by Piter Kehoma Boll
Nematodes are famous because of their parasitic members, which do not only parasitize animals but also plants. People that deal with gardening or agriculture may know that sometimes a plant becomes sick because of “nematodes”.
A genus of nematodes that is commonly associated with grapevines is Xiphinema, whose species are known as dagger nematodes. The two most widely studied species are Xiphinema americanum, the American dagger nematode, and Xiphinema index, the California dagger nematode, but during the last decades it became clear that those species are actually a complex of very similar species and new ones are constantly been described. One of them, described in 2016, is Xiphinema browni, which I decided to call Brown’s dagger nematode. It was named after the nematologist Derek J. F. Brown.
Brown’s dagger nematode was found associated with the roots of grapevines and apple trees in Slovakia and the Czech Republic. Among 86 identified females there was only one male, indicating a huge disparity in sex ratios and the probability that females are parthenogenetic, i.e., they can lay fertile eggs without being fertilized by a male. Females measure up to 2.5 mm in length and the only known male measured 1.8 mm.
Since Brown’s dagger nematode was found associated with grapevines, its life cycle is likely similar to that of most other dagger nematodes. Adults are external parasites of grapevine roots and eventually of other woody plants. They live on the root surface and use their long odontostyles (a needle-like proboscis) to perforate the roots and suck the content of their vascular tissue. As a reaction, the plant produces swollen club-like galls on the root tips. The root then branches behind the swollen tip, only to be attacked again, developing another gall and having to branch again. This starts to weaken the plant, which can compromise grape production.
Females lay their eggs scattered through the soil, not forming clusters, and juveniles pass through about 4 stages in the soil before turning to the parasitic mode.
As another grapevine-feeding dagger nematode, Brown’s dagger nematode is probably also a vector of the grapevine fanleaf virus, which is transmitted to grapevines by the California dagger nematode. This happens when the nematode feeds on an infected plant and then moves to a healthy plant, carrying the virus with it. Grapevine fanleaf causes chlorosis (loss of chlorophyll) and distorts the leaves, making them look like fans, hence the name. As you can imagine, the poor plant becomes even weaker than it already was due to the nematodes sucking it. This can be a nightmare to vineyard owners.
The grapevine fanleaf virus can be a devastating disease for grapevines but in the nematode’s body it seems to have benefitial effects, increasing the survival of these small roundworms. Perhaps this stimulates the dagger nematodes to spread it further, in a sort of “evil coalition”.
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Lazarova S, Peneva V, Kumari S (2016) Morphological and molecular characterisation, and phylogenetic position of X. browni sp. n., X. penevi sp. n. and two known species of Xiphinema americanum-group (Nematoda, Longidoridae). ZooKeys 574:1–42. https://doi.org/10.3897/zookeys.574.8037
van Zyl S, Vivier MA, Walker MA (2012) Xiphinema index and its Relationship to Grapevines: A review. South African Journal of Enology and Viticulture 33(1):21–32.
Wikipedia. Xiphinema. Available at <https://en.wikipedia.org/wiki/Xiphinema>. Access on 29 June 2020.
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* This work is licensed under a Creative Commons Attribution 4.0 International License.