Ploidy Level Effects and Effects of Inbreeding on Single and Double Cross Performance in Autotetraploid Maize
A potential use of induced polyploidy in maize (Zea mays L.) is to capitalize on the direct consequences of chromosome duplication i.e. larger cell and plant parts. Theory suggests that in autotetraploids performance of double crosses (DC) is expected to exceed that of single crosses (SC) if the SC parents are inbred. The objectives of this study were to determine (1) the effects of ploidy level per se on morphological traits and grain and stover yields in maize, and (2) the relative performance of SC's and DC's from inbreds with different levels of inbreeding in autotetraploid maize. Three autotetraploid maize inbreds, their genetically comparable diploid counterparts, and the three possible hybrids at each ploidy level were evaluated for per se ploidy level differences. In general, autotetraploid inbreds and hybrids had larger plant parts, and higher percent grain and stover moisture than their diploid counterparts. Despite the larger plant parts of tetraploids; stover, cob, grain, and total biomass yields were greater for diploid inbreds and hybrids. Significant ploidy x inbred and ploidy x hybrid interactions resulting in reverse rankings at the diploid and autotetraploid levels were found for certain traits. Thus, ranking of genotypes at the diploid level is not necessarily indicative of their rankings at the autotetraploid level. SC's and DC's were produced from parents at two different levels of inbreeding (S$\sb1$ and S$\sb3$) originating from three autotetraploid maize synthetics. Grain yield and moisture, plant and ear height, pollen shed date, and percent lodging were evaluated. Results agreed with theoretical and experimental results in maize and alfalfa in that (1) for most traits DC's had higher levels of performance than SC's, (2) for most traits generation means were ordered as predicted based on the coefficient of inbreeding (S$\sb1$DC $>$ S$\sb3$DC $>$ S$\sb1$SC $>$ S$\sb3$SC), and (3) the difference between SC and DC means increased as inbreeding of the parents increased. Deviations from expectation were found for grain yield such that S$\sb3$DC $>$ S$\sb1$DC $>$ S$\sb1$SC $>$ S$\sb3$SC, therefore, inbreeding at least to the S$\sb3$ generation before initiating a DC program may be possible.
Agriculture, Agronomy, Biology, Genetics
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign