Propagation rate of a Japanese isolate of Meloidogyne incognita (MI) was compared among ground cherry species (Physalis spp.) including up to seven varieties in two pot experiments in a greenhouse. The gall index (0–4), egg mass number and second stage juvenile density in soil were evaluated about one and half months after nematode inoculation. Two varieties of P. pruinosa had significantly greater gall index, egg mass number and juvenile density than the other Physalis species examined, indicating the species could be susceptible to MI. Furthermore, three varieties of P. peruviana, and a single variety of P. ixocarpa (syn. P. philadelphica) as well as a single variety of P. alkekengi had the opposite trend, indicating these three species could be resistant or moderately resistant to MI.

The southern root-knot nematode (SRKN) includes at least nine races, SP1 to SP9, which were identified based on their different responses to five differential sweetpotato cultivars, ‘ Norin-1’, ‘ Norin-2’, ‘Tanegashimamurasaki-7’, ‘Elegant Summer’, and ‘J-Red’. In this study, we propose a modified method for SRKN race identification in which the threshold of response is 10 egg masses instead of the two-egg-mass threshold used in the original method, when a sweetpotato plant was inoculated with 500 second-stage juveniles. According to this method, two isolates of SP6, Okiishi-12 and Ishigaki-2, showed the same response to each of these five cultivars. We found, however, that three sweetpotato cultivars, ‘Murasakimasari’, ‘Suzukogane’, and ‘Chienoha’, were resistant to the Okiishi-12 isolate and susceptible to the Ishigaki-2 isolate. These results indicated that the Okiishi-12 and Ishigaki-2 isolates were distinct and that SP6 included at least two races. We suggest that the Okiishi-12 and Ishigaki-2 isolates should be distinguished by sub-numbers and designated SP6-1 and SP6-2, respectively. Five isolates of SP6 collected from a sweetpotato field in Chiba prefecture were examined, and all of them were identified as SP6-1.