Main symptoms

Fusarium oxysporum f. sp. lactucae can attack seedlings in nurseries; these turn yellow, wither (Figure 1), and die. There is a reddish-brown alteration extending into the vessels of the taproot and some roots and diffusing into the cortex.

Affected adult plants show root and vascular symptoms comparable to those seen on seedlings. A longitudinal section reveals vessels of brown color (Figures 2 to 4). As a result, leaves on one side of the lettuce turn yellow and necrotize around the edge of the leaf blade.

The growth of some plants may be reduced and the head may not take place figure 5.