Biology Reference
In-Depth Information
disease severity ranging from 42 to 49% (Yandoc et al. 2005). An amended spore and
oil emulsion suspension (4% horticultural oil, 10% light mineral oil, and 86% water)
resulted in higher levels of disease severity than the 1% gelatin. Higher levels of dis-
ease severity were achieved when a mixture of both these pathogens was applied
under field conditions. Foliar injury ranged from 30 to 86% for
B. sacchari
and from
9 to 70% for
D. gigantea
. Despite the promising levels of disease severity and weed
mortality recorded for these fungi, the regenerative potential of the cogongrass rhi-
zomes allowed the plants to outgrow the effects of both pathogens.
In an attempt to explore the feasibility of using fungal pathogens that are effective
against different geographic populations of cogongrass, a limited study was con-
ducted by examining the genetic diversity between the USA and West African
cogongrass by Den Breeÿen (Den Breeÿen 2007). Inter simple sequence repeat mark-
ers (ISSR) were used as a novel approach to understand the relationship between
cogongrass accessions from these two regions. Included in the study were three
closely related
Imperata
species:
Imperata brasiliensis
Trin.,
I. brevifolia
Vasey, and
I. cylindrica
var.
rubra. Imperata brasiliensis
is native to North, Central, and South
America and overlaps in its distribution with cogongrass in Florida and possibly else-
where in the US Southeast, and is morphologically and genetically very similar.
Imperata brevifolia
is native to California, and
I. cylindrica
var.
rubra
is an ornamen-
tal variety sold in nurseries throughout the USA. The US and West African
I. cylin-
drica
accessions were found to be geographically and genetically distinct. Within the
USA cogongrass, there was a distinction between cogongrass accessions collected
throughout the state of Florida, which confirmed that cogongrass was introduced into
the USA multiple times.
Imperata brasiliensis
was not genetically distinct from the
USA
I. cylindrica
population forming a sister species to the Florida
I. cylindrica
accessions. In addition,
Imperata cylindrica
var.
rubra
was more closely related to the
African accessions.
Imperata brevifolia
was found to be genetically distinct from all
the
Imperata
accessions. In addition,
B. sacchari
and
D. gigantea
isolates from the
USA and West Africa were evaluated in greenhouse trials to determine their efficacy
as biological control agents on the West African
I. cylindrica
. There were no signifi-
cant differences in disease incidence and disease severity between the Florida and
Benin isolates inoculated on the Benin cogongrass. These findings have implications
for implementing a biological control approach to manage cogongrass. The hypothe-
sis that fungal biological control within the USA and African cogongrass would result
in differential responses across the different accessions was not supported by this
study as the West African cogongrass was found to be equally susceptible to the
Florida and Benin isolates of
B. sacchari
and
D. gigantea
(Den Breeÿen 2007).
10.6 Conclusions
Here, we have presented a brief overview of several biological control programs
using microbial agents against invasive forest weeds. Our emphasis has been on
successful projects as well as those that appear to be heading for success. For examples
