Relationship Between the Density of in Soil at Harvest Evaluated Using Real-Time PCR and Sweetpotato Disease Incidence.

Sweetpotato stem rot nematode () causes the most devastating disease affecting sweetpotato production in China. The objectives of this study were to (i) establish a quantification method using real-time PCR for of sweetpotato; (ii) analyze the effect of density at harvest on the percentage of disease incidence in sweetpotatoes; and (iii) evaluate the effect of soil physical properties on disease incidence. Populations of isolated from 28 different production areas in Henan Province exhibited identical sequences, and then real-time PCR-specific primers (PRNf and PRNr) were designed. The primer set demonstrated a 100% match with the sequences of from three regions in China but did not align perfectly with different species within the genus isolated from nine other countries. There were two and thirteen base mismatches with the closely related species and , respectively. The log-transformed number of inoculated nematodes () to soil was highly correlated with the corresponding Ct value (), resulting in the quantification curve ( = -1.0859 + 32.025, = 0.9866, 0.01). This quantification curve was utilized to evaluate the densities of in wheat fields that were not cultivated with sweetpotato and in fields under continuous sweetpotato cultivation. The results showed no detection in the wheat fields, and the densities ranged from 0 to 13,300 ± 1,020 individuals per 20 g of dry soil. At harvest, the density established a negative correlation with soil pH ( = -1.7431 + 12.568, = 0.6028, < 0.05). When soil pH values were between 5.6 and 6.8, and the density of at harvest was less than 160 ± 30 per 20 g of soil, the percentage of disease incidence at harvest was 0. A significant correlation was established between density and the severity of sweetpotato disease. The results indicate that the specific primer set developed in this study allows for the accurate and rapid quantification of density in the soil, as well as the prediction of disease incidence in sweetpotato.