INBREEDING DEPRESSION RATES OF SEMI-EXOTIC MAIZE (ZEA-MAYS L) POPULATIONS

Two semi-exotic maize (Zea mays L.) populations, ESALQ-PB1 x ENTRELACA DO 1 (EE1) and ESALQ-PB1 x CRAVO 4 (EC4) were used to evaluate the eff ects of inbreeding depression of important agronomic traits and the po ssibilities to use them as sources of inbred lines. Two types of proge nies (S-1 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 in bred progenies. Population EE1 had greater ear length and tassel branc h number. The effects of inbreeding depression were more evident in EE 1 for all traits, except ear yield and grain yield. Estimates of inbre eding depression were similar for both populations for ear and grain y ield. 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 samp le of homozygous lines (A = mu + a) were smaller than the overall cont ribution of the heterozygotes to the mean (d) for ear yield and grain yield. Increasing homozygosity through continuous selfing and selectio n against recessive deleterious genes would contribute to enhance the agronomic pattern of inbred lines in both populations.