Antibiosis And Colonization Of Endophytic Antagonistic Bacteria From Rice

Isolates J215 and G87 of Bacillus subtilis were two endophytic bacteria from rice stems and roots, and antagonistic to many plant pathogens. After the antagonistic bacterica were cultured for one day to two days, their culture and the culture filtrate exerted obvious inhibition on rice pathogenic fungi such as Magnaporthe grisea and Gibberella fujikuroi.The culture filtrate of the antagonistic bacterica could not only inhibit the mycelial growth of the pathogens, but also damage the hyphal shape. After treated by the culture filtrate of the antagonistic bacterica, the hyphae of M. grisea were swollen and abnormal, with the cytoplasm concentrated and outflowed, the cell wall disrupted and the hyphal cells collapsed; the hyphae of G. fujikuroi were abnormally swollen and grew slowly. The damage of the culture filtrate of the antagonistic bacterica to the hyphae of the pathogenic fungi became bigger as the treatment time (12h~48h) was prolonged. In addition, the culture filtrate of the antagonistic bacteria showed significant inhibition on the sporulation and conidial germination of the pathogens. When the culture filtrate was diluted 10 times, the inhibitory rates to the sporulation and spore germination of M. grisea were over 85% and 95%, respectively, and when the culture filtrate was diluted 100 times, the inhibition rates reached 60%~70% generally. The culture filtrate of the antagonistic bacteria could reduce the sporulation of G. fujikuroi by the inhibition of the hyphal growth, and inhibit the conidial germination by stimulating chlamydospore formation and delaying the sprore germination.The resistant mutants to 350ug/ml rifampicin of two antagonistic bacteria were induced and their antagonism was not changed. The antagonistic bacteria resistant to rifampicin were used to study the colonization in or on rice plants. By the method of seed soaking in the culture (109cfu/ml), the antagonistic bacteria could enter rice plants, move from roots to stems and leaves, and then colonize in rice roots, stems and leaves for long time. The bacterial population at the four-leaf stage was almost the same as at the one-leaf stage. There was still a certain quantity of the bacteria (102cfu/g~103cfu/g) at tillering or tasselling stage. One day after dipping seedling roots in the culture (109cfu/ml), the antagonistic bacteria could be isolated from rice roots, stems and leaves, then the bacterial population decreased and maintained about 102cfu/g fouty days later. In addition, The antagonistic bacteria in the roots was generally more than in the stems or the leaves after both soaking seeds and dipping seedling roots. By the spray of the bacterial culture (109cfu/ml), The antagonistic bacteria could well colonize on or in the leaves of the rice plants. Eleven days after sprayed, the bacteria on the leaf surface was 105cfu/g~106cfu/g, which was close to the population at the beginning, then decreased rapidly, and were hardly inspected 20 days later. Three days after the spray, the bacterial population in the leaves reached the maximum, then decreased gradually, and still appeared 103cfu/g eleven days later, but was little found 15~20 days later. Moreover, the antagonistic bacteria were not detected in rice roots or stems after sprayed on the leaves, which showed that the antagonistic bacteria could move upwards in rice plants but not downwards, which might go with water transportation in the xylem.Through the seed soaking, rice endophytic antagonistic bacteria could evidently promote the growth of rice seedlings. They could significantly increase the seed germination rate, the root length and the plant hight. The promotion of dipping seedling roots and spraying to the growth of rice plants needs a further study.