Madison, Wisconsin

University of Wisconsin

 tb1 is epistatic to ba2 --Hurkman, MM, Tracy, WF The genes teosinte branched1 (tb1), barren stalk1 (ba1), and barren stalk2 (ba2), affect branch development. Homozygous tb1 plants lose apical dominance and exhibit many elongated lateral branches at axillary buds along the main culm. In ba1 plants, tillers, ears, and the concave groove on the culm are absent while the tassels lack branches or spikelets. ba1 is epistatic to tb1 and suppresses lateral branching in both the vegetative and inflorescence meristems. ba2 plants, like ba1, lack ears and the concave groove on the culm, but the tassels exhibit bundled branches that have peduncles fused to the culm at the base. The tassels usually develop fertile spikelets. ba2 plants often have tillers and sometimes develop an ear at the soil surface (Fig. 1). Our objective was to determine the epistatic relationship of ba2 and tb1.

An F2 population segregating for ba2 and tb1 was created. In the F2 there was a significant excess of tb1 individuals. tb1 homozygotes and putative ba2/tb1 double mutants were impossible to distinguish. The F2 fit a 9 (wild type): 3 (ba2) : 4 (tb1) ratio, indicating that tb1 is epistatic to ba2 (Shroeck and Tracy, 1998 Maize Genetics Conference Abstracts, p. 81).

In 2001 we grew the same F2 and collected DNA from all the tb1 plants. We used a SSR marker that was closely linked to ba2 to determine what proportion of the tb1 segregates were also homozygous for ba2. Of 76 tb1 plants 25 of them were also homozygous for the ba2 marker. This was not significantly different from expected (C2 = 2.51, p<0.10). These tb1tb1 ba2 ba2 plants were all indistinguishable from tb1tb1 Ba2- plants. Thus, tb1 is epistatic to ba2, while ba1 is epistatic to tb1.

Given the phenotype of these mutants it appears that ba1 suppresses lateral branching at all nodes including those in the tassel. tb1 induces branching at both juvenile and adult vegetative nodes but does not affect the development tassel. Since ba2 plants have tillers, no ears, but relatively normal tassels it appears that ba2 suppresses branch development in the adult vegetative section of the plant.

Figure 1. The base of a homozygous recessive ba2 plant, showing the development of an ear from an underground node.
 
 

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