Segregation and linkage analyses in two complex populations derived from the citrus rootstock Cleopatra mandarin. Inheritance of seed reproductive traits
Two complex populations derived from the salt-tolerant citrus rootstock Cleopatra mandarin were used to investigate (1) the genomic regions affected by segregation distortion and (2) gene segregation heterogeneity and their causes and to obtain (3) a Citrus reshni linkage map to genetically analyze (4) the duration of the juvenility period and the seed embryony type. Both populations differed in the extent and origin of segregation distortion. The population derived from the cross between C. reshni and Poncirus trifoliata (R × Pr) showed 75 % of codominant markers with distorted segregation. The origin of this distortion was prezygotic in most cases. Meanwhile, 100 % of codominant markers in the self-pollinated population [F2(R × Pr)] showed genotypic distortion, and the origin of such distortion was mostly postzygotic, with the heterozygote being the most frequent genotype in all cases. In the R × Pr population, where two pollinator varieties were used, allele segregation was significantly heterogeneous not only in P. trifoliata (28.6 % of markers) but also in C. reshni (19.5 %). The results on segregation heterogeneity in the F2(R × Pr) suggest the presence at linkage group 4c of a postfertilization system of balanced lethal factors that reduces homozygosis in self-compatible hybrids. Four low to medium contributing quantitative trait loci (QTLs) were detected for the duration of juvenility period by both Kruskal–Wallis and interval mapping methodologies. For seed embryony type, three QTLs were detected by both methodologies, with the previously reported Apo2 being the QTL contributing the most. CR14,290 and TAA15 are good markers for early selection of polyembryonic rootstocks in progenies derived from C. reshni, Citrus aurantium, and Citrus volkameriana.
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