Colonization and infection of Ralstonia Solanacearum in weed roots

Parasitism and saprophytism of Ralstonia Solanacearum in different weeds were studied to provide basis for preventing tobacco bacterial wilt. Growth and decline trends and infectivity ability of the bacteria in winter were monitored. Disease was induced by inoculating tobacco seedlings with rifampicin-resistant R. solanacearum. Bacteria in 49 weed roots in tobacco planting land. Weed roots from infected soil in winter were determined using a selective culture medium containing rifampicin. The occurrence of tobacco bacterial wilt was monitored by planting tobacco seedlings in pots with uninfected soil. 7 weeds such as Polygonum plebeium R.Br and Cyperus rotundus L. were susceptible, 18 such as Pospalum orbiculare Forst. and Solanum mgrum L. were moderately susceptible, while 24 weeds such as Youngia japonica (Linn.) DC and Echinochloa crusgalli (L.) Beauv. were low susceptible. R.Solanacearum were just noted on the root surface of Bidens bipinnata L. and Phytolacca acinosa Raxb., but were both noted in vivo and in vitro of 6 weed roots such as Poa annua L. and Pospalum orbiculare Forst..3 weeds, i.e. Eleusine indica (L.) Gaertn and Portutulaca oleracea. R.Solanacearum was highly saprophytic in 8 rotten roots such as Eleusine indica (L.) Gaertn and Polygonum hydropiper L., moderately saprophytic in 7 rotten roots such as Pospalum orbiculare Forst. and Soliva anthemifolia (Juss), low saprophytic in 6 rotten roots such as Ranunculus sceleratus L. and Siegesbeckia orientalis L. Result showed R.Solanacearum can overwinter in roots of 6 annual weeds and then cause tobacco bacterial wilt in the following year. The disease occurrence can be induced by 7 weeds, while the disease was early and serious in Alopecurus aequalis Sobol. 4 weeds such as Polygonum orientale L. and Altemanthera philoxeroides (Mart) Griseb had the strongest infectivity ability, the morbidity was 85.7%~100%. R. Solanacearum can colonize in weed roots, then proliferate during root decay and overwinter in the weed roots such as Alopecurus aequalis Sobol, and finally become the effective resources of primary infection. It was an important factor that caused the occurrence and epidemic of tobacco bacterial wilt.