Turmeric; LEAF BLOTCH; LEAF SPOT

Turmeric: Curcuma longa Roxb. Family: Zingiberaceae   1. LEAF BLOTCH The disease is widely distributed in India where crop is grown such as Andhra Pradesh, Bihar, Gujarat, Maharashtra, Tamil Nadu, Uttar Pradesh and West Bengal. The disease has also been reported from Japan. The disease is causing considerable damage in the crops. Symptoms: The spots are appearing in large number on both the leaf surfaces but they are more prominent on upper surfaces and covering most of the leaf blade. The spots are arranged in rows along the leaf veins which are minute (1-2 µm in diameter) light yellow to dark yellow. The plants are not killed but due to the destruction of large number of photosynthetic area by pathogen, a heavy yield loss observed. The infected leaves appear as reddish brown coloured and become chlorotic and pale yellow at later stage. As the disease advances, the affected leaves wither and dry or severely blotched. Causal Organism: The leaf blotch disease is caused by Taphrina maculans Butler. The fungal hyphae are present between the cuticle and epidermis or inside the epidermal cells. The pathogen sends branched or lobed haustoria inside the host cells for drawing nutrition from it. The fully developed spots have hyphal mat at sub-cuticular regions. The outermost cells of this mat grow into cylindrical or club shaped, thin walled projections which rupture the epidermis and become asci and contain eight ascospores. The ascospores are hyaline, ovoid, unicellular and measuring 4-7 x 2-3 µm. Disease Cycle: The fungus is mainly air borne but its mode of perpetuation is not known. The pathogen may remain in dormant stage in the dried rhizomes and become active when the crop is grown in the field and initiate infection. The dried infected leaves which contain asci may be the chief source of inoculum in the subsequent year. Disease Management: The diseased leaves of host plants should be removed and burnt. The spray of timely interval of Blitox 50, Bordeaux mixture, Cupravit, Dithane Z-78, Fytolan and Perenox effectively control the disease. The cultivation of resistant varieties such as China, Jaweli, Ca 69 and Shillong can completely control the disease.     2. LEAF SPOT The disease is commonly found in south India and recently causing severe damage to crop. Symptoms: The leaves shows characteristic oblong brown spots with black concentric rings. The plants of all ages showed variable size of spots initiated as oblong spot with grey centres of 1-2 cm long and 1 cm width. The affected leaves have indefinite number of spots and as the disease advances, these spots enlarge covering a major portion of leaf lamina. The black coloured dots of fungal acervuli occur in concentric rings on the spot. The severely infected leaf become dry and wilts. Causal Organism: The leaf spot disease is caused by Colletotrichum capsici (Syd.) Butler and Bisby. The septate hyphae is found inter and intra-cellularly in the host tissues. The fungus produces characteristic acervuli on the spots. The club shaped single celled conidiophores arise from the hymenial layer below the epidermis and emerge by rupturing of epidermis or stomata. The conidiophores bear single conidia which are cylindrical, densely granular, hyaline, single celled with oil globules and blunt ends. The conidiophores and conidia formed between numerous setae which are dark brown, septate, stout, tapering upwards and measuring 75-100 x 2-6 µm. Disease Cycle: The primary infection of the fungus is started from the infected seed materials which carry fungal inoculum on the scales of rhizomes. The secondary spread of the disease is through air, water and other biological and physical means. The disease rapidly spread during rainy season with shade. The fungal pathogen also infects chilies and transmitted through seed borne infections, if the crop rotation is used with this crop the fungus perpetuates easily year after year.  Disease Management: The diseased leaves of host plants should be removed and burnt. The seed material should be taken from disease free areas and treated with organomercurials before planting. The excess shade from mixed cropping should be avoided. The spray of timely interval of Blitox 50, Bordeaux mixture, Cupravit, Dithane Z-78, Fytolan and Perenox effectively control the disease.