Dekalb-Pfizer Genetics


Iowa State University

Detection of RFLPs among strains of W22 --E.B. Godshalk and M. Lee Inbred lines of maize exhibit various levels of genetic stability over generations of self-pollination (Bogenschutz and Russell, Euphytica 35:403-412, 1986). Inbred W22, released in 1948 by the University of Wisconsin, has been maintained at Iowa State University for at least 25 generations of self-pollination (strain W22-IA). Replicated comparisons of two strains of W22 (W22-IA and W22-WI, maintained at the University of Wisconsin) detected significant differences for 1000-kernel weight (243 vs. 199 g for W22-IA and W22-WI, respectively). W22-IA and W22-WI were not significantly different from each other for nine other traits; however, significant mid-parent heterosis values were detected for four traits (grain yield, kernel row number, cob diameter, and tassel branch number) in the W22-IA/W22-WI hybrid (Lamkey et al., Crop Sci 28:896-901, 1988).

The strains were evaluated for RFLPs with 29 mapped clones distributed throughout the genome. Five clones detected polymorphisms between the strains; four of the clones have been placed to chromosome ten.

The origin of the polymorphisms is unknown. Pollen contamination or seed mixture do not seem to be likely explanations given the overall morphological similarity of the strains. Residual heterozygosity in the original W22 could account for some or all of the observations. Whatever the cause(s), our observations for W22 strains and similar reports for inbred P39 (Gerdes and Tracy, MNL 63:93, 1988) suggest limitations (and opportunities) for identification of inbred lines with RFLPs.

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