NEMATICIDAL AND PHYTOTOXIC EFFICACY OF PHOTORHABDUS METABOLITES FOR CONTROL OF PLANT PARASITES

In the United States, plants are subject to attack from over 50,000 different parasites and pathogens. Among them are plant-parasitic nematodes (PPNs), which cause billions of dollars in crop losses annually and threaten food security. Currently, PPN management depends on the use of synthetic nematicides. Many studies documented the deleterious effects of these chemicals on wildlife, the environment, and human health. Owing to emerging PPN resistance, these chemicals are increasingly losing their effectiveness. In addition, the recent banning of several effective nematicides and the phase-out of methyl bromide from the pest-control market due to its ozone-depleting potential led to limited chemical treatment options for annual and perennial crops. Nematicides continue to be an essential part of integrated pest management (IPM) systems, together with culture practices, and resistant cultivars. This presents an urgent need for new nematicide alternatives that are environmentally safe and cost-effective. One promising approach to develop novel control methods is to study microorganisms that antagonize PPNs by producing biologically active secondary metabolites (SMs). The roles of these SMs are in defense/competition, regulation, and communication. The long-term goal is to expand the application of SMs as biological control agents, benefiting growers by offering environmentally safe and biodegradable bio-nematicides as alternatives to chemical nematicides. This will contribute to food and nutritional security for current and future generations, while safeguarding the environment and the ecosystem.To achieve the long-term goal, the proposed research will focus on nematicidal effects of SMs from the Arizona-native 'insect-attacking' bacterium, Photorhabdus luminescens sonorensis, as a bio-rational strategy to control plant parasites. This bacterium is a symbiont of insect parasitic nematodes. Only limited research has been conducted to test the nematicidal and/or phytotoxic effects of Photorhabdus-produced SMs against PPNs using plants (in planta). To address this lack of knowledge, the assessment of the nematicidal SMs against economically important root-knot nematodes, Meloidogyne incognita (RKN) will be performed under three-factor (SM, nematodes, and host plants) and four-factor (SM, nematodes, host plants, and soil) interactions. The specific aims (SAs) will assess RKN root infection (galls and egg masses), and physiological (leaf chlorophyll) and agronomical (plat growth) responses of plants upon the use of the Arizona-native Photorhabdus-produced nematicidal SMs. The proposed SM trials in controlled growth chambers (SA1 and SA2) and in greenhouses (SA3) will support future field trials. Specific activities for each SA will be:SA1. Optimize in planta synergistic nematicidal activities of Photorhabdus SMs against representative plant parasites SA1-1) Assess the nematicidal effects of the synergistic SM mixtures at different ratios, monitoring the virulence and reproductive fitness of RKNs.SA1-2) Investigate the toxic effects of the nematicidal SM mixtures on the host plant.SA2. Assess the interactions of the nematicidal SMs with soil SA2-1) Study distribution/movement and bioavailability of the nematicidal SMs in the soilSA2-2) Determine the stability or degradation of the nematicidal SMs in the soilSA3. Evaluate different methods of application for nematicidal SMsSA3-1) Test root drench SM application for control of RKNsSA3-2) Assess SM-treated seeds for prevention of RKN damageSA3-3) Quantify the systemic efficacy of foliar SM sprays against RKNs