The radicles of a total 10,090 accessions including cultivars, experimental lines and wild strains were checked with fluorescent light. However no variant was found ; the radicles of all accessions gleamed pale white. Then we checked 16,480 plants of Fuji Nijo which were irradiated with 9OkR gamma-rays (3OkR x 3 generations).
Three of the plants segregated a new mutant in which the radicles gleamed pink with fluorescent light. The growth point of young seedling also gleamed pink. The mutant is very weak and hard to propagate but it can be kept in the heterozygous condition.
The segregation mode for the fluorescent reaction within heterozygous lines for the character indicates that the mutant character is controlled by a single recessive gene, named frp (fluorescent reaction-pink). However irrespective of the seed viability, the proportion of frp/frp plants was ca. 21% and was less than the theoretical value of 25%, indicating the transmission rate of the frp gene was low for some reason (Table 1).
Table 1. Segregation of the fluorescent reaction-pink mutant in relation with seed viability
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Age of seeds Number of seeds Germination Proportion
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(month) Normal Mutant Ungerm. Total (%) of mutant (%)
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5 4,738 1,257 51 6,046 99.2 21.0
7 2,724 742 151 3,617 95.8 21.4
19 1,971 500 389 2,860 86.4 20.2
31 1,258 331 1,609 3,198 49.7 20.8
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For analyzing the mechanism of the distorted segregation, a cross experiment
between heterozygous female (Frp/ftp) and homozygous normal male
(Frp/Frp) was conducted. The progeny test of a total 340 F/1/ plants
resulted in 174 heterozygous and 166 homozygous normal plants. It clearly
coincided with 1:1 segregation rate (X²=0.19, p=0.5-0.7) indicating that the
transmission rate of frp gene through female gamete was quite normal.
In other words, the transmission of frp gene is disturbed only through
male gamete.Putting the transmission rate of frp and Frp through the male gamete p and 1-p, respectively, p equals 0.42 and the relative transmission rate (p/1-p) is 0.72, when the proportion of frp/frp plants is 21% as mentioned before. A total 1,141 progeny plants of heterozygous Frp/frp Fuji-Nijo segregated 422 normal and 719 heterozygous plants as expected 0.5(1-p) : 0.5(p+1-p) or 418.85 : 722.15 (X²=0.04, p=0.8-0.9).
The Frp/frp heterozygous plants were crossed with 12 linkage testers representing the seven chromosomes of barley. About half the F/1/ plants were homozygous (Frp/Frp), while the other half were heterozygous (Frp/frp) and used for linkage analysis. Because frp/frp plants were lethal, only phenotypically normal plants were grown in the field. They were checked for marker characters and harvested to check the fluorescent reaction of the radicles in F/3/ generation.
In the F/2/ populations examined, the proportion of frp/frp plants was 14 to 23% and the relative transmission rate of frp was 0.59 on average.
Analyzing the joint segregation of frp and marker genes, frp was found to be independent of following genes: br (brachytic plant) and n (naked karyopsis) on chromosome 1. V (two-rowed), e (wide outer glume), li (ligule-less) and mt,, e (mottled leaf) on chromosome 2. als (absent lower laterals), uz (uzu or semi-brachytic growth) and al (albino lemma) on chromosome 3. B (black lemma and pericarp), trd (third outer glume) and fs-2 (fragile stem-2) on chromosome 5. o (orange lemma) on chromosome 6. s (short haired rachilla) and fs (fragile stem) on chromosome 7.
The frp showed linkage with K (hooded lemma), gl-3 (glossy seedling-3) and Bl (blue aleurone) on chromosome 4 (Table 2).
Table 2. Joint segregation of frp with K (hooded lemma), gl-3 (glossy seedling-3) and Bl (blue aleurone) genes in an F/3/ population crossed with OUL056
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Marker (A) A-BB a-Bb aaBB aabb Total X²A(3:1) X²B(1:2) X²L
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K 110 186 10 42 348 18.77** 0.21 4.79**
gl-3 32 213 88 15 348 3.92* 0.21 191.30**
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AABB AABb AaBB AaBb aaBB aaBb
Bl 76 16 39 187 5 25 348 53.17** 0.21 141.53**
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* and ***: Significant at the 5% and 1% levels, respectivelly.Table 3. Joint segregation of frp with Bl (blue aleuron) in F/2/ populations
______________________________________________________________________ Cross A-B- A-bb aaB- aabb Total X²A(3:1) X²B(3:1) X²L RCV(%) ______________________________________________________________________ x OUL017 439 24 65 108 636 1.64 6.11** 228.64** 15.4± 1.6 x OUL053 505 20 60 97 682 1.42 22.38** 210.99** 13.7± 1.4 x OUL056 562 36 89 90 777 1.60 31.97** 142.14** 19.7± 1.6 ---------------------------------------------------------------------- Total 1,506 80 214 295 2,095 0.55 56.33** 570.24** 16.4± 0.9 ______________________________________________________________________**: Significant at the 1% level.
Here, segregation mode of the marker genes was distorted by the linkage with the lethal frp gene; thus the recombination value between frp and the marker genes was hard to estimate. However, because Bl showed xenia, joint segregation analysis between frp and Bl genes was possible in three F2 populations (Table 3). The frp is a novel new marker gene of barley.
Reference
Sawada, S. and R. G. Palmer 1987. Genetic analyses of nonfluorescent root
mutants induced by mutagenesis in soybean. Crop Sci. 27: 62-65.