3. Other minor nematode species

Ditylenchus dipsaci, also known as the stem and bulb nematode, is more common in garlic, but it also damages other plant species as well, including potato, and affects stalks, stolons and tubers. Affected potato tubers show gray to brownish lesions with an overall poor plant growth. Diseased stems become swollen and curved. Galls may also form on the leaves, which

The use of crop rotation for controlling D. destructor and D. dipsaci is not feasible due to their wide host ranges. The use of resistant genotypes is the most effective, economically and environmentally safe control method for nematode infection. Currently, there is limited information on the availability of resistant and tolerant potato cultivars against these nematodes. The authors [55] evaluated 25 potato varieties for resistance and tolerance against infection of D. destructor and D. dipsaci, and based on the nematode reproduction factor (RF), 16 varieties were rated as susceptible (S), while 5 other as resistant (R) to D. destructor; potato varieties 'Innovator', 'Aveka' and 'Spunta' were rated as resistant to D. dipsaci as well. In their study, the potato cultivar 'Désirée' was rated as highly susceptible to both D. destructor and D. dipsaci.

Other control measures for these nematodes include the use of nematode free field, nematode free seed potato tuber, and ultimately the use of chemical nematicides may be recommended.

The stubby-root nematodes, Trichodorus and Paratrichodorus spp. (Trichodorids), belong to the family Trichodoridae (Thorne). Nematodes of this family are a group of important plant parasitic pathogens and include nearly 100 described species within five genera [56]. The stubby-root nematodes are ectoparasites that usually aggregate at the root tips and have a long, solid and curved stylet called onchiostyle that they use to pierce plant cells during feeding, preferably meristem cells of root tips. The damage caused by their direct feeding may be considerable, with thickened root and atrophy, early senescence and interruption of

Trichodorids have a wide distribution around the world, although some species are restricted to a particular region. Studies on the distribution and ecology of trichodorids, as well as the mechanisms involved in the transmission of certain viruses, may eventually result in new strategies for their control [56]. Trichodorus spp. are found in sandy soils in several regions worldwide. Although they are more specialized to monocots, they parasitize dicots as well and are considered an important nematode to potato in the tropics and subtropics. However, the level of damage in the field, their overall distribution and economic losses associated with their

Even though there is a considerable amount of data reporting the impact of these nematodes as a plant parasite, their ability to vector certain viruses has increased their importance to the agriculture, when several species of Trichodoridae were identified as a viral vector [56]. Thus, they are considered economically important for potato production, both because of their direct damage and due to the viruses they transmit. For instance, Trichodorus spp. have the ability to disseminate viruses to potato varieties, especially the Tobacco Rattle Virus—TRV, a virus of the genus Tobravirus, which cause the potato disease known as corky-ring spot [6, 57]. The juvenile and adult stages of Trichodorus spp. can vector these viruses after feeding on diseased plants. The viruses are stuck in the stylet region and do not circulate inside the nematode

2.6. The stubby-root nematodes (Trichodorus and Paratrichodorus spp.)

plant growth (stunting), a condition known as 'stubby root' [56].

infection are not well studied [57].

cause significant leaf distortion [54].

118 Potato - From Incas to All Over the World

Other nematode species, including the sting nematode (B. longicaudatus), the spiral nematode (H. pseudorobustus), the lance nematode (H. galeatus), the stunt nematode (T. claytoni) and the dagger nematode (Xiphinema spp), among others (Table 1), may be of economic importance to potato fields at some regions, for instance, some regions in the USA. Among these ectoparasitic nematode species, B. longicaudatus seems to be the most impacting one [59]. Other minor nematode species might be associated with potato, however, with isolated importance
