RA 00015.pdf - OAR@ICRISAT

fungus remained restricted to the underground
parts of plants not showing wilt symptoms. Two
distinct types of symptoms-wilting with and
wilting without a necrotic band on the stem -
were observed.
Our observations of the past 3 years at
1CRISAT Center indicate that the appearance of
wilt symptoms increases rapidly from November
onwards. We have started studies of the yield loss
in relation to time of wilting, and preliminary
results show a progressive decline in losses with
symptoms appearing in successively later stages
of pod formation and development. Surveys of
disease incidence may tend to overestimate yield
losses if seed production on diseased plants is
ignored.
Sterility Mosaic
The causal agent of this disease has not yet been
identified. We have been unable to transmit the
disease either by mechanical transmission or by
grafting. In the case of diseases caused by a
mycoplasma-like organism, treatment with tetracycline
has been found to give remission of
symptoms. Tetracycline applications, made in
several ways, had no effect on symptoms of
plants infected with sterility mosaic. Electron
microscope observations to date have not revealed
virus or mycoplasma-like drganisms.
Although the organism has not been identified,
the vector has been known for several
years. Our studies have shown that a minimum
30-minute inoculation-access period was required
for transmission by the mite (Aceria
cajani). A single mite can transmit the causal
agent.
Although infected plants are usually sterile,
seed is sometimes produced and we have grown
several thousand seeds from diseased plants. In
no case has sterility mosaic been transmitted
through the seed; we consider that the causal
agent is not seed-borne.
Disease Surveys
Surveys are being made each year to assess losses
in farmers' fields. This year the central and
western districts of Maharashtra, not included in
our previous survey, and the states of Karnataka
and Tamil Nadu were surveyed. Wilt and sterility
mosaic were found to be the most important
diseases, with a very low incidence of root rot and
leaf diseases observed. The relative importance
of sterility mosaic increased in areas further
south (Table 31).
Table 31. Observations of wilt and sterility
mosaic in farmers' pigeonpea fields in
three states of India, 1976.
State
Maharashtra (western &
central districts)
Karnataka
Tamil Nadu
Pest Surveys
Wilt
Sterility
mosaic
Range Mean Range Mean
— ( % ) — — ( % ) —
0-38 7.6 - 3.9
0-17 1.1 0-95 9.7
0-65 1.4 0-93 12.8
The relative importance of various insect pests
on pigeonpea was recorded by surveying and
sample collection in Karnataka, Tamil Nadu,
Maharashtra (Akola and Sholapur districts),
Bihar, Orissa, Andhra Pradesh, and Uttar Pradesh.
The borer damage ranged from 3 to 84
percent. Severe pod damage was recorded in
southern states of India (Table 32).
H. armigera was found to be the major cause
of loss in pigeonpea but Exelastis atomosa Wals.
and Maruca testulalis Geyr. were also common
as pod borers.
N u t r i t i o n a l Quality
One of our objectives is to improve the nutritional
quality of pigeonpea. We recognize that
the first priority is to increase production of
pulses, so have not included nutritional factors as
selection criteria in the breeding program. Emphasis
to date has been on screening the germ-
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