BP Singh

Symptoms of Fungal and Bacterial Diseases 139extend toward the stem and downwards in the roots producingsame symptoms of discolouration and softening of. tissues.Otherwise in general, roots remain healthy. Examples: Stem andfoot rot of papaya (Pythium aphanidermatum)i red rot of sugarcane(Colletotrichum falcatum); foot rot of linseed (Phoma exigua var.linicola); stem rot of jute (Macrophomina phaseolina).Powdery mildewInitial symptom starts as minute, pale coloured spot on theupper surface of the leaves. From these spots whitish, powderygrowth of the fungus develo~~". Later on, the powdery growthspread an.d gradually cover the whole leaf, and then to all aerialparts including stem and fruits. Minute pin head sized, darkcoloured bodies (c1eistothecia) may develop and scattered in thepowdery growth. Ultimately, the leaves turn greyish or lightbrown and finally wither away. Examples: Powdery mildew of pea(£rysiphe polygoni); powdery mildew of wheat (E. grnminis); grapepowdery mildew (Uncinula necator). . .Downy mildewOn Monocots : The plants are infected systematically from earlygrowth stage. Leaves appear pale yellow, severe stunting of plantand excessive tillering. The leaves show chlorotic stripes ofvarying size on the upper surface. On the underside or on bothside of the leaves, there is a whitish downy growth of the fungus.Many severely diseased plants die during the tillering to earlyelongation growth stage. Plants may remain sterile. In case ofpearl millet, the diseased plants may develop thickened andtwisted leaves and usually fail to head. The floral parts aretransformed into green leafy structures (green ear phase). Theseplants rarely produce viable grain. Examples: green ear of bajra(Sclerospora graminicola); downy mildew of sorghum(Peronosclerospora sorghi).On Dicots : Upper surface of the leaves (infected plants) turnyellowish, grey, light yellow with fine downy growth of whitegrey, purplish or bluish colour. Symptoms also appear on stem,twigs, petioles and fruits in the form of downy growth. In caseof severe infection, inflorescence may become deformed due tohypertrophy. Examples: Downy miidew of crucifers (Peronosporaparasitica); blue mold of tobacco (P. tabacina)j downy mildew of