[Pseudocercospora liebenbergii the cause of leaf spot disease on Rauwolfia serpentia

English. The experiment were conducted at Research Institute for Spice and Medical Crops from October 1995 to March 1996. The objective of the experiments were to identify the causal agent of leaf spot disease on Rauwolfia serpentina and some ecobiological aspects. The experiments were divided into two steps. The first step was observation on the disease intensity and identification of the causal agent. The second step was testing the effect of temperature and light on the mycelia growth and the germination of conidia and the survival of conidia at different ranges of relative humidity. The result showed that the pathogenic of the leaf spot disease is Pseudocercospora liebenbergii, newly reported of pathogenic fungus in Indonesia. The fungus infected leaf only. The disease intensity ranged between 0-85 percent of plant with the average 22.23 percent. The first symptoms i.e. light spots were observed 2-3 weeks after inoculation. Stroma were found on the upper and bottom of the oldest spots. The optimum temperature for fungal growth ranged between 20-28 deg. C. Continuous light was able to induce the growth of aerial mycelia but failed against the fungal rate. The germination of conidia occurred at temperature between 20-32 deg. C with an optimum of 24 deg. C. Conidia on the surface of the oldest leaf spots were still viable after the leaf were incubated for 48 hours at 55 percent relative humidity

unknown. Penelitian dilakukan di instalasi penelitian Cimanggu dan Laboratorium Hama dan Penyakit Balittro mulai Oktober 1995 sampai Maret 1996. Tujuan penelitian adalah mengidentifikasi patogen penyebab bercak daun pada tanaman akar tikus Rauwolfia serpentina dan mempelajari beberapa aspek ekobiologinya. Kegiatan penelitian terdiri dari dua tahap. Tahap pertama meliputi pengamatan tingkat serangan dan identifikasi jamur patogen, sedangkan pada tahap kedua menguji pengaruh suhu dan cahaya terhadap pertumbuhan miselia dan perkecambahan konidia serta daya tahan hidup konidia pada beberapa tingkat kelembaban. Hasil identifikasi menunjukkan patogen penyebab penyakit bercak daun adalah Pseudocercospora liebenbergii, merupakan jamur patogen yang baru dilaporkan terdapat di Indonesia. Jamur tersebut hanya menyerang daun dengan tingkat serangan berkisar 0-85 persen pertanaman dengan rata-rata 22.23 persen. Gejala tampak berupa bercak transparan terjadi 2-3 minggu setelah diinokulasi. Pada permukaan atas/bawah gejala yang telah lanjut dibentuk tubuh buah jamur. Suhu optimum untuk pertumbuhan jamur pada media agar kentang dekstrosa berkisar antara 20-28 derajat C. Pemberian cahaya merangsang pembentukan miselia udara dan tidak berpengaruh pada kecepatan pertumbuhan. Perkecambahan konidia dapat terjadi pada kisaran suhu 20-32 derajat C, optimum pada 24 derajat C. Konidia yang terdapat pada permukaan daun sakit ternyata tetap hidup setelah daun disimpan selama 48 jam pada kelembaban 55 persen