Main symptoms

Pectobacterium carotovorum subsp. carotovorum mainly attacks stem the zucchini , and develops particularly inside it. To realize this, it is advisable to make a cross section (figure 1) or longitudinal (figure 2) to see the devastating effects of this bacterium. There are moist, brownish to orange lesions, and numerous cavities associated with local liquefaction of internal tissues. Rot can spread to the outside of the stem, a dark brown to blackish lesion extending and surrounding it over a longer or shorter length. Ultimately, the tissues end up decomposing and liquefying, only the vascular system remains (figure 3).

The internal deterioration of the stem is not without consequences on the functioning of the zucchini plants, and in particular on the transport of water and mineral elements. This is limited or even interrupted in the long term, which leads to yellowing and leaf wilting (figure 4),  and the collapse of the plants (figure 5), in particular during hot climatic periods. If conditions are right, the disease progresses and plants can die (Figure 6).

Symptoms can also be seen on the leaves and petioles of zucchini and squash. Blackish moist lesions form on the leaf blade, surrounded more or less by a large chlorotic halo (Figure 7). Sections of the petioles are sometimes surrounded by wet rot, eventually leading to a disruption of leaf feeding, and therefore their drying out (figures 8 and 9)

When it invades the fruit , this bacterium causes a rapidly evolving wet rot . Moist and soft tissues show a dark brown to blackish tint (Figures 10 to 11). Let us note that the invasion of the fruits is carried out preferentially starting from the stylar scar (figure 12), and that the rot extends inside; eventually the squash can rot completely (Figure 13).