The resistance of soybean (Glycine max (L.) Merr.) to soybean cyst nematode (SCN, Heterodera glycines Ichinohe), which is a devastating pathogen in soybean production and causes a large quantity of annual yield loss worldwide, can shift during the long-term interaction and domestication.  It is vital to identify more new resistance genetic sources for identification of novel genes underlying resistance to SCN for management of this pathogen.  In the present study, first, two ethane methylsulfonate-mutagenesis soybean M2 populations of PI 437654, which shows a broad resistance to almost all of SCN races, and Zhonghuang 13, which is a soybean cultivar in China conferring strong resistance to lodging, were developed.  Many types of morphological phenotypes such as four- and five-leaflet leaves were observed from these two soybean M2 populations.  Second, 13 mutants were identified and confirmed to exhibit alteration of resistance to SCN race 4 through the forward genetic screening of 400 mutants of the PI 437654 M2 population, the rate of mutants with alteration of SCN-infection phenotype is 3.25%.  Third, these identified mutants were further verified not to show any changes in the genomic sequences of the three known SCN-resistant genes, GmSHMT08, GmSNAP18 and GmSANP11, compared to the wild-type soybean; and all of them were still resistant to SCN race 3 similar to the wild-type soybean.  Taken together, we can conclude that the 13 mutants identified in the present study carry the mutations of the new gene(s) which contribute(s) to the resistance to SCN race 4 in PI 437654 and can be potentially used as the genetic soybean sources to further identify the novel SCN-resistant gene(s).   

Fusarium is usually thought to cause soybean root rot, which results in a large quantity of annual yield loss in soybean production, by its secretions including Fusarium toxins and cell wall degrading enzymes, but not by the conidia themselves that do not underlie any virulence so far.  Here we report that the conidia of one Fusarium solani isolate are able to be virulent to soybean and make soybean seedlings wilted alone.  We isolated them from the wilted plants in a soybean-production field and molecularly identified 17 Fusarium isolates through phylogenetic analysis.  Of them, except for one isolate that showed diversity of virulence to different soybeans (virulent to one soybean whereas avirulent to another soybean), the others were all virulent to the two tested soybeans: both conidia cultures and secretions could make soybean seedlings wilted at 5 days post infection, and their virulence had dosage effects that only conidia cultures of at least 5×106 conidia mL^–1 could show virulence to soybean; however, the sole conidia of the F. solani isolate #4 also exhibited virulence to soybean and could make soybean seedlings wilted.  Finally, we developed the specific cleaved amplified polymorphic sequences (CAPS) markers to easily differentiate Fusarium isolates.  The isolate #4 in this work will likely be used to investigate the new mechanism of virulence of Fusarium to soybean.