Fungal Disease Prevention in Seedlings of Rice (Oryza sativa) and Other Grasses by Growth-Promoting Seed-Associated Endophytic Bacteria from Invasive Phragmites australis

Satish K. Verma, Kathryn L. Kingsley, Marshall S. Bergen, Kurt P. Kowalski, James F. White

Non-cultivated plants carry microbial endophytes that may be used to enhance development and disease resistance of crop species where growth-promoting and protective microbes may have been lost. During seedling establishment, seedlings may be infected by several fungal pathogens that are seed or soil borne. Several species ofFusarium,Pythiumand other water moulds cause seed rots during germination.Fusariumblights of seedlings are also very common and significantly affect seedling development. In the present study we screened nine endophytic bacteria isolated from the seeds of invasivePhragmites australisby inoculating onto rice, Bermuda grass (Cynodon dactylon), or annual bluegrass (Poa annua) seeds to evaluate plant growth promotion and protection from disease caused byFusarium oxysporum. We found that three bacteria belonging to genusPseudomonasspp. (SLB4-P. fluorescens, SLB6-Pseudomonassp. and SY1-Pseudomonassp.) promoted seedling development, including enhancement of root and shoot growth, and stimulation of root hair formation. These bacteria were also found to increase phosphate solubilization in in vitro experiments.Pseudomonassp. (SY1) significantly protected grass seedlings fromFusariuminfection. In co-culture experiments, strain SY1 strongly inhibited fungal pathogens with 85.71% growth inhibition ofF. oxysporum, 86.33% growth inhibition ofCurvulariasp. and 82.14% growth inhibition ofAlternariasp. Seedlings previously treated with bacteria were found much less infected byF. oxysporumin comparison to non-treated controls. On microscopic observation we found that bacteria appeared to degrade fungal mycelia actively. Metabolite products of strain SY1 in agar were also found to inhibit fungal growth on nutrient media.Pseudomonassp. (SY1) was found to produce antifungal volatiles. Polymerase chain reaction (PCR) amplification using specific primers for pyrrolnitirin synthesis and HCN (hydrogen cyanide) production suggested presence of genes for both compounds in the genome of SY1. HCN was detected in cultures of SY1. We conclude that microbes from non-cultivated plants may provide disease protection and promote growth of crop plants.