In vitro studies of lactic acid bacteria against the causative agent of papaya dieback disease

Papaya is an economically significant fruit crop grown in Malaysia. Nevertheless, the outbreak of Papaya Dieback disease has caused major threats to the papaya plantation for almost a decade as effective treatment found to date has been limited. Endophytic bacteria have been used as biological control agent against several plant diseases. This study proposed that bacterial endophytes isolated from papaya plant might be used as biological alternative to synthetic bactericide to restrain this disease. The aim of this study is to find an effective microorganism to suppress Papaya Dieback disease. In this study, a total of 230 bacterial endophytes with antagonistic activities against Erwinia mallotivora were isolated from seeds and sarcotesta of two papayas (Carica papaya L.) collected from Sabak Bernam (PPS) and Perak (PPK) through rapid screening using Agar Overlay method. Twenty-eight pure isolates from the respective PPS and PPK showed significant inhibitory effect against Erwinia mallotivora as revealed by Agar Disc Diffusion technique. PPKSD19 showed the highest value of inhibition zone at 21.7 mm during in vitro screening on MRS agar. The isolates were characterized as Gram-positive rods, cocci or coccobacilli, catalase - negative and positive in acidity test, suggesting that they are potentially Lactic Acid Bacteria. API 50 CH profiles and 16S rRNA sequencing allowed identification of bacteria as Weissella sp. and Lactococcus sp. The selected high-performing endophytic bacteria will be investigated for their synergistic activities and bacteriocin-production. Their effects on infected papaya plant will be tested under greenhouse experiment. Our findings suggest that Carica papaya L. seed-borne bacterial endophytes could potentially be applied as biological control agent to inhibit Papaya Dieback disease

Biological control of Erwinia mallotivora, the causal agent of papaya dieback disease by indigenous seed-borne endophytic lactic acid bacteria consortium

Dieback disease caused by Erwinia mallotivora is a major threat to papaya plantation in Malaysia. The current study was conducted to evaluate the potential of endophytic lactic acid bacteria (LAB) isolated from papaya seeds for disease suppression of papaya dieback. Two hundred and thirty isolates were screened against E. mallotivora BT-MARDI, and the inhibitory activity of the isolates against the pathogen was ranging from 11.7–23.7 mm inhibition zones. The synergistic experiments revealed that combination of W. cibaria PPKSD19 and Lactococcus lactis subsp. lactis PPSSD39 increased antibacterial activity against the pathogen. The antibacterial activity was partially due to the production of bacteriocin-like inhibitory substances (BLIS). The nursery experiment confirmed that the application of bacterial consortium W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39 significantly reduced disease severity to 19% and increased biocontrol efficacy to 69% of infected papaya plants after 18 days of treatment. This study showed that W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39 are potential candidate as biocontrol agents against papaya dieback disease

Biobleaching of sago waste using xylanolytic Aspergillus sp. for potential use in handsheet preparation

Bio-bleaching of sago 'hampas' is completed with hemicellulolytic enzymes (xylanases) which hydrolyze hemicelluloses (xylan) in pulp. Aspergillus xylanases are usually used in bio-bleaching of pulp. Three different strains locally isolated of Aspergillus sp. is used in this research, namely Aspergillus flavus NSH9, AspergilJlus niger PANl and Aspergillus versicolor FPI3. The general aim of this study was to screen for Aspergillus sp. that produces the most xylanase and less cellulase or xylanase free cellulose of enzyme for potential application in enzymatic biobleaching of sago'hampas' pulp in paper making. In order to achieve this, solid-state fermentation (SSF) of sago waste using selected Aspergillus sp. for xylanase production was performed. The xylanase produced was extracted and assayed to be utilized for bio-bleaching of sago 'hampas' pulp. Enzymatic bio-bleaching on sago 'hampas' was carry out to yield a good quality paper in terms of brightness from enzymatic pre-treated sago 'hampas '. In this study, A. flavus NSH9 showed moderate enzyme activity with average diameter of clearing zone 2.95 cm on MEA medium and 3.1 cm on corn cob agar during plate screening. Subsequently, it showed the highest xylanase producing strain, with least amount of cellulase activity during submerged fermentation (quantitative screening). In SSF, extracellular xylanase activity ofA. flavus NSH9 reached a maximum (0.597 U/ml) after 5 days of incubation which also revealed the most reduced Kappa number than controls (15.094 points)