Symptoms

During the growing cycle, plants severely infected by Meloidogyne spp. may by stunted, turn yellow, wilt or die if affected by heat and lack of water.
Because of the nematodes’ feeding habit, symptoms occur on roots and tubers at harvest.

In roots, galls (photo 1) form, usually of irregular size, as an obvious proliferation of root tissues. Galls keep their whitish colour unlike powdery scab galls, which are initially white at harvest and then turn black after oxidation.

Easier to see are the symptoms on tubers. Both species cause characteristic blisters or galls on the surface of infected tubers (photo 2). These can be confused with common scab pustules (photo 3). When cutting the tuber across the galls, small white (gelatinous and translucent) masses are visible in the flesh (cortex), these are the mature pear-shaped female nematodes with their egg masses. Over time, these spots turn into dark lesions (photos 4 , 5 and 6).

Tuber infection by M. chitwoodi may subsequently develop into internal reddish spots around the female nematodes (photo 7).

Species identification requires laboratory expertise. Recent molecular tools have contributed to an easier and more reliable identification of these closely related species.