Agriculture Reference
In-Depth Information
systems in the fi eld prior to harvest or in the packhouse (http://www.agrogreen.co.il).
It is used to prevent the development of rots caused by a wide range of fungal pathogens,
such as
P. digitatum
and
P. italicum
on citrus,
P. expansum
on pome and soft fruits, and
B. cinerea
and
Rhizopus stolonifer
on grapes and strawberries. Integration of Shemer
with physical control measures such as hot-water wash, heat or modifi ed atmosphere
increases effi cacy (Blachinsky
et al
., 2007). The mode of action of the yeast is believed
to be through competition.
3.5
Factors affecting variable effi cacy and constraints
on commercial developments
Inconsistency in effi cacy of potential BCAs when evaluated in large-scale glasshouse
or fi eld trials is one of the major constraints in biological disease control. This can arise
from various causes, especially extrinsic factors of the environment, refl ecting the bio-
logical nature of the BCA. The BCA must fi rst survive potential stresses of formulation
and application procedures, and then remain active at the target site during the period
when effective control is required. In addition, it must survive fl uctuations in the natural
environment, especially temperature, as well as the action of indigenous and competi-
tive microbiota. Consequently, poor disease control at the scale-up stages of evaluation
is always likely to be high (Whipps & Lumsden, 2001). In an attempt to resolve this
problem and increase the number of BCAs reaching the market, it is recommended that
all selection, screening and development processes adopt an ecological approach which
takes into account the extrinsic factors of the environment of use (Whipps, 1997a, b, c;
Whipps & Lumsden, 2001). It is unfortunate that most BCAs are only active under
particular environmental conditions. Consequently, biological disease control in environ-
mentally controlled structures, such as glasshouses and polytunnels, tends to be more
successful and cost-effective compared to large-scale fi eld application.
Economical, mass production of stable inoculum and appropriate formulation is imper-
ative for the successful development of BCAs. Potential BCAs must also be easy to use
and cost-effective, or they will never reach the market or be used by growers. Currently,
many fungicides are relatively cheap and more effective than BCAs, and are unlikely to
be substituted for by BCAs unless they are withdrawn from the market. Very few growers
or extension workers know how to store and use BCAs, which often results in inadequate
disease control and subsequent poor sales. Clearly, there is need to train growers on how
to use BCAs effectively and integrate their use into crop protection programmes.
Another constraint to the development of bacteria and fungi as commercial BCAs
has been poor long-term storage stability. Good long-term stability, preferably for
18-24 months at room temperature (
ca.
21°C), is required to improve market competi-
tiveness. Despite the hurdles in obtaining stability, considerable progress has been made,
with stability of most current commercial products often being achieved by mixing
propagules with various additives during formulation (Jones & Burges, 1998). Improved
stability can also be achieved by treatment before formulation, for example, by appro-
priate growth conditions during production and by processing after production, such as
drying. Furthermore, regulation of water availability in the formulation is important for
stability.
