Diseases
Phytophthora infestans de Bary A. - Late Blight of Tomato
Systematic position.
Division Oomycota, order Pythiales, family Pythiaceae, genus Phytophthora.Biological group.
Specialized biotroph parasite.Morphology and biology.
Late Blight affects leaves, stalks, and fruits of tomato. Large brown spots appear on leaves, locating mainly on margins of leaf plate. White farinaceous or webby bloom is formed on the lower side, representing conidial sporulation of the agent. Diseased leaves quickly dry up. On leaf petioles and on stalks the spots are brown, elongated, without bloom. On fruits brown indistinct spots appear, being under high humidity covered with weak white bloom. Tissue inside fruit turns brown, becoming hard. The disease affects unripe fruits in field and at afterripening. Mycelium of the activator is distributed between or inside plant cells. Zoosporangiophores leave stomata as bunches, by 2-5 ones, being about 10 microns in diameter. Zoosporangia ovoid or lemon-shaped, 25-30 x 15-20 microns, colorless, with thin smooth coat, and with apical tubercle. Sprouting in water, they form 6-16 biflagellate zoospores. Oospores spherical, 30 microns in diameter, colorless, with coat having thickness 3-4 microns. The infecting agent attacks also potato.Distribution.
Late Blight is distributed in the former USSR in all zones of tomato cultivation. The most frequent and strong epiphytoties (yield losses 50-100%) arise in areas with high relative air humidity and moderate temperatures. The areas include Baltic States, Northwest zone of Russia, Byelorussia, Western Ukraine, the North Caucasus, Transcaucasia, Western and Eastern Siberia, the Far East and Sakhalin.Ecology.
The main conditions for the disease development are high air humidity (about 100%), fogs and dews (at air temperature 22-24.C in the afternoon, 10-12.C and lower at night). Mass infection of tomatoes is frequently observed at the end of August - in the beginning of September. Oospores are a source of the infection, keeping in affected fruits, seeds, and in ground.Economic significance.
At epiphytoties the disease results in loss of 50-100% of yield of fruits; to 71% of seeds, in decrease of germinating velocity by 20% and germinating capacity by 20.8 %. Affected by the Late Blight fruits of tomato decrease content of sugars in 1.2-2.4 times, of ascorbic acid in 1.5-5 times; flavoring quality of fruits worsens. Protective actions are dressing of sowing material; 3-4 sprayings of plants by fungicides; planting of tomatoes far from potato fields; removing and destruction of affected fruits and vegetation residues; maintenance of high agriculture with application of mineral fertilizers; external disinfection of fruits before afterripening; cultivation of resistant varieties.Related references.
Hawksworth D.L., Kirk P.M., Sutton B.C., Pegler D.M. 1995. Ainsworth & Bisby's Dictionary of the fungi. CAB International. 616 p.Glushchenko E.Ya., Lukovnikova G.A. 1971. Changes of chemical composition of fruits of the tomatoes affected by Late Blight (Rhytophthora infestans D.B.). Byulleten' VIR (Leningrad): 57-60. (In Russian)
Kuprashvili T.D., Tsomaya N.N., Vartanov K.A., Mulkidzhanyan K.G. 1982. Changes of some biochemical parameters of seeds and sprouts of tomatoes affected by Late Blight. Soobshcheniya AN Gruz.SSR (Tbilisi) 105(1): 157-159. (In Russian)
Meladze E.I., Dolidze M.I. 1980. Distribution of diseases of tomatoes in East Georgia. In: Materials of Transcaucasian coordination meeting on plant protection o (May, 15-16 1980, Tbilisi), p. 84-85. (In Russian)
Osnitskaya E.A. 1968. Diseases of vegetables. In: Polyakov I.Ya., Chumakov A.E., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1967 and the forecast of their appearance in 1968. Moscow: Rosselkhozizdat: 120-125. (In Russian)
Osnitskaya E.A. 1969. Diseases of vegetables. In: Polyakov I.Ya., Chumakov A.E., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1968 and the forecast of their appearance in 1969. Moscow: Rosselkhozizdat: 137-144. (In Russian)
Osnitskaya E.A. 1970. Diseases of vegetables. In: Polyakov I.Ya., Minkevich I.I., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1969 and the forecast of their appearance in 1970. Moscow: MSKH RSFSR, VIZR: 252-263. (In Russian)
Osnitskaya E.A. 1971. Diseases of vegetables. In: Polyakov I.Ya., Minkevich I.I., eds. Pests and diseases distribution on agricultural crops in RSFSR in 1970 nd the forecast of their appearance in 1971. Moscow: MSKH RSFSR, VIZR: 187-198. (In Russian)
Prodchenko T.I. 1977. Distribution and harmfulness of Late Blight of tomato in irrigation zone of southern Ukraine. Zroshuvane zemlerobstvo (Kiev) 22: 72-78. (In Ukrainian)
Zakharova T.I. 1973. Late Blight of potato and tomato. In: Chumakov A.E., ed. Diseases distribution on agricultural crops in the USSR in 1968-1972. Leningrad: VIZR, p.54-60. (In Russian)