Recurrent Selection for Reduced Tassel Branch Number and Reduced Leaf Area Density above the Ear in Tropical Maize Populations

Tropical maize (Zea mays L) is characterized by large tassels, broad, long leaves above the ear, and by a low harvest index. This study was conducted to evaluate direct and correlated responses to selection for reduced tassel primary branch number and for reduced leaf area density above the ear (LADAE). Leaf area density above the ear was defined as (number of leaves above the ear ✕ mean area of leaves EL + 1, EL + 3)/(plant height — ear height) ✕ land area occupied per piano, where EL refers to the position of the ear leaf. Six cycles of full-sib recurrent selection for each of these traits was conducted in each of two populations (‘Tuxpeño-l’ and ‘Antigua-República Dominicana’). In a third population, ‘ETO Blanco’, there was simultaneous selection for both traits. Evaluation of Cycles 0 and 6 of single trait selections and Cycle 0,2,4, and 6 of combined trait selection, plus checks, was at several plant densities at three locations in Mexico over 2 yr. Significant (P = 0.05) mean gains per cycle for tassel branch number, LADAE, grain yield, and harvest index were: (i) Tuxpeño-l: selection for reduced tassel branch number:−7.4, not significant (NS), 2.2, and 2.4%; selection for reduced LADAE: −1.2, −3.8, NS, and 3.8%; (ii) Antigua-República Dominicana: selection for reduced tassel branch number: −8.6, −1.6, 2.4, and 2.2%; selection for reduced LADAE: −5.7, −2.6, 2.0, and 2.2%; and (iii) ETO Bianco, selection for reduced tassel branch number and LADAE: −6.8, −1.8, 2.5, and 2.9%, respectively. The correlation between LADAE and mean maximum leaf width, after removing the population effect, was 0.95**, significant at the 0.01 probability level (13 df. In all populations, selections resulted in significant increases in the predicted optimum plant density for grain yield, significant decreases in the anthesis-to-silking interval, and a shorter interval from planting to 50% silking.