Corn (Zea mays) is one of the major agricultural crops in North Dakota (ND) on the basis of production value. Plant-parasitic nematodes (PPN) are one of the greatest threats to world crop production. Over 120 species of PPN are associated with corn throughout the world, of which over 60 species of PPN have been reported in North America corn fields. PPN ranked among the top ten pests of corn in the US as they are responsible for yield losses of more than 294 million bushels from 2012 to 2015. The nematode survey conducted in ND corn fields revealed that 82% and 73% of the fields were positive for PPN in 2015 and 2016, respectively, and a total of eight groups of PPN were detected.
Root-lesion nematodes (Pratylenchus spp.) and stunt nematodes (Tylenchorhynchus spp.) are common nematode pests found in corn fields of ND. Root-lesion nematodes completely enter root tissue, move inside the root to extract water and nutrients, and cause lesions on roots and reduce root volumes and weight. Other fungi and bacteria usually invade the lesions to cause more damage. In the Midwestern Corn Belt, the most important species are P. hexincisus, P. penetrans, and P. scribneri. Experimental data are lacking for other root-lesion nematode species.
Four species of root-lesion nematodes (P. neglectus, P. scribneri, and two new Pratylenchus spp.) were detected in ND corn fields. Use of resistant varieties is one of the most environmentally friendly approaches among the sustainable management strategies. The reproduction rates of root-lesion and stunt nematodes vary with different corn varieties. Therefore, it is increasingly important to know the resistant (insensitive) or susceptible (sensitive) responses of commercial corn varieties to these nematodes to help select resistant varieties. The objectives of this study were to screen ten corn varieties used in ND for resistance to the new root-lesion nematode species, root-lesion nematode Pratylenchus neglectus, and stunt nematode (Tylenchorhynchus spp.).
Four fields with target nematodes (one for new Pratylenchus species, one for P. neglectus, and two for stunt nematodes) from three counties in ND were selected. Five experiments were conducted under controlled greenhouse conditions. Ten corn varieties in ND each with five replications were used in each of the experiments. The cultivars included LR 9487 VT2PRIB, 4913 VT2RIB, DKC 44-13, DK 43-48 RIB, DK 43-46, L-2916 VT2PRO, GX 89 VT2P, 1392 VT2P, PFS74K89, and X5B-8801. The species identities of the new root-lesion nematode and P. neglectus were confirmed by DNA-based diagnostic methods.
The results from two trials for the new root-lesion nematode species showed that this nematode reproduced significantly high on GX89 VT2P and L-2916 VT2PRO, suggesting they are susceptible whereas the nematode reproduced the least on DK 43-46 in trial 1 and on PFS 74K89 in trial 2, suggesting they are resistant in at least one experiment. Third experiment is ongoing to further confirm the results. From the experiment with P. neglectus, this nematodereproduced best on DK 43-48 RIB and DK 43-46, suggesting they are susceptible whereas the nematode reproduced the least on DKC 44-13, PFS 74K89, and 4913 VT2RIB, suggesting they are resistant to P. neglectus.
From one experiment with stunt nematode, we found that in general the reproduction rates of the stunt nematode population were low. This population reproduced best on X5B-8801 and LR 9487 Vt2RIB while it reproduced the least on L-2916 VT2PRO, 1392 VT2P, and 4913 VT2RIB. In another experiment with a very low stunt nematode population from a different county, we observed that this population had the highest reproduction rate on corn variety DK 43-46 while it reproduced the least on LR 9487 VT2PRIB and X5B-8801. Variation in reproduction between the stunt nematode populations from two counties could be attributed to the differences in nematode species, population density, soil property, and virulence of individual populations from different locations. The stunt nematodes from these two fields will be identified to species and additional greenhouse bioassays are needed to confirm the observations.
To conclude, the resistance evaluation study of corn varieties gives us an insight about the reproduction ability of these nematodes on the ten corn varieties in ND and help understand resistance or susceptibility of these varieties to the tested nematode species. The knowledge from this study will be useful to accelerate the selection of suitable varieties for farmers. This information will also be helpful for future studies that evaluate the nematode impact on ND corn production and develop effective and specific pest management strategies for control of the nematode diseases to increase corn yield.