Etiology and chemical control of stem rot of salago (Wikstroemia lanceolata L.) and the survival and host range of its pathogen

Stem rot of salago was characterized by browning, reddening and drying of the stem followed by yellowing and defoliation formation of numerous stroma containing pycnidia on the stem surface was noted as the disease progressed. The bark became brown and rotted. Death of the plant occurred when the fungus attacked the base of the plant. Wounding was essential to stem rot development. Mycelia was efficient in rot development than pycnidiospores. Stem inoculated with Botryodiplodia theobromae produced symptoms similar to naturally-infected stem. The shape of pycnidia and pycnidiospores in culture, inoculated and naturally-infected stem were similar but not their sizes. The isolated causal fungus was identified as Botryodiplodia theobromae Pat. Mycelial growth, pycnidia and pycnidiospore yield were affected by agar media light, pH, and temperature. Yeast extract agar, light, UV light, 25 C and slightly acidic to slightly alkaline conditions enhanced sporulation of B. theobromae. Botryodiplodia theobromae germinated best at 25 C to 30 C, at 36 to 98% relative humidity and produced the longest germ tube at 20 C and 98% RH. It survived longer in diseased tissue and in yeast extract agar slant than in sterile soil and produced disease on atis, citrus, mango, papaya, jackfruit, cassava tuber, cotton, mungbean, banana, cacao, cowpea, and corn but not on gabi and sweet potato. Pycnidiospores of B. theobromae germinated on the surface of salago stem 2 hr after inoculation. Hyphae entered through the epidermal cells and spread intercellularly and intra-cellularly causing necrosis of the parenchyma and phloem cells disintegration and collapse of the fibers. Uniloculated and multiloculated pycnidia were formed on the inoculated salago stem. All of the four salago species tested was resistant to stem rot. Benomyl, Thiophanate methyl, Captan, Mancozeb, and Maneb were effective in suppressing mycellial growth of B. theobromae in culture and in protecting salago plants to infection. None of the fungicides used caused complete arrest of the fungus when applied as eradicant.