Antagonistic Activity of Selected Rhizobacterial Isolates against Erwinia carotovora causing Potato Soft Rot Disease
Keywords:
antagonistic activity, rhizobacterial isolates, Soft rot of PotatoAbstract
Potato soft rot, caused by Erwinia carotovora, is recognized as one of the most devastating and widely distributed diseases affecting potatoes. Samples exhibiting symptoms of soft rot were collected from various regions including Rawalpindi, Islamabad, Taxila, and Gujranwala, and the pathogen responsible for the disease was isolated. Additionally, rhizobacteria were isolated from the rhizosphere of potato plants and assessed for their ability to antagonize the rot pathogen in vitro using the zone inhibition technique. Among the 18 isolates tested, three isolates (AS-5, AS-12, and AS-18) demonstrated efficient antagonistic effects on the pathogen, exhibiting inhibited zones with radius measuring 15 mm, 12 mm, and 9 mm, respectively. Notably, biochemical tests resulted that isolates AS-5 and AS-12 belong to Gram-negative Pseudomonas spp., whereas AS-18 is a Gram-positive Bacillus spp. All these isolates display advantageous traits including phosphate solubilization, IAA production, catalase and oxidase activity, and siderophore production, which enhance plant growth and potentially aid in plant disease suppression. Further experimentation involved the application of seven treatments of antagonistic rhizobacterial isolates individually and in combination on potato tubers to determine disease reduction percentage, disease severity percentage, and various plant growth parameters: plant height (cm), number of leaves, mean fresh weight (g), and mean dry weight (g), under laboratory conditions with three different time intervals. After 63 days, the results showed varying levels of effectiveness among the treatments, with the highest efficacy observed in treatment T7 (PS-I + PS-II + Bacillus sp.), which significantly reduced disease incidence %, severity % and resulted in the maximum improvement in plant growth.
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