Judul: Bacterial Wilt Disease of Eucalyptus pellita: Disease Trigger Factors, Pathogen and Host Plants Diversity
Abstrak: The productivity of forest plantations such as Eucalyptus pellita in Indonesia is low, one of which is severely affected by bacterial wilt disease. The serious threat of this disease in Indonesia began in 2006, which attacked lowland eucalyptus plantations in Jambi. The disease has been widely spread in Riau, South Sumatra and East Kalimantan provinces. However, studies of bacterial wilt disease on E. pellita in Indonesia are still inadequate, particularly regarding to the integration of site and genetic factors; thus, a comprehensive study is required. The main objective of this study was to analyze the dominant variables of sylviculture, soil properties, and climate factors that can trigger bacterial wilt disease epidemics on eucalypts; identify and describe the phenotypic and genotypic diversity of the causal agent; characterize pathogen strains that have the highest virulence level based on phenotype and genotype diversity; evaluate the resistance of eucalyptus progenies and clones, and analysis SSR markers related to eucalyptus resistance to bacterial wilt disease. The surveys in four provinces in Indonesia showed that bacterial wilt incidence on E. pellita varied from 0–33.5% in plants aged 2–23 months. The initial disease symptoms are yellowing of the leaves followed by branches wilting and causing plant death. Color changes, turning blackish-brown, occurred in the inner cortex of the stem associated with bacterial ooze. Analysis of the triggering factors that contribute to the emergence of bacterial wilt disease was carried out on silvicultural factors (e.g. topography, site classification, diversity eucalyptus clones, seedling propagation technique, plant age, crop rotation, weed cover, incidence of root malformations, and expose to herbicide drift), soil properties (e.g. pH, C-org, N-total, P-available, S-total, Ca2+, Mg+, K+, Na+, and % soil texture) and climate variables (e.g. temperature, humidity, and rainfall). In silvicultural factors, three of the nine variables showed a significant correlation to disease incidence. The variables were plant age, eucalyptus clones, and root malformations incidence. The early growth of eucalyptus plants is a critical period of the disease epidemic, especially in susceptible. For the soil property factor, the soil texture variable is the dominant variable that partially associated with the disease incidence. The incidence of moderate and severe disease generally develops in clay loam soils. Meanwhile, for climatic factors, rainfall has a positive correlation with bacterial wilt incidence. Description of the diversity of pathogens that cause bacterial wilt is carried out by phenotypic and genotypic analyses. 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. All isolates were confirmed as Ralstonia species complex based on morphological characteristics and molecular studies using species-specific primers. These pathogen strains were dominantly classified as biovar 3 and 4 and had a high variation in virulence and EPS production (0.13 - 8.38 g/mL). Based on the alignment of the egl gene sequences, 29 strains of Ralstonia originating from E. pellita belonged to Phylotype I and were grouped into four sequevars (sequevars 14, 17, 18, 30) and one new sequevar 58. New sequevars were identified
Keyword: epidemi, silvikultur, Ralstonia pseudosolanacearum, klon tahan, marka molekuler