BGS 208, Fragile stem 2, fst2

Fragile stem 2 = fs2 (12).

Monofactorial recessive (9, 12).
Located in chromosome 1HL (8, 10, 11); fst2.b is over 19.0 cM proximal from the nec1 (necrotic leaf spot 1) locus (2); fst2.b is 1.9 cM distal from molecular markers wg789d and bcd351b in 1H bin 08 (1); fst2.b is associated with SNP markers 1_0259 to 2_0997 (positions 70.78 to 89.01 cM) in 1H bins 07 to 08 of the Bowman backcross-derived line BW374 (1), in 1H bin 08.

The brittle leaf and stem characteristics of fst2 plants are similar to those of fst1 plants (8). Leaves and stems are very fragile and easily broken when slightly bent (12). Young leaves generally wither in the afternoon in the greenhouse and in the field during the spring. Most of the leaf blade tips turn yellow prior to heading and gradual die back is observed (8). Plants are about one-half normal height when protected in the greenhouse, but in the field plants are weak and are easily damaged by wind. Culm internodes are often curved (3). For the semidwarf, brittle stem mutants, fst2 alleles fst2.b and fst2.e in their original stocks, the maximum flexural load (Newtons) required to bend the midpoint of each internode was 2 to 3 times lower than the load causing bending in their parents (1, 6, 7). Heading was delayed about four days in the Bowman backcross-derived line BW374. Compared to Bowman, plants of the BW374 line were about 1/2 normal height. Spikes had 3 to 4 fewer kernels. Kernels were small and thin and 1/2 to 2/3 of normal weight. Grain yields are very low (3). The fst2 mutants were shown to have reduced levels of crystalline cellulose in their culms compared with their parental lines (5, 7). A custom-designed microarray used by Burton et al. (1) revealed a marked decrease in transcript levels of mRNA for the HvCesA4 cellulose synthase gene. Sequencing of the HvCesA4 gene of fst2 mutants revealed the presence of a 964-bp solo long terminal repeat of a Copia-like retroelement in the first intron, which interferes with transcription or processing of the mRNA from the of the HvCesA4 gene (1).

A spontaneous mutant in Oshichi (OUJ755, PI 190273) (8, 9, 12).

fst2.b (Oshichi-hen, OUL006, OUX054, GSHO 578) in Oshichi (OUJ755, PI 190273) (8, 9, 12); fst2.e (OUM245) in Shiroseto (OUJ156) (7).

fst2.b (GSHO 578, OUX054) in Oshichi; fst2.b in Bowman (PI 483237)*7 (GSHO 2046); fst2.b in Bowman*8 (BW374, NGB 20613).

1. Burton, R.A., G. Ma, U. Baumann, A.J. Harvey, N.J. Shirley, J. Taylor, F. Pettolino, A. Bacic, M. Beatty, C.R. Simmons, K.S. Dhugga, J.A. Rafalski, S.V. Tingey, and G.B. Fincher. 2010. A customized gene expression microarray reveals that the brittle stem phenotype fs2 of barley is attributable to a retroelement in the HvCesA4 Cellulose Synthase Gene 1. Plant Physiol. 153:1716-1728.
2. 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.
3. Franckowiak, J.D. (Unpublished).
4. Jensen, J., and J.H. Jørgensen. 1973. Locating some genes on barley chromosome 5. Barley Genet. Newsl. 3:25-27.
5. Kimura, S., N. Sakurai, and T. Itoh. 1999. Different distribution of cellulose synthesizing complexes in brittle and non-brittle strains of barley. Plant Cell Physiol. 40:335-338.
6. Kokubo, A., S. Kuraishi, and N. Sakurai. 1989. Culm strength of barley: correlation among maximum bending stress, cell wall dimensions, and cellulose content. Plant Physiol. 91:876-882.
7. Kokubo, A., N. Sakurai, S. Kuraishi, K. Takeda. 1991. Culm brittleness of barley (Hordeum vulgare L.) mutants is caused by smaller number of cellulose molecules in cell wall. Plant Physiol. 97:509-514.
8. Takahashi, R., J. Hayashi, and U. Hiura. 1966. Inheritance and linkage studies in barley. III. Linkage of the gene for fragile stem-2 and orientation of the linkage map on barley chromosome 5. Ber. Ohara Inst. landw. Biol., Okayama Univ. 13:199-212.
9. Takahashi, R., J. Yamamoto, S. Yasuda, and Y. Itano. 1953. Inheritance and linkage studies in barley. Ber. Ohara Inst. landw. Forsch. 10:29-52.
10. Tsuchiya, T. 1972. Revision of linkage map of chromosome 5 in barley by means of telotrisomic analysis. J. Hered. 63:373-375.
11. Tsuchiya, T., and R.J. Singh. 1973. Further information on telotrisomic analysis in barley. Barley Genet. Newsl. 3:75-78.
12. Walker, G.W.R., J. Dietrich, R. Miller, and K.J. Kasha. 1963. Recent barley mutants and their linkages II. Genetic data for further mutants. Can. J. Genet. Cytol. 5:200-219.

T.E. Haus and T. Tsuchiya. 1971. Barley Genet. Newsl. 1:153.

R. Takahashi. 1972. Barley Genet. Newsl. 2:192.
J.D. Franckowiak and T. Konishi. 1997. Barley Genet. Newsl. 26:211.
J.D. Franckowiak. 2011. Barley Genet. Newsl. 41:114-115.