Identification and inheritance of an Rdc gene resistance to soybean stem canker (Diaporthe phaseolorum var. caulivora)
2019
Peruzzo, A. M. | Hernández, F. E. | Pratta, G. R. | Ploper, L. D. | Pioli, R. N.
Soybean stem canker (SSC) is caused by two varieties of the fungus Diaporthe phaseolorum: var. meridionalis (Dpm) and var. caulivora (Dpc). The objective was to identify and characterize the mode of inheritance of Rdc genes through a classical Mendelian analysis. Resistant (R) and susceptible (S) genotypes were used to make 288 RxS and 132 RxR crosses, including their reciprocals. Segregating F₂ generations were obtained by self-fertilization of the respective F₁. The incorporation of codominant molecular markers (Single Nucleotide Polymorphism, SNP) allowed the molecular validation of 48.75% of F₁ heterozygous individuals. Parents (R and S), F₁ individuals, and F₂:₃ families (Progeny Test, PT) from COD 1–258-2 population were inoculated with an isolate of Dpc (Dpc16), previously identified morphologically and molecularly. The assay showed 21 F₂:₃ families categorized as R, 42 segregated R and S, and 11 as S. Particularly, this F₃ population showed 466 individuals R and 274 S. The chi-square goodness of fit test verified that phenotypic segregation for individual plants in F₃ adjusted to a 5:3 ratio (R:S) and the PT results corresponded to the genotypic ratios (1RR: 2Rr: 1rr) of F₂ individuals. Results allowed the identification of a major resistance gene of simple Mendelian inheritance to SSC that was named Rdc1. Also, independent segregation 9:3:3:1 was verified between this Rdc1 gene and the gene that regulates flower colour, a typical phenotypic marker in soybean. Based on literature review, this is the first report on resistance genes (Rdc) identified for SSC caused by Dpc.
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