Bird's Eye Spot Disease (Cercospora theae) in Tea Estates of South India

摘要

Prevalence of the leaf spot disease in tea estates of South India among 38 clones and seedlings that are widely cultivated for commercial purpose of manufacturing tea was studied. The disease was surveyed in 13344 hectares using quadrates sampling on bushy canopy. The disease severity was more on UPASI clones and areas like Wynaad and Central Travancore of Kerala were severely affected by the disease. UPASI clones such as UPASI-3, 17, 19 and 25-27, and Sri Lankan clones, like TRI-2024 and TRI-2025 showed less than 30% disease index. The popular private estate clones such as SA-6, BSS-1, ATK-1 and BSB-1 were tolerant to the disease. The disease severity of tea clones depended on the sandy loam soil type and severity of drought in the respective planting districts. The causal agent of Bird's eye spot disease in tea plants was isolated on PDA and identified as Cercospora theae Petch. Three isolates were obtained from the infected tea leaves in Koppa area of Karnataka (KC10), Munnar of Kerala (MC24) and Valparai of Tamil Nadu (VC38). All the isolates showed minor variations in terms of mycelial growth, culture characteristics and in vitro life cycle. The pathogen could invade the leaf tissue by both inter-cellular and intra-cellular invasions. C. theae produced erupting perithecium initially in the upper epidermis followed by lower epidermis in late infection stage. Perithecia were orange red whose conidia were cylindrical, 1-3 septa and produced by apical budding and its size varies from 38-68 x 4-5 mu m. Pathogenicity of the three isolates were confirmed by their virulence in potted plants. Tthe life cycle of the three isolates in detached leaves varied among isolates ranging from 19 d in MC24 to 21d in KC10 and VC38.