A community-level sampling method for detection of Meloidogyne enterolobii and other root-knot nematodes in sweetpotato storage roots

Abstract

Meloidogyne enterolobii is an aggressive root-knot nematode (RKN) species that has emerged as a significant pathogen of sweetpotato in the Southeastern United States. M. enterolobii is spread primarily through the movement of infected ‘seed’ sweetpotatoes used for propagation. The RKN resistance in commercially grown sweetpotato cultivars has proven ineffective against this nematode. Detecting RKN in sweetpotato by eye is unreliable, and further distinguishing M. enterolobii from other RKN species that infect sweetpotato is labor intensive; relying on molecular tests conducted on individual nematodes dissected out of host roots. It is often impractical to collect enough nematodes to gauge the composition of RKN species from a single root or multiple roots from across a field. Here, we have developed a community-level survey method to collect skin samples and extract total DNA from batches of sweetpotato storage roots. Combining this method with species-specific PCR assays allowed for quick and sensitive detection of M. enterolobii and other RKN species infecting sweetpotatoes. We tested this method using batches of infected storage roots at varying levels of M. enterolobii infection. We also inoculated skin samples with varying numbers of individual M. enterolobii eggs to determine the method's detection threshold and used this method to conduct surveys for RKN on fresh market sweetpotatoes. Our results show that this method can consistently and reliably detect M. enterolobii in sweetpotato batches at levels as low as 2 eggs per 10 mL skin sample. This method will be a useful tool to help screen for the presence of M. enterolobii in ‘seed’ sweetpotatoes before they are replanted, thereby helping to slow the spread of this nematode to M. enterolobii-free sweetpotato growing operations.