Agriculture Reference
In-Depth Information
heterogeneous soil matrices changes as a function of available free water. Biofi lms can
trap phages (Storey & Ashbolt, 2001), soil clay particles can reversibly adsorb phages
(Williams et al., 1987), and low soil pH can inactivate phages (Sykes et al., 1981). In
natural environments, as a result of low rates of phage diffusion and high rates of phage
inactivation, low numbers of viable phages are available to lyse target bacteria (Gill &
Abedon, 2003). One additional factor needed for a high degree of success is that high
populations of both phage and bacterium exist in order to initiate a chain reaction of
bacterial lysis (Gill & Abedon, 2003).
In the phyllosphere, a harsh environment exists and phages in this location degrade
extremely rapidly (Civerolo & Keil, 1969; McNeil et al., 2001; Balogh, 2002; Balogh
et al., 2003). This ephemeral existence on plant leaf surfaces is a limiting factor of
phage treatment. In fi eld and laboratory studies, viruses were shown to be inactivated
by high temperatures, high and low pH and sunlight, and were readily dislodged by rain
(Ignoffo et al., 1989; Ignoffo & Garcia, 1992). The environmental factor most destruc-
tive to viruses was UV-A and UV-B spectra of sunlight (Ignoffo & Garcia, 1994). Initial
studies showed that phage applied in the mid-morning was not effective in controlling
bacterial spot of tomato (J. Jones, unpublished results). We speculated that short residual
activity of the phage existed as a result of UV degradation and hindered effi cacy of
phage treatment when applied during daytime. This was confi rmed in fi eld experiments,
in which phages on tomato foliage exposed to high intensities of sunlight during day-
time were eliminated from the phyllosphere within hours after application (Iriarte et al.,
2007). In experiments conducted in greenhouses where sunlight UV irradiation is less
of a factor because UV cannot penetrate glass, phages can persist up to a week (Balogh,
2006) (Figure 13.4).
13.6
Phages as part of an integrated management
strategy
Multifaceted, integrated strategies carry the promise for effective, reliable and sustainable
management of bacterial plant diseases. Several approaches have been explored for using
phage treatment within an integrated management strategy. Tanaka et al. (1990) reduced
tobacco bacterial wilt by co-application of an avirulent strain of the pathogen, R. solan-
acearum , with a phage that was active against both virulent and avirulent strains. Using a
similar approach, Svircev et al. (2006) reduced fi re blight of pear with co-application of
an antagonistic epiphyte, Pantoea agglomerans and a phage that lysed both the antagonist
and the pathogen, Erwinia amylovora .
Obradovic and co-workers (Obradovic et al., 2004, 2005) used tomato bacterial spot
as a model system for developing a comprehensive phage-based integrated management
strategy for foliar bacterial diseases. They combined phage treatment with SAR inducers,
PGPR and antagonistic bacteria to control bacterial spot of tomato. They achieved better
and more reliable disease control when combining phages with SAR inducers; however,
integration with bacterial biocontrol agents did not improve control effi cacy, as compared
to phage alone.
Lang et al. (2007) evaluated phage treatment in combination with acibenzolar- S -
methyl, an SAR inducer, or with copper-mancozeb for the control of Xanthomonas leaf
blight of onion and found that both combinations resulted in enhanced disease control. On
Search WWH ::




Custom Search