Articles

Inbreeding and yield of synthetic varieties derived from single and double cross hybrids


Abstract


Maize (Zea mays L) seed saving among producers in low-income and lesser in developed countries is often prac-ticed. In México, advanced generations of maize hybrids and even mixtures of single-cross (SCs) and double-cross hybrids (DCs) are grown. These populations are expected to perform similar to the synthetic varieties (SVs) . srenibmocd ooge ra, ylbamuserp, tahts dirbyhe htf on oitavirede htn id evlovnis enile htm orfd evirede bd luoct ahtThe derivation of SVs from hybrids seems attractive because would be easier because of the reduced number of potential parents. The frequencies of the genes of the SCs, however, may differ from those of the DCs, may affect the inbreeding coefficient, and thereby the genotypic mean. To address these and related issues, this study was conducted to derive formulae to calculate the inbreeding coefficient (IC) and to predict the genotypic mean (GM) of SVs derived from a mixture of s SCs and d DCs, each represented by m individuals. Formulae for its IC (FSynSC,DC) and GM (YSynSC,DC) were derived. For hybrid parents derived from fully inbred and unrelated lines, FSynSC,DC = [2ms+d(m+1)]/[4m(s+d)2] and, independently of the type of lines, YSynSC,DC = YPS/(s+d)+YPC(s+d−1)/(s+d), where YPS is the genotypic mean of the s + d populations that result from randomly mating the m individuals of each par-ent, and YPC is the mean of all crosses between the s + d parents. From eight lines, three sets of parents (each set involved all eight lines) were considered: 1) four SCs (4SC), 2) two SCs and one DC (2SC+DC), and 3) two DCs (2DC). The SV produced by 4SC shows the lowest IC, although for large m (m > 10) the IC of the SV produced by 2DC is about equal. The largest IC, and thereby the smallest GM, is associated to 2SC+DC because the coances-try between individuals and gene frequencies in SCs are twice those of DCs. What is more noticeable, however, is that 2DC produces the cheapest way of deriving and predicting a SV since only three entries are required (two parents and their cross) and with large m the IC is about the minimum.

Keywords

Zea mays L, yield prediction, inbreeding coefficient, synthetic variety

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Maydica - A journal devoted to maize and allied species

ISSN: 2279-8013