Two genotypes of root‐knot nematode, Meloidogyne arenaria (A2‐O and A2‐J), are found in Japan. They were distinguished from each other based on mitochondrial DNA sequences. The primer set (C2F3/1108) amplified a 1.7‐kb fragment from A2‐J, whereas a 1.1‐kb fragment was amplified from A2‐O. M. arenaria (A2‐O) was detected in local regions of southern Japan, whereas M. arenaria (A2‐J) was widespread from the Kyushu region to the Tohoku region. The distribution of M. arenaria (A2‐J) overlaps with the cultivation area of eggplant. Solanum torvum is used worldwide as a rootstock for eggplant cultivation, and it is resistant to Meloidogyne spp. In particular, it is reported that S. torvum is resistant to M. arenaria outside Japan. In this study, we inoculated S. torvum rootstock cultivars with M. arenaria (A2‐J), M. arenaria (A2‐O) and Meloidogyne incognita populations. Although M. incognita and M. arenaria (A2‐O) produced only a few egg masses on S. torvum, thereby confirming its resistance, the four geographical populations of M. arenaria (A2‐J) produced large numbers of egg masses on S. torvum. This study confirmed that S. torvum is resistant to M. incognita and M. arenaria (A2‐O) populations, but susceptible to populations of M. arenaria (A2‐J) in the eggplant production area of Japan.

Differences in the resistance of sweet potato cultivars and lines to Melodogyne incognita populations. Zen-ichi Sanol, Hideki Iwahoril, Yasushi Tateishil and Yumi Kai2.Differences in resistance of sweet potato cultivars to some populations of Meloidogyne incognita were examined in greenhouse assays. Twenty-four major sweet potato cultivars rooted in 200 g of potted soil were inoculated with approximately 500 juveniles of four M. incognita populations collected from different areas. Reproduction rates (eggs produced per J2 inoculated) were determined after 35 days of growth at 27t. Nine cultivars with reproduction rates higher than 11 were rated as susceptible and five cultivars with reproduction rates lower than one were rated as highly resistant to the four populations. However distinct differences were observed in reproduction rates of those populations on the other 10 cultivars. In an assay similar to the one described above with 13 newly developed cultivars or breeding lines, all four populations produced many egg-masses on three and produced only a few egg-masses on 6 of those cultivars or breeding lines. However, the remaining cultivars or breeding lines did not have a consistent response to the four populations. Among purple sweet potato cultivars grown primarily in Okinawa and Tanegashima Island, two similarly shaped cultivars, Bise and Tanegashima-murasaki 7, exhibited different levels of resistance to two populations as indicated by a marked difference between the numbers of egg masses produced. These results clearly demonstrate that resistance of sweet potato to populations of M. incognita distinctly differs with cultivars or breeding lines. Jpn. J. Nematol. 32 (2), 77-86 (2002).

The southern root-knot nematode Meloidogyne incognita is an important pathogen of solanaceous plants worldwide. To assess resistance and suppressiveness to the nematode of the Japanese cultivars of eggplant rootstocks, we conducted greenhouse experiments. Numbers of nematode egg masses were significantly lower on Solanum tor vum rootstock cultivars, Tonashimu, Torero, and Torvum vigor, than the cultivars of the other Solanum species after 45 days of cultivation. Next, we examined the effect of Tonashimu on the population density of the nematode in soil. After 116 days of cultivation, the second-stage juvenile density of the nematode in soil was reduced, and was significantly lower in pots of Tonashimu, than in those of Solanum melongena cultivars. These results suggest that the Japanese rootstock cultivars of S. torvum are resistant to the nematode, and could suppress nematode density in soil. Nematol. Res. 46(2), 87-90 (2016).Key words: grafting, resistance, root-knot nematode, Solanum torvum INTRODUCTIONEggplant (Solanum melongena) is cultivated worldwide and is especially popular in Asian countries such as China and India. Eggplant was introduced into Japan during the Nara period (AD 710 to 794) and today is an important domestically produced vegetable (Saito, 2004). Many crops, including eggplant, are attacked by the southern root-knot nematode Meloidogyne incognita, resulting in yield losses. In eggplant, 20-29% of total yield is estimated to be lost because of Melodogyne spp. (M. incognita is dominant) in the tropics (Sasser, 1979) and the economic threshold level of eggplant is reported to be 5.4 M. incognita second-stage juveniles (J2) per 100 g soil (Netcher and Sikora, 1990). Recently, Watanabe et al. (2013) reported that soil densities of two J2 per 20 g soil or greater with the Baermann technique have been shown to significantly reduce eggplant yield (cultivar Senryo 2go) at 50 days after planting.Most plant nematode control methods rely on chemical agents. Although soil fumigants such as 1,3-dichloropropene are commonly used, the use of such chemicals is likely to be subject to increasing restriction owing to environmental and safety concerns. The exploitation of resistant cultivars is the most effective and environmentally benign method to reduce nematodeinduced crop loss. However, no eggplant cultivar resistant to M. incognita has been found.Eggplant cultivars grafted onto resistant rootstocks are used to prevent various diseases, including bacterial wilt (caused by Ralstonia solanacearum), and Fusarium wilt (caused by Fusarium oxysporum) (Yoshida, 2004). Solanum torvum has a poor germination rate and slow seedling development but is employed as rootstock for eggplant cultivation because of its vigor and resistance to serious soil-borne diseases as described above (Gousset et al., 2005;Miceli et al., 2014). Moreover, S. torvum has been found to exhibit resistance to M. incognita in several studies conducted in Japan and abroad (Ali et al., 1992; Daunay and Dalmasso, 1985; Dhivya et al., 2014;Ha...

Bacterial wilt, caused by Ralstonia solanacearum, is one of the most serious diseases of tomato (Solanum lycopersicum). Concomitant infection of R. solanacearum and root‐knot nematode Meloidogyne incognita increases the severity of bacterial wilt in tomato, but the role of this nematode in disease complexes involving bacterial pathogens is not completely elucidated. Although root wounding by root‐knot nematode infection seems to play an important role, it might not entirely explain the increased susceptibility of plants to R. solanacearum. In the present study, green fluorescent protein (GFP)‐labelled R. solanacearum distribution was observed in the root systems of the tomato cultivar Momotaro preinoculated with root‐knot nematode or mock‐inoculated with tap water. Fluorescence microscopy revealed that GFP‐labelled R. solanacearum mainly colonized root‐knot nematode galls, and little or no green fluorescence was observed in nematode‐uninfected roots. These results suggest that the gall induced by the nematode is a suitable location for the growth of R. solanacearum. Thus, it is crucial to control both R. solanacearum and root‐knot nematode in tomato production fields to reduce bacterial wilt disease incidence and effects.