Search for a command to run...
Introduction. Understanding the inheritance pattern of the response to soybean stem canker (SSC), caused by Diaporthe phaseolorum var. caulivora (Dpc), is essential for the incorporation of genetic resistance into soybean breeding programs. Objective. To apply classical qualitative and quantitative genetic approaches to identify the presence of the Rdc1 gene conferring resistance to soybean stem canker caused by Dpc. Materials and methods. The study was conducted at the Universidad Nacional del Rosario, Argentina, between 2012 and 2020. Segregating populations PS-258, PS-157, and PS-172 were evaluated after inoculation with the Dpc16 strain in early (F2:3 families) and advanced generations (F3:5 and F4 families). A completely randomized experimental design was used. Results. The qualitative approach unequivocally identified a single Mendelian locus only in population PS-258. Using the quantitative approach, heritability estimates for PS-258 were 0.68 (F2:3 incidence), 0.17 (F3:5 incidence), 0.55 (F2:3 severity), and 0.18 (F3:5 severity). The estimated number of genes was 0.78 (rounded to one, for severity only). In PS-157, heritability values were 0.76 (F2:3 incidence), 0.48 (F4 incidence), 0.60 (F2:3 severity), and 0.21 (F4 severity), with an estimated gene number of 4.1 for incidence and 0.18 for severity, indicating that both parents contribute resistance alleles at different loci. For PS-172, heritability estimates were 0.89 (F2:3 incidence), 0.92 (F4 incidence), 0.04 (F2:3 severity), and 0.13 (F4 severity), and the estimated number of genes was 0.2 for incidence and 0.24 for severity, consistent with the absence of known Rdc genes in the parental lines. In all populations, phenotypic correlations between incidence and severity were high. Conclusion. The combined use of qualitative and quantitative genetic approaches confirmed the presence of the Mendelian resistance gene Rdc1 in the PS-258 cross, whereas in PS-157 and PS-172, the quantitative approach revealed the involvement of more than one major gene and polygenic effects.