SlyA, a MarR family transcriptional regulator, controls an assortment of biological functions in several animal-pathogenic bacteria. In order to elucidate the functions of SlyA in the phytopathogen Dickeya dadantii (formerly Erwinia chrysanthemi) 3937, a slyA gene deletion mutant (denoted ⌬slyA) was constructed. The mutant exhibited increased sensitivity to sodium hypochlorite, the cationic antimicrobial peptide polymyxin B, and oxidative stress. The mutant showed reduced production of pectate lyase and exopolysaccharide and an inability to form a pellicle. The mutant lacking a functional slyA gene showed a significantly reduced ability to cause maceration of potato tubers. Accordingly, the mutant exhibited significantly reduced bacterial growth and failed to hyperinduce pectate lyase production in planta. Introduction of a plasmid containing slyA into the ⌬slyA mutant caused all of these phenotypes to recover to wild-type levels. These results suggest that SlyA plays an important role in virulence to plants by positively regulating the expression of multiple pathogenicityrelated traits of D. dadantii 3937.

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Recently, most of sonokembang, Pterocarpus indicus trees are dying in Malang. In 2012, the death rate of trees reached ca. 11%. In addition, death of trees spread to other regencies in East Java. Euplatypus parallelus is a specific species of ambrosia beetles that were the causal agents to the dying and wilting of sonokembang trees in Malang. Wilting is caused mainly by the pathogenic fungi carried by ambrosia beetles. To confirm the microbial communities related to E. parallelus that attack sonokembang, E. parallelus and some attacked trees were collected in Malang city. Isolation and identification of these species were conducted at the Laboratory of Mycology, Faculty of Agriculture, University of Brawijaya and Laboratory of Molecular Biology, Islamic State University, Malang. Results showed that there were nine microbes including five genera of fungi, two genera of yeasts and one genus of bacterium were identified. The microbial communities that were found namely Aspergillus spp., Penicillium spp., Trichoderma spp., Fusarium spp., Acremonium spp., Gliocladium spp. (fungi), Streptomyces spp. (bacteria), Saccharomyces spp., and Candida spp. (yeast).

Abstract. Inayati A, Sulistyowati L, Aini LQ, Yusnawan E. 2020. Trichoderma virens-Tv4 enhances growth promoter and plant defense-related enzymes of mungbean (Vigna radiata) against soil-borne pathogen Rhizoctonia solani. Biodiversitas 21: 2410-2419. Trichoderma virens has been studied for its ability to control various soil-borne pathogens as well as to induce plant resistance. The ability of T. virens control R. solani and its capability to induce resistance was evaluated in two different genotypes of mungbean (Vigna radiata (L.) R. Wilczek). Plant growth-promoting capability and production of plant defense-related enzymes during plant-pathogen-Trichoderma interaction were investigated. Pathogen infection caused the morphological and biochemical changes as well as increased plant defense enzymes activity such as peroxidase, polyphenol oxidase, PAL, phenolics, and flavonoid compared to control uninoculated plants. T. virens improved mungbean seedling growth in terms of increased total biomass, root weight, and root length as well as improved chlorophyll content and IAA-synthase from leaves and roots. T. virens treatment alone or in the presence of pathogen-induced mungbean defense-related enzymes indicated by the increasing of PO and PPO activity, and higher accumulation of total phenolic and flavonoid content. Although most of plant induced resistance parameters showed low and non-significant in direct single-factor comparison, Pearson’s correlation showed there was a positive correlation between plant growth promoter compounds (IAA and chlorophyll) with plant defense-related enzymes (total phenol, and flavonoid content). T. virens treatment can induce systemic defense response of mungbean seedling directly by increasing the activity of some defense-related enzymes, and indirectly by improving plant health, and promoting plant growth. In conclusion, T. virens-Tv4 has potential to be developed as bio-control agents to control R. solani as well as to induce mungbean resistance.

In 2011, we found a new bacterial disease characterized by wilt, dwarf and blight symptoms on sweet corn in Batu, East Java, Indonesia. The objective of this study is to characterize the causal agent of the disease. In this study, several assays were conducted, including hypersensitive response, pathogenicity, physiological and biochemical characteristics, PCR detection using two specific species primer pairs for Pantoea stewartii pv. stewartii, and homology analysis of 16S rRNA gene sequence. Four Gram-negative, non-motile, facultative anaerobic bacteria were isolated from the diseased tissue. Only two strains, BD1 and BB2, gave positive result in hypersensitive reaction, pathogenicity, and Koch's postulate assays. BB2 and BD1 strains also showed positive results in the PCR amplification using specific primers derived from the P. stewartii subsp. stewartii 16-23S gene region but showed negative result when using primers derived from P. stewartii subsp. stewartii hrpS gene region. Sequence of partial 16S rRNA gene of BD1 and BB2 showed highest homology at 96% to P. stewartii subsp. stewartii strain ATCC 8199 (NR. 044800.1). This results suggest that bacterial pathogens isolated from sweet corn in Batu were strains of Pantoea spp.