Copy Number Quantification for the Soybean Cyst Nematode Resistance Locus <i>rhg1</i> in the Soybean Varieties of Taiwan

Disease resistance is one of the most successful strategies in crop protection. For example, the implementation of PI 88788 type resistance, which contains high copy numbers of <i>Resistance to Heterodera glycines 1</i> (<i>rhg1</i>) loci, into the commercial soybean varieties of the United States has significantly reduced the yield losses caused by soybean cyst nematode (SCN, <i>H. glycines</i>). Vegetable soybean, or edamame, has become a major exporting agricultural product in Taiwan with an annual revenue over $80 million USD since 2017. Several local varieties have been developed to fulfill the market needs such as the traits of flavor and sweetness. However, it remains unclear if the historical breeding programs ever incorporated <i>rhg1</i> resistance into the varieties of Taiwan. This study applied the TaqMan qPCR method to measure the fluorescent signals specific to the <i>rhg1</i> locus on the chromosome 18 of soybean, and the ratio of VIC and FAM signals were analyzed to predict the <i>rhg1</i> copy number in the 21 soybean varieties of Taiwan. The results indicated the copy number and the single nucleotide polymorphisms of the 21 soybean varieties were identical to the susceptible soybean variety ‘Williams 82’. As importation of soybean will be continuously needed to fulfill the market and because SCN is absent in the soybean fields of Taiwan, lacking <i>rhg1</i> resistance in the local soybean varieties may put the edamame industry at risk and early implementation of SCN resistance in the breeding program, alongside the application of quarantine regulations, will be the key to maintain the SCN-free status and to sustain the edamame industry in Taiwan.