STUDIES ON PURPLE BLOTCH [Alternaria porri (Ellis) Cif.] OF ONION [Allium cepa L.] AND ITS MANAGEMENT
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Date
2012
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AAU, Anand
Abstract
Purple blotch of onion caused by Alternaria porri (Ellis) Cif. is one
of the important foliar diseases. Present investigation was carried out at
AAU Anand during the year 2010-12 on cultural and morphological
characterization of the pathogen, protein profiling of the six isolates of A.
porri by SDS PAGE, biological interaction of phylloplane mycofloras of
onion against A. porri, in vitro efficacy of fungicides and bioagents on the
growth of pathogen, and evaluation of fungicides and bioagents against
purple blotch of onion under field conditions.
The pathogen was isolated from infected onion leaves collected
from six different onion growing areas of Gujarat. The isolates were
named as AP 1, AP 2, AP 3, AP 4, AP 5 and AP 6 for Anand, Kheda,
Bhavnagar, Amreli, Junagadh and Rajkot districts, respectively.
Pathogenicity test of each of the six isolates was proved by inoculating
the spore suspension and homogenized mycelial bits (1× 104 conidia/ml)
of A. porri on healthy onion seedlings. Pathogen was identified as
Alternaria porri. Protein profile by SDS-PAGE of six isolates of A. porri
showed variability in terms of number of protein bands. On the basis of
dendrogram, first main cluster consisted of isolates AP 1, AP 2, AP 3, AP
4 and AP 5, whereas the second cluster included only AP 6 isolate.
Evaluation of eight phylloplane mycofloras against A. porri under in vitro
revealed relatively higher antagonistic capability of Aspergillus niger,
Trichoderma sp., Aspergillus flavus and Aurobasidium sp. as compared
to Alternaria alternata, Curvularia sp., Cladosporium sp. and Fusarium
sp. Among the nine fungicides tested in vitro for their efficacy,
Azoxystrobin and Propiconazole completely inhibited the mycelial
growth of A. porri at all the three concentrations. The next effective
fungicides were Carbendazim 12% + Mancozeb 63%, Propineb and
Hexaconazole at 0.15, 0.2 and 0.025 per cent, respectively. Trichoderma
viride, T. harzianum and T. virens were found more effective as compared
to Pseudomonas fluorescens and Bacillus subtilis under in vitro
evaluation against A. porri. Under field conditions, purple blotch of onion
can be effectively managed by three sprays of Propiconazole @ 0.01 per
cent followed by three sprays of Mancozeb @ 0.15 per cent and
Azoxystrobin @ 0.025 per cent. Trichoderma sp. showed higher
antagonistic capability under in vitro, but failed to perform in vivo.
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Keywords
agriculture, plant pathology, study