Classical and augmentative biological control against ... - IOBC-WPRS

Nicot et al.
One striking aspect of this inventory is that although the five target diseases / pathogens
included in our review are airborne and affect mostly the plant canopy, the vast majority of cited
biocontrol microorganisms are soil microorganisms. The scarcity of biocontrol agents originating
from the phyllosphere could be due to actual lack of effectiveness, or it could be the result of a bias
by research groups in favour of soil microbes when they gather candidate microorganisms to be
screened for biocontrol activity. This question would merit further analysis as it may help to devise
improved screening strategies. As "negative" results (the lack of effectiveness of tested
microorganisms, for example) are seldom published, the completion of such an analysis would in
turn necessitate direct information from research groups who have been implicated in screening for
biocontrol agents, or the development of a specific screening experiment comparing equal numbers
of phyllosphere and of soil microbial candidates.
Another striking aspect is that most of the beneficial micro-organisms inventoried in this study
(49 fungi/oomycetes, 28 yeasts and 41 bacteria) are cited only for biocontrol of one of the five types
of airborne diseases included in the survey (Figure 2). However, several species clearly stand out
with a wide range of effectiveness, as they were successfully used against all five types of target
diseases on a variety of crops. This includes the fungi Trichoderma harzianum and Trichoderma
viride (2 of 12 species of Trichoderma reported as biocontrol-effective in the reviewed literature)
and the bacteria Bacillus subtilis and Pseudomonas fluorescens.
Number of species
50
45
40
35
30
25
20
15
10
5
0
fungi / oomycetes
yeasts
bacteria
1 2 3 4 5
Number of controlled target diseases / pathogens
Figure 2:
Range of efficacy of 157 microbial biocontrol agents against five main types of airborne
diseases. Detailed data are presented in Table 4.
Concerning Fusarium oxysporum. A data base interrogation with the key words “Fusarium
oxysporum AND biological control” provided 2266 for the period 1973-2009. Using these key
words we did not select only papers regarding biological control of diseases induced by F.
oxysporum but also all the paper dealing with the use of strains of F. oxysporum to control diseases
and weeds. There are quite many papers dealing with the use of different strains of F. oxysporum to
control Broom rape (orobanche) and also the use of F. oxysporum f. sp. erythroxyli to eradicate
coca crops.
We decided to limit our review to the two last years and to concentrate on references for which
full text was available on line. Finally we reviewed 48 papers. All these papers were dealing with
the selection and development of micro-biological control agents; only two were considering others
methods. One was addressing the use of chemical elicitors to induce resistance in the plant; the
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