Piramidação de alelos visando resistência múltipla ao nematoide do cisto da soja

Abstract

The presence of certain pathogens has significantly affected the yield potential of soybean crops, particularly the soybean cyst nematode (Heteroderaglycines). Although various management strategies are available to control this pathogen, the use of resistant cultivars remains the most effective approach. However, the genetic control of resistance—being a quantitative trait poses challenges for the selection of new cultivars, especially when resistance alleles are linked to undesirable agronomic characteristics. Therefore, this study aimed to select recombinant genotypes with broad resistance to soybean cyst nematode combined with yellow seed coat coloration. The research was conducted by hybridizing two soybean lines: "TMG4182" and "PI437654". The resulting population was advanced through the Bulk method up to the F4 generation. Seeds from the F4 generation were phenotyped and genotyped in four separate experiments, each corresponding to a specific nematode race of interest (races 2, 4, 4+, and 14+). The experiments were carried out at the GDM experimental station located in Cambé, Paraná, Brazil. An augmented block design was employed, consisting of nine control treatments and regular treatments (F4 plants), with six and one replication(s), respectively. Each plot was composed of a single plant, individually placed in seedling trays. Inoculation was performed seven days after sowing, using 4,000 eggs and juveniles of the cyst nematode. Genotyping material was collected at the V3 vegetative stage. Thirty days after inoculation, root phenotyping was conducted to quantify the number of females. Following the female count, female index values were calculated. Individual analysis of variance (ANOVA) was performed for each experiment. Subsequently, a joint analysis was carried out using a Linear Mixed Model (LMM). Genotypic data were visualized through Sankey diagrams, alongside phenotypic responses, to reveal patterns and associations between genotypes and phenotypes. All statistical analyses were conducted in the R environment. Significant differences (p < 0.05) were observed among all regular treatments across all experiments. Sankey diagram analyses revealed clear patterns between phenotypes and genotypic markers for races 2 and 4. However, reduced consistency in these patterns was observed for races 4+ and 14+, suggesting a more complex resistance mechanism. This complexity is likely associated with factors such as Rhg1 and Rhg4 copy number variation and the contribution of minor effect genes.Based on the results, it can be inferred that the use of PI437654 as a parent in breeding programs enables the development of recombinant genotypes that combine resistance to soybean cyst nematode with yellow seed coat coloration. Nonetheless, the three molecular markers employed were insufficient to fully explain the phenotypic variation in resistance, reflecting the polygenic nature of the trait. Broader genotyping efforts are necessary to enhance the efficiency of marker-assisted selection.