Agriculture Reference
In-Depth Information
Specht and Murray 1990; Bockus et al., 1994).
Cool, wet weather during autumn and winter
favors profuse sporulation on infested plant debris
at or near the soil surface (Wiese and Ravenscroft
1975, 1978; Mathre and Johnston 1977). Disease
incidence is often more prevalent when seed is
planted into wet soil (Bruehl 1968; Pool and
Sharp 1969; Anderegg and Murray 1988).
Numbers of propagules in soil decline rapidly
during spring.
Pathogen entry into the plant does not require
preexisting tissue damage (Anderegg and Murray
1988) but is strongly amplifi ed by injuries caused
by emerging secondary roots and tillers (Douhan
and Murray 2001), freezing of roots (Bailey et al.,
1982; Martin et al., 1989), root breakage during
freeze and thaw cycles (Bruehl 1968), insects
(Slope and Bardner 1965), and acid soils (Bockus
and Claassen 1985; Anderegg and Murray 1988;
Stiles and Murray 1996).
when volunteer cereals and grass weeds are con-
trolled during the overwinter fallow period to
prevent an increase in pathogen inoculum density.
Cephalosporium stripe is especially damaging in
direct-drill (no-till) planting systems (Latin et al.,
1982; Bockus et al., 1983). The amount of patho-
gen inoculum can be greatly reduced by burning,
removing, or deeply burying infested residue
(Pool and Sharp 1969; Wiese and Ravenscroft
1975; Bockus et al., 1983; Christian and Miller
1984). Planting as late as possible during the
autumn reduces disease incidence and severity
(Bruehl 1968; Pool and Sharp 1969; Martin et al.,
1989) by limiting the colonization of root and
crown tissue by the pathogen (Pool and Sharp
1969; Douhan and Murray 2001), provided plant-
ing is not delayed such that yield potential is
reduced more than may be caused by Cephalo-
sporium stripe in earlier plantings (Raymond and
Bockus 1984). Disease severity on winter wheat
grown on acid soils can be reduced by applying
lime (Bockus and Claassen 1985; Anderegg and
Murray 1988), but the benefi t is mostly limited to
years when root wounding from frozen soil is
minor (Murray et al., 1992).
Winter wheat cultivars with partial resistance
are available (Bockus 1995; Murray et al., 2001;
Mundt 2002). Susceptible cultivars are consis-
tently susceptible and resistant cultivars vary
widely in disease reaction from year to year
(Martin et al., 1989). Repeated plantings of mod-
erately resistant cultivars reduce the level of
pathogen inoculum in soil and adequately manage
the loss of yield over time (Shefelbine and Bockus
1989; Murray et al., 2001). Two mechanisms of
resistance have been described. The pathogen
may be excluded from entering the plant, result-
ing in lower levels of disease incidence, or the
pathogen may have restricted ability to move
through root and crown tissue, resulting in fewer
infected tillers and delayed symptom develop-
ment (Morton and Mathre 1980; Mathre and
Johnston 1990; Douhan and Murray 2001). Genes
conveying a high level of resistance to
C. gra-
mineum
were derived from a wheat-
Thinopyrum
amphiploid (Mathre et al., 1985), were character-
ized (Cai et al., 1996, 1998), and are being intro-
gressed into commercial cultivars.
Causal organism
Cephalosporium gramineum
Y. Nisik. & Ikata pro-
duces small unicellular conidia in a slimy exo-
polysaccharide matrix (Stasinopoulos and Seviour
1989). The
Cephalosporium
stage occurs in the
xylem of living plants and on the surface of dead
straw at or near the soil surface. In most but not
all regions the fungus also produces a saprophytic
sporodochial stage (
Hymenula cerealis
Ellis &
Everh.) mostly near nodes of dead straw that was
infested while living (Wiese and Ravenscroft
1978). Sporodochia are formed during cool, wet
periods from late autumn to early spring. Hyaline
conidia are produced in great abundance on
moistened sporodochia.
Disease management
Cephalosporium stripe incidence and severity
increase with frequency of winter wheat produc-
tion (Latin et al., 1982; Bockus et al., 1983).
Disease is greatest where wheat is grown annually
and is much less damaging in two-year rotations
where summer rainfall is common and in three-
year rotations where precipitation occurs mostly
during the winter. Rotations are most effective
