Journal of Phytology 2023, 15: 7-11 doi: 10.25081/jp.2023.v15.7641 https://updatepublishing.com/journal/index.php/jp J Phytol • 2023 • Vol 15 7 INTRODUCTION Oil palm cultivation in Southeast Asia has severe problems with basal stem rot (BSR) disease caused by fungi of the genus Ganoderma (Siddiqui et al., 2021). Ganoderma boninense has been the most identified species associated with the BSR (Midot et al., 2019). BSR fungi decay the xylem tissue, stopping the translocation of water and nutrients and resulting in plant death (Rees et al., 2009). In the endemic area of Sumatra, Indonesia, the disease caused plant mortality and reduced plantation stand by 31-67% (Pujianto et al., 2016; Riyanto et al., 2020). Both direct loss of plantation stands and reduced yield of diseased palms contribute to the yield loss caused by the disease. BSR disease was predicted to cause losses of oil palm yields by 68% in an endemic area (Kamu et al., 2021). Cultural practices and mechanical and chemical treatment have been introduced and applied as control measures for BSR control but have not proved satisfactory (Siddiqui et al., 2021). Oil palm plantations commonly operate large-scale monoculture cropping practices for 25-30 years of a single generation plantation. A long-term monoculture practice of genetically homogenous populations is vulnerable to increasing infection pressure by soil-borne fungal pathogens (Yang et al., 2020). The marked increase in BSR infestation over the generation of monoculture oil palm plantations has been widely reported in Indonesia (Priwiratama et al., 2020) and Malaysia (Kamu et al., 2021). Mixed cropping practices have long been known to contribute to the control of soil-borne diseases (Yang et al., 2014; Gibson & Nguyen, 2021). Mixed cropping with understory herbaceous plants has suppressed the white root disease of rubber trees caused by a polypore fungus, Rigidoporus microporus (Situmorang et al ., 2007; Silva et al ., 2014). Water yam (Dioscorea alata) is a perennial herbaceous plant usually grown for its tuber as an understory of smallholder plantation crops, including rubber (Yulianti et al., 2017) and oil palm (Teuscher et al., 2016). Under pot experiments, water yam could reduce the mycelium growth and viability of R. microporus and accelerate the decaying of rubberwood colonized by the white root fungus (Yulianti et al., 2017). This study aimed to determine the effects of mixed cropping with water yam on the infection and survival of Ganoderma boninense on oil palm seedlings. Effect of mixed cropping of water yam (Dioscorea alata) on Ganoderma disease of oil palm Rahmad Fadli 1 , Suwandi Suwandi 2 *, Nurhayati Damiri 2 , A. Muslim 2 , Chandra Irsan 2 1 Crop Sciences Graduate Program, Faculty of Agriculture, Universitas Sriwijaya, Palembang 30139, Indonesia, 2 Department of Plant Protection, Faculty of Agriculture, Universitas Sriwijaya, Indralaya, 30662, Indonesia ISSN: 2075-6240 Copyright: © The authors. This article is open access and licensed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/) which permits unrestricted, use, distribution and reproduction in any medium, or format for any purpose, even commercially provided the work is properly cited. Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. Research Article ABSTRACT Basal stem rot caused by a soil-borne fungus, Ganoderma boninense, is one of the most severe diseases in monoculture oil palm plantations. The effect of mixed cropping with water yam on infection and inoculum potential of Ganoderma boninense on oil palm seedlings was assessed under a pot experiment. Plant inoculation with rubber woodblock (RWB)-colonized Ganoderma induced disease on both mixed cropped hosts (multiple host infection), but with less severe root necrotic and less plant mortality relative to inoculation on a single oil palm host. Inoculum potential of the pathogen was reduced under mixed cropping, as shown by more considerable RWB decay than a single host, and the fungal survival was suppressed to be 55% for 12 months trial. Water yam mixed cropping did not interfere with the growth of the inoculated oil palm seedling. This study revealed the multiple host infection under mixed cropping with water yam suppressed damage caused by Ganoderma boninense to oil palm as the primary host. KEYWORDS: Basal stem rot, Ganoderma boninense, mixed cropping, water yam Received: April 13, 2022 Revised: February 15, 2023 Accepted: February 16, 2023 Published: February 24, 2023 *Corresponding Author: Suwandi Suwandi E-mail: suwandi@unsri.ac.id