BGS 320, Intermedium spike-b, int-b

The int-b mutants are alleles at the vrs2 (six-rowed spike 2) locus based on DNA sequencing (9). Although phenotypic expression of spike type is somewhat between int-b and vrs2 in Bowman backcross-derived lines BW420 and BW901, respectively (4), SNP molecular marker are retained in the same region of 5HL in both lines (3). See BGS 314 for more information about the alleles at the vrs2 locus.

None.

Monofactorial recessive (6, 7).
Located in chromosome 5HL (5); int-b.3 is near the raw1 (smooth awn 1) locus based on linkage drag (5); int-b.3 is associated with SNP markers 2_0134 to 2_1355 (positions 163.29 to 234.98 cM) in 5H bins 10 to 13 of the Bowman backcross-derived line BW420 (3), likely in 5H bin 10.

The spike appears similar to the six-rowed spike, but developmental irregularities occur commonly in the lower portion of the spike. All lateral spikelets are reduced in size, and their lemma awns are short or reduced to a pointed tip. Commonly, only lateral spikelets in the middle of the spike set seed (6, 9). Plants of the Bowman backcross-derived line for int-b.3, BW420, showed reduced vigor and tillering (1). Plants of BW420 headed 2 to 3 days earlier than Bowman and more lodging was observed. The BW420 kernels were slightly longer, but weighed less, 52 vs. 58 mg, compared to those of Bowman. Grain yields of BW420 were 10 to 30% of those recorded for Bowman (4). Combining the int-b.3 and cul2.b (uniculm 2) mutants produced uniculm plants having spikes without spikelets (1). The double mutant combination, int-b.3 and low number of tillers 1 (lnt1.a), produced uniculm plants (2). The Vrs2 (Int-b) locus encodes for a SHORT INTERNODES (SHI) transcriptional regulator during barley inflorescence and shoot development (10).

A neutron induced mutant in Bonus (NGB 14657, PI 189763) (9).

int-b.3 (NGB 115421, GSHO 1764), -b.6 (NGB 115424) in Bonus (NGB 14657, PI 189763) (6, 9); int-b.75 (NGB 115493) in Bonus (8).

int-b.3 (NGB 115421, GSHO 1764) in Bonus; int-b.3 in Bowman (PI 483237)*6 (GSHO 2129); int-b.3 in Bowman*7 (BW420, NGB 20653).

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2. Dabbert, T., R.J. Okagaki, S. Cho, S. Heinen, J. Boddu, and G.J. Muehlbauer. 2010. The genetics of barley low-tillering mutants: low number of tillers-1 (lnt1). Theor. Appl. Genet. 121:705-715.
3. 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 Physiol. 155:617-627.
4. Franckowiak, J.D. (Unpublished).
5. Franckowiak, J.D. 1995. Notes on linkage drag in Bowman backcross derived lines of spring barley. Barley Genet. Newsl. 24:63-70.
6. Gustafsson, Å., and U. Lundqvist. 1980. Hexastichon and intermedium mutants in barley. Hereditas 92:229-236.
7. Gustafsson, Å., A. Hagberg, U. Lundqvist, and G. Persson. 1969. A proposed system of symbols for the collection of barley mutants at Svalöv. Hereditas 62:409-414.
8. Lundqvist, U. (Unpublished).
9. Lundqvist, U., and A. Lundqvist. 1988. Induced intermedium mutants in barley: origin, morphology and inheritance. Hereditas 108:13-26.
10. Youssef, H.M., K. Eggert, R. Koppolu, A.M. Alqudah, N. Poursarebani, A. Fazeli, S. Sakuma, A. Tagiri, T. Rutten, G. Govind, U. Lundqvist, A. Graner, T. Komatsuda, N. Sreenivasulu, and T. Schnurbusch. 2017. VRS2 regulates hormone-mediated inflorescence patterning in barley. Nature Genet. 49:157-161.

U. Lundqvist and J.D. Franckowiak. 1997. Barley Genet. Newsl. 26:268.

U. Lundqvist and J.D. Franckowiak. 2014. Barley Genet. Newsl. 44:118-119.
U. Lundqvist and J.D. Franckowiak. 2017. Barley Genet. Newsl. 47:118-119.