BGS 124, Six-rowed spike 4, vrs4

Multiflorus = mul (8, 19).
Intermedium spike-e = int-e (6, 13).
Six-rowed spike 4 = v4 (3).
Hordeum vulgare RASMOSA2 = HvRA2 (10).

Monofactorial recessive (3, 4, 5, 7).
Located in chromosome 3HL (5, 16, 17, 18); vrs4.k is about 27.5 cM from the uzu1 (uzu 1) locus (5); int-e.58 is associated with SNP markers 1_0672 to 2_1083 (positions 38.56 to 156.06 cM) in 3H bins 04 to 10 of the Bowman backcross-derived line BW423 (1); mul1.a is associated with SNP markers 1_0762 and 2_0115 (positions 38.56 and 126.83 cM) in 3H bins 04 and 08 of line BW606 (1); vrs4.k is associated with SNP markers 1_0863 to 1_0926 (positions 64.85 to 85.26 cM) in 3H bin 05 and with SNP markers 2_1493 to 1_1330 (positions 161.43 to 178.12 cM) in 3H bin 10 of the Bowman backcross-derived line BW903 (1); the lack of SNP marker heterogeneities in the centromeric region of the BW lines and more markers retained in 3HS indicate that the vrs4 locus is more likely in 3H bin 05 (1, 2).

Alleles at this locus enhance the development of lateral spikelets and formation of additional spikelets to various degrees. The int-e mutants, which were isolated in two-rowed cultivars, have enlarged lateral spikelets that may set seed in the upper two-thirds of the spike. Kernels in lateral spikelets are smaller than those from central spikelets in int-e mutants. The rachilla may be deformed by partial formation of an extra spikelet. The awn size on lateral spikelets ranges from a pointed apex to 3/4 normal length (14). The mul1.a and vrs4.k alleles, which were isolated in six-rowed cultivars, may produce numerous extra spikelets at the base of the lateral spikelets and on the rachilla (4, 8). Plants of the backcross-derived line BW903 with the vrs4.k allele and BW606 with mul1.a are slightly taller than Bowman, plants lodge easily, and rachis internodes are slightly longer. Kernels of BW423 with int-e.58 had weights that range similar to those of Bowman to 10% less. Kernels of BW606 and BW903, which include small lateral ones, had average weights 20 to 40% less than those of Bowman. The kernel weights for BW606 were slightly less than those of BW093. Kernels of all BW lines with vrs4 alleles are about 10% shorter than those of Bowman (2). Compared to Bowman, BW903 had more kernels per spike, but tiller numbers and seed weights were reduced (11). Expression analyses through mRNA in situ hybridization and microarray showed that Vrs4 (HvRA2) controls the row-type pathway through Vrs1 (Six-rowed spike 1, Hordeum vulgare Homeobox 1 = HvHox1), which is a negative regulator of lateral spikelet fertility (10). Scanning electron microscopy imaging of wild type and vrs4 mutants at double ridge stage revealed no morphological differences. However, the appearance of two additional mounds on either side of the lateral spikelet meristems was the first visible deviation observed in vrs4 mutant inflorescences. The additional spikelets emerging at rachis internodes were frequently fertile and developed into kernels (10).

A gamma-ray induced mutant in MFB 104 (PI 232921) (5).

mul1.a (Alb Acc 321, GSHO 561) in Montcalm (CIho 7149) (8, 19); vrs4.k (Gamma III 3B, MFB-2, GSHO 775) in MFB 104 (PI 232921), vrs4.l (Xc 41.5, Piro-2) in Piroline (PI 262210) (5); vrs4.m (X17 2497, Piro-7) in Piroline ( 4, 5); int-e.4 (trans) (NGB 115423) in Bonus (NGB 14657, PI 189763), -e.20 (trans) (NGB 115438), -e.23 (NGB 115441), -e.26 (NGB 115444) in Foma (NGB 14659, CIho 11333), -e.58 (NGB 115476, GSHO 1776), -e.66 (NGB 115484) in Kristina (NGB 14461, NGB 1500), -e.65 (NGB 115483) in Bonus (13); int-e.72 (NGB 115490), -e.87 (NGB 115505) in Bonus, -e.89 (NGB 115507), -e.90 (NGB 115508), -e.91 (NGB 115509), -e.92 (NGB 115510), -e.101 (NGB 115519) in Hege (NGB 13692) (12); hex-v.46 (NGB 115583), hex-v.47 (NGB 115584), hex-v.48 (NGB 115585) in Bonus (9, 12).

vrs4.k (Gamma III 3B, GSHO 775) in MFB 104; int-e.58 (GSHO 1776, NGB 115476); mul1.a in Bowman (PI 483237)*6 (GSHO 1985); mul1.a in Bowman*7 (BW606, NGB 22172); vrs4.k in Bowman*6 (GSHO 1986); vrs4.k in Bowman*7 (BW903, NGB 22335); int-e.58 in Bowman*6 (GSHO 1987); int-e.58 in Bowman*7 (BW423, NGB 20656).

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