AGRIVITA Journal of Agricultural Science www.agrivita.ub.ac.id AGRIVIT AGRIVITA Journal of Journal of Agricultural Science. 2019. 41(1): 129-138 129 INTRODUCTION Cocoa (Theobroma cacao L.) is an important estate-crop commodity for the food chocolate industry, cosmetics, beverages, and other derivative products (Lima, Almeida, Rob Nout, & Zwietering, 2011). Currently, Indonesia is the third largest producing country of cocoa commodity in the world (ICCO, 2018). The production of cocoa in Indonesia has the potential to increase if the limiting factor can be minimized. One of several limiting factors in cocoa cultivation is the attack of vascular- streak dieback (VSD) pathogen that causes yield loss up to 60 %, it even causes the plants to die out (Sukamto & Junianto, 1986). The spreading of VSD pathogen’ attacks have been found in the center of cocoa production area, especially in Sulawesi, and the total area attacked by VSD was around 950 thousand hectares in 10 provinces (Khaerati, Wiyono, & Tondok, 2016). Several efforts to control the VSD pathogen attacks are by planting resistant plant material to VSD and by applying the concept of Good Agricultural Practices (GAP). Under VSD pathogen infection, the phenotypic of plant is controled by genetic factor, environmental factor and both interactions. However, the severity of VSD is mostly infuenced by the level of plant resistance. The statement reported by Anita- Sari & Susilo (2014) stated that under the same enviromental condition, the VSD disease severity was genetically controled, that resistant clones is lower than susceptible clones. Santoso, Miftahudin, Sulistyaningsih, & Wiyono (2017) reported that Scavina 6 and Sulawesi 01 clones worked as VSD- resistant clones, while TSH 858, ICS 13, and ICS 60 was VSD-susceptible clones. ARTICLE INFO Keywords: Cacao Fungal Staining Physiological Vascular Streak Dieback Article History: Received: 9 October, 2017 Accepted: 16 January, 2019 * ) Corresponding author: E-mail: tisantoso.iccri@gmail.com ABSTRACT The physiological response of cocoa plants under VSD infections is still limited because there is no method in artifcial inoculation since Oncobasidium theobromae was reported as parasitic obligates. The investigation of correlation between cocoa responses and VSD attack becomes important information to fgure out the effect of decreased productivity as the consequences of the physiological damages. The objective of this research was to describe the pathogen infection and the symptom of VSD through fungal staining method and to asses the changes of some physiological aspects (chlorophyll and gass exchange character) under VSD pathogen infection. This study was conducted in Kaliwining experimental station, ICCRI, Jember, East Java, Indonesia. The result of the study indicated that late infection stage caused chlorophyll degradation, decreasing transpiration rate, and increasing temperature in both tolerant clone (Scavina 6) and susceptible clone (TSH 858). The rate of photosynthesis, stomatal conductance, and concentration of CO2 in susceptible clone (TSH 858) showed a drastic decrease when infected by VSD pathogen than that of in healthy plants. In resistant clone (Scavina 6), photosynthesis rate, stomatal conductance, and concentration of CO2 showed no signifcant decrease when infected by VSD pathogen compared to that non-infected condition. ISSN: 0126-0537 Accredited First Grade by Ministry of Research, Technology and Higher Education of The Republic of Indonesia, Decree No: 30/E/KPT/2018 Cite this as: Santoso, T. I., & Zakariyya, F. (2019). Several physiological changes of cocoa (Theobroma cacao L.) in response to vascular streak dieback diseases. AGRIVITA Journal of Agricultural Science, 41(1), 129-138. https:// doi.org/10.17503/agrivita.v41i1.1668 Several Physiological Changes of Cocoa (Theobroma cacao L.) in Response to Vascular Streak Dieback Diseases Teguh Iman Santoso *) and Fakhrusy Zakariyya Indonesian Coffee and Cocoa Research Institute, Jember, East Java, Indonesia