Response of soybean genotypes from Northeast China to Heterodera glycines races 4 and 5, and characterisation of rhg1 and Rhg4 genes for soybean resistance

Y Soybean cyst nematode (SCN, Heterodera glycines) is a devastating plant-parasitic nematode worldwide. Two SCN races, race 4 (HG Type 1.2.3.5.6.7) and race 5 (HG Type 2.5.7), with increased virulence were previously identified in Northeast China. To obtain new resistance sources to these SCN populations, the response of 62 genotypes, including 51 local varieties and breeding lines, and 11 indicator lines for SCN race and HG Type identification, were evaluated. Four new primers in the regions of two loci of GmSHMT08 (Rhg4) and GmSNAP18 (rhg1) were designed for PCR amplification and subsequent sequencing to characterise haplotypes instead of genome resequencing. Results indicated three haplotypes among 51 local genotypes; there were 26 lines in Haplotype I carrying both the rhg1-a and Rhg4-a resistant loci as in 'Peking', 13 lines in Haplotype II containing only the resistant rhg1-a locus but Rhg4-b susceptible loci, and 12 lines in Haplotype III with rhg1-c and Rhg4b susceptible loci. Interestingly, there was no 'PI 88788'-type resistance identified in Northeast China, although it accounts for 90% of sources in the USA. Two local breeding lines in Haplotype I displayed resistance to both SCN races. The resistance lines carried higher copy number (>1) of the tandem duplication at the rhg1 locus compared with susceptible lines (<= 1). The combination of the two microsatellite markers, Sat_162 on Chr 8 and 590 on Chr 18, distinguished the three haplotypes and predicted the resistance/susceptibility for SCN race 5. The knowledge of the phenotypes and molecular characteristics of 51 local breeding lines in Northeast China will accelerate the utilisation of sources for broad-based SCN resistance and marker-assisted selection.