A guide to barley mutants

Abstract

Background: Mutants have had a fundamental impact upon scientific and applied genetics. They have paved the way for the molecular and genomic era, and most of today's crop plants are derived from breeding programs involving mutagenic treatments.

Results: Barley (Hordeum vulgare L.) is one of the most widely grown cereals in the world and has a long history as a crop plant. Barley breeding started more than 100 years ago and large breeding programs have collected and generated a wide range of natural and induced mutants, which often were deposited in genebanks around the world. In recent years, an increased interest in genetic diversity has brought many historic mutants into focus because the collections are regarded as valuable resources for understanding the genetic control of barley biology and barley breeding. The increased interest has been fueled also by recent advances in genomic research, which provided new tools and possibilities to analyze and reveal the genetic diversity of mutant collections.

Conclusion: Since detailed knowledge about phenotypic characters of the mutants is the key to success of genetic and genomic studies, we here provide a comprehensive description of mostly morphological barley mutants. The review is closely linked to the International Database for Barley Genes and Barley Genetic Stocks ( bgs.nordgen.org ) where further details and additional images of each mutant described in this review can be found.

Keywords: Hordeum vulgare; Barley; Biodiversity; Cereal; Genebank; Induced mutants; Mutagenesis; Mutation; Triticeae.

Fig. 1

1.1 The root system of an adult barley plant is mainly formed by postembryonic nodal roots. The white bar corresponds to 1 cm. 1.2 Two culms showing the node flanked by two internodes. The culm is enclosed by the leaf sheath that is the lower part of the leaf. The auricle is at the junction between the leaf sheath and the leaf blade. The white bar corresponds to 1 cm. 1.3 The top leaf of each tiller is called the flag leaf. Like other leaves, the flag leaf consists of a sheath and a blade as well as a ligule and an auricle at the junction between them. The junction between a barley spike and culm is called collar. The peduncle is the first (top) internode of the culm. The white bar corresponds to 1 cm. 1.4 The spike is the reproductive part of barley. A spike is composed of approximately 20 to 30 successive triplets of spikelets, which consist of one central and two lateral spikelets. In the two-rowed spikes shown in the figure, only the central spikelet has a fertile floret. The awns extend from the floret of the central spikelets and are usually as long as the spike. The top leaf is called flag leaf. The peduncle is the top (first) internode of the culm. The white bar corresponds to 5 cm. 1.5 The stem of the spike is called rachis, which consists of rachis nodes and rachis internodes. The spikelets are attached at the rachis nodes. The figure shows two-rowed barley where the lateral spikelets are sterile. A and B. All spikelets except the one triplet of spikelets attached at one rachis node have been removed. The flower is surrounded by the lemma, the palea and two glumes. The awn is an extension of the lemma. The palea is inside the lemma and closest to the rachis. C. The central spikelet has been removed. D. The rachis has been removed to show the palea side of the central spikelet with the rachilla attached slightly below the palea. The rachilla is a rudimentary branch of the rachis. The white bars correspond to 1 cm. 1.6 Close-up of three barley spikes, which are of the two-rowed type with sterile lateral spikelets. In the left spike, the lateral spikelets are very small. The central spikelet is fertile and has resulted in a mature seed in the right spike. The white bar corresponds to 1 cm. 1.7 A. The floret is composed of two leaf-like structures, the lemma and the palea. In the shown spike, all fertile flowers, except one, have been pollinated and therefore remain closed. In the open floret, the lemma and palea are separated exposing the cavity where the flower organs are kept. The bar corresponds to 1 cm. B. In the dissected floret, the upper rachis and the lemma have been removed to show the ovary with the featherlike stigmata and the three anthers (still not mature in the photo). The lodicules, situated between the palea and the lemma, can swell and thereby push away the lemma to facilitate exposure of the anthers and stigmata. In barley, usually this happens exclusively if self-pollination fails and capture of pollen from other florets is required (like shown in A). The bar corresponds to 1 mm. 1.8 A. Dissected anthers and ovary of a barley floret at the stage of pollination. Pollen can be seen dehiscing out from one anther. The stigma is dusty because it has received pollen. B. After a week the fertilized ovary has expanded longitudinally. The bar corresponds to 1 mm. 1.9 A barley grain one month after fertilization. A. The naked grain after removal of the lemma and palea. The embryo is facing the lemma side. B. The grain after removal of the seed-coat layer displaying the starch-containing endosperm. C. The embryo has been detached from the grain. The bar corresponds to 1 mm

