BGS 97, Accordion rachis 1, acr1

The accordion rachis phenotype was developed by Robert I. Wolfe at the Beaverlodge, Alberta Station of Agriculture and Agri-Food Canada. The F2 progenies from crosses and backcrosses of Bowman to this stock, ACBV89B229, contained very few plants with the accordion rachis phenotype. Examination of the SNP molecular data for the Bowman backcross-derived line, BW009 (Bowman*7/ACBV89B229), identified three chromosomal regions that were retained from the donor parent (1). Only a region of 2HL near the centromere was not present in other BW lines with elongated rachis internodes. This region was assumed to be where the acr1.a allele is located. The other regions were present in BW lines showing a dominant inheritance pattern for slightly elongated rachis internodes. The locus in the retained 4HL region was named Accordion rachis 2, Acr2, and the locus in the 1HL region was named Accordion rachis 3, Acr3.

Lax rachis internode = ril (2).
Accordion rachis = acr (5, 6).

Monofactorial recessive (2, 5, 6), part of a multiple genic series involving acr1, Acr2 and Acr3 required for expression (3).
Located in chromosome 2HL (3); acr1.a is near the vrs1 (six-rowed spike 1) locus because no recombination with the Vrs1.t (deficiens1) allele was observed (3); acr1.a is associated with SNP markers 1_0525 to 2_0667 (positions 65.03 to 117.73 cM) in 2H of the Bowman backcross-derived lines BW009 and BW439 (1), likely in 2H bins 06 to 08.

Rachis internodes are greatly elongated and often bent or pleaded as the spike emerges from the boot or sheath of the flag leaf (5). The line ACBV89B229, developed by R.I. Wolfe to maximize rachis internode length, exhibits extreme elongation of rachis internodes, rachis internode length values up to 7.7 mm, and occasionally trapping of the spike tip in the boot (3, 7). Elongation of the rachis internodes is associated with slightly elongated outer glumes and the deficiens (Vrs1.t) spike phenotype. Two dominant modifiers, Acr2 (see BGS 189) and Acr3 (see BGS 241), caused variable expression of the accordion trait in different genetic backgrounds. In crosses to Bowman, segregation for acr1 fit a three gene model based on DNA segments retained in the Bowman backcross-derived lines BW009 and BW439 (1, 3). Although the acr1 gene is apparently associated with the deficiens spike type, the large centromeric segment of 2H retained does not overlap the six-rowed spike 1 (vrs1) locus (1). A pericentric inversion cannot be eliminated as a possibility. Plants in the BW009 and BW439 lines were about 3/4 of normal height and peduncles were about 1/2 of normal length. The number of fertile rachis nodes was reduced by about 3 and heading was delayed by up to 4 days. Kernels appeared thinner and weighted about 10% less. Test weights were low and grain yield was about 3/4 of normal (3).

A naturally occurring deviant (4) incorporated into several genetic stocks, acr1.a in Beaverlodge stock ACBV89B229 was used to study this locus (3, 7).

acr1.a in ACBV89B229 (GSHO 1617) and ACBV89232 (GSHO 1573) (7).

acr1.a in ACBV89B229 (GSHO 1617); acr1.a in Bowman (PI 483237)*4 (GSHO 1899); acr1.a in Bowman*7 (BW009, NGB 20417 and BW439, NGB 20671).

1. Druka, A., J. Franckowiak, U. Lundqvist, N. Bonar, J. Alexander, K. Houston, S. Radovic, F. Shahinnia, V. Vendramin, M. Morgante, N. Stein, and R. Waugh. 2011. Genetic dissection of barley morphology and development. Plant Physiology. !55:617-627.
2. Enns, H. 1961. Inheritance and linkage studies in barley using chromosomal interchanges and marker stocks. Ph.D. Thesis. Univ. Saskatchewan. pp. 70.
3. Franckowiak, J.D. (Unpublished).
4. Franckowiak, J.D. 1995. Notes on linkage drag in Bowman backcross derived lines of spring barley. Barley Genet. Newsl. 24:63-70.
5. Haus, T.E. 1957. Inheritance of rachis internode length and an abnormal rachis type in barley. Dissertation Abstr. 49:179-180.
6. Nilan, R.A. 1964. The cytology and genetics of barley, 1951-1962. Monogr. Suppl. 3, Res. Stud. Vol. 32, No. 1. Washington State Univ. Press, Pullman.
7. Wolfe, R.I. 1990. (Personal communications).

J.D. Franckowiak. 2002. Barley Genet. Newsl. 32:85.

J.D. Franckowiak. 2010. Barley Genet. Newsl. 40:56-57.
J.D. Franckowiak. 2017. Barley Genet. Newsl. 47:68-69.