In order to identify desirable segregates, F/2/ progenies were space planted in nurseries at the Langdon Research Extension Center. Two or three plants from each progeny, which segregated for a given morphological marker, were selected and later harvested. Seeds for one plant were sown in the fall greenhouse nursery and the plants were crossed to Bowman. The F/1/ plants were grown in the spring greenhouse nursery. Notes on phenotypic characters were taken prior to harvest of plants in both greenhouse nurseries. This set of procedures permitted an advance of one backcross generation per year.

Even though selection for the Bowman phenotype was practiced in the BC/x/F/2/ progenies, several traits of the donor parent were retained. Because most progenies contained less than 120 plants, data were not collected for linkage estimates. After several backcross generations, traits from the donor parent were observed in a few of the Bowman backcross derived lines. A summary of these observations is presented in Table 1.

When a gene is transfer from one cultivar to another via backcrossing, a few traits of the donor parent are expected to show linkage drag. The association of qualitative and quantitative characters in barley has been reported by many researchers (Hockett and Nilan, 1985). Inadvertent retention of a second qualitative character has been observed in the case of barley leaf rust (Feuerstein et al., 1990). Thus, both linkage theory and observations indicate that some genes should exhibit linkage drag in backcross derived lines. However, other factors can cause association of traits when no linkage exists. For example, the Bowman backcross derived line for the yst3.c (yellow streak 3) gene has the brittle rachis (bt) gene from BGS462 (Table 1), but trisomic analysis data suggest that the yst3 locus is not in chromosome 3 (Tsuchiya and Alanko, 1976).

The summary of notes on linkage drag in Table 1 includes some associations, which are expected based on linkage data published by other researchers. But, several new associations are reported. Bowman has the recessive allele at the Rs (red stem) locus in chromosome 1S, and the dominant allele at the l (dense spike) locus. Most two-rowed spring barley cultivars from Northern Europe have the Rs gene, and naked barley cultivars from Japan often have the l-n pair of linked genes.

The Ea gene for strong photoperiod response is located in chromosome 2S, and occurs in diverse array of spring and winter barley cultivars (Franckowiak, 1992). Bowman has the two-rowed allele (V or V1.b), while some of the donor parents have the six-rowed allele (v or v1.a) or have the deficiens allele (V or V1.t). Bowman has barbs on the lemma veins (G), while most two-rowed cultivars with a spring growth habit do not. The g, v, and pr (non-purple stem) loci are located in chromosome 2L.

The Bt (brittle rachis) locus in chromosome 3S controls disarticulation of the rachis. Since Bowman has the allele commonly found in barley of Oriental origin, spike breakage is observed in progenies from crosses to spring barley cultivars from Europe. The linkage between the uz (uzu dwarf) and the sld (slender dwarf) loci in chromosome 3 was reported by Konishi et al. (1984). The dominant allele at the I (intermedium) locus in chromosome 4L is observed in a few Bowman backcross derived lines. Thus, retention of the large lateral trait may indicate a linkage association between the mutant and the I allele.

A close linkage between the msg1.ca (male sterile genetic 1) allele and small lateral spikelets was noted in its backcross derived line. The lateral spikelets in the upper part of the spike gradually become smaller so that they are rudimentary at the terminal rachis nodes. Later, segregation for a few two-rowed plants with this trait was observed in many progenies from crosses between six- and two-rowed barley cultivars. The gene symbol sls is recommended for this recessive trait, which probably is located in chromosome 5S.

Many genes showed association with the R (rough awn) gene in chromosome 7L because Bowman has semismooth awns. The Lga (long glume awn) gene is present in many six-rowed cultivars. This trait was studied by Neatby (1926) and Helgason (1964) and assigned the gene symbol Log (long outer glume), but subsequently several reports considered this gene as part of the allelic series at the e (wide glume) locus (Tsuchiya, 1974). Therefore, another gene symbol is used in this report. Although the msg34 gene does not recombine with either the o (orange lemma) or the Lga genes (Franckowiak, 1991), attempts to map the Lga locus in chromosome 6 have been unsuccessful (Schondelmaier et al., 1993).

To facilitate reporting the information in Table 1, several new locus and allele symbols are proposed. The locus symbols dsp (dense spike), pyr (pyramidatum or pyramid-shaped spike), and Zeo (zeocriton or dominant compact spike) are used for genes affecting spike density. Because a wide array of phenotypic expressions, including a number of naturally occurring dominant genes, alter rachis internode length, it was difficult to classify them all as erectoides (ert) mutants. Recommended allele symbols for the brachytic (br) class of semidwarf mutants are presented by Franckowiak (1995).

The locus symbols f14, mss2, and pmr are suggested for mutants having chlorina seedling, mid-season streak, and premature ripe phenotypes, respectively. The locus symbols m4 (many noded dwarf) and r6 (smooth awn) are used, but a review of the literature does not indicate conclusively how many other loci belong in these phenotypic classes. Two incomplete dominant traits, which are reported to have relatively simple gene control, are assigned the symbols Sil and Vbn for subcrown internode length and vascular bundle number, respectively. Temporary allele symbols are used for mutants in the globosum (glo), laxatum (lax), semidwarf (sdw), shrunken endosperm xenia (sex), and slender dwarf (sld) classes of genes. A narrow leaf mutant (nl.k) was assign the symbol nlk before it was obtained from Montana State University.

References

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Table 1. Genes in barley for which evidence of linkage drag has been observed in Bowman backcross derived progenies.