Productivity of forest plantation such as Eucalyptus pellita in Indonesia is strongly decreased by bacterial wilt disease (Ralstonia solanacearum Smith). However, studies of bacterial wilt disease on E. pellita in Indonesia is still inadequate, so several comprehensive research are required. This research was aimed to analyse the dominant silviculture factors and soil properties which can contribute to disease epidemiology. Observation on disease incidence was conducted by the transect method on 40 observation plots selected by the purposive random sampling in 4 provinces in Indonesia. Nine silviculture factors were collected by tracking the identity and the history of plot maintenance, while soil properties were analysed from soil samples. The correlation among disease incidence to silviculture factors and soil properties was carried out by chi-square and multiple regression analysis, respectively. Planting age, Eucalyptus clones, and root malformation were the top 3 of silviculture factors which has shown significant correlation to disease incidence. Early growth of Eucalyptus sp. plant was a critical period of the disease epidemic, especially in the susceptible clone. On the other hand, soil texture (percentage of sand, clay, and silt) were the dominant variables of soil properties which strongly affected the disease incidence.
Abstract. Siregar BA, Giyanto, Hidayat SH, Siregar IZ, Tjahjono B. 2021. Diversity of Ralstonia pseudosolanacearum, the causal agent of bacterial wilt on Eucalyptus pellita in Indonesia. Biodiversitas 22: 2538-2545. The Ralstonia species complex was initially classified into five races and five biovars but the classification could not accommodate the isolates' phylogenetic history or geographic origins. A phylotype and sequevar system is based on the geographic distribution and characteristics of endoglucanase (egl) and hypersensitive response and pathogenicity (hrp) gene sequences. This study aims to describe pathogen diversity of the causal agent of bacterial wilt on Eucalyptus pellita F. Muell. Pathogens were isolated from wilting seedlings and trees in several Eucalyptus plantations. The phenotypic diversity analysis included biovar, exopolysaccharide quantification and virulence tests, while genotypic diversity included phylotypes and sequevar determination based on egl gene sequences. A total of 35 strains were isolated from the field and nurseries of Eucalyptus in various locations. All isolates were confirmed as Ralstonia species complex based on morphological characteristics and molecular studies using species-specific primers. These isolates were dominantly classified as biovar 3 and 4 and had a high variation on virulence and EPS production. Based on the egl sequence's alignment, 29 strains of Phylotype I are grouped into four sequevar references (sequevars 14, 17, 18, 30) and new a sequevar 58. This study shows that strains of R. pseudosolanacearum causing bacterial wilt on E. pellita in Indonesia have high phenotypic and genotypic diversities.
Since its first introduction to the Indonesian forest plantations, eucalyptus has been associated with pests and diseases. As a component of integrated disease management, some biocontrol agents have been developed to manage eucalyptus diseases. Application of endophytic Trichoderma is a critical option in this effort; it has been demonstrated in other pathosystems that the fungus can improve seedling growth and health. This study aims to screen and evaluate the effect of endophytic Trichoderma isolates on the growth and health of E. pellita seedlings. Field isolation resulted in 43 endophytic Trichoderma isolates. The isolates have the antagonistic ability with varied percentages of inhibition of radial growth (PIRG) against Rhizoctonia sp. (4.2–48.6%); Cylindrocladium sp. (4.8–43.5%); and Fusarium sp. (3.3–52.2%). Based on the Analytical Hierarchy Process on the variables of the growth rate of the isolates and their ability to inhibit several fungal pathogens, the best six isolates were selected for further tests. In general, the use of single and/or a consortium of the isolates increases seedling height and reduces the mortality rate of the seedlings. In summary, the tested isolates can improve plant vigor, which would later make the plant more resilient against root and foliar diseases in plantations.
Bacterial wilt is one of major threats to eucalyptus plantations which may cause significant losses. Until now, study about bacterial wilt on Eucalyptus pellita in Indonesia is still very limited, especially about the presence of the pathogen on or in the seeds. This study aims to provide evidence of the existence of the R. solanacearum bacterium on or in E. pellita seeds. Detection of seed-borne bacteria is determined by several approaches such as (i) direct detection using universal and selective medium in the laboratory, (ii) nursery test, and (iii) species-specific molecular detection. Results of our study indicate that R. solanacearum can be detected from eucalyptus seeds using universal and selective medium in the laboratory, nursery test, and molecular-based detection using the Enrichment PCR method. The bacterial inoculum is also proven to exist both on the surface of and inside the eucalyptus seeds. This is the first report that R. solanacearum is a seed-borne pathogen in E. pellita seeds. Previous studies in different agricultural systems show that the effective method used to control the pathogen is through seed treatments using biological, physical, and chemical approaches.
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