Investigation on gummosis of sweet orange (citrus sinensis osbeck) incited by phytophthora species
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Date
2011-05-31
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Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani
Abstract
crop of the world trade for fresh fruits and its processed products,
by-products. With globalization of world trade the avenues of export of sweet
orange have increased manyfold for earning foreign exchange. In India it has
played a major role in the agro-industries of Maharashtra. To take the benefit of
this world scenario, product and productivity of sweet orange needs to be
stabilized. Although large number of diseases due to fungi and virus have been
reported on sweet orange. The root rot, collar rot, brown rot and gummosis
caused by Phytophthora spp. is most important and are found widely prevalent in
citrus growing area of the country. Thousands of citrus plants succumb to
Phytophthora diseases every year in India. More than 20 per cent plants die due
to this pathogen in citrus nurseries of central India.
Typical symptoms of the Phytophthora diseases observed such as
dull chlorotic foliage, veinal chlrosis, fever fibrous roots, stunted growth of plant,
brownish black oozing (gurnmosis) from the dead bark, less canopy volume with
naked branches leads die back and slow decline symptoms; resulting in increased
cost of production and reduced yield of sweet orange fruits very drastically.
Highest disease incidence and severity was noticed in Nanded
district followed by Jalna, Parbhani, Hingoli, Aurangabad and Latur while lowest
disease incidence and severity was noticed in Osmanabad district. The per cent
gummosis incidence was high in months of August-September which was
concomitant with heavy rainfall, high humidity and temperature range of l 8-35°C.
The sweet orange productivity was more in adopted farmers
orchards than non adopted orchards but still it is far below the national average
productivity as 10.7 t/ha.
All the six bioagents tested significantly inhibited the mycelial
growth of Phytophthora nicotianae, Phytophthora citrophthora and Phytophthora
palmivora. However, T harzianum was found most effective followed by T
viride, T koningii, T hamatum, G. virens and P. jluorescens in case of
Phytophthora nicotianae. In case of Phytophthora citrophthora, T viride was
found most effective followed by T harzianum, T hamatum, G. virens, T
koningii and P. jluorescens. In case of Phytophthora palmivora, T viride was
found most effective followed by T harzianum, T hamatum, T koningii, G.
virens and P. fluorescens.
All the six botanicals/plant extracts tested at various concentrations
significantly inhibited the mycelial growth of Phytophthora nicotianae,
Phytophthora citrophthora and Phytophthora palmivora. However, Garlic extract
was found effective followed by Neem, Onion, Ginger, Tulasi and Turmeric
extract in case of Phytophthora nicotianae and Phytophthora palmivora while in
case of Phytophthora citrophthora Garlic extract was found most effective
followed by Neem, Onion, Tulasi, Turmeric and Ginger extract.
All the nine fungicides tested at various concentrations
significantly inhibited the mycelial growth of Phytophthora nicotianae,
Phytophthora citrophthora and Phytophthora palmivora. However, Cymoxynil 8
% + Mancozeb 64% (Curzate M-8) and Metalaxyl M-4% + Mancozeb 64%
(Ridomil Gold) were found most effective followed by Metyram (Polyram),
Chlorothalonil (Kavach), Pyraclostrobin 5% + Metyram 55% (Cabrio-Top),
Fosteyl-Al (Aliette), Metalaxyl (Ridomil), and Azoxystrobin (Amistar) while
fungicide Mancozeb (Dithane M-45) was found comparatively least effective
against all the Phytophthora species.