Main symptoms

Lettuce affected by Pectobacterium carotovorum subsp. carotovorum wilt quite quickly at first. This symptom appears following rainy periods or in overly irrigated plots, near the harvest. In fact, it is induced by the invasion of the vessels of the stem and the pivot by this bacterium (figure 1). A longitudinal or transverse section of these organs shows that the vessels show a pink coloration which rapidly evolves to brown (figure 2). The marrow is particularly affected (Figures 3 and 4). It becomes glassy and gelatinous and takes a greenish tint before blackening and liquefying entirely under the effect of pectinolytic enzymes (" butt rot ", " jelly butt ").

A few dark spots are sometimes visible on the leaves. Subsequently, a moist, viscous, dark brown to black rot begins on a few leaves and then spreads over the entire apple (" slime head ") (figure 5). Eventually, affected salads can completely liquefy (Figure 6). No particular structure is observed on the tissues, unlike the parasitic fungi responsible for wilting and leaf rots ( Botrytis cinerea , Sclerotinia spp.).

Pectobacterium carotovorum subsp. carotovorum also causes damage during transport and storage of salads stored in poor thermal conditions, sometimes in association with Pseudomonas marginalis pv. marginalis.