Fig. 2

2.1 A. Phenotype of a six-rowed Hexastichon barley vrs1.a1 mutant (left) compared to cultivar Bowman with a two-rowed Distichion Vrs1.b spike (right). B. Spikelets of a vrs1.a1 plant. Each central spikelet is flanked by two lateral spikelets. All spikelets are fertile in six-rowed barley. The awns of the lateral spikelets are shorter than the awn of the central spikelet. 2.2 A Deficiens (Vrs1.t) spike to the left compared to Bowman with a spike of Distichion (Vrs1.b) to the right. Deficiens barley has rudimentary lateral spikelets

Fig. 3

3.1 Mutant Intermedium spike-a (int-a.1). A. Mutant to the left, cultivar Bowman to the right. The upper two-thirds of the spike has fertile lateral spikelets. B. Three mutant seeds with different double awn phenotypes to the left compared with normal Bowman. C. Three triplets of spikelets. The two lateral spikelets are smaller than the central spikelet, but still fertile. 3.2 Mutant Intermedium spike-b (int-b.3). The spike appears similar to the six-rowed spike, but developmental irregularities occur commonly in the lower half 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. Cultivar Bowman is to the right. 3.3 Mutant Intermedium spike-c (int-c.5) to the left compared to Bowman. The lateral spikelets are fairly large and broad, the lemma is often rounded or weakly pointed, awnless or short-awned at the apex. Lower lateral spikelets may develop poorly in some int-c mutants, while seed development may occur in all lateral spikelets of others. Variability in lateral floret development exists among the int-c mutants and environmental conditions can alter expressivity. 3.4 Int-d.12 (middle) compared to hex-v.3 (left) and Bowman (right). Mutations in int-d are semidominant. The awns of lateral spikelets of int-d mutants will vary in length from ¾ to nearly as long as those of the central spikelets. Mutants in int-d are allelic to vrs1 and hex-v [1]. 3.5 Mutants of the Six-rowed spike 4 (vrs4) locus. A. int-e.58. B. mul1.a. Mutants to the left compared to Bowman to the right. 3.6 Two spikes of mutant int-f.19 compared to Bowman to the right. This locus is only represented by the int-f.19 allele. The spike appears six-rowed, but the lateral spikelets are much smaller (less than half the size of the central spikelets). Lateral spikelets are pointed and often have short awns. Seed set occurs in the lateral spikelets in the upper third of the spike. The base of the spike has shortened rachis internodes and appears Erectoides-like [47]. 3.7 Mutant int-h.42 to the left compared to Bowman. Lateral spikelets are enlarged and have an inconspicuously pointed apex, but they do not set seed. Induced mutants show early heading and have an elongated basal rachis internode. The spike appears lax but with shortened rachis internodes at the base [46]. A Bowman backcross-derived line is slightly shorter (5/6 normal) and produces extra spikelets (up to five fertile ones) at several rachis nodes in the lower half of the spike [50]. 3.8 Mutant Lower number of tillers 1 (lnt1.a) compared to Bowman to the right. This mutant is allelic to int-l [51]. Various spike malformations occur in most environments. The spike may have irregular rachis internode lengths. The lower portion of the spike appears denser. Lateral spikelets in two-rowed cultivars are enlarged and have a pointed apex. B is a close-up of the spikes shown in A. 3.9 Mutant int-m.85 to the left compared to Bowman. The spike of int-m mutants is very short due to few rachis internodes and has irregular rachis internode lengths. Lateral spikelets are enlarged and pointed, but they do not set seed. The density of spikelets at the base of the spike is increased. Rachis internodes at the tip of the spike are very short, and the spike appears to have two or three fused terminal spikelets

Fig. 4

4.1 Double mutant F₂-segregants from crosses (middle) flanked by their int mutant parents. Most combinations of int mutants in the crosses result in double mutants with a typical six-rowed spike. A. From left to right: int-c.15, double mutant, int-a.32. B. From left to right: int-c.16, double mutant, Int-d.28. C. Deformed double mutant F₂-segregant from poor combining partners. From left to right: int-e.20, double mutant, int-a.46. 4.2 Spikes of triple mutant combination from the six-rowed double mutant int-c.5 int-a.34 combined with the six-rowed mutant hex-v.3. From the left to right: int-c.5 int-a.34 double mutant, “King-size” spike of triple mutant int-c.5 int-a.34 hex-v.3, six-rowed mutant hex-v.3

