Etiology of stem bleeding disease of coconut (Cocos nucifera L.) in the Philippines

The cause of the infectious disease was determined as Thielaviopsis paradoxa (de Seynes) von Honel. The initial symptom is the appearance of a reddish brown or rust colored liquid which oozes out from the diseased stem. Later the oozing ceases and the reddish brown areas become black. The extent of damage of naturally infected palm depended on age. In young palms, extensive damage of internal tissues take place in the central core of the stem. In older palms, damage is confined to the bark and seldom involves the central core of the stem. The appearance of characteristic lesions at the point of inoculation appeared similar to these found in naturally infected palms with reddish brown tissues at the center surrounded by a yellowish zone. In pathogenicity test using mycelial agar block and injection of inoculum suspensions, both inocula produced typical symptoms at the inoculation point. However, the injection of inoculum suspensions resulted in a larger area of decayed internal tissues. Four inoculation trials were done to confirm the pathogenicity of the pathogen. All inoculation experiments reproduced typical symptoms of the disease. Wounding was essential for occurrence of stem bleeding infection. The shape and color of the Conidiophores and conidia of T. paradoxa isolated from coconut were similar to those isolated from black rot of pineapple. Conidiophore were slender, separate, hyaline and phialidic when young but pale brown when old. Two kinds of conidia, phialospores (thin-walled) and aleuriospores (thick-walled) were formed by each T. paradoxa isolate from infected coconut. The size of phialospores ranged from 7.2-13.2 u and aleuriospores ranged from 11.8-19.4 u, respectively, while the Medina isolate had the lowest measurements of both phialospores and aleuriospores (7.2 u and 11.8 u)