The guava root-knot nematode (GRKN, Meloidogyne enterolobii) is an invasive soilborne pest to North Carolina. It is particularly aggressive and has a wide host range including soybean, cotton, tobacco, and numerous vegetables. It causes root galling and root damage, and can reduce yield under high levels of the nematode.

Trials looking at nematicides in sweetpotato and tobacco have shown that fumigants are the most effective controlling GRKN. However, this type of control is not feasible for soybean production given the expense associated with fumigation. Host resistance (that is, immunity of the plant to infection) is used to control other species of root-know nematode, such as the Southern root-knot nematode (Meloidogyne incognita). However, this host resistance is unfortunately not effective against GRKN, and because of this, GRKN can impact soybean yield.

The goal of this project was to look at wild soybean varieties as a place to discover new pools of host resistance to GRKN. Although these wild soybean varieties are not viable for commercial production, these wild varieties have highly diverse genetic makeup, making them a good place to look for new resistance to GRKN. If resistance to GRKN is found in a particular wild soybean line, that line could be studied further, with the goal of harnessing it and incorporating it’s resistance genes into commercial soybean varieties through breeding, so as to impart resistance to GRKN in the offspring.

We looked at 91 wild soybean varieties in our study, of which we were able to collect data on 78 varieties. From these, we found 3 varieties that showed significantly less root galling and number of GRKN eggs per root system. The number of eggs per root system is often used as a measure of how resistant the plant is to nematodes – a lower number of eggs means stronger resistance (greater immunity).

This is a good result, and we are excited by the findings. We are currently re-testing these 3 varieties and we plan to pass the information along to soybean breeders, who may use it to further study the resistance and determine if resistance can be included into new commercial varieties. We will also present this information in extension soybean production meetings and share this information with our scientific collaborators. Although we realize this work does not provide short-term management recommendations, this work lays the foundation for long-term management of GRKN in soybean by looking for genetic resistance to this troubling pest.