Groundnut;TIKKA DISEASE OR LEAF SPOT; RUST

Groundnut: Arachis hypogaea L. Family: Fabaceae 1. TIKKA DISEASE OR LEAF SPOT Tikka disease is reported from all groundnut growing countries of the world such as Africa, Australia, China, India, Indonesia, Malaysia, Philippines, Sri Lanka and USA. The disease is caused by two fungal plant pathogens i.e. Cercos

pora arachidicola and Cercosporidium personatum. The perfect stages of both these fungal pathogens (Mycosphaerella arachidicola and M. berkeleyii) play important role in primary infection and pathogen survival. The yield loss from tikka disease has been reported from 20-50 per cent but may be increased with association other diseases. The all groundnut varieties grown in India are susceptible to tikka disease. Symptoms: The primary symptoms of the disease are appearing in 35 to 60 days old plants. The tikka disease occurs as two distinct types of lea spots caused by two species of Cercospora. C. personatum causes small (1-6 mm), almost circular and dark coloured spots on the leaves, stipules, petioles and stem which may coalesce to form a large dark brown to black irregular patch. There may be few to many spots on each leaf. The severe infection or spotting on the leaves causes premature dropping. The disease is more severe at the time between flowering and harvesting, when the climatic conditions are favourable. The leaf spots caused by Cercospora arachidicola are almost circular to irregular, large (1-10 mm), surrounded by bright yellow haloes and dark brown centre. The conidia are formed on upper surface of leaf while C. personatum produced conidia on lower surface of leaves with concentric rings.   Causal Organism: The causal organism of tikka disease are Cercospora arachidicola Hori (perfect stage of the pathogen: Mycosphaerella arachidicola W. A. Jenkins) and Cercosporidium personatum (Berk & Curt) Deighton (perfect stage of the pathogen: Mycosphaerella berkeleyii W. A. Jenkins). The mycelium of C. personatum is intercellular, brown, septate, branched and slender with haustoria. The conidia are hyaline, 18-60 x 6-11 µm, 2-7 septate and borne singly on short, 26-54 x 5-8 µm conidiophores. The conidiophores are produced in bunches from the hymenial layer of sub-epidermal region. The mycelium of C. arachidicola is inter and intracellular, brown, septate, branched and without haustoria. The conidiophores are 22-45 x 3-5 µm, yellowish brown, septate and conidia are hyaline or pale yellow, obclavate, 4-12 septate measuring 38-108 x 3-6 µm. Disease Cycle: The tikka disease of groundnut is soil borne. The pathogen C. arachidicola and C. personatum disseminated by wind which is blown from leaf to leaf. The primary infection of disease is caused by conidia found on the plant debris in the soil. The spores remain viable in the soil for a long time and infect the succeeding crop under favourable environmental conditions. High humidity and relatively low temperature is essential for initiating the fungal infection. It is observed that the high nitrogen fertilizer increases disease intensity. Disease Management: The disease can be controlled by long crop rotation and sanitation practices. The intercropping with pigeon pea and use of phosphatic fertilizers also reduced the disease incidence. The early sowing crop varieties reduce the disease. The use of Dithane Z-78 (0.2%), Dithane M-45 (0.2%), Cosan, Breston (0.1%) and copper sulphate mixture (15-25 kg/ha) effectively controlled the disease. Some other effective systemic fungicides are benomyl, bavistin, brestanol and cercobin. 2. RUST The rust of groundnut is distributed in Central and South America, China, India, West Indies and USSR. The disease is found in Andhra Pradesh, Punjab, Tamil Nadu, West Bengal and Uttar Pradesh. The rust of groundnut is an economic disease and causing 14-32 per cent yield loss. Symptoms: The disease is found on 6 weeks or more old plants. The small orange coloured uredial pustules appear on lower surface of the leaves. At later stages, these pustules may appear on upper leaf surface and other aerial parts of the plant except flower. The ruptured epidermis exposes a powdery mass of uredospores. The infected leaves are showed small, brown and necrotic lesions on the upper leaf surface. The severely infected leaves wither and drop prematurely. The seeds formed on infected plants are small and shriveled. Causal Organism: The rust of groundnut is caused by Puccinia arachidis Speg. The uredial and telial stages of the pathogen are known till now. The uredospores are one celled, subglobose, ovoid to round, light brown, thin walled, 2-3 germ pores and measuring 24 x 21 µm with short and hyaline pedicels. Disease Cycle: The uredospores are short lived in infected plant debris. The continuous cultivation of the crop in India without any significant break may perpetuate the disease. The uredospores found in southern India may act as potential source of disease in northern India blown by wind during monsoon season. Disease Management: The application of a mixture of Carbendazim (0.5 %) and Mancozeb (0.25 %) at 2-3 weeks interval on 4-5 weeks old plants effectively controlled the disease.