Characterization of Dickeya fangzhongdai KPJ 1, the causative agent of soft rot of Aglaonema ‘MARIA’ and its biological control

Aglaonema ‘Maria’ is a popular indoor plant, which is vulnerable to soft rot, a bacterial disease that causes serious losses in nurseries and is a major barrier in producing export-quality planting materials. Biocontrol agents are the best eco-sustainable alternatives for agrochemicals in managing plant diseases. This study was focused on isolating the causative agent of soft–rot disease of Aglaonema ‘Maria’ and evaluating the biocontrol potency of Bacillus velezensis strain DCJ 2 (DCJ 2) in situ under different delivery methods. The causative bacterium isolated from infected Aglaonema ‘Maria’ plants, coded as KPJ 1 was subjected to morphological, and biochemical, molecular and physiological characterization. The tests were performed in duplicate, indicating that the bacterium was positive for all of the tests that should be positive, except the oxidase test, which should be negative. The bacterium was tested to be gram-negative. Molecular characterization revealed that the KPJ 1 is Dickeya fangzhongdai. A pot experiment with healthy plants of Aglaonema ‘Maria’ was carried out to evaluate the biocontrol potency of DCJ 2 on KPJ 1 using a Completely Randomized Design with eight treatments and six replications.  T1 and T2 represented untreated controls whereas the plants inoculated with only the pathogen (KPJ 1) considered as the negative controls [T3 (drench) and T4 (foliar spray) ].  T5 and T6 represented the plants treated sequentially with KPJ 1 and DCJ as a soil drench. Similarly, foliar spray was performed in the T7 and T8. The data were analyzed using SAS software (version 9). Among both inoculum application protocols T5 and T6 (soil drench) showed the lowest disease severity (p=0.05).  In conclusion, the antagonistic bacterium DCJ 2 demonstrated potent activity against soft-rot disease in Aglaonema caused by D. fangzhongdai which could be effectively used as an eco-friendly biological control agent in Aglaonema  nurseries.