Fig. 5

5.1 Dense spike mutants often show a compact and wide spike with their awns protruding from the longitudinal axis of the plants. Mutant Pyramidatum 1 (pyr1.i) to the left compared to Bowman. 5.2 Less drastic dense spike mutants. A. Mutant Erectoides-a (ert-a.6) to the left compared to Bowman. B. Mutant ert-k.32 to the left compared to Bowman. 5.3 The barley Erectoides-c mutants display a pyramid-shaped spike phenotype due to shorter distance between the rachis internodes at the lower part of the spike. Mutant ert-c.1 to the left compared to Bowman. 5.4 Spikes of barley mutant Erectoides-m (ert-m.330) where awns and the lateral flowers have been removed. A. The rachis internode distances are irregular and the rachis nodes can sit more or less opposite to each other. B. The irregular rachis internode distance is especially pronounced in the top of the spike, which imposes twists of the spike. 5.5 Zeocriton mutants. A and B. Zeo1.a to the left compared to Bowman. C and D. Zeo2.c to the left compared to Bowman

Fig. 6

6.1 A. Spike of Laxatum-a (lax-a.8) at early maturity compared with normal Bowman. In lax mutants the rachis internodes are typically 10 to 20% longer than in their corresponding mother cultivars. Combined with thin and small kernels this results in a very sparse spike. The exposed caryopses are shown in the kernels of the lax-a.8 mutant. B. The awns of lax mutants have a very wide base, without a distinct notch in the lemma attachment region. Four kernels of lax-c.21 to the left compared to Bowman. 6.2 A. Mutant Long basal rachis internode 3 (lbi3.c) in a Bowman genetic background to the left with typical elongated basal rachis internode, which is approximately ten times longer than that of Bowman (right). The lbi3.c mutation was originally isolated from the six-rowed cultivar Montcalm. In a Montcalm genetic background the basal rachis internode can be more than 10 cm [71]. B. The slightly curled or wavy basal rachis internode of Accordion rachis 1 (acr1.a) to the left compared to Bowman. The arrows point at the basal rachis internodes

Fig. 7

Accordion rachis mutants have greatly elongated rachis internodes causing a wavy or undulating form. All photos show mutant acr1.a. A. Mutant to the left, Bowman to the right. B. Elongation of the rachis internodes is associated with slightly elongated glumes and the deficiens-like spike phenotype. C. Spikelets have been removed to show the wavy form of the spike

Fig. 8

8.1 A. Spikes of Compositum 1 (com1.a) mutant to the left compared to cultivar Bowman. B. A single com1.a spike that has been bent to better visualize the branches of a few small spikes from the rachis at the lower part of the spike. Several thread-like awns are protruding from the cluster of small spikelets. 8.2 Mutant Opposite spikelets 1 (ops1.3) to the left in each photo, displays variable lengths of rachis internodes, which causes an irregular arrangement of spikelets in the spike. A. Spike of ops1.3 compared to Bowman. B. Spikelets have been removed in order to view the rachis nodes and internodes. 8.3 Lateral spikelets at the base of the spike fail to develop or are partially developed in Absent lower laterals 1 (als1.a) mutants (left) compared to Bowman (right)

Fig. 9

9.1 Two Extra floret-a (flo-a.3) spikes compared to Bowman (right). The awns have been removed from the central spike to better view the extra bracts. 9.2 A. Mutant Subnodal bract 1 (snb1.a) to the left, Bowman to the right. B. Four single spikelets of snb1.a flanking a spikelet of Bowman in the middle. 9.3 Two spikes of Curly lateral 1 (crl1.a) to the left with bent awns compared to Bowman. The awns are approximately 20% shorter than those of Bowman. 9.4 Two spikes of Leafy bract 1 (Lfb1.a) with different expressions to the left compared with normal Bowman. 9.5 A. Top part of a vir-a.5 mutant tiller with a Viviparoides phenotype remaining vegetative. B. In the near-isogenic line BW896 carrying the viv-a.5 mutation, spikes are formed on most tillers (left). Bowman (right). 9.6 A. Four spikes of Rattail spike 1 (rtt1.a) with numerous immature spikelets compared to cultivar Bowman (right). B. A single rtt1.a spike

