Guiping Yan, NDSU Department of Plant Pathology
Andrew Friskop, NDSU Department of Plant Pathology
Joel Ransom, NDSU Department of Plant Sciences

Plant- parasitic nematodes (PPN) are one of the greatest threat to world crop production today. These pests of roots are reported to cause yield losses of up to 20% in some U.S. corn fields. It was estimated that these parasites of roots reduced annual statewide grain corn yield by 4% in Iowa and 7% in Georgia. Similar results were observed in South Dakota where corn grain yield losses due to nematodes averaged in 9.5 bu/ac. However, very little is known about nematode occurrence and their populations in North Dakota corn fields. In order to reduce crop losses and determine what management tactics are needed to control these pests, it is important to be aware of density, incidence and species of nematode populations. Thus the objectives of this study were to conduct a survey of 100 corn fields to determine nematode occurrence in ND and to screen ten corn varieties for resistance to root-lesion nematode and spiral nematode.

In 2016 soil samples were collected from 100 corn fields or fields that had a history of corn production across 18 counties. Vermiform (motile) nematodes were then extracted from these soil samples to identify and quantify them. Among these fields, 73% of them were found to be infested with plant-parasitic nematodes. Seven major groups (genera) of vermiform PPN were detected. The most common group in these fields was spiral nematode followed by stunt, pin, root-lesion, dagger, lance and stubby root nematodes. Juveniles of soybean cyst nematode were also detected.
In addition, the species identities of five nematode groups were confirmed by morphological and DNA-based methods, including one species of each of spiral, stubby root, lance, and pin nematodes, and four species of root-lesion nematodes. Further research is needed to evaluate the effect of these nematodes on corn plant growth and grain yield, and develop efficient assays to detect and identify different species for designing effective nematode management strategies.

Root-lesion nematode is one of the most common nematode pests of corn. Spiral nematode is consistently found in very high numbers in ND corn fields. Thus we evaluated resistance reactions of ten corn varieties in ND to these two nematode field populations. The varieties 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. Soil samples were collected from a corn field in Cass County to screen these corn varieties for their reactions to the root-lesion nematode and spiral nematode. The initial population of spiral nematode in this soil was 4,627 per kg of soil, whereas the initial number of lesion nematode was 510 per kg of soil.

From the results of the experiment we primarily concluded that spiral nematode population of this corn field reproduced best on X5B-8801, DKC 44-13, and GX 89 VT2P whereas the nematode reproduced the least on PFS74K89. On the other hand the root-lesion nematode population of this field reproduced well on 4913 VT2RIB, DKC 44-13, and DK 43-48 RIB. Further experiments are needed to confirm the resistance or susceptibility of the ND corn varieties to these nematode species.

These research findings are important, as it gives us an insight into nematode population dynamics in North Dakota corn fields. It is very important to be aware of nematode populations and their characteristics in corn fields for determining if and what management actions are needed to control these pests of roots. Knowing such information we will be able to determine strategies and help farmers in combating this threat caused by plant-parasitic nematodes to increase corn yield.