Selection Among and Within Full‐sib Families to Develop Single‐crosses of Maize1

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Abstract
Systematic genetic advance in maize (Zea mays L.) hybrid yields depends on the improvement of breeding populations and the efficient extraction of inbred lines. We evaluated the efficacy of selection among and within fullsib families produced in two 2‐eared populations for the extraction of lines and for the identification of superior yielding hybrids. Intra‐ and interpopulation crosses were made among selected and unselected lines developed from ‘Iowa Two‐ear Synthetic’ (BSI0) and ‘Pioneer Prolific Composite’ (BSll). The selected lines were superior paired‐plant interpopulation crosses tested from the S0 ✕ S0 through S4 ✕ S4 generations. Six sets, each containing 28 crosses, produced from selected and unselected lines, were grown in three locations for 3 years.Interpopulation crosses averaged 5.8 quintals/ha (7.4%)greater yields than intrapopulation crosses, and the crosses of selected lines yielded 8.7 quintals/ha (11.2%) more than crosses of unselected lines. On the average, the tested paired‐plant crosses yielded 3.7 quintals/ha (4.2%) more than the untested crosses among selected lines and the specific combining ability (SCA) effects tended to be strongly positive for the tested line pairs. The yields of the previously untested crosses among the selected lines also showed that the selected lines expressed high general combining ability (GCA) with other selected lines.If the five best single‐crosses from each set were selected (9% selection intensity), 28 of 30 were from interpopulation crosses, 23 of 28 from selected lines, and II of 23 from the tested‐line pairs. If only the selected interpopulation crosses were grown (96 entries), 23 of the best 30 hybrids were identified from 336 entries. The method of selection, therefore, does develop an elite group of lines having high SCA with its tested mate and also high GCA with other elite lines with a minimum of testing. Thus selection among and within full‐sib families seems to be an efficient method of developing superior parental lines for hybrids.

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