Fig. 10

10.1 In Elongated outer glume 1 (eog1) mutants, the glumes have been enlarged and display an awn that can be as long as the awn of the lemma in some mutant alleles. A. eog1.a to the left, Bowman to the right. B. Two spikelets of eog1.a (top) and one of Bowman (below). The glumes, subtending the spikelet with the lemma awn, are both wider and taller in the mutant. 10.2 Spikelets of Long glume awn 1 (Lga1.a) compared to Bowman (right). The dominant variant causes elongated glume awns, which are much longer than the kernel. 10.3 A. Spikes of barley Bracteatum-c (bra-c.1) compared to Bowman (right). The arrows indicate the third outer glume at the two lowest spikelets. The glume-like structure associated with the lowest spikelets are always the largest and they become progressively smaller toward the top of the spike. B. A close-up of the lower part of a spike of Third outer glume 1 (trd1.b) showing the pronounced glume-like structure at the base of the spike. 10.4 Short and long rachilla hairs in cultivar Morex (left) and Barke (right), respectively. Scale bar 1 mm. Image kindly provided by Twan Rutten, IPK Gatersleben

Fig. 11

11.1 Three Triple awned lemma 1 (trp1.a) mutant grains to the left compared to Bowman. In trp1.a, the awn extending from the lemma of the central spikelet forks to form one normal central awn and one or two shorter lateral appendages. 11.2 A spike of Hairs on lemma nerves 1 (Hln1.a) (bottom) compared to Bowman (top). Hln1.a causes additional hairs of 1 to 2 mm on the lateral veins of the lemma (encircled)

Fig. 12

In Awned palea 1 (adp1.a) mutants the palea has two awns in addition to the awn protruding from the lemma. A. Mutant adp1.a to the left compared to Bowman. B. Two grains of adp1.a. The two awns of the palea are shorter than the awn of the lemma

Fig. 13

Three different short-awn mutants. A. Mutant Breviaristatum-n (ari-n.45) to the left compared to Bowman. B. Mutant ari-a.8 to the left compared to Bowman. C. Field plot of ari-g.18 showing its strong dwarf phenotype

Fig. 14

Awns of cultivars Barke (A) and Morex (B). Barke (Raw1/Raw1) and Morex (raw1/raw1) have rough and smooth awns, respectively. The white bars correspond to 100 μm. Image kindly provided by Twan Rutten, IPK Gatersleben

Fig. 15

15.1 A and B. Lks1.b (Awnless 1) to the left compared to Bowman. 15.2 A. Mutant Short crooked awn 1 (sca1.a) to the left compared to Bowman. B. Enlarged upper part of a spike of sca1.a. 15.3 Kap1.a (Hooded lemma 1) is a dominant mutation that causes the appearance of an extra flower of inverse polarity on the lemma. The trifurcate structure consists of a deformed floret at its center with two triangular leaf-like projections called lemma wings. The supernumerary spikelet often contains stamens with fertile pollen grains and occasionally bears a kernel within it. Bowman is to the left in A and top in B. 15.4 A. In mutant Subjacent hood 1(sbk1.a) the lemma is modified into a sac-like structure also including a short thin awn. B. Calcaroides-c mutants (Cal-c.15) bear a sac plus pronounced lemma wings. A normal Bowman spikelet to the right. C. Spike of cal-e.23 to the left compared to Bowman

Fig. 16

Semi-dwarf mutants. A. Mutant Brachytic 1 (brh1.e) in the near-isogenic line BW077 to the left compared to Bowman. B. Two spikes of BW074 (brh1.a) compared to Bowman exemplifies the short awns of many semi-dwarf mutants. C. BW515 (min1.a, Semi-minute dwarf 1) compared to Bowman. D. BW199 (cud2.b, Curly dwarf 2) compared to Bowman. E and F. sld2.b, Slender dwarf 2. G and H. sld3.e. I and J. sld6.g. Bowman is shown to the right in E to J

Fig. 17

17.1 A. Semi-dwarf and dwarf mutants are often easy to identify at the early seedling state as “small and cute” seedlings. The near-isogenic lines BW078 (brh1.t, front left) and BW077 (brh1.e, front right) compared to more normal seedlings in the back exemplified by BW125 (cer-w.48, back left) and BW126 (cer-x.60, back right). B. Mutant sdw1.d (Semidwarf 1, left) can be distinguished from a normal plant also later in the vegetative phase. Most short-culm phenotypes typically appear after transition to the reproductive growth phase. 17.2 A. Mutant uzu1.a (left) compared to cultivar Bowman. The short-awned spike is more compact at the basis. B. A row of uzu1.a. Opposite spikelets in the tip of the spike can form a crown-like structure and is caused by irregular elongation of the top rachis internodes. 17.3 A. Mutant sdw1.d (Semidwarf 1) is a common allele in short culm barley cultivars due to relatively few pleiotropic effects. The mutation in the near-isogenic line BW828 to the left compared to Bowman. B and C. Mutant sdw2.b has a slightly stronger phenotype. BW829 (sdw2.b) left, Bowman right

