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.
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