<![CDATA[Trichoderma viride is a microorganism that is commonly found in moist soil and can be isolated from the root area of the shallot plant (Allium ascalonicum L.). The study aim was to determine the mechanism and the difference in percentage of inhibitory power by Trichoderma viride in inhibiting growth of Alternaria porri pathogen at pH 4.8 and 7. The descriptive method was used by descriptive method to isolate Alternaria porri and Trichoderma viride fungi and then purified, and the experimental method tested Trichoderma viride fungal antagonists against Alternaria porri with two PDA media treatments pH 4.8 that observed for 3 days and pH 7 observed for 4 days. The results of the percentage of inhibitory power on the day 1,2,3 were 9%, 34.2% and 35% (pH 4.8), and the results of the percentage of inhibition power of the day 1,2,3 and 4 were 1.9%, 29.9%, 35% and 39.4% (pH 7). The inhibition mechanism of Trichoderma viride in inhibiting Alternaria porri fungi through the stages of antibiosis, parasitism and lysis. Keywords: Trichoderma viride, Alternaria porri, shallot plants, pH 4,8 and pH 7. ABSTRAK Jamur Trichoderma viride merupakan mikroorganisme yang umum dijumpai dalam tanah yang lembab dan dapat diisolasi dari daerah perakaran tanaman bawang merah (Allium ascalonicum L.) Penelitian bertujuan untuk mengetahui mekanisme dan perbedaan persentase daya hambat oleh jamur Trichoderma viride dalam menghambat pertumbuhan patogen Alternaria porri pada pH 4,8 dan 7. Metode yamg digunakan metode deskriptif dengan mengisolasi jamur Alternaria porri dan Trichoderma viride lalu dimurnikan, dan metode eksperimen melakukan uji antagonis jamur Trichoderma viride terhadap Alternaria porri dengan dua perlakuan media PDA pH 4,8 yamg diaamati selama 3 hari dan pH 7 yang diamati selama 4 hari. Hasil persentase daya hambat pada hari ke 1,2,3 yaitu 9%, 34,2% dan 35% (pH 4,8), dan hasil persentase daya hambat hari ke 1,2,3 dan 4 yaitu 1,9%, 29,9%, 35% dan 39,4% (pH 7). Hal ini diketahui bahwa hasil terakhir persentase daya hambat 35% (pH 4,8) dan 39,4% (pH 7). Mekanisme Penghambatan Jamur Trichoderma viride dalam menghambat jamur Alternaria porri melalui tahap antibiosis, parasitisme dan lisis. Kata kunci: Trichoderma viride, Alternaria porri, tanaman bawang merah, pH 4,8 dan pH 7.]]>
