Plant introductions (PIs) can be used to increase the genetic diversity of soybean [Glycine max (L.) Merr.] populations. A recurrent selection program was initiated to determine if populations with PI parentage would exhibit greater genetic gain for seed yield than a population with no PI parentage. The objective of our study was to evaluate the genetic gain for seed yield and correlated responses in maturity and lodging from three cycles of recurrent selection in five soybean populations, AP10 to AP14, formed with different percentages of PI parentage. The percentages of PI parentage were 100% in AP10, 75% in AP11, 50% in AP12, 25% in AP13, and 0% in AP14. In each cycle, 200 F4‐derived lines for each population were evaluated and the 20 highest yielding lines were chosen as parents for the next cycle. For our study, the 20 parents of Cycles 1, 2, and 3 were grown in a randomized complete‐block design at three Iowa locations. There was a significant (P < 0.01) linear increase in seed yield for all populations across the three cycles. The gain from selection for seed yield was 153 kg ha−1 (5.4%) cycle−1 for AP14, 80 (2.8%) for AP13, 85 (3.1%) for AP12, 54 (2.0%) for AP11, and 66 (2.5%) for AP10. AP14 had the highest mean yield of the parents of each cycle and the highest yielding parent of each cycle. A significant linear increase in mean days to maturity was observed in all populations, except AP13. Lodging scores exhibited a significant linear decrease in AP10 and AP13, but no significant response was observed in the other three populations. The results indicated that after three cycles of selection, Pis used to form AP10 to AP13 did not increase genetic gain for seed yield compared with AP14 that was developed from only adapted cultivars and experimental lines.
The success in identifying heterosis in hybrid maize (Zea mays L.) breeding depends on the availability of reliable genetic diversity among maize inbred lines. Conventional methods of breeding have been boosted by the availability and efficiency of molecular markers. Coupling simple sequence repeat (SSR) markers with morphological markers provides thorough starting information for new inbred lines, especially from different genetic backgrounds. Furthermore, recent evidences that the environment can influence the epigenetic structure of the genome have necessitated morphological screening of crops during breeding programmes. This study used 28 agronomic traits and 14 SSR markers which are distributed uniformly in ten (1-10) inbred lines, namely EM11-133, EM12-210, OSU23i, CML395, CML202, CML442, CML444, CML208, CML312 and CML204 from Kenya, International Centre for the Improvement of Maize and Wheat (CIMMYT), and another (OSU 23i) from USA. The aim was to investigate their morphological and genetic diversity, categorise the inbred lines into useful groups based on the molecular profiles and morphological traits, and lastly determine the level of phenotype-genotype correlation. The dissimilarity calculated using SSR markers had a mean morphological dissimilarity of 0.895403, an r value of -0.1421 and a p -0.9840. The dissimilarity between the molecular and morphological traits was 0.860465. Comparison between the molecular and morphological data had a dissimilarity matrix with an r -0.2323 and a p value of 0.0120. This was probably due to intrinsic synteny in maize genome. The dendrograms generated with hierarchical Unweighted Pair Group Method with Arithmetic mean (UPGMA) cluster analysis of the Jaccard's similarity coefficient matrices revealed four major clusters. The Co-ancestry distance showed six tied groups with the Kenya cluster showing some differentiation with Exact Tests for population differentiation with a p = 0.0513. The American inbred line (OSU 23i) segregated alone, while the Kenya lines (EM11-133 and EM12-210) had close homology with the CIMMYT inbred lines (CMLs). A total of 2.0 alleles were detected among the inbred lines using bulk DNA samples and 14 SSR loci. Clustering analysis based on the genetic similarity coefficients separated the inbred lines into 4 groups with the American inbred line seeming to be genotypically more diverse from the others.Key Words: Genetic diversity, molecular markers, SSR, Zea mays RÉSUMÉLe succès dans l'identification des hétérosis de maïs hybrides (Zea mays L.) dépend de la disponibilité d'une diversité génétique fiable dans les lignées endogames du maïs. Les méthodes conventionnelles de l'hybridation avaient été améliorées par la disponibilité et l'efficacité des marqueurs moléculaires. Le couplage des marqueurs simples de sequence répétée (SSR) avec les marqueurs morphologiques fournit des informations fondamentales précises pour les nouvelles lignées endogames, principalement de différente constitution génétique. En outre, les recentes évidences selon...
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