BGS 189, Accordion rachis 2, Acr2

Lax spike = lax (4, 9, 11).
Accordion rachis = acr (7, 9, 12).
Accordion rachis 1 = acr1.a (6).
Accordion rachis b and c = acr.b, acr.c (3, 5).
Laxatum spike stocks = Lax.aa, Lax.ab, Lax.am, lax.ao, (5, 12).

Monofactorial incomplete dominant for lax spike, one of three factors required for expression of accordion rachis trait (5, 12).
Located in chromosome 4HL (3); Acr2.ab is associated with SNP markers 1_0123 to 2_1018 (positions 158.82 to 183.54 cM) in 4HL of the Bowman backcross-derived lines BW445; Bowman backcross-derived lines BW007, BW008, BW009, BW439, BW444, and BW456 have identical heterogeneous SNP markers in 4HL, but their segments from the donor parent are longer (3), in 4H bins 11 or 12.

Rachis internodes are elongated and kernels appear longer than normal. The Acr2 gene is in the second of three chromosomal regions associated with expression of the accordion rachis trait in Bowman backcross-derived lines BW009 and BW439. The long rachis internode trait was specifically added to the original accordion rachis stock by R.I. Wolfe (12). Characteristics associated with variants at the Acr2 locus are difficult to determine, because only the Bowman backcross-derived line BW444 (Lax.aa or Acr2.aa) did not have more than one chromosome segment from its donor parent (3). Rachis internodes of BW444 plants were about 30% longer, 5.7 vs. 4.4 mm, than those of Bowman. Leaf blades were slightly longer and wider. Kernels were slightly longer and heavier, 61 vs. 58 mg. Grain yields were equal or slightly more than those of Bowman. The donor parent (FN280) of the BW444 line traces to lines developed by Mary L. Martini and Harry V. Harlan (8) in Idaho via crosses to six-rowed barley made by D.C. Rasmusson (10). The Bowman backcross-derived lines BW007 (Acr2.b2) and BW008 (Acr2.c2) had the identical segment of chromosome 4HL plus a 1H segment retained from their donor parents; however, the 1H segments in these lines differed for SNP marker patterns (3). The Bowman lines BW007 and BW008 are 10 to 15% taller than Bowman. The rachis internodes of BW007 are about 25% longer than those of Bowman, 4.7 vs. 3.7 mm. Burma Girl (GSHO 1071, Acr2.b2), the original stock for BW007, has several sterile rachis nodes at the base of the spike before spikelet development is initiated (4). BW007 had kernel weights that varied across experiments from smaller to slightly larger than those of Bowman. The rachis internodes of BW008 were nearly twice as long as those of Bowman, 8.2 vs. 4.5 mm, but they did not show the accordion-like bending associated with the accordion phenotype. Kernels of the BW008 line were slightly longer and heavier than those of Bowman (5). Two other Bowman backcross-derived lines, BW439 and BW456, have the 4HL SNP pattern associated with the Acr2 locus. Both originate from the same donor stock AB1398 (GSHO 1115) from Aberdeen, Idaho and are assigned the gene symbol Acr2.am. BW456 was selected based on lax spikes while BW439 was selected based on tall plants (5).

A naturally occurring deviant possibly in Long Rachis Internode (CIho 6164), developed by M.L. Martini and H.V. Harlan (8), or Burma Girl (CIho 14831), donated to the USDA Small Grains Collection by G.A. Wiebe. The Acr2 gene has been incorporated into several genetic stocks from that source.

Acr2.b2 in Burma Girl (CIho 14831, GSHO 1071) (5, 12); Acr2.aa in FN280 (GSHO 1572) (5, 10); Acr2.ab in ACBV89B229 (GSHO 1617) and ACBV89B232 (GSHO 1573) (12); Acr2.c2 in T188 (GSHO 1480) from R.W. Woodward (2); Acr2.am in AB 1398 [GSHO 1115, likely CIho 14785 from G.A. Wiebe (1)]; all alleles may have been derived from one stock (3, 5).

Acr2.aa in FN280 (GSHO 1572); Acr2.b2 in Burma Girl (GSHO 1071); Acr2.a2 in ACBV89B229 (GSHO 1617); Acr2.c2 in T188 (GSHO 1480); Acr2.am in AB 1398 (GSHO 1115); Acr2.a2 from ACBV89229 in Bowman*4 (GSHO 1899); Acr2.a2 in Bowman*7 (BW009, NGB 20417 and BW439, NGB 20671); Acr2.aa from FN280 in Bowman*4 (GSHO 2276); Acr2.aa in Bowman*5 (BW444, NGB 20676); Acr2.ab from ACBV89B232 (GSHO 1573) in Bowman*4 (GSHO 2277); Acr2.ab in Bowman*6 (BW445, NGB 20677); Acr2.b2 from Burma Girl in Bowman *2 (GSHO 1898); Acr2.b2 in Bowman*5 (BW007, NGB 20415); Acr2.c2 from T188 in Bowman*6 (BW008, NGB 20416); Acr2.am from AB 1398 in Bowman*4 (BW456, NGB 20688).

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2. Doney, D.L. 1961. An inheritance and linkage study of barley with special emphasis on purple pigmentation of the auricle. M.S. Thesis. Utah State Univ., Logan.
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4. Enns, H. 1961. Inheritance and linkage studies in barley using chromosomal interchanges and marker stocks. Ph.D. Thesis. Univ. Saskatchewan. pp. 70.
5. Franckowiak, J.D. (Unpublished).
6. Franckowiak J.D. 2001. BGS 97, Accordion rachis 1, acr1. Barley Genet. Newsl. 32:85.
7. Haus, T.E. 1957. Inheritance of rachis internode length and an abnormal rachis type in barley. Dissertation Abstr. 49:179-180.
8. Martini, M.L., and H.V. Harlan. 1942. Barley freaks. J. Hered. 33:339-342.
9. 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.
10. Rasmusson, D.C. (Personal communications).
11. Smith, L. 1951. Cytology and genetics of barley. Bot. Rev. 17:1-55, 133-202, 285-355.
12. Wolfe, R.I. 1990. (Personal communications).

J.D. Franckowiak 2010. Barley Genet. Newsl. 40:65-66.

J.D. Franckowiak 2017. Barley Genet. Newsl. 47:101-102.