Fig. 18

Mutant cur2.b (Curly 2). A and B. Mutant cur2.b in the near-isogenic line BW220 to the left compared to Bowman at different stages of development. At maturity, the mutant is 1/3 to 1/2 of the Bowman height. C. The very curly awns of two mutants to the left compared to Bowman

Fig. 19

A. Four spikelets of BW381 (gig1.a, Gigas 1) compared to one spikelet of Bowman (top). The gig1.a spikelets have a pronounced wax coating. B. Spike of BW381 (left) compared to Bowman (right). C. BW382 (gig2.c) is almost twice as tall as Bowman

Fig. 20

A. Two spikes of the near-isogenic line BW906 carrying the wnd1.a (Winding dwarf 1) allele to the left compared to Bowman. The mutant is characterized by a coiled upper portion of the first internode. B. The original wnd1.a mutant to the left carries also the dense spike 1 (dsp1.a) allele which results in a compact spike

Fig. 21

21.1 A. Mutant mnd1.a (Many-noded dwarf 1) to the left compared to cultivar Bowman. B, C and D. A single culm of mnd1.a, mnd5.g and mnd6.6, respectively. 21.2 A. Mutant sid1.a (Single internode dwarf 1) to the left compared to cultivar Bowman. B. The lower part of sid1.b with only one single elongated internode (the peduncle) and concentration of nodes at the base of the plant. C. A spike of sid1.b to the left compared to Bowman

Fig. 22

22.1 Mutants in the gra-a (Granum-a) locus have an increased number of tillers, which are thin with narrow leaves and short internodes. A. Mutant gra-a.1 to the left compared to Bowman. B. The tiller formation at the base of three gra-a.2 mutants compared to Bowman (right). 22.2 Barley Uniculme (cul) mutants. Cultivar Bowman to the right in each photo. A and B. Near-isogenic line BW206 (cul2.b + rob1.a (Orange lemma 1). C. BW207 (cul3.c). D. BW211 (cul4.3). E and F. BW212 (cul4.5)

Fig. 23

Barley mutants with a reduced number of tillers. A. Mutant lnt1.a (Low number of tillers 1) to the left, Bowman to the right. B. Two spikes of lnt1.a compared to Bowman. The lnt1.a mutation causes asymmetry and irregularity. C. Corn stalk 1 (cst1.a) compared to Bowman (right). D. Mutant Absent lower laterals 1 (als1.a) forms only a few tillers which are coarse and stiff

Fig. 24

Three loci are associated with fragility. In these mutants leaves and stems are easily broken when physically bent. A. Mutant Fragile stem 3 (fst3.c, left) demonstrates the dwarfish of the fst mutants compared to Bowman. B. Small broken pieces of fst2.b. C. Mutant fst1.a obtain an open wound when physical bent, which does not occur in Bowman D

Fig. 25

25.1 The near-isogenic line BW875 expressing the srp1 (Serpentina 1) gene has lost its ability to grow upward. 25.2 Seedlings of lzd1.a (Lazy dwarf 1) and Bowman (right)

Fig. 26

26.1 Broad leaf 1 (blf1.a) leaf blade to the left compared with Bowman. 26.2 Narrow leaf blades in Angustifolium-a (fol-a.1) to the left compared to Bowman. 26.3 A. Narrow leafed dwarf 1 (nld1.a) seedlings to the left compared with Bowman. B. Two leaves of Narrow leafed dwarf 2 (nld2.b) compared with Bowman

Fig. 27

27.1 A. Single culm of Eligulum-a (eli-a.3) with typical eligulum formation. B. A close-up of the eli-a.3 leaf sheath. 27.2 Liguleless 1 (lig1.my) tillers are missing both ligule and auricle of all leaf blades. Bowman is to the right

Fig. 28

28.1 The inward U-shaped folding of leaf blades of Scirpoides-b (sci-b.4). Bowman is to the right in B. 28.2 Revoluted leaf blade 1 (rvl1.a) rolled into a tube through a counterclockwise spiral. 28.3 A. Scirpoides leaf-b (scl-b.5) single culm with spike. B. Close-up of the base of a spike with curled upper basal rachis internode and typical rolled leaf blades

