Resumen

SAHAGUN-CASTELLANOS, Jaime  y  RODRIGUEZ-PEREZ, Juan Enrique. Inbreeding of synthetic varieties derived from lines and single crosses. Rev. Chapingo Ser.Hortic [online]. 2011, vol.17, n.3, pp.107-115. ISSN 2007-4034.

The exploitation of heterosis in crops such as tomato (Licopersicon esculentum Mill.), onion (Allium cepa L.) and corn (Zea mays L.) has been limited by the high cost of F₁ seed. To avoid this, producers have resorted to using F₂, F₃ ... seed. However, the inbreeding depression that this practice produces has led plant breeders to consider the synthetic varieties (SVs), particularly for cross-pollinated crops, which are not, however, without problems. In this work, the derivation of a SV whose parents are L lines and s single crosses (Syn_L'SC) is proposed as a way of decreasing the parent number (originally L+2s lines) and thereby also the costs and work involved in prediction. However, the most important Syn_L'SC quality indicators must be known in order to make an objective assessment. Thus, the study objectives related to Syn_L'SC were to determine: 1) the inbreeding coefficient (FSyn_L'SC) and 2) the best combination of L and s values. The derivation of FSyn_L'SCwas based on the replacement of the general genotype of the genotypic array of Syn_L'SC(GASyn_L'SC) by the coancestry between the individuals that contribute the genes that make up this genotype, and the best combination of L and s values was the one that produced the lowest inbreeding coefficient. From a fixed even number of L + 2s fully inbred and unrelated lines and from two decompositions of GASyn_L'SC, it was found that FSyn_L,_SC={1+Ls/[2(L+s)²]}/(L+2s). By inspection of the formula, FSyn_L'SC reaches its minimum in two cases: when L = 0 and when s = 0. However, the use of (L+2s)/2 single crosses requires fewer resources for prediction.

Palabras llave : Allium cepa L.; Zea mays L.; coancestry; prediction; genotypic array.

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