Occurrence and control of Pseudomonas cichorii, the bacterial pathogen causing midrib rot on 'Batavia' lettuce under a deep-flow technique hydroponic system

Abd El-Rahman, Ashraf Fathy; Abd-El-Aziz, Rabab Mohamed; Ali, Ayat Mahmoud

doi:10.21608/ejp.2025.427628

Occurrence and control of Pseudomonas cichorii, the bacterial pathogen causing midrib rot on 'Batavia' lettuce under a deep-flow technique hydroponic system

Document Type : Original Article

Authors

¹ Bacterial Diseases Research Department, Plant Pathology Research Institute, Agricultural Research Center (ARC), Giza 12619, Egypt

² Central Lab of Organic Agriculture, Agricultural Research Center (ARC), Giza 12619, Egypt

10.21608/ejp.2025.427628

Abstract

Pseudomonas cichorii is a bacterial pathogen affecting lettuce (Lactuca sativa L.) plants, causing midrib rot (varnish spots) disease in many agricultural systems. No recommended chemical control compounds or programs are known to manage this disease. In this study, midrib rot appeared on 'Batavia' lettuce under a deep flow technique (DFT) hydroponic system. Two isolates (Lett7 and Lett8) out of ten isolates recovered from the diseased plants showed symptoms of dark brown rot when injected into the leaf midribs of "Batavia" lettuce. The two isolates showed negative results with levan production, pectolytic activity, and arginine dihydrolase activity. While, positive results with Gram-reaction (KOH 3%), fluorescence on King’s B agar medium, oxidase reaction, and hypersensitive reaction test on the tobacco plants. The 16S rRNA gene sequences of the two isolates (GenBank PP748272, PP748273) showed 99.70 to 99.85% similarity to P. cichorii (NR_117824), P. cichorii strain PC1 (NR_026532), and P. cichorii strain ATCC 10857 (NR_112070). Also, the pathogenicity gene cluster (hrcRST) sequences of the two isolates (GenBank PQ821676, PQ821677) showed 98.11 to 100% similarity to P. cichorii strain SF0057-3A1 (GU324121), P. cichorii strain AF0089-01 (GU324123), and P. cichorii strain SF0063-01 (GU324122). Single Bacillus sp., a mixture of two Bacillus spp., and H₂O₂ significantly decreased disease incidence while improving the growth parameters of the lettuce plant. A greater effect was observed when a mixture of two Bacillus spp. was used. In conclusion, combining Bacillus subtilis and Bacillus velezensis as bioagents can control midrib rot and improve lettuce growth characteristics under the DFT hydroponic system.

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