Response of soybean genotypes to Meloidogyne incognita and M. hapla in Heilongjiang Province in China

Root-knot nematodes (RKN, Meloidogyne spp.) are among the economically important root parasites of soybean (Glycine max). RKN has been reported to infect soybean in central China, but no information existed about its presence in northern China, the major soybean production area. The northern RKN (M hapla), however, was recently found in vegetable fields in Liaoning Province in northern China. The southern RKN (M incognita) was reported under protected cultivation of vegetables in northern China, where the soybean cyst nematode (SCN) is the known damaging parasite on soybean. Although host-plant resistance is the best cost-effective strategy to control nematodes, no knowledge was available about the response of local soybean cultivars to RKN infection. To identify potential resistance sources of soybean to RKN, eleven local varieties originally bred for resistance to SCN race 3, five local cultivars susceptible to SCN race 3 and additional uncharacterised germplasms were inoculated with both M incognita and M hapla under controlled glasshouse conditions. The root galling index (GI) (0-10 scale), number of egg masses per gram of root (EM), eggs per gram of root (EGR) and nematode reproduction factor (Rf value) were used to evaluate how the different soybean genotypes reacted to RKN. The results indicated that out of 21 genotypes tested, 11 and 8 genotypes showed low GI (0-3) for M. incognita and for M hapla, respectively. Low nematode reproduction (Rf <= 1) was observed on 13 and 3 genotypes for M. incognita and for M hapla, respectively, suggesting most local soybean cultivars are better hosts for M hapla than M incognita. The distribution of GI, EM, EGR and Rf for M incognita and M. hapla suggested that they have different infection mechanisms. The great GI but with low number of nematode reproduction or low GI with high number of nematode reproduction on soybean suggested the genetic independence of resistance from root galling and/or nematode reproduction. Identification of resistant or tolerant varieties would be valuable resources for broad-based resistance breeding against RKN.