Effect of foliar applied plant elicitors on microbial and nematode populations in the root zone of potato.

摘要

Systemic acquired resistance (SAR) is a process whereby a plant that successfully resists a pathogen becomes highly resistant to subsequent infection not only by the original pathogen but also by a wide variety of pathogens. Most SAR research has focused on resistance in leaves, so much less is known about the effectiveness of foliar applications of SAR compounds in the protection of plant roots and associated microorganisms in soil. This study was conducted in 2002 and 2003 at the Washington State University Irrigated Agriculture Research and Extension Center, Benton County, Washington, USA, to determine if foliar SAR-inducing applications (BTH or harpin) negatively impact the potato root system beneficial rhizosphere microbial populations and activity or influence pathogenic nematode populations. Foliar applications of benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH) and the microbial protein harpin applied in various combinations, timings, and rates showed no effects on microbial biomass, culturable bacteria, Pseudomonas populations, or N-mineralization potentials over 2 years. No stimulatory or inhibitory effects on major bacterial populations were observed, indicating that SAR induction does not have a negative effect on general microbial populations or activities. BTH and harpin both reduced the numbers of lesion nematodes (Pratylenchus spp.) by potato harvest. BTH reduced root knot nematodes, Meloidogyne chitwoodi at the end of the season. In addition, BTH and high-dose harpin (applied at the 4x rate) reduced the nematode infection index in comparison to the control. The SAR elicitors increased the population densities of nontarget free-living nematodes in the soil compared to the control. Potato yields were not affected by plant elicitors but BTH and harpin both reduced the number of culled potatoes 26% compared to the control. Future studies are designed to determine if these plant elicitors have any direct effect on rhizosphere diversity or if plants with active defence pathways alter carbon flow and root exudates into the soil..