIZOBIA AND PLANT GROWTH-PROMOTING RHIZOBACTERIA AND THEIR EFFECTS ON GROWTH OF RICE SEEDLINGS

Abstract

Biofertilizer is a relatively safer, environmentall y friendly and cost-effective approach as an altern ative to reduce chemical fertilizer usage. The selection of bacterial strains with multiple beneficial characte ristics are important to maximize the effectiveness on the host plant. Due to aforementioned interest, several Plant Growth-Promoting Rhizobacterial (PGPR) and rhizobial strains were isolated from rice and legume roots, respectively, at four locations in Malaysia namely Universiti Putra Malaysia (UPM), Serdang, Selangor; Besut, Terengganu; Tunjung, Kelantan and Sik, Kedah. Bacterial isolations were undertaken to select th e best isolates which exhibit multiple beneficial eff ects to the rice plant and a total of 205 bacterial strains were isolated and categorized as follows; 94 rhizos pheric and 107 endophytic bacteria from rice roots, one rhizobial strain from soybean and three from Mimosa pudica . These isolates were screened for their abilities to fix N 2 and solubilize phosphate; 52 were positive for bot h tests. The selected isolates were then tested for IAA production and other biochemical tests such as pota ssium solubilization, hydrolyzing enzymes (cellulas e and pectinase) and iron siderophore productions. Four i solates, namely UPMB19 (rhizospheric PGPR from Tunjung, Kelantan), UPMB20 (endophytic PGPR from Besut, Terengganu), UPMR30 (rhizobia from soybean) and UPMR31 (rhizobia from Mimosa ) were selected for subsequent plant inoculation te sts with UPMB10, a PGPR isolated from oil palm root, as the reference strai n. Based on 16S rDNA gene sequencing, these bacterial strains were identified under several genera: Lysinibacillus , Alcaligenes , Bradyrhizobium , Rhizobium and Bacillus , respectively. Results of plant inoculation test ind icated that UPMB19 significantly enhanced the seedling height at the early growth stage (7 days after tran splanting, DAT) which could be attributed to the hi gher N 2 fixation rate of this strain as compared to the oth er strains, except UPMB20. UPMB10 and UPMR31 also showed significant effects with increased seedling height and Total Dry Weight (TDW) at the later stage (14 DAT) possibly due to the higher bacterial populatio n and IAA produced as observed in the residual nutr ient solution without addition of fertilizer-N. This stu dy has successfully demonstrated the effectiveness of locally isolated PGPR and rhizobial strains with multiple b eneficial characteristics on early growth and vigor of rice seedlings under controlled condition. The result pr oved to be a vital information in the development o f a liquid biofertilizer for rice; thus further studies will b e done to evaluate the effectiveness of these isola tes under glasshouse and field conditions on growth, tillerin g and yield of rice.