Comparison of identification methods of bacterial wilt resistance in Casuarinaceae and screening of resistant germplasm resources

Objective To select convenient, accurate and reliable identification methods of bacterial wilt resistance in Casuarinaceae, identify and evaluate the bacterial wilt resistance of Casuarinaceae germplasm resources in China, and screen out highly resistant clones.

Method Based on the screening techniques of Casuarinaceae resistant lines as well as the identification methods of bacterial wilt in other plants, such as Lycopersicon esculentum, Nicotiana and Eucalyptus, we designed eight different approaches to inoculate Ralstonia solanacearum into Casuarinaceae. The effects of using hydroponic rooting seedling, twig, lignified green branch, lignified brown branch, bacterial wilt crude toxin, and root with or without injure of potted seedlings in inoculation on bacterial wilt resistance identification were studied.

Result After injured root inoculation of potted seedling, the mortalities of different Casuarinaceae clones ranged from 25.79% to 83.06% with significant differences among A14, K18 and G1, 30 clones(P < 0.05). After hydroponic inoculation of lignified brown branch, the disease indexes of different clones ranged from 2.16 to 69.48 with significant differences among A14, K18 and G1, 30 clones(P < 0.05). These two inoculation approaches enabled effective discrimination between resistant and infected clones, and had highly significant positive correlation (r=0.856 5). Non-injured root inoculation of potted seedling, hydroponic inoculation of rooting seedling and tender branch did not result in significantly differences in disease resistance among clones(P > 0.05), and they couldn't help with effective identification of bacterial wilt resistance in Casuarinaceae. Inoculation of lignified green branch only resulted in small differences among clones, and therefore it led to difficulties in classification and could easily cause detection error. The concentration of bacterial wilt crude toxin was hard to control during inoculation. Using hydroponic inoculation of lignified brown branch, 53 Casuarinaceae clones were evaluated and 12 highly resistant clones such as X1, 30, hybrid and G1 clones were screened out.

Conclusion Injured root inoculation of potted seedling and hydroponic inoculation of lignified brown branch are both preferred inoculation approaches for identifying bacterial wilt resistance of Casuarinaceae. The rest inoculation approaches tested in this study were not suitable for identification of bacterial wilt resistance in Casuarinaceae.