Triticurn aestivum, bread wheat, spring wheat, uniculm effect, ideotype. SUMMARYThe concept of the uniculm habit as an important feature of a wheat ideotype for a mediterranean environment was evaluated under field conditions. A uniculm plant produces a single shoot and when sown in a stand exemplifies a non-tjllering crop with a fixed density of shoots throughout the growing season. Yield and harvest index of normal tillering spring wheat was compared with that of the same crop surgically detillered throughout the growing season to a constant density of 2 shoots per plant. The use of a biculm, whilst retaining the uniculm principle of a fixed density of shoots throughout the growing season, permitted comparison on a single crop sowing at normal field density.The control plots followed the usual pattern of tillering for the region attaining a maximum of about 4.0 shoots per plant by early spring. Shoot number declined to 2.3 and 2.6 per plant by maturity in 1978 and 1979, respectively.
Eight full‐season tropical maize (Zea mays L.) populations were improved by the International Maize and Wheat Improvement Center (CIMMYT) using full‐sib (FS) selection and international testing. Cycles CO, C2, and the latest (fourth or fifth) cycle of selection were evaluated at six locations to measure the progress from FS selection. Gains per cycle, averaged over the eight populations for yield, days to silk, plant height, ear height, ear rating, and ears per plant were 1.31, −0.59, −1,06, −1.77, −1.15, and 0.87%, respectively. The ranges in improvement for the same traits were, −0.04 to 1.90, −0.93 to 0.27, −1.89 to 0.75, −3.38 to 0.36, −3.41 to 0.71, and 0 to 1.92%, respectively. In all environments, the latest cycles of selection yielded higher than CO. Our results suggest that FS selection is an effective method for improving maize populations and that the progress per cycle would vary with the selection intensity, quality of data, type of FS selection, and the heritability of the trait. Improved CIMMYT maize populations as such, experimental cultivars developed by recombining among their superior families, as well as their superior FS families are being used by national programs as cultivars, in hybrid combinations, and for extraction of inbred lines.
The International Maize and Wheat Improvement Center uses full‐sib (FS) family selection based on internationally replicated trials to improve several tropical maize (Zea mays L.) populations. Improvements made in four medium maturity tropical maize populations are reported here. Selection from CO to C1 in ‘ETO Blanco’ (EB) and ‘Antigua‐Republica Dominicana’ (ARD), and from C0 C2 in ‘Blanco Cristalino‐l’ (BC) and ‘Mezcla Amarilla’ (MA), involved formation of 250 FS families in one season, and their evaluation in three to six environments in the second season in a 16 ✕ 16 simple lattice design using 40% selection intensity. Additional cycles of selection involved selection among and within FS families using a 2‐yr four‐season system; evaluation and selection of families were done as above, superior S1 plants of the selected FS families were bulk‐sibbed, and the resulting half‐sib families used to develop FS families for subsequent cycles of selection. The C0, C2, and C5 of BC and MA, and CO, C1, and C4 of EB and ARD were evaluated in seven environments to measure progress from selection. Gains per cycle (%) averaged over populations and environments for yield, days to silk, plant height, ear height, ear rating, and ears per plant were 2.11** (significant at the 0.01 probability level), −0.31**, −0.26**, −0.47**, −1.35**, and 1.05**, respectively. The regressions of entries on environmental means generally did not differ significantly from 1.0, indicating stability in the performance of the materials for yield, days to silk, and plant height. Our results indicate that FS selection is an effective method to improve tropical maize populations for the six traits studied.
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