Sorghum Diseases in India

Table 5. Yield and gray leaf spot severity levels
for cv Tortillero, grown during the 1984 cropping
season at La Lujosa Experiment Station,
Choluteca, the Honduras.
Treatment
Fungicide every
2 weeks
Fungicide every
4 weeks
Nonprotected control
Yield
(t ha- 1 )
5.6250a 1
5.5650a
4.5250b
Severity
(%)
1.0b 2
7.5b
21.0a
1. Means with different letter are different at .05 level
(Duncan's Multiple Range Test).
2. Means with different letter are different at .01 level
(Duncan's Multiple Range Test).
Effect of Downy Mildew on Grain
Yield
Peronosclerospora sorghi (Weston and Uppal) C.G.
Shaw causes the disease sorghum downy mildew
(SDM) on Sorghum bicolor. Plants systemically
infected by SDM are usually barren. The
disease is generally recognized as one of the
most important sorghum diseases (Frederiksen
et al. 1973). Sorghum downy mildew was first
reported in the Honduras in 1974, and is well
established in Comayagua.
Materials and methods
Three near-isogenic sorghum populations were
created with F3 progeny from a cross between
the resistant line SC 414-12 and the susceptible
inbred line Tx 412 (Craig et al 1988). The F3
families were tested for reaction to disease, and
were combined into a resistant, an intermediate,
and a susceptible population. In the latter, the
families showed more than 90% SDM incidence,
the intermediate family showed 25%; and the
resistant population showed less than 10%.
To test for yield differences between populations,
all three were sown in a complete randomized-block
design with four replications at
Choluteca, where SDM was believed absent.
Plots were four 5-m rows, with 0.8 m between
310
rows and 0.15 m between plants. Plots were
sown on 3 Sep and harvested on 11 Dec, 1983.
An identical test was sown 19 Sep in Comayagua,
where SDM is endemic. Fertilizer application
and cultivation were carried out in the
same manner in both locations. The two central
rows were harvested in each plot. The Comayagua
experiment was harvested on Dec 27.
The number of plants, panicles, plants with
SDM 21 days after emergence, plants with SDM
at harvest, panicle mass, and grain mass were
recorded for each plot.
The SDM (%) data from Comayagua were
subjected to an arcsine transformation, then to
analysis of variance. Grain weight (yield) data
were also subjected to analysis of variance.
There were significant differences in SDM (%)
and in yield between populations, so regression
analysis were performed, using the nontransformed
SDM (%) data as the independent variable
and yield as the dependent variable.
Results
In Comayagua SDM significantly reduced yields.
These losses were directly proportional with the
incidence of disease (Fig 4). In Choluteca, where
there was no SDM, there were no yield differences
between the near-isogenic sorghum
populations.
The resistant population in Comayagua, with
a mean of 2.8% SDM, yielded 1.5 t ha- 1 . The
1.8
1.6
1.4
1.2
1.0
0.8
y = 1425.83 -14.28 x
r = -0.733354
0.6
0 10 20 30 40 50 60
Incidence (%)
Figure 4. Regression of yield on sorghum
downy mildew incidence on near-isogenic
sorghum populations sown at Comayagua,
the Honduras, in 1983.