Theoretically, in a recurrent selection program, the use of doubled haploids (DH) can increase genetic advance per unit of time. To evaluate the efficiency expected from the use of DH for the improvement of grain yield in a maize (Zea mays L.) population, two recurrent selection programs for testcross performance were initiated using testcross progenies from DH lines and S1 families. In 4 years one selection cycle using DH and two selection cycles using S1 families were carried out with the same selection intensity for both methods. As expected, testcross genetic variance was twice as high among DH lines as among S1 families. The predicted genetic gain was 8.2% for the DH selection cycle, and 10.6% for the two S1 selection cycles, giving a per year advantage of 29% for the S1 family method over the DH method with a cycle of 4 years. With a 3-year cycle for the DH method, both methods were expected to be equivalent. Using a tester related to the one used for selection, the genetic gains obtained were equivalent for both methods: 6.6% for the DH cycle and 7.0% for the two S1 cycles. With a 3-year cycle for the DH method, the advantage would have been in favor of DH method. Furthermore, the DH method has the advantage of simultaneously producing lines that are directly usable as parents of a hybrid. Thus, if the genetic advance per unit of time is evaluated at the level of developed varieties even with the same or with a lower genetic advance in population improvement, the DH method appears to be the most efficient.
Progress made in the in situ gynogenesis technique since 1990 now allows production of a high number of maize (Zea mays L.) doubled-haploid (DH) lines. The aim of the study was to compare DH lines versus selfing lines for testcross performance. DH and single-seed descent (SSD) lines were produced from random S 1 progenies of a broad-base population. For grain yield, kernel moisture, plant height, ear height and leaf length, the three population means were similar. Except for kernel moisture, the genetic variance of DH lines was nearly twice as high as the genetic variance of S 1 families, as expected. On the other hand, genetic variance among SSD lines was only 1.5 times higher than the genetic variance of S 1 families. This lower variance could be due to a selection bias in the method of production of SSD lines. However, for all traits, heritability of SSD or DH lines was higher than heritability of S 1 families. Epistasis effects in DH progenies were not significant. The consequence was a high correlation between S 1 testcross progenies and DH or SSD testcross progenies, meaning that the S 1 testcross value can be used to select the best families from which DH lines will be extracted. As a whole, the observed variation in DH lines appeared to be more in accordance with the observed variation among S 1 families than with the observed variation among SSD lines.
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