Abstract
The durability of a control method for plant protection is defined as the persistence of its efficacy in space and time. It depends on (i) the selection pressure exerted by it on populations of plant pathogens and (ii) on the capacity of these pathogens to adapt to the control method. Erosion of effectiveness of conventional plant protection methods has been widely studied in the past. For example, apparition of resistance to chemical pesticides in plant pathogens or pests has been extensively documented. The durability of biological control has often been assumed to be higher than that of chemical control. Results concerning pest management in agricultural systems have shown that this assumption may not always be justified. Resistance of various pests to one or several toxins of Bacillus thuringiensis and apparition of resistance of the codling moth Cydia pomonella to the C. pomonella granulovirus have, for example, been described. In contrast with the situation for pests, the durability of biological control of plant diseases has hardly been studied and no scientific reports proving the loss of efficiency of biological control agents against plant pathogens in practice has been published so far. Knowledge concerning the possible erosion of effectiveness of biological control is essential to ensure a durable efficacy of biological control agents on target plant pathogens. This knowledge will result in identifying risk factors that can foster the selection of strains of plant pathogens resistant to biological control agents. It will also result in identifying types of biological control agents with lower risk of efficacy loss, i.e., modes of action of biological control agents that does not favor the selection of resistant isolates in natural populations of plant pathogens. An analysis of the scientific literature was then conducted to assess the potential for plant pathogens to become resistant to biological control agents.
Highlights
The durability of a control method for plant protection is defined as the persistence of its efficacy in space and time
An analysis of the scientific literature was conducted and scientific papers reporting the diversity of efficacy of biocontrol agents toward plant pathogens or those describing the ability of plant pathogens to produce natural mutants with reduced susceptibility under the selection pressure exerted by biocontrol
Some level of variability in the sensitivity to biocontrol agents has been encountered in other studies involving fewer strains of plant pathogens. This was the case for example, among eight isolates of Rhizoctonia solani examinated for their sensitivity to antibiotic-producing bacterial strains of Bacillus subtilis, Serratia plymuthica, Pseudomonas putida, and Streptomyces setonii (Faltin et al, 2004) and among six strains of Ophiostoma novo-ulmi evaluated for their sensitivity to four endophytic fungi of elm and two Trichoderma strains (Diaz et al, 2013)
Summary
In contrast with the situation for pests, the durability of biological control of plant diseases has hardly been studied and no scientific reports proving the loss of efficiency of biological control agents against plant pathogens in practice has been published so far. Knowledge concerning the possible erosion of effectiveness of biological control is essential to ensure a durable efficacy of biological control agents on target plant pathogens. This knowledge will result in identifying risk factors that can foster the selection of strains of plant pathogens resistant to biological control agents.
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