Experiments were performed to determine the nature of
maize influence on bean disease in additive-type
intercrops. Overall effects of intercrops on angular leaf
spot (caused by Phaeoisariopsis griseola) in Kenya
indicated >23% reductions (P<0.05) in area under the
disease progress curve (AUDPC) in two of three season-site
combinations. Fertilization tended to increase disease
(135-205%, P<0.10), but changes in bean density or planting
pattern had no effect. Intercrops reduced temperature and
wind velocity, but increased relative humidity. A 27%
AUDPC reduction (P=0.07) in bean rust (caused by Uromyces
appendiculatus) due to intercropping was observed in Oregon
in 1989 and 1990 in two of three locations.
Mechanisms of maize influence on rust were also
assessed in Oregon. Intercropping, and competition of
maize with beans alone, consistently steepened dispersal
gradients (P<0.10). Interference of maize with dispersal
alone tended to flatten gradients. Spore retention in
plots was increased in mid-season, then decreased late in
the season, due to competition in both years (P<0.05).
Intercropping reduced infection by 96% late in 1989
(P<0.05), probably due to microclimatic influence of maize.
The data from these experiments were used as inputs
for computer simulation to evaluate effects of specific
mechanisms on disease dynamics. Combination of all
mechanisms (= intercrop) reduced AUDPC to 32% of monocrop,
using 1989 data. Infection efficiency reductions, and to a
lesser extent dispersal effects, were responsible for these
changes. Intercrop effects declined as pathogen
multiplication rate (DMFR) increased. No intercrop effect
occurred at any DMFR using 1990 data, although interference
and competition effects of maize alone both increased AUDPC
at low DMFR. Partitioning dispersal effects into those due
to gradient slope changes and spore retention indicate that
the latter accounts almost entirely for disease alteration. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36577 |
| Date | 13 September 1991 |
| Creators | Boudreau, Mark Alan, 1958- |
| Contributors | Mundt, Christopher C. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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