Sorghum Diseases in India

levels of free phenolic compounds (1-2%) at anthesis,
and these levels increase to 2-10% during
normal development. Inoculation with fungi
caused an increase in phenolic compounds at 10,
14, and 20 days after anthesis (Fig. 7), especially
in resistant and moderately resistant cultivars.
Levels of free phenolic compounds in sorghum
caryopses were similar for inoculated and control
treatments during development, i.e., concentration
and time effects were not apparent in
caryopses.
Free p-hydroxybenzoic acid significantly
contributed to the higher levels of phenolic compounds
at 7, 10, and 14 days after anthesis for
both glumes and caryopses (Figs. 8, 9). However,
higher levels of free p-hydroxybenzoic acid
did not correspond to resistance to grain molding.
Free p-coumaric acid also contributed to the
higher levels of phenolic compounds in glumes
and caryopses; and the resistant cultivars and
one of the moderately resistant cultivars had
30
20
10
0
50
40
30
20
10
0
12
8
4
(R)
(M)
(S)
0
0 10 20 30 40 50
Time after anthesis (days)
Figure 8. Free p-hydroxybenzoic acid in sorghum
glumes that were inoculated with F.
moniliforme at anthesis and evaluated during
caryopsis development. Legend: (see Fig. 7).
120
90
60
30
0
60
45
30
15
0
45
30
15
(R)
(M)
(S)
0
5 15 25 35 45 55
Time after anthesis (days)
Figure 9. Free p-hydroxybenzoic acid in
sorghum caryopses that were inoculated with
E moniliforme at anthesis and evaluated during
caryopsis development. Legend: (see Fig.7).
earlier or higher levels than their control treatments
(Figs. 10, 11). Free caffeic acid in the caryopsis
was higher in concentration for all cultivars,
except one of the susceptible cultivars (Fig.
12). Hence p-coumaric and caffeic acids appear to
be involved in the biochemical response to fungal
invasion of sorghum glumes and caryopses.
Significant changes in concentrations of these
(and other) phenolic acids during development is
noteworthy, as it implies that significant biochemical
activity occurs in glumes and caryopses
during development. Glumes appear to be the
plant's first defense against fungal invasion and
colonization; later it is the chemical and physical
properties of the caryopsis that appear to be more
important in the resistance of grain to molding.
Other Resistance Mechanisms
Several structural characteristics of the sorghum
grain correspond to improved resistance to
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