Maize Genetics Cooperation Stock Center

The dominant inhibitor of R1-ch aleurone color, M-ch, and the Spotted-dilute inhibitor Dil map to the same location as inr1 and are likely inr1 alleles.

—Stinard, PS

Kermicle (1988, Recombinant Mutable Alleles of the Maize R Gene, pp. 81–89, in Plant Transposable Elements, ed. by O. Nelson) describes a dominant factor called M-ch that selectively inhibits R1-ch aleurone pigmentation. We previously reported on r1 haplotype-specific inhibitors of aleurone color, Inr1 and Inr2, that also inhibit R1-ch aleurone pigmentation (Stinard and Sachs, 2002, J Hered 93:421–428). We obtained seeds of M-ch from Jerry Kermicle and performed tests to determine whether M-ch maps to the same location as either inr1 (10L) or inr2 (9L). The crosses were set up as follows: Plants of the homozygous genotype r1-r M-ch were crossed as males onto plants homozygous for either Inr1-JD R1-Randolph or Inr2-JD R1-Randolph. Seeds from both sets of crosses were planted, and the resulting plants were crossed by either R1-Randolph or R1-ch(Stadler) (both of which are inhibited by M-ch and Inr1-JD) without inhibitors. Crosses involving Inr2-JD showed independent segregation of two dominant aleurone color inhibitors. However, the Inr1-JD test crosses showed no recombination in a large sample of kernels (3,146), indicating a map distance between the two inhibitors of less than 0.06 centiMorgans. Since both M-ch and Inr1-JD share the same phenotypic interactions with suppressible r1 haplotypes, and since they map to virtually the same location, it is likely that they are allelic, if not identical.

Last year (MNL 78:62–63), we reported preliminary data suggesting that the dominant r1 haplotype-specific inhibitor from the Spotted-dilute controlling element system, Dil, maps to the same location as inr1. One full-colored putative crossover was recovered out of a population of 7,112 kernels, indicating separation of 0.03 centiMorgans. When this putative crossover kernel was planted and the resulting plant crossed to the suppressible haplotype tester R1-Randolph, the testcross ear segregated for pale purple kernels, indicating that the putative crossover carried an inhibitor and was not a crossover after all. (Segregation ratios suggest that the full colored exception was the result of the change of one of the suppressible r1 haplotypes present in the linkage cross, R1-Randolph or R1-r(spotted dilute2), to a nonsuppressible form.) One more round of linkage tests between Dil and inr1 was performed this summer (testcross: [Inr1-JD R1-Randolph × Dil R1-r(spotted dilute2)] × inr1 R1-Randolph), yielding 5,162 pale purple parental type kernels and no putative full colored crossovers. Combining the two years of data, we obtained no crossovers in a population of 12,274 kernels, indicating less than 0.02 centiMorgans separation. Thus, Dil is very likely another inr1 allele.

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