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Inbreeding depression rates of semi-exotic maize (Zea mays L.) populations^*

Luciano Lourenço Nass^I; José B. de Miranda Filho^II

^ICENARGEN/EMBRAPA, SAIN Parque Rural, 70770-900 Brasilia, DF, Brasil
^IIDepartamento de Genética, ESALQ/USP, Caixa Postal 83, 13400-970 Piracicaba, SP, Brasil. Send correspondence to J.B.M.F.

ABSTRACT

Two semi-exotic maize (Zea mays L.) populations, ESALQ-PB1 x ENTRELAÇADO 1 (EE1) and ESALQ-PB1 x CRAVO 4 (EC4) were used to evaluate the effects of inbreeding depression of important agronomic traits and the possibilities to use them as sources of inbred lines. Two types of progenies (S₁ and full-sib) were used. The semi-exotic population EC4 had higher means for plant height, ear height, ear diameter, stand, number of ears per plot, ear yield and grain yield for both noninbred and inbred progenies. Population EE1 had greater ear length and tassel branch number. The effects of inbreeding depression were more evident in EE1 for all traits, except ear yield and grain yield. Estimates of inbreeding depression were similar for both populations for ear and grain yield. The estimates per 1% increase in homozygosity were 0.85 for ear yield and 0.71 g/pl for grain yield in EE1, and 1.20 for ear yield and 1.02 g/pl for grain yield in EC4. The expected means of a random sample of homozygous lines (A = m+ a) were smaller than the overall contribution of the heterozygotes to the mean (d) for ear yield and grain yield. Increasing homozygosity through continuous selfing and selection against recessive deleterious genes would contribute to enhance the agronomic pattern of inbred lines in both populations.

Keywords: inbreeding depression; semi-exotic maize.

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* Part of a thesis presented by L.L.N. to Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ), Universidade de São Paulo (LISP), in partial fulfillment of the requirements for the Doctoral degree.