Molecular and ultrastructural characterization of Heterodera glycines (soybean cyst nematode) eggs

Heterodera glycines (Soybean Cyst Nematode, SCN) is an obligate plant parasite inflicting damage to soybean by establishing a feeding site in the root known as a syncitium, which acts as a sink diverting nutrients needed for seed production to SCN. Damage due to SCN causes significant annual monetary losses in crop yield worldwide. The aim of this study has been to gain molecular and ultrastructural information about the hatching of SCN eggs so that future research can focus on determining ways to disrupt its development before it hatches. A candidate gene of interest is the hch-1 gene, which is important for hatching of C. elegans , a free-living nematode. SCN was found to have a homologous gene to hch-1.; Phenotypic differences in hatching were found in the previously developed inbred lines, TN17 and TN18 that were selected for fast and slow rates of hatching respectively. Here, we show TN17 and TN18 also have differences in hatch yields compared to greenhouse maintained field populations. To better study genes that are differentially expressed during the development of the nematode in the egg, a sucrose gradient method was developed to separate eggs into two subpopulations, one enriched for early embryos and the other enriched for late embryos of the first and second juvenile stage. The predicted future treatment to control SCN hatching will need to pass through the eggshell in order to disrupt SCN development prior to hatching. Thus, the ultrastructure of the eggshell was also examined. Previous studies reported that there was an inner lipid layer, a middle chitin layer and an outer chitin layer. Upon re-examination, it was determined that only the middle eggshell layer is composed of chitin and the outer layer is most likely vitelline. This research has provided both molecular and ultrastructural insights into the hatching of SCN.