Agriculture Reference
In-Depth Information
Romero
et al.,
2001; Obradovic
et al.,
2004),
Xanthomonas
leaf blight on onion (Gent &
Schwartz, 2005) and fi re blight on apple (Maxson-Stein
et al.,
2002) (see also Chapter 4).
Although these inducers may reduce disease, they may also have some negative effects on
certain plant species, such as by affecting yield (Romero
et al.,
2001; Gent & Schwartz,
2005). In some pathosystems, plant inducers have been ineffective for disease control
(Graham & Leite, 2004; Chapter 4).
13.2
Biological control has gained recent interest for controlling bacterial diseases (see
Chapter 3). Various strategies for using biological control for bacterial diseases include
the use of nonpathogenic or pathogenically attenuated strains of the pathogen (Frey
et al.,
1994; Liu, 1998; Hert, 2007), saprophytic bacteria (Ji
et al.,
2006), and plant growth-pro-
moting rhizobacteria (PGPR) (Ji
et al.,
2006) to suppress pathogen populations or induce
a reaction in the plant such that the pathogen is reduced in its ability to colonize the plant
and cause disease. Disease control using these approaches has been variable.
Biological control
13.3
Bacteriophages were evaluated for controlling a number of human and animal bacterial
diseases, soon after their discovery by Twort (1915) and by d'Herelle (1917) at the begin-
ning of the twentieth century (Brunoghe & Maisin, 1921; Beckerich & Hauduroy, 1922;
Davison, 1922). Fairly soon after, they were proposed as plant disease control agents
(Moore, 1926).
In 1924, Mallman & Hemstreet (1924) isolated the 'cabbage-rot organism,'
Xanthomonas
campestris
pv.
campestris
, from rotting cabbage and demonstrated that the fi ltrate of the
liquid collected from the decomposed cabbage inhibited
in vitro
growth of the pathogen.
The following year, Kotila & Coons (1925) isolated bacteriophages from soil samples
that were active against the causal agent of blackleg disease of potato,
Erwinia carotovora
subsp.
atroseptica
. They demonstrated in growth chamber experiments that co-inoculation
of
E. carotovora
subsp.
atroseptica
with phage successfully inhibited the pathogen and
prevented rotting of tubers (Kotila & Coons, 1925). These workers also isolated phages
against
E. carotovora
subsp.
carotovora
and
Agrobacterium tumefaciens
from various
sources, such as soil, rotting carrots and river water (Coons & Kotila, 1925). Thomas
(1935) treated corn seeds that were infected with
Pantoea stewartii
, the causal agent of
Stewart's wilt of corn, with bacteriophage isolated from diseased plant material. The seed
treatment reduced disease incidence from 18% to 1.4%.
Despite promising early results, phage was generally considered an ineffective and
unreliable means for controlling plant pathogenic bacteria. Okabe stated in 1963, in a
review article on bacteriophages, that the phage in general appears to be ineffective as
a control strategy (Okabe & Goto, 1963). Goto concluded in 1992 that practical use of
phages for control of bacterial plant disease in the fi eld was unsuccessful (Goto, 1992).
Furthermore, it was believed that because of their narrow spectrum of activity, phages
were much more likely to fail than antibiotics (Summers, 2005). As a result of these fac-
tors, interest in phages waned for controlling bacterial plant diseases and antibiotics and
copper compounds became standard.
Early use of bacteriophages in agriculture
