TRENDS IN BIOSCIENCES 6-1, 2013 EDITION

Trends in Biosciences 6 (1): 40-42, 2013
Losses Caused Due to Alternaria Blight Disease in the Grain Yield of Pigeonpea
LAXMAN PRASAD BALAI 1 AND R.B. SINGH
Department of Mycology and Plant Pathology, Institute of Agricultural Sciences, Banaras Hindu University
(BHU), Varanasi 221 005, India
e-mail: laxmanbhu08@gmail.com 1
ABSTRACT
A field trial was conducted during 2010-11 and 2011-12 to
ascertain the losses caused by alternaria blight disease in the
grain yield of pigeonpea. A susceptible variety ‘Bahar’ was sown
in the research field. The artificial inoculations of mass culture
of Alternaria tenuissima (Kunze ex pers.) Wiltshire was done in
the inoculated plots at 60 DAS to create the desirable level of
disease pressure of alternaria blight. The uninoculated plots
(control) were sprayed with Mancozeb 75 WP (0.25%) to check
the alternaria blight disease. It revealed that inoculated plots
showed maximum disease intensity (44.19%) was recorded in
plots which did not receive any spray of Mancozeb. In plots
with one, two three and four sprays of Mancozeb, disease
intensity was recorded as 31.01, 20.57, 13.75 and 11.88% and
the mean % disease control was 29.88, 53.45, 68.88 and 73.09%
respectively. Almost similar trend of disease intensity, crop
yield and number of 100 grain seed weight was recorded in
different treatments with Mancozeb.
Key word
Pigeonpea, alternaria blight, losses and disease
intensity
Pigeonpea [Cajanus cajan (L.) Millsp.] is one of the
important food legume crops and rank second after chickpea
in area, production and productivity of the tropics and subtropics.
The crop suffers from many fungal diseases, of which
foliar diseases take a heavy toll. Assessment of the effect of
any disease on yield of a crop is pre-requisite for preparing
rational disease management programme. Among the diseases,
alternaria blight disease has been reported to cause yield
losses between 20-80% (Sharma, et al., 2012, Kushwaha, et
al., 2010). Alternaria blight (Alternaria tenuissima (Kunze ex
pers.) Wiltshire) was reported for the first time from Varanasi,
India by Pavgi and Singh, 1971. Later, Kannainyan and Nene,
1977 reported its occurrences from Hyderabad as a disease of
minor importance but recently alternaria blight has become
one of the serious fungal diseases of pigeonpea, especially in
September sown crop. This disease has thus become the most
limiting factor for rabi cultivation of pigeonpea in eastern
Uttar Pradesh, Bihar and Bengal. The disease symptoms start
appearing as circular, chlorotic, dark brown minute spots with
yellow halo on the upper surface of leaf lets, followed by
development of black spots which increase in size showing
purple margin around the black necrotic spots. The spots
enlarge and coalesce with each other forming big lesions.
These symptoms appeared in the second or third weeks of
November and attain maximum disease severity at the second
or third weeks of January onward. Reliable estimates of loss
facilitate the objective identification of the relative importance
of biotic pests. Consequently, limited resources can be
assigned on a priority basis and optimize returns from a given
effort. Accurate information concerning losses is also needed
by growers and plant protection specialists to develop
decision thresholds for determining, when cost effective
control measures should be deployed (Nutter, 1993). The need
for reliable crop loss assessment methodology (to develop
reliable decision aids) assumes added importance given, the
current worldwide concern about improving or maintaining
environmental quality by reducing the use of pesticides (Stern,
et al., 1959). Keeping in view the above facts, the present
investigation was undertaken the estimation of yield losses
in pigeonpea production under agro-climatic conditions.
MATERIALS AND METHODS
An experiment was conducted during the years 2010-11
and 2011-12 at the Entomological Research Trials Field,
Banaras Hindu University (BHU),Varanasi in the crop season
under artificial inoculation condition to find out the extent of
grain yield loss due to Alternaria blight. Susceptible cultivar
(Bahar) was used in randomized block design with three
replications. The plot size was 4.50 3.0 m with row spacing
of 45 cm and plant to plant distance of 20 cm. Seeds were
sown in second week of September. Weeds were controlled
by using Glyphosate @ 3 liter/ ha pre-emergence application
15 days before sowing. Optimum moisture in the soil for proper
seed germination was maintained by rolling the field with a
roller. Endosulphan one liter/ha was sprayed twice to prevent
crop damage by different insects. After attaining the age of
two months, the plants were artificial inoculated with spore
cum-mycelial suspension of the pathogen and the plots were
irrigated from time to time to maintain proper moisture. One,
two, three and four sprays of Mancozeb 75 WP (0.25%) were
applied separately in each plot. The first spray of fungicide in
recommended dose was given 48 hrs after inoculation and
subsequent sprays were done at 10 days interval. Check plot
was sprayed with sterilized water only. Observations on
disease intensity were recorded on the basis of percent of leaf
area affected after 15 days of last spray and disease intensity
recorded using 0-5 scale (Mayee and Datar, 1986) following
Table 1.
Data on the per cent infection of the disease were also
converted into angular values and analyzed statistically. Grain
yield (kg/ha), 100 seed grain weight (g) per plot and per cent
disease control was recorded after harvest of the crop. Finally