Ayako Kusakabe's Abstracts

Ayako Kusakabe

Ph.D. Candidate

Entomology & Insect Sciences

 

 

SIP/IOBC 2019

Valencia, Spain

July 28th - August 1st, 2019

 

The banning of several chemical nematicides has prompted the need for new and environmentally-friendly methods to enhance current management of plant parasitic nematodes. Insect pathogenic Photorhabdus bacteria, the natural symbionts of Heterorhabditis entomopathogenic nematodes, are considered a goldmine for the discovery and application of biologically active secondary metabolites (SMs) with antibacterial, antifungal, insecticidal, and nematicidal activities. In this study, we evaluated three metabolites that were isolated and purified from culture filtrates of P. l. sonorensis (strain Caborca). The chemical identification of active SMs was done by bioassay-guided fractionation. Spectral analyses identified two of these compounds as phenylpropanoids (AK1 and AK2) and one alkaloid (AK3). In vitro assays were carried out to assess the nematicidal activity of these SMs on the infective stage (second-juvenile stage or J2) of the root-knot nematode, Meloidogyne incognita. The activity of these SMs was also tested on four non-target nematode species: Caenorhabditis elegans (free-living bacterivore) and three entomopathogenic species, Steinernema carpocapsae, H. bacteriophora, and H. sonorensis. These compounds revealed different inhibitory activity ranging from a transient quiescence to death. AK1 and AK2 exhibited nematicidal activity to M. incognita. The LC50 for AK1 was 64 μg/ml and 45 μg/ml for AK2. AK3 showed nematicidal activity to M. incognita and C. elegans at the two highest concentrations tested (300 and 400 μg/ml). At 60 to 200 μg/ml, AK3 induced reversible quiescence in both nematodes species. All entomopathogenic species tested were resistant to AK3. This work sheds light on ascertaining the potency of the Photorhabdus-derived SMs as nematicides.

 

Abstract for Lay Audience

In the United States alone, crops are subject to attack from over 50,000 different parasites and pathogens. Among them are plant-parasitic nematodes (roundwprms), which account for billions of dollars in crop losses annually. At present, management of plant-parasitic nematodes greatly depends on the use of synthetic chemical pesticides. Many studies have shown the deleterious effects of these chemicals on human health, wildlife, and the environment. Moreover, the recent banning of several chemical nematicides and the loss of methyl bromide from the pest-control market due to contribution to ozone layer depletion has prompted the need for new and environmentally-friendly methods to enhance current management of plant parasitic nematodes.

A promising approach to develop novel control methods is to study microorganisms that antagonize plant-parasitic nematodes by producing biologically active compound such as secondary metabolites (SMs). For example, insect pathogenic Photorhabdus bacteria, the natural symbionts of Heterorhabditis nematodes, are considered a goldmine for the discovery and application of SMs with antibacterial, antifungal, insecticidal, and nematicidal activities. In this study, we evaluated three SMs that were isolated and purified from culture filtrates of an Arizona-native symbiotic bacteria, P. l. sonorensis (strain Caborca). Three active molecules have been so far identified which are temporarily identified as AK1 and AK2 (phenopropanoids) AK3 (alkaloid).


Laboratory assays were carried out to assess the nematicidal activity of these above-mentioned SMs on the infective stage (i.e. the one that infects the roots of plants) of the root-knot nematode, (Meloidogyne incognita), which is worldwide distributed plant parasite that affects diverse crops. In Arizona, this plant-parasitic nematode species is the most important plant parasite. We also tested the effect of these SMs on four beneficial soil nematode species to make sure these compounds only affect plant parasites.


Results from these experiments showed these SMs have different inhibitory activity ranging from a transient immobility to absolute death (nematicidal). AK1 and AK2 had nematicidal activity against M. incognita at concentrations higher than or equal to 60 μg/ml. AK3 caused reversible quiescence in M. incognita at 60 to 200 μg/ml. AK3 had only nematicidal activity at the two highest concentrations tested (300 and 400 μg/ml). These three compounds, however, had no effect on other beneficial soil nematode species at concentrations at 200 μg/ml or lower.

 
Last updated 27 Jan 2020