STUDIES ON MANAGEMENT OF ROSE POWDERY MILDEW (Podosphaera pannosa (Wallr.) de Bary)
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Date
2017-11
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UHF,NAUNI
Abstract
ABSTRACT
Rose powdery mildew caused by the Podosphaera pannosa (Wallr.) de Bary is one of the most serious and devastating
diseases of roses grown worldwide including Himachal Pradesh in natural as well as protected cultivation. Rose powdery mildew was
recorded to occur in moderate to severe form in different rose growing areas of districts Bilaspur, Kangra, Mandi, Sirmour, Shimla
and Solan. The mean disease incidence and per cent disease index (PDI) varied between 48.50 to 66.75 and 22.22 to 36.02,
respectively with highest incidence in district Solan and highest PDI at Shimla while lowest incidence and PDI in district Kangra.
Pathogenicity test revealed that symptoms appeared after 161 hours of incubation. Different isolates of six districts were
morphologically distinguished from one another with respect of the size of the mycelium, conidia and conidiophores which ranged
between 4.0 to 4.8, 22.8 x 12.4 and 72.0 to 78.0 μm, respectively. Molecular characterization with RAPD markers revealed the
similarity index among the ten fungal isolates ranged between 19 to 73 per cent with an average of 46 per cent. Maximum similarity
about 73 per cent was found between isolate-5 and isolates-8. Least similar was isolate-7 which had 19 per cent similarity with other
isolate as it belongs to wild roses. Association of Ampelomyces quisqualis with Podosphaera pannosa was observed in months of the
September to November and in other hosts like Chotta dhatura (September to November), Zinnia and Dahlia (May to July) at Nauni.
Maximum growth of mycelium was reported in malt extract agar medium. Fusarium sp., Botrytis sp., Cladosporium sp., Penicillium
sp., Aspergillus sp., Alternaria sp., Trichothecium sp., Trichoderma sp. and two bacterial isolates (1 and 2) were isolated from the
phylloplane of the rose leaves in summer and winter seasons in year 2015. The highest conidial inhibition of 21.88% was recorded
from the culture filtrate of Trichoderma sp. among all the culture filtrates. The disease initially appeared in the second week of April
with severity of 5.85 per cent and increased upto 48.35 per cent at mid of June month. Simple correlation was between per cent
disease index, mean temperature (0.910), cumulative rainfall (-0.545), average relative humidity (0.616) and total sunshine hours (-
0.760). Partial correlation was between per cent disease index, mean temperature (0.475), cumulative rainfall (-0.872), average
relative humidity (0.172) and total sunshine hours (-0.273) and reported to be positive and negative according to different
environmental factors. Multiple correlation of determination indicated powdery mildew severity was dependent upon meteorological
factors about 97.2 per cent for the disease development during 2015 and 2016. Germplasm screening of 50 rose cultivars were
undertaken, none of cultivar was immune, 6 were resistant, 8 were moderately resistant, 24 were moderately susceptible, 12 were
susceptible to powdery mildew in their reaction. Under in vitro evaluation among fungicides, bio-control agents, bio-products,
botanicals, the best efficacy was obtained with difenoconazole, Bacillus subtilis, neem oil, and garlic (Allium sativus). Under
greenhouse evaluation of fungicides, difenoconazole gave the highest efficacy against Podosphaera pannosa for two years 2015 and
2016 with 85.96 per cent disease control. Best efficacy of Ampelomyces quisqualis was observed among the bio-control agents
application under greenhouse conditions with 78.51 per cent of disease control. Neem oil gave maximum per cent disease control of
76.18 per cent under greenhouse condition among all the bio-products. Among the botanicals, garlic (Allium sativus) gave the highest
efficacy against powdery mildew of rose with 71.87 per cent disease control. Maximum anti-sporulant activity was obtained with
difenoconazole, Ampelomyces quisqualis, neem oil and garlic among the fungicides, bio-control agents, bio-products and botanicals,
respectively. Dipotassium orthophosphate have the highest efficacy against rose powdery mildew at both 0.05 and 0.075 per cent
concentration. Dipotassium orthophosphate increased the content of the reducing (146.33 μg/g) and non-reducing sugar (39.28 μg/g),
total phenol (137.67 μg/g), polyphenol oxidase activity (0.261), peroxidase activity (0.416) and PAL activity (0.586). In
compatibility test, Ampelomyces quisqualis was not compatible while Bacillus subtilis was moderately to highly compatible with
fungicides, bio-products, botanicals and SAR chemicals. From the integrated disease management trial highest disease control was
obtained with two applications from treatments with dipotassium orthophosphate + Bacillus subtilis + neem oil (86.88%) and
difenoconazole + Bacillus subtilis + neem oil (85.43%) in comparison to individual treatments where six sprays were applied.
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