ETIOLOGY AND MANAGEMENT OF LEAF ROT DISEASE OF ONION CAUSED BY Enterobacter cloacae
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Date
2019-11
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University of Horticultural Sciences, Bagalkot
Abstract
Onion (Allium cepa L.) is called as “queen of kitchen” (Priya et al., 2015).
South-west Asia is considered as the primary centre of domestication of onion. Leaf rot
disease is one of the emerging diseases of onion in northern part of Karnataka and also
causing a considerable crop loss in recent years. An intensive roving survey was
conducted during monsoon season in 2017-18. The results of the survey revealed that
the disease incidence was ranged from 6.60 to 24.00 per cent. Among the five districts
surveyed, average highest per cent disease incidence was observed in Gadag (16.50%).
Whereas least incidence at Chitradurga (7.35%). The disease incidence was maximum
during kharif season. Initially small water soaked spots appeared, later became small
constricted area, which later formed irregular translucent water soaked oily lesions,
which later became necrotic and hanging down of leaves at constricted area. At severe
stage, leaves turned yellow and all the leaves were collapsed to the ground and the
plants were died. The pathogenicity test was proved that, the bacterium is pathogenic on
onion seedlings. The individual colonies were creamy white in colour, round and
convex shaped. The bacteria was negative to starch hydrolysis, indole production,
hydrogen production, whereas it was positive to catalase activity, KOH test, acid
production from methyl-α, cellobiose, etc. Through 16S rRNA molecular analysis, the
test bacterium was identified as Enterobacter cloacae, which is amplified at 493bp.
Among ten different isolates of bacterial bio agents tested, PM-2A
(Brevibacilus sp.) (19.33 mm) was found effective with highest mean zone of
inhibition of E. cloacae. Among the fifteen tested botanicals, Prosophis juliflora and
Garcinia indica were shown the highest mean zone of inhibition of 20.55 and 19.22
mm, respectively. Among the four antibiotics evaluated streptocyclin (33.39 mm)
shown highest mean zone of inhibition against the E. cloacae. Among the fungicides,
copper hydroxide (19.06 mm) recorded highest mean zone of inhibition. The results on
evaluation of chemicals, botanicals and bio agents against leaf rot disease revealed that,
among the treatments, treatment T1 (streptocycline at 500 ppm + copper oxy chloride at
0.3%) and 2-bromo – 2 nitropropane-1, 3-diol (Bactinash-200) at 500 ppm + copper
hydroxide at 0.2% were found most effective in controlling the disease. The least
observation was shown by Bravibacillus spp. - 108 cfu / ml.