Agriculture Reference
In-Depth Information
Table 5.8. Inherent characteristics that can be used to predict the host-diversity effect for
reduced disease, showing whether selected host-pathogen systems possess these attributes
(from Garrett and Mundt, 1999)
Characteristic
a
Small
host
genotype
unit area
Shallow
dispersal
gradient
Small
lesion
size
Short
pathogen
generation
time
Strong host
specialization
b
Host
Pathogen
Coffee
Hemileila
vestatrix
-
+
+
-
+
Xanthomonas
campestris
Pepper
-
-
-
+
+
pv.
vesicatoria
Phytophthora
infestans
Potato
-
+
-
+
+
Magnaporthe
grisea
Rice
+
+
+
+
+
Blumeria
graminis
Wheat
+
+
+
+
+
f.sp
.
tritici
Puccinia
recondita
+
+
+
-
+
Puccinia
striiformis
+
+
-
-
+
Mycosphaerella
graminicola
+
-
-
-
-
Rhizoctonia
cerealis
+
-
-
-
-
a
-, Host-pathogen system does not have the characteristic, so a host-diversity effect for reduced disease is
less likely; +, host-pathogen system has the characteristic, so a host-diversity effect for reduced disease is
more likely.
b
High degree of host specialization in local pathogen populations.
To date there is little evidence of the effect of induced resistance on the natural spread
of disease. Hervas
et al
. (1997) have reported the use of non-pathogenic
Fusarium
oxysporum
as a seed treatment to control
Fusarium oxysporum
f.sp.
ciceris
on
chickpea. They describe an increase in the incubation period from 35.4 days to 46.8
days and from 21.7 days to 46.5 days for the chickpea varieties ICCV 4 and PV 61,
respectively, when the inoculum level of
F. oxysporum
f.sp.
ciceris
in the soil was
500 chlamydospores per g of soil. At higher inoculum concentrations, the treatments
were less effective. Similarly, decreases in the final disease level and overall area
under the disease progress curve were observed (Table 5.9). These results indicate a
quantitative effect of induced resistance against soil-borne pathogens.
