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Bioherbicide Safety Zones and the Plant Disease–Inoculum Density Relationship

Published online by Cambridge University Press:  20 January 2017

Graeme W. Bourdôt  and
David J. Saville
Graeme W. Bourdôt*
Affiliation:
AgResearch Limited, Private Bag 4749, Christchurch 8140, New Zealand
David J. Saville
Affiliation:
Saville Statistical Consulting Limited, P.O. Box 69192, Lincoln 7640, New Zealand
*
Corresponding author's E-mail: graeme.bourdot@agresearch.co.nz.
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Abstract

Broad- host-range pathogens are appealing as candidates for commercial development as bioherbicides because of the wider market potential of a product that is effective against a range of weeds. But when these pathogens are able to spread in space (or time), a risk analysis is necessary. Here we test the hypothesis that a safety zone around a bioherbicide application site is adequate so long as it is wide enough to ensure that dispersing inoculum has diluted sufficiently that the density of inoculum occurring naturally in a susceptible crop is no more than doubled by the influx of bioherbicide spores. To this end the plant disease–pathogen inoculum density relationship using data from nine published experiments was modeled using the logistic equation. This revealed that a doubling of the natural spore density of a plant pathogen in the range of 103.4 to 106.7 spores/ml may generally be expected to result in unacceptable increases in disease in a susceptible crop. A doubling outside this range (< 103.4 or > 106.7) is less likely to do so. Therefore when the natural density of inoculum in a crop's environment occurs outside this range, an “acceptable” safety zone for the pathogen's use as a bioherbicide can in most cases be defined by the 1 : 1 ratio of added : natural inoculum. However, if a more “risk averse” safety zone is desired, it can be defined using a 1 : 10 ratio of added : natural inoculum.

Los patógenos presentes en un gran espectro de hospederas ya son tan atractivos candidatos para el desarrollo comercial como son los bio-herbicidas debido al mercado potencial para un producto que sea efectivo en contra de un rango amplio de malezas. Sin embargo, es necesario hacer un análisis de riesgo cuando dichos patógenos son capaces de diseminarse a través del espacio y el tiempo. En este trabajo evaluamos la hipótesis de que una zona segura alrededor del sitio de aplicación del bio-herbicida es adecuada mientras sea suficientemente amplia para garantizar que el inoculante se diluya, de tal manera que la densidad del inoculante natural en un cultivo susceptible no aumente más del doble con la introducción de las esporas del bio-herbicida. Para evaluar dicha hipótesis, se creó un modelo con una ecuación logística, utilizando la relación de densidad del inoculante patógeno-enfermedad reportada en nueve experimentos publicados. El análisis reveló que puede esperarse que vaya a ocurrir un incremento del doble en la densidad de esporas de un patógeno en un rango de 103.4 a 106.7 esporas/ml en casos de incrementos no aceptables en las enfermedades en un cultivo. Afuera del mencionado rango (<103.4 O > 106.7) es menos probable que ocurra. Por lo tanto, cuando la densidad natural de inoculante en el medio ambiente del cultivo ocurre fuera de ese rango, una zona de seguridad “aceptable” para el uso del patógeno como bio-herbicida puede definirse con un radio de 1:1 referente al inoculante agregado vs el inoculante natural. Si se desea tener una zona segura de menor riesgo, ésta puede lograrse utilizando un radio de 1:10 de inoculante agregado vs inoculante natural.

Keywords

Risk analysismyoherbicideplant pathogenbiological weed controlbroad-host-range pathogensplurivorous plant pathogenslogistic model
Type
Symposium
Information
Weed Technology , Volume 24 , Issue 2 , June 2010 , pp. 193 - 196
Copyright
Copyright © Weed Science Society of America 

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