Epidemiology of Pseudomonas cichorii, the Cause of Lettuce Midrib Rot

Abstract

Bacterial midrib rot, caused by Pseudomonas cichorii, has become a serious threat to the production of greenhouse butterhead lettuce (Lactuca sativa L. var. capitata) in Belgium. Currently, there are no strategies for controlling this pathogen. Therefore, greenhouse experiments were conducted to obtain more knowledge about the epidemiology of P. cichorii on butterhead lettuce. Greenhouse butterhead lettuce becomes susceptible to lettuce midrib rot infections at head formation, and a single overhead irrigation with water containing 10 2 CFU ⁄ ml P. cichorii was sufficient to cause disease. The use of surface drip irrigation instead of overhead sprinkler irrigation significantly reduced midrib rot incidence in the greenhouse. P. cichorii isolates can be divided into subgroups based on BOX-PCR genomic fingerprinting, with isolates belonging to subgroup C1 and C2 being more virulent than those of (or related to) subgroup C3. P. cichorii infections with distinct symptoms comparable to midrib rot have also been observed on field-grown crisphead lettuce in California and Japan which, respectively, are referred to as Ôvar-nish spotÕ or ÔtarÕ. We showed that symptom expression is strongly influenced by the lettuce cultivar group, irrespective of the P. cichorii isolate, resulting in varnish spot ⁄ tar on crisphead lettuce and midrib rot on butterhead or cutting group lettuce.

Multiple downy mildew effectors target the stress‐related NAC transcription factor LsNAC069 in lettuce

“…This Gram‐negative bacterium infects a wide range of hosts and has an important economic impact on greenhouse‐grown lettuce. It is one of the bacteria known to induce lettuce midrib rot (Pauwelyn et al ., ). The first appearance of symptoms involves water‐soaked lesions that develop in the infected leaf area and progressively turn black or brown.…”

“…Even though no significant change in susceptibility to B. lactucae was observed in LsNAC069 silenced lines, we observed a significantly increased resistance against P. cichorii , the causal agent of midrib rot in lettuce (Pauwelyn et al ., ). Although our data indicate that LsNAC069 plays a role in susceptibility to this necrotrophic pathogen, it remains to be determined if interactions between LsNAC069 and effectors from P. cichorii occur during pathogen infection, or if silencing of LsNAC069 enhances resistance through systemic changes in the physiology of the silenced lettuce lines.…”

Population dynamics of Pseudomonas savastanoi pv. phaseolicola in bean, throughout the epiphytic and pathogenic phases

“…These authors observed a bacterial population that was 100-fold larger in the intercropping system, in which bean leaves took 40% more time to dry. Pauwelyn et al (2011) reported the same effect for Pseudomonas cichorii, when the use of surface drip irrigation, instead of overhead sprinklers, caused the reduction of midrib rot incidence. The relationship between P. savastanoi pv.…”

SrfC of Pseudomonas cichorii JBC1 affects its attachment to the host surface and host tissue infection

“…Pseudomonas cichorii is a Gram‐negative and multihost bacterial pathogen that produces effectors, toxins and cyclic lipopeptides to infect a wide range of host plants (Cottyn et al ., ; Pauwelyn et al ., ). Each infected host shows symptoms in a distinct way in different parts of the plant, including varnish spot on lettuce (Delisle‐Houde et al ., ), midrib rot on butterhead lettuce (Pauwelyn et al ., ) and kimchi cabbage (Hung et al ., ), leaf blight on soybean (Yu & Lee, ), and stem melanosis on spring wheat (Piening & Macpherson, ).…”

“…Pseudomonas cichorii has been reported to cause disease without a dependence on the T3SS, indicating that it possesses T3SS‐independent pathogenicity factors. For example, the phytotoxic cyclic lipopeptides, cichofactin and cichopeptin, produced by P. cichorii SF1‐54 caused midrib rot on butterhead lettuce (Pauwelyn et al ., , ; Huang et al ., ). Hikichi et al .…”