Tlr1 may be allelic to tb1
--Patricia S. Springer and J.L. Bennetzen

Crosses were performed to determine if there is an interaction between Tillered1 (Tlr1) and teosinte branched1 (tb1). Tlr1 is a dominant mutation reported to confer excessive tillering in the heterozygous state (Neuffer et al., MNL 61:50-51, 1987). In the W23/L317 background supplied by the Maize Genetics Coop, this phenotypic effect is not severe. Tlr1 had previously been mapped to the long arm of Chromosome 1. The recessive mutation tb1 causes excessive tillering and the conversion of ear shoots into vegetative branches (Burnham, MNL 35:87, 1961). Schnable recently reported (MNL 66:5, 1992), and we have also observed, that tb1 acts as a semi-dominant allele for increased tiller number in some environments.

Self pollination of a Tlr1/+ plant resulted in F2 progeny that segregated for the teosinte branched phenotype, including ear shoots converted into vegetative tassels. A cross between Tlr1/+ and tb1/tb1 plants resulted in 15 teosinte branched and 25 wild-type progeny. The deviation from a 1:1 ratio may be due to the poor penetrance of the teosinte branched phenotype (our unpublished observations).

These results, together with the fact that Tlr1 and tb1 map to the same region of 1L, suggest that Tlr1 and tb1 are allelic. Alternatively, Tlr1 and tb1 may be semi-dominant mutations in different genes that both condition the same phenotype and, when heterozygous in the same plant, provide an additive effect that mimics allelism. 

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