Roles of ß-Indole Acetic Acid (IAA) Producing Endophytic Bacteria on the Recovery of Plant Growth and Survival Ability of Sugarcane Infected White Leaf Disease (SWLD).

ß-Indole acetic acid is produced in the rhizosphere by endophytic bacteria and promotes plant growth. Effects of bacterial IAA producers (BIPs) on plant growth and recovery of sugarcane seedlings infected with phytoplasma causing white leaf disease (SWLD) were examined. Fifty-five endophytic bacteria isolated from rice roots were collected from the Mekong River Delta, Vietnam. Seven isolates showed ß-Indole acetic acid production in culture medium supplemented with tryptophan. Interestingly, two of them (BC17 and BTII2) produced the highest ß-Indole acetic acid after 4 days of culture. Based on 16S rRNA sequences and phylogenetic analysis, the BC17 and BTII2 isolates were identified as Delftia lacustris and Rahnella aquatilis, respectively. Plant growth induced by the BC17 and BTII2 isolates showed statistically significant differences in height, root length and fresh weight of rice seedlings compared with non-treatment as the control. Treatment of two bacterial isolates in SWLD infected sugarcane plants also showed differences in height of sugarcane seedlings, while gradual symptoms of exposure decreased plant mortality compared to non-treatment as the control. BIPs were shown to be efficient biofertilizer inoculants that promoted plant growth and also ameliorated damage caused by phytoplasma-associated diseases at the sugarcane seedling stage.

Loop-mediated isothermal amplification (LAMP) assay for detection of sesame phyllody phytoplasmas in Vietnam.

Phloem-limiting phytoplasmas are known to be causal agents of phyllody, which is recognized by the abnormal development of floral structures resulting in serious yield losses in sesame plants. Currently, identification of the various groups of phytoplasmas that cause sesame phyllody (SP) is conducted by nested PCR, RFLP, and multiplex real-time qPCR assays. However, these methods require intensive labor and are costly and time-consuming so can only be undertaken in well-equipped labs. Here, diagnostic loop-mediated isothermal amplification (LAMP)-based assays allowing rapid detection of specific groups of phytoplasmas within 30 min were developed based on detection of the 16S rRNA sequence of phytoplasmas. Universal 16S rRNA phytoplasma primers and seven primer sets of different 16Sr group phytoplasmas (16SrI, 16SrII, 16SrIII, 16SrIV, 16SrV, 16SrX, 16SrXI) and universal plant cytochrome oxidase (cox) gene primers were used to detect 16S rRNA group phytoplasma sequences and the cox gene in sesame plants. The LAMP assays were carried out using a real-time fluorometer with amplification plots and annealing curves visualized directly. Results demonstrated that the 16SrI and 16SrII group phytoplasmas were causal agents of sesame phyllody in Vietnam. LAMP-based assays for in-field detection of sesame phyllody-causing phytoplasmas revealed advantages and potential applicability in comparison with conventional approaches. To the best of our knowledge, this is the first assessment of multiple phytoplasma infection associated with sesame phyllody disease in Vietnam using LAMP-based assays.