Biology Reference
In-Depth Information
drought tolerance, adaptability to fire, wind-disseminated seeds, and high genetic
plasticity (MacDonald 2004). Despite the importance of the problems caused by
cogongrass throughout the tropical areas of the world, biological control efforts
have been rather limited (Caunter 1996). This has paralleled the general absence of
attempted, and thus of successful, biological control projects against grasses in
general (Waterhouse 1999). Other factors that complicate biocontrol of cogongrass
include the existence of closely related grasses of economic or ecologic value
(Holm et al. 1977) and potential conflict of interest with groups that value
cogongrass (Evans 1991). Similarly, little information exists on pathogens of
cogongrass and their potential as biological control agents (Evans 1991). It is likely
that fungi associated with cogongrass are more diverse and abundant than indicated
by herbarium records (Evans 1991; Charudattan 1997; Minno and Minno 2000).
Evans (1987, 1991) suggested that some of the known fungal pathogens of
cogongrass should be considered for introduction as classical biological control
agents on this invasive weed. Promising species include three rust fungi,
Puccinia
fragosoana
Beltrán,
P. rufipes
Dietel, and
P. imperatae
(Magnus) G. Poirault
(Evans 1987) and a smut fungus,
Sporisorium (=Sphacelotheca) schweinfurthiana
(Evans 1987), which are well represented on cogongrass in the Old World, mainly
Africa (Evans 1991), and the hemibiotrophic fungus
Colletotrichum caudatum
(Caunter 1996). It is interesting to note that these pathogens are common in the
Mediterranean region where
I. cylindrica
is not a serious weed (Evans 1991; Holm
et al. 1977). The aecial stages of
P. imperatae
and
P. fragosoana
are unknown while
P. rufipes
has a known aecial stage on
Thunbergia
, an alternate host (Cummins
1971) potentially excluding it from further evaluation as a biocontrol agent due to
potential nontarget-host effects. Caunter (1996) cited that
P. rufipes
, although
present in Malaysia, was having little effect on the cogongrass. The smut fungus,
Sporisorium (=Sphacelotheca) schweinfurthianum
(Thümen) Sacc. (Evans 1987) is
well represented on cogongrass in the Old World, mainly Africa (Evans 1991). The
host range of the genus
Sporisorium
is restricted to the
Poaceae.
A single
cogongrass plant can produce up to 3,000 seeds per inflorescence; implementing a
classical biological control program with a smut fungus could effectively reduce the
number of seeds produced and ultimately reduce cogongrass density. Determining
the value of implementing
S. schweinfurthianum
as an inundative biocontrol agent
and integrating a mycoherbicide with the two classical biocontrol rust pathogens
would be invaluable to the success of biocontrol of this invasive weed.
Biological control using plant pathogens to manage cogongrass infestations was
considered to have potential in the USA (Van Loan et al. 2002). In the southeastern
USA, two fungi,
Bipolaris sacchari
(Breda de Haan) Subram., isolated from
cogongrass, and
Drechslera gigantea
(Heald & F.A. Wolf) S. Ito, isolated from
large crabgrass [
Digitaria sanguinalis
(L.) Scop.], were shown to be pathogenic on
a Florida
Imperata cylindrica
accession from Lake Alice, University of Florida by
Yandoc (2001). Yandoc et al. (2005) evaluated the efficacy of
B. sacchari
and
D. gigantea
in greenhouse and miniplot trials. Amended spore suspensions of
B.
sacchari
and
D. gigantea
, containing 10
5
spores per mL in a 1% aqueous gelatin
solution, caused disease symptoms on cogongrass under greenhouse conditions with
