Biological Control Of Bacterial Wilt Of Tomato Crops With Avirulent Isolates Of Ralstonia Solanacearum

Bacterial wilt of tomato (Ralstonia solanacearum) is an important disease on the crop worldwide. The disease is difficult to control because the pathogen is soil-borne and vascular parasite. In the present study, three different techniques were applied to obtain avirulent isolates of R. solanacearum and these avirulent isolates were further screened for antagonistic bacteria against the pathogen.1.A number of 198 avirulent isolates of R. solanacearum were isolated directly from diseased tomato stem tissues, 45 were obtained through ultraviolet radiation treatment, and 17 were induced via continuous culturing in vitro.2.Of the avirulent isolates, 39 were found antagonistic against R. solanacearum by antagonism test on PDA plates. These antagonistic bacteria were mostly from the isolates directly isolated (38), only one was from the UV-induced isolates and none from the continuous culturing induced avirulent isolates.3.Tests on tomato plants (cultivar: Hezuo 903) showed that two avirulent isolates (numbered 100# and 134#) had strong antagonistic activity against R. solanacearum; the disease control efficiency was 86.4% and 81.7% at 8 days, and 37.7% and 44.4% at 20 days following treatment, respectively.4. Different methods of application of 134# bacteria were compared on tomato plants. Results showed that root-soaking is more effective than seed coating. The disease suppression efficiency was 90% and 44% at 7 and 20 days respectively after root soaking, but only 31% and 19% at 7 and 20 days after seed treatment.5. Tests showed that the activity of POD, PAL PPO enzymes increased apparently in tomato plant tissues treated with 134# bacteria. The change of PAL activity was most sensitive and exhibited first in the defence system of the plants. A quick increase of POD activity was detected after 134# bacteria application, indicating that the antagonistic bacteria could activate the processes of removing active oxygen and disease resistant metabolisms in the plant tissues. The increase of PPO activity was also significant and this may indicates that the antagonistic bacteria can increase the synthesis of quinones and thus activate the immuosystem of the plants.