|Abstract or Summary
- The success of a plant breeding program depends upon the availability of
useable genetic diversity. Such diversity may be enhanced depending on the type of
hybridization strategy employed. Segregating progenies resulting from F2
populations, a double cross, and a top cross were compared for the amount of
useable genetic diversity associated with six traits in durum wheat. The parental lines
were three winter selections, H7092-11, H7092-52, and WD5, and two spring
cultivars, WPB 881 and Altar 84. Traits evaluated were (1) plant height, (2) days to
maturity, (3) harvest index, (4) kernel weight, (5) grain yield, and (6) pigment
Analysis of the population mean values suggested the superiority of the F1 top
cross for plant height, kernel weight, and grain yield. The F1 top cross progeny also
had the highest genetic variability for grain yield. F2 population of the cross Altar
84 I H7092-52 gave the highest mean values for days to maturity and harvest index,
and showed the highest genetic diversity for traits other than grain yield. The only
population showing detectable genetic variance for pigment content was the F2
progeny of the single cross WPB 881 / H7092-11. When genetic diversity was
detected, the double cross was approximately intermediate between the two F2
populations from which it was derived. Transgressive segregation was more frequent
in the top cross population for grain yield, kernel weight, and plant height.
No associations between grain yield and the other traits were noted for the F2
population of the single cross Altar 84 I H7092-52 and the top cross population. For
the second F2 population (WPB 881 / H7092-11) and the double cross population,
grain yield was found to be associated with harvest index and plant height.
The only consistent relationship across all segregating generations was a negative
correlation between plant height and harvest index.
Based on the genetic diversity and the transgressive segregation observed, top
crossing appears to be the more promising in improving grain yield in the
experimental material investigated. For specific traits other than grain yield, it would
appear that single crosses would be a more productive approach, however progress
would depend on the specific parental combination. The double cross was inferior
to the other crossing strategies for the traits measured.