Main symptoms

Monosporascus cannonballus soil-borne causes symptoms quite comparable to those associated with other pests of Cucurbitaceae.

The plants may have reduced growth, and introduce a progressive death of lower leaves. The symptoms that most attract the attention of growers are the more or less sudden manifestation of leaf wilting occurring late in the season and often near harvest, and affecting a large number of plants. Yellowing and leaf dryness are also observed, as well as the death of whole branches.

In fact, the leaf wilting observed is the result of primary symptoms located on the roots (figures 1 and 2). On the latter, we can observe generally orange to brown lesions, of limited size at first. On zucchini, these lesions have the shape of an orange ring with a lighter center (Figure 3). Subsequently, root degradation is accentuated and generalized (figure 4). Thus, most of the damaged secondary and tertiary roots break off and decompose. They are therefore generally not visible when diseased plants are pulled up. It should be noted that secondary microorganisms can invade root tissues, in particular those of the cortex, and thus contribute to their destruction.

Tiny black spherical structures , perithecia M. cannoballus and ascospores, are visible on the surface of the roots (Figures 4 and 5) and characterize the presence of this fungus. These signs, materializing the sexual or teleomorphic form of this ascomycete, are not always easy to observe because they can form on already well decomposed root tissues which will not be recovered during the uprooting of the root systems. Also, take care to gently pull them out with the help of a tillage tool.