Abstract

SAHAGUN-CASTELLANOS, Jaime  and  VILLANUEVA-VERDUZCO, Clemente. Synthetic varieties derived from single or double crosses?. Rev. Chapingo Ser.Hortic [online]. 2012, vol.18, n.3, pp.279-289. ISSN 2007-4034.  https://doi.org/10.5154/r.rchsh.2012.06.31.

The use of synthetic varieties (SVs) derived from single (Syn_SC) or double (Syn_DC) crosses is a way of avoiding the high seed cost of hybrid maize (Zea mays L) and onion (Allium cepa L.) varieties, among others. In addition, these SVs could be used to more economically predict the genotypic means (GMs) of the SVs derived from the hybrid parental lines (Syn_L). It is known, however, that the inbreeding coefficients (ICs) of the Syn_L, Syn_SC, and Syn_DC derived from the same lines can differ, but the reason why is unknown. This lack of knowledge makes it difficult for the breeder to improve the representation of the Syn_L through the Syn_DC and Syn_SC and thereby to improve the estimation of the Syn_L GM. The objective of this study was to determine the reason why the Syn_L, Syn_SC, and Syn_DC can differ. From unrelated L lines whose IC is F_L, L/2 single (SCs) and L/4 double crosses (DCs) were derived; and each line, SC, and Dc were represented by m individuals. By randomly mating each set of parents, the Syn_L, Syn_SC, and Syn_CD were formed. It was found that the genotypic arrays of the three SVs differ because with the same 4 initial lines the number of non-identical by descent genes contributed to the genotypic array is larger as fewer lines are involved in a parent [lines (1), single crosses (2), and double crosses (4)]. Thus, the ICs of Syn_L and Syn_DC are the smallest and largest, respectively; and it is expected that the GMs show the opposite ordering. In addition, as m and F_L are smaller the differences among the genotypic arrays of the SVs are larger. On the contrary, when the L lines are pure, the genotypic arrays of Syn_L and Syn_SC are equal, and their IC must be equal as well. To be equal to Sin_L, Syn_DC requires, in addition, a large m. However, even with F_L < 1, as m is larger the genotypic arrays of Syn_SC and Syn_DC tend to the genotypic array of Syn_L, although slowly, particularly for Syn_DC.

Keywords : Allium cepa L.; Zea mays L.; inbreeding; synthetic varieties; hybrids; genotypic array.