Fig 1.
In vitro screening of endophytic bacteria for antagonistic activity using agar well diffusion method against E. mallotivora BT-MARDI, the causative agent of papaya dieback disease.
(A) Inhibition zones formed by bacterial isolates isolated from papaya sample located in Perak (PPK); (B) Inhibition zones formed by bacterial isolates isolated from papaya sample located in Selangor (PPS). Values are means of three replications. Error bars show standard deviation. Bars marked with an asterisk indicate a significant antagonistic activity compared to positive control (Ampicillin) by Kruskal-Wallis test (N = 114, p < 0.05).
Fig 2.
Dendrogram showing clustering and relationships of 24 potential isolates used in the study based on API 50 CH fermentation of 49 carbohydrates.
The analysis was performed by calculating the Euclidean distance and the associations of isolates were constructed using the single linkage method (Nearest neighbour) in the IBM SPSS Statistic 22.0.
Fig 3.
Phylogenetic tree showing the relative position of selected endophytic LAB isolates based on 16S rDNA partial sequences, using the Neighbor-Joining method.
Pseudomonas aeruginosa was used as an outgroup. Bootstrap values of 1000 replications are displayed at the nodes of the tree, using MEGA 6. The scale bar corresponds to 0.02 units of the number of base substitutions per site. The GenBank accession numbers for nucleotide sequence data are shown in brackets.
Table 1.
Identification of endophytic LAB isolates isolated from papaya seeds using API 50 CH and 16S rDNA sequencing.
Fig 4.
In vitro compatibility test between W. cibaria PPKSD19 and ten different isolates of L. lactis subsp. lactis.
All L. lactis subsp. lactis isolates (PPSSD7, PPSSD38, PPSSD39, PPKSD7, PPKSD8, PPKST1, PPKST3, PPKST4, PKST5 and PPKST11) were streaked circularly while the W. cibaria PPKSD19 isolate was spread on the MRS agar plate.
Table 2.
Synergistic effect of W. cibaria and L. lactis subsp. lactis applied as single treatment or as consortia on inhibiting the growth of E. mallotivora BT-MARDI using agar well diffusion method.
Table 3.
The effect of antibacterial substance produced by two LAB isolates with protease and heat treatment on inhibitory activity against E. mallotivora BT-MARDI.
Fig 5.
Disease severity of papaya dieback after treatment with single and mixture of W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39.
(A) 6th; (B) 18th; (C) 30th day after inoculation with bacterial antagonists and E. mallotivora BT-MARDI. The data are the means of three replications per treatment with five plants per replication. Error bars show standard deviation of three replicates of each treatment. The means followed by different letters within a day of measurement indicate significant difference between treatments (ANOVA; p < 0.05).
Fig 6.
Biocontrol efficacy of papaya dieback after treatment with single and mixture of W. cibaria PPKSD19 and L. lactis subsp. lactis PPSSD39.
(A) 6th; (B) 18th; (C) 30th day after inoculation with bacterial antagonists and E. mallotivora BT-MARDI. The data are the means of three replications per treatment with five plants per replication. Error bars show standard deviation of three replicates of each treatment. The means followed by different letters within a day of measurement indicate significant difference between treatments (ANOVA; p < 0.05).