Analisis keragaman genetik Phytophthora palmivora penyebab busuk buah pada kakao di Indonesia

Abstract

The objectives of this research were to determine the disease intensity of pod rot in cocoa plantations in Lampung Selatan, Cianjur and Jember, to identify Yl1ytophlhora species amclung cocoa in Indonesia, to evaluate the virulence of isolates of P/yiophthom sp. and the resistance of selected cocoa clones, and to analyse genetic variation of isolates of Phytophthorca sp. collected from several cocoa producing provinces in Indonesia. Monitoring and evaluation of disease were carried out in Larnpung Selatan (Lampung), Cianjur (Jawa Barat) and Jember (Jawa Timur) using survey method llth purposive sampling technique. Development of disease was evaluated on the base of disease incidence and disease severity of cocoa pod caused by natural infection. Data were also collected through interview with farmers or plantation managers. The pathogen was identified based on morphological characteristics (colony type, hyphal swellings, production and diameter of chlamydospores, sporangiophore branching, shape and size of sporangia, caducity, pedicel length and papi llate) and on molecular c haractenstic using Internal Transcribed Spacer (ITS) technique. Test of virulence and resistance were conducted in the field using randomized complete block design, with 24 treatment combinations between six isolates of the pathogen from Sumatera Utara, Larnpung, Jawa Barat, Jawa Timur, Sulawesi Selatan and Sulaivesi Tenggara and four cocoa clcnes namely SCA12, DRC16, DR2 and GC7, and each replicated three times. Latent period, ex-tent of blight and infection rate were recorded to determine degree of virulence of the pathogen and resistance of cocoa clones. Genetic variation was analysed using Randomly Amplified Polymorphic DNA (RAPD) and Amplified Frabment Length Polymorphism (AFLP) techniques. Disease incidence and disease severity in private plantation in Cianjur was higher than in smallholder plantation in Lampung Selatan and government plantation in Jember. That two variables were apparently affected by favourable environmental condition for deveIopment diseases especially high rainfall (32500 mmlyear) and high relative humidity (>90%), and low temperature (h27"C). Based on the morphological and molecular characteristics, all the 20 isolates that causing pod rot and stem canker were Phytup/rfhura pulrnivoru. Isolate from SuIa~vesi Tenggara had the higher virulence among isolates tested, followed by isolates from Jawa Timur, Sumatera Utara, Java Barat, Lampung and Sulawesi Selatan. Clone SCAlZ is the most resistant among the other clones tested, followed by DRC16, DR2 and GC7. There is different level of latent period, extent of blight and infection rate on the clones indicating that these were different physiological race among isolates. While Isolates of P. pulmivora showed low genetic variations, eventhough the isolates were from separated geographical origin. AFLP techque was more efticient, consistent and discriminative than RAPD technique.

Penelitian ini bertujuan untuk menganalisis intensitas penyakit busuk buah kakao di kebun akibat infeksi PL palmivora yang terjadi secara alami, melakukan identifikasi species Phytophthora yang menyerang tanaman kakao di Indonesia, melakukan evaluasi tingkat virulensi beberapa isolat P. palmivora dan resistensi beberapa klon kakao serta melakukan analisis keragaman genetik beberapa isolat P. palmivora yang dikumpulkan dari berbagai provinsi penghasil kakao di Indonesia.