BGS 743, Tweaky spike 1, twk1

Tweaky = tw (1, 5).
Tweaked spike (3).

Monofactorial recessive (5).
Located in chromosome 7H (5).

Tweaky is a spike development abnormality in which one or more rachis internodes in the upper third of the spike are elongated and rounded in shape giving the appearance of a short stem. As a result, the spike is misshapen or twisted and appears to have missing kernels (6). Often rachis internodes just above the tweaked area are foreshortened and give a bunched appearance of spikelets. The tweaky characteristic has been reported only in the cultivar Wisconsin Barbless (CIho 5105) where it occurs in only a small percentage of the spikes (6). See Reid and Wiebe (3) for a photo of the twk1.a mutant. Chemically induced mutants in barley that exhibit instability in inflorescence and floral organ development have been isolated (4, 7). These mutants resemble some of the traits associated with twk1.a mutant. Partial rescue of specific phenotypic features of tweaky mutants following treatment with auxin inhibitors and the synthetic auxin 2,4-dichloroacetic acid (2,4-D) has been reported (4).

Natural occurrence in Wisconsin Barbless (CIho 5105) (1, 6).

twk1.a in Wisconsin Barbless (CIho 5105) (1, 6); a tweaky-like spike phenotype might be present in the two-rowed cultivar ND Genesis (PI 677345) (2). Chemically induced mutants in Auksiniai II have somewhat similar, but more extreme, phenotypes (4, 7); however, they have not been tested for allelism with the twk1.a mutant.

twk1.a in Wisconsin Barbless.

1. Åberg, E., and G.A. Wiebe. 1948. Taxonomic Value of Characters in Cultivated Barley. U. S. Dept. Agr. Tech, Bul. 942. 88 pp.
2. Franckowiak, J.D. (Unpublished).
3. Reid, D.A., and G.A. Wiebe. 1968. Taxonomy, botany, classification, and world collection. p. 61-84. In Barley: Origin, Botany, Culture, Winterhardiness, Genetics, Utilization, Pests. USDA Agric. Handb. No. 338.
4. Šiukšta, R., V. Vaitkūnienė, G. Kaselytė, V. Okockytė, J. Žukauskaitė, D. Žvingila, and V. Rančelis. 2015. Inherited phenotype instability of inflorescence and floral organ development in homeotic barley double mutants and its specific modification by auxin inhibitors and 2,4-D. Ann. Bot. 115:651-663.
5. Smith, L. 1951. Cytology and genetics of barley. Bot. Rev. 17:1-51, 133-202, 285-355.
6. Wiebe, G.A., and D.A. Reid 1961. Classification of Barley Varieties Grown in the United States and Canada in 1958. U. S. Dept. Agr. Tech, Bul. 1224. 234 pp.
7. Žvingila , D., V. Vaitkūnienė, J. Patamsytė, A. Leistrumaitė, M. Staniūtė, L. Balčiūnienė, T. Cėsnienė, V. Kleizaitė, R. Šiukšta, and V. Rančelis. 2012. DNA polymorphism and agronomic traits of revertants from barley (Hordeum vulgare L.) mutant tw. Žemdirbystė=Agriculture 99:138-148.

J.D. Franckowiak 2017. Barley Genet. Newsl. 47:185-186.