Abstract:To determine the relationship between flowering syndrome and hybrid performance in some maize (Zea mays L.) crosses, selection on early and late flowering plants was undertaken. Selection was applied on plants of four inbreds; Zm19, Zm32, Zm51, and Zm61. Selected plants were propagated in the next season, grown in the third season and crossed to two testers (Zm21 late, and Zm60 early). The F1 seeds were planted in the fourth season in a randomized complete block design of three replicates in 83'000 plants/ha. This was done in the farm of the College of Agric., Univ. of Baghdad. The results showed that selection for divergent flowering of inbred gave significant difference in days to silking among all crosses. The days ranged between 62 d for early selects, to 66 d for late selects. This was reflected on time of seed filling that increased grain yield. The best crosses gave plant growth rate of 18.3 -21.6 g.m , and seed filling of 35 -38 d. The cross that gave highest response of selection (61 x 21) gave 1.79 kg.m -2 dry matter for early select, and 2.20 kg.m -2 for late flowering select cross. It was recommended to select on maize inbreds to create new variations for better traits provided using large inbred populations.

A field experiment was conducted for 4 seasons on the farm of the Dept. of Field Crop Sci., Coll. of Agric., Univ.of Baghdad in spring and fall plantings in 2014 and 2015. That was to determine the relationship of hybrid performance in maize (Zea mays L.) crosses with early and late selects of inbreds. Four inbreds; Zm19, Zm32, Zm51, and Zm61 were grown and the very early and very late silking plants were selected and selfed for propagation in the first two seasons. The third season involved growing the selects and top-crossing with early and late inbreds (Zm60 and Zm21). The sixteen crosses were planted in season 4 in RCBD of 3 replicates in population density of 83'000 plants. ha ). The same cross gave higher grain yield than late Zm19 crossed to late inbred (Zm21) (6.64 t. ha -1 ). Early selects on inbreds crossed to testers showed significant differences in kernel growth rate (KGR), kernel filling duration (KFD) and kernel weight. Values of KGR ranged between 3.2 -3.5 g. plant , and kernel weight could be good candidates for selection on inbreds that could help developing new high grain yield hybrids.