Biocontrol Of Wheat Leaf Rust Caused By Puccinia Triticina And Induction Of Systemic Acquired Resistance By Salicylic Acid

Wheat leaf rust caused by Puccinia triticina is the most widely distributed disease in the world,and it is one of the main diseases causing great loss in wheat production. In order to obtain strains with potential biological control effects of wheat leaf rust and investigate the effective biological control method, experiments with inhibition of urediospore germination and bioassays of biological control of wheat leaf rust, using both rhizosphere and endophytic bacterial strains, and antibiotics producing Streptomyces strains, were performed. The main results were described as follows.1 Screening of biocontrol agents for suppression of wheat leaf rust caused by Puccinia triticinaEleven bacterial strains, including five endophytic bacterial strains, CN015r, CN017r, CN078, CN180, and SH, two rhizosphere bacteria, JM218 and WCS417r, two genetically modified strains of WCS358, WCS358::phl, WCS358::phz, and two Streptomyces strains, S. rimosus CN124 and S. aureus CN182, were screened for their inhibitive ability to urediospore germination of Puccinia triticina, the pathogen of wheat leaf rust. And seven effective strains were obtained. The rifampcin resistant mutants of these effective strains were selected respectively by growing them on KB agar plates supplemented with increasing rifampcin concentration. These strains with antibiotics resistant marker were tested for their suppression effects against wheat leaf rust using seed soaking and leaf spraying of bacterial suspension. The results showed that seed soaking treatment in suspension of endophytic bacterial strain CN180r had obvious control effect against wheat leaf rust and the disease severity dropped 50.2 percent compared with the control. In spraying treatment, CN124 had more significant effect than the control, and the disease incidence dropped 71.1 percent. Endophytic strain CN180 was identified as Pseudomonas aurantiaca by molecular identification, with a sequence homology similarity of 97% to the strain EU761590.1 through BLAST in NCBI. It can be detected not only inside the tissue of root, stem and leaf, but also on the surface of the wheat seedlings.2 Biological control of wheat leaf rust by endophytic bacterial strains Six endophytic bacterial strains were isolated from the in vitro grown seedlings of wheat cultivar 5389 on MS medium, and these endophytic bacterial isolates were tested for their inhibition of urediospore germination. Bioassays of biological control against wheat leaf rust were performed using seed soaking and leaf spraying with bacterial suspension at 109 CFU/ml. The results showed that CN181 had obvious control effect against wheat leaf rust in seed soaking treatment. Its disease severity and incidence had significant difference compared with the control. Endophytic strain CN180 was gram-positive bacteria, and was identified as Bacillus subtilis by molecular identification, with a sequence homology similarity of 99% to the strain DQ520955.1 through BLAST in NCBI. To our knowledge, this is the first time to obtain an endophytic bacterial strain with potential effects for control of wheat leaf rust.3 Study on resistance of wheat leaf rust induced by salicylic acidDifferent densities of salicylic acid (SA) were tested for their inhibition of urediospore germination. No obvious inhibitive effects to urediospore germination were observed, but 5.0 mM had a bit suppression. SA were also tested for their suppression effects against wheat leaf rust in the greenhouse. In spraying treatment, the concentration of SA at 2.0 mM had obvious control effect against wheat leaf rust and the induction effects were up to 40 percent compared with the control. In roots dipping treatment, the concentration of SA at 5.0 mM had obvious control effect against wheat leaf rust and the induction effects were up to 30 percent compared with the control. In order to determine the most suitable times, SA at 2.0 mM and 5.0 mM, respectively, in spraying and roots dipping treatments, had the best induction effects at the fifth day after treatment with SA in both assays. This is the first report for application of SA to induce systemic acquired resistance against wheat leaf rust.