Study On Endophytic Bacteria Of Rice

736 endophytic bacteria were obtained from the roots, stems and seeds of healthy rice plants in Yangzhou, Nantong, Changzhou and Xuzhou of Jiangsu Province. Among the endophytic bacteria, there were 196 isolates antagonistic against one, or two or three pathogens such as Pyricularia grisea, Gibberella fujikuroi, Rhizoctonia solani and Xanthomonas oryzae pv. oryzae, with the percentage of 26.63%. The antagonistic isolates from rice stems and roots were more than from seeds. The bacteria antagonistic against one pathogen were much more than those antagonistic against two or three pathogens. After the isolates were transferred fom tube to tube for 20 times, the antagonism against P. grisea and G fujikuroi was more stable and the rate of unchanged antagonistic isolates was 92.86% and 82.35% respectively, while the antagonism against R. solani and X oryzae pv. oryzae was easily decreased or lost. Isolates G87 antagonistic strongly against P. grisea, G. fujikuroi, X. oryzae pv. oryzae and J215 antagonistic strongly to P. grisea, G fujikuroi were identified as Bacillus subtilis (Ehrenberg) Cohn.The associative nitrogen-fixing activity of 276 endophytic bacteria was tested by in vitro acetylene reduced activity (ARA) determination and 234 isolates of endophytic associated diazotrophs were obtained. Among them, there were 190 isolates with middle nitrogen-fixing activity (1≤ARA≤100), accounting for 68.84% and 5 isolates with high nitrogen-fixing activity (ARA ≥ 100), accounting for 1.81%. 5 isolates with high nitrogen-fixing activity were stable after transferred fom tube to tube for 20 times. According to morphological, physiological and biochemical feathers, isolates G161 (9212.3130umol/ml · h) and J115(20987.8200umol/ml · h) with stable nitrogen-fixing activity were identified as Enterobacter cloacae (Jordan) Hormaeche & Edwards.Through dipping seedling roots and spraying, isolates G161 and Jl 15 with high associative nitrogen-fixing activity could significantly promote the growth of rice plants,which increased 15.46%~20.55% of plant height, 6.86%~17.14% of chlorophyll content and 16.67%~31.03% of the dry weight of above-ground-part respectively. But they had no obvious growth-promoted effects by way of soaking seeds in contrast with the control.All endophytic bacteria were inoculated on rice seeding by way of needle-pricking and scissors-cuting leaf. The results showed that 24 isolates had pathogenicity to rice plants out of 196 antagonistic isolates, accounting for 12.20%, and among them there were 14 isolates antagonistic to P. grisea, 9 isolates to G.fujikuroi, 7 isolates to R. solani and 2 isolates to X. oryzae pv. oryzae respectively. Among 234 endophytic associative nitrogen-fixing bacteria, 38 isolates were pathogenic to rice plants, accounting for 16.24%. Terefore, most endophytic bacteria of rice had no pathogenicity though a few were potential pathogens.