Identification of Quorum Quenching Bacteria and Its Biocontrol Potential Against Soft Rot Disease Bacteria, Dickeya Dadantii

Dickeya dadantii is one of newly found bacteria causing soft rot on orchids in Indonesia. Infected plants showed severe rot rapidly only in few days. An effort to control the bacteria was conducted by utilizing selected quorum quenching (QQ) inducer bacteria which produce AHL-lactonase by aiiA gene. The aims of this research were to screen and identify of quorum quenching bacteria, and also assayed their biocontrol potential ability against D. dadantii in laboratory. The screening of QQ bacteria was achieved using the anti-QS test, anti-microbial activity, and detection of aiiA gene using specific primer. The determination of the ability against D. dadantii was done using the soft rot assay on potato and orchid. Among thirty one bacteria isolates screened, four isolates (in succession namely B37, BT2, GG3, and GG6) were selected to control D. dadantii. All of these bacteria showed QQ ability to suppress the virulence of D. dadantii infection on orchids, significantly. Based on nucleotide sequences of 16S ribosomal RNA, those of bacteria isolates had the highest identity with Brevibacillus brevis, Bacillus cereus ATCC14579, Bacillus cereus ATCC14579 and Bacillus thuringiensis ATCC 10792. Brevibacillus brevis was reported for the first time as QQ bacteria in this study

Efektivitas Isolat-Isolat Bacillus sebagai Pengendali Penyakit Bulai dan Pemacu Pertumbuhan Tanaman Jagung pada Kondisi Terkontrol

The main disease in maize is downy mildew caused by the fungus Peronosclerospora spp.. This pathogen can cause yield losses of up to 100%. Therefore, efforts to control this disease are continuously carried out, including technical culture, assembly of resistant plants, and use of synthetic fungicides. At the farm level, the use of metalaxyl, synthetic fungicides is the most common practice. On the other hand, it has been reported that some Peronosclerospora groups are starting to become resistant to metalaxyl. These problems lead to the need for alternative controls, for example with biological agents. Biological agents from bacterial groups have been developed to control plant disease, but for downy mildew is still limited. The purpose of this study is to screen and test Bacillus spp. ability to suppress downy mildew and promote the growth of maize. The assay was carried out on seeds by invitro to investigate growth-promoting reactions and also testing under controlled conditions in greenhouses to investigate the suppression ability of downy mildew disease development. The results showed B. polymyxa strain BP18, Bacillus subtilis strain BS41, Bacillus sp. strain BT1, and Bacillus sp. strains can stimulate the growth of corn seedlings and suppress downy mildew. The best isolate in suppressing downy mildew was Bacillus sp. strain BT1 with the smallest AUDPC value (3.94) and the highest protection index (82.71%). It is hoped that these results will find potential isolates and have the potential to be developed into biopesticides and biofertilizers

The Incidence and Severity of Downy Mildew Disease on Local Madurese Maize Crops in Sumenep District, East Java, Indonesia

In Madura island, corn is the main commodity that is widely planted with an area of 301,725 ha or about 30% of the area of maize in East Java. Madura Island has local cultivars, such as: Tambin, Talango, Guluk-guluk, Manding, and Kretek. Efforts to increase production are continuously being made, starting from improving varieties until managing plant pests. One of the main diseases in maize is downy mildew. However, information about the incidence, incidence, severity, and species that cause downy mildew in local cultivars has not been reported. So, this study aims to identify the causes of downy mildew in local cultivars of Madura and disease severity in the field. The research method is a survey on local maize centers. Sampling was done by using the diagonal sampling method. Each plant sample was observed for symptoms of disease and scoring to calculate the value of disease severity. Fungi identification was carried out by microscopic observation of the fungus. The results showed that the cause of downy mildew in Madura local maize in Sumenep Regency was P. maydis. The highest incidence, disease severity, and AUDPC value after 4 MST were found in Guluk-guluk cultivars in Padangdangan Village, but had the lowest disease progression rate values. Meanwhile, the highest rate of disease progression was found in the Manding cultivar in Mandala Village. Based on the resistance category, Talango cultivar had the best resistance when compared to other cultiva