RA 00015.pdf - OAR@ICRISAT

the plants to produce some yield under unfavorable
environmental conditions and also to withstand
insect attacks; it has important implications
for the development of minimum-input
pest-management systems.
10
8
6
4
100-seed weight
L.S.D.
(0.05)
Effects of Defoliation
Last year, which was an unusually wet year with
late rains, we found that removing different proportions
of the leaves from the plants throughout
the reproductive phase led to proportionate
decreases in yield. This year the rainy season
ended unusually early and as a result growth and
yields were reduced. Under these conditions,
with four different cultivars, we found that half
or more of the leaves could be removed throughout
the reproductive phase without affecting the
yield significantly. Data for cv ICP-1 are plotted
in Figure 32. These results indicate that leaf area
was not limiting pod-set and yield. The difference
from last year's observations suggests that under
conditions of moisture stress the photosynthetic
efficiency of the leaves may be limited by water
supply; perhaps the removal of half the leaves
results in an increased water supply to the
remaining leaves and an increase in their photosynthetic
efficiency.
2
0
3
2
1
0
160
140
120
100
80
60
40
20
0
Seeds per pod
Pods per plant
L.S.D.
(0.05)
L.S.D.
(0.05)
Diseases and Pests
Fusarium Wilt
In our continued studies of the wilt disease, we
found three pathogenic Fusarium species associated
with wilted plants: F. udum, F. oxysporum,
and F. solani. Twelve distinct cultural
isolates of F. udum, and two each of F. oxysporum
and F. solani are being maintained for
further studies.
Preliminary studies indicated that F. udum
colonized roots of pigeonpea plants in the sick
plot between 16 and 30 days after planting. The
pathogen could be detected in the plants prior to
the appearance of wilt symptoms. In infected
plants, F. udum was isolated from the root, stem,
branches, and pod hulls, but not from seed. The
32
28
24
20
16
12
8
4
0
Y i e l d per plant
L.S.D.
(0.05)
0 10 20 30 40 50 60 70 80 90 100
D e f o l i a t i o n (%)
Figure 32. Effect of different degrees of defoliation
throughout the reproductive
phase on yield and yield components of
cv ICP-1.
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