Meloidogyne

Bernard, Ernest C, Chaffin, Angel G & Gwinn, Kimberly D, 2022, Review of nematode interactions with hemp (Cannabis sativa), Journal of Nematology 54 (1), pp. 1-18 : 3

Root-knot nematodes ( Meloidogyne spp.)

Parasitism of hemp by species of Meloidogyne , the root-knot nematodes (RKN), is well-established, although based on just a handful of papers. The Web of Science and CABI databases contain 40,355 and 29,679 records, respectively, of root-knot nematode publications as of 16 August 2021, but only 20 deal with specific root-knot nematodes on hemp ( Fig. 1 ). Of the many described species of Meloidogyne , five have been examined at least cursorily for their ability to reproduce on hemp: M. chitwoodi , M. enterolobii , M. hapla , M. incognita and M. javanica . All are cosmopolitan except M. chitwoodi , which nevertheless is widespread in North America and Europe. Many other economically significant root-knot species still must be checked to determine if they can parasitize hemp. Early reports (pre-1949) of root-knot nematodes identified them as Heterodera marioni or as H. radicicola , taxa that included all root-knot nematodes. Passon (1909) reported H. radicicola on hemp in Brazil, but the particular nematode species is unknowable. Buhrer et al. (1933) listed Cannabis sativa as a host of Heterodera marioni but did not cite the source of that record. The first definitive U.S. report of root-knot nematode (as H. radicicola ) on hemp was that by Whittle and Drain (1935), who listed hemp as slightly infested. Mateeva (1995) reported hemp to be resistant to Meloidogyne spp . relative to tomato and cucumber but did not indicate a particular nematode species nor the hemp source. The susceptibility of plants to root-knot nematodes and other parasitic nematodes, especially in controlled greenhouse studies, is often calculated as Rf = Pf/Pi, where Rf is the reproductive factor, Pf is the final number of nematodes or eggs, and Pi is the initial inoculum. However, very few papers have reported Rf values or provided enough information to calculate this value.

Galls induced on hemp roots by M. hapla , M. incognita and M. javanica are small, whitish and hard ( Fig. 2 ), not exceeding about 4 mm in diameter ( Kotcon et al., 2018; Coburn and Desaeger, 2019; Bernard and Chaffin, 2020). Both small and large galls on hemp were formed by M. enterolobii ( Ren et al., 2020) but gall dimensions were not given.

Figures

Figure 1: Time chart of primary literature reporting root-knot nematode-Cannabis sativa associations. Mh, Meloidogyne hapla; Mi, M. incognita; Mj, M. javanica.

Figure 2: Galling of Meloidogyne incognita on Cannabis sativa ‘Cherry’, Pi = 10,000 eggs. (A) Entire root system. (B) Closeup of small, white galls. Scale = 5 mm.