Fig. 29

29.1 A. Pubescent leaf blade 1 (Pub1.a) with scattered small hairs on the leaf blade surface. B. A Bowman leaf blade without hairs. 29.2 A. Basal part of a Hairy leaf sheath 1 (Hsh1.a) plant. B. Single basal culm of Hsh1.a to the left compared to Bowman

Fig. 30

30.1 Globosum-a (glo-a.1003) in a Bowman genetic background shows short and rounded kernels. Bowman to the right. 30.2 Kernels of Shrunken endosperm genetic and Shrunken endosperm xenia mutants. The three plus three seeds in each group display the lemma side and palea side, respectively. A. Near-isogenic line BW836 seg3.c. B. Near-isogenic line BW844 sex1.a. C. Bowman. The bar corresponds to 1 cm

Fig. 31

31.1 In the barley Naked caryopsis 1 (nud1.a) mutant (left) the lemma and palea do not adhere to the caryopsis and the grain will thresh free of the hull at maturity. 31.2 The barley Seminudoides 1 (smn1.a) to the left compared with Bowman. There are gaps between the lemma and palea at maturity but the grain does not thresh free from the hull at maturity

Fig. 32

Two Tip sterile 2 (tst2.b) spikes to the left compared with Bowman

Fig. 33

Day-of-heading and day-of-awn-appearance are often used to approximate the start of flowering in barley since they do not require dissection of the closed barley flowers. A. The day-of-heading is typically said to be the day when at least 50% of the first spike of a barley plant emerge above the flag leaf. B. Similarly, the day-of-awn-appearance is the day when approximately one cm of the awns is visible

Fig. 34

34.1 Barley plants 30 minutes after being sprayed with water. The plants in the right box retain water droplets on their surface due to lack of epicuticular waxes. They are Glossy leaf 1 (glf1.a) leaf blade wax mutants (wax code ++ ++ -). (- = absent, + = reduced, and ++ = normal wax coating). 34.2 Three spikes of Waxy spikes 1 (wxs1.a) to the left compared with two spikes of normal Bowman at different stages of maturity. 34.3 Mutants with reduced epicuticular wax layers. A. Bowman with epicuticular waxes (wax code ++ ++ ++). B. Mutant cer-c.36 (Eceriferum-c, - - ++). C. cer-q.42 (- - ++). D. cer-u.21 (+ + ++). E. Bowman to the left, cer-b.2 to the right (- - ++). F. Bowman left, cer-yr.492 right (-/+ + ++)

Fig. 35

35.1 Seedling phenotype of segregating white Albina (A, alb-d.15) and yellow Xantha (B, xan-g.65) mutants. Homozygous Albina and Xantha mutants are white and yellow, respectively. 35.2 Examples of barley mutants with a light green color due to a low but visible amount of chlorophyll. A. Segregating Viridis mutants (vir-s.44). The light green homozygous vir-s.44 seedlings are not able to set seeds since Viridis mutations are lethal in contrast to vital Chlorina mutations. B. A mutant seedling of Chlorina seedling 12 (fch12.b) surrounded by darker green wild-type seedlings. C. Mutant fch12.b is also possible to distinguish from wild-type plants at later stages of development, which is often more complicated with other light green chlorophyll mutants

Fig. 36

Transversally striped barley mutants. The stripes correspond to tissues elongated during the light/dark cycles of the day. A. Mutant Zebra stripe 1 (zeb1.a) grown in the field. B. Segregating seedlings of a Tigrina mutant (tig-a.6) grown under light/dark cycles. The green parts correspond to leaf segments elongated in the light, while pale necrotic bands correspond to segments elongated during the dark. When segments developed during the dark phase are illuminated during the light phase they degrade

Fig. 37

Example of longitudinally striped barley mutants. A-D. Four mutant leaves to the left, one wild-type leaf to the right. A. Midseason stripe 2 (mss2.b). B. White streak 7 (wst7.k). C. Yellow streak 3 (yst3.c). D. Yellow streak 5 (yst5.e). E. Yellow streak 2 (yst2.b). F. Varigated 2 (var2.b)

Fig. 38

Barley anthocyanin-less mutants. A. Bowman near-isogenic lines carrying the mutant allele ant1.b (left) and the wild-type allele Rst1.a (right) of the Ant1 locus. The recessive ant1.b (also called rst1.b) allele has a natural occurrence in cultivars like Bowman and Morex and can be traced through their pedigrees to Manchurian-type cultivars [61]. B. Anthocyanin-less auricle of ant1.2. C. Anthocyanin containing auricle of cultivar Bonus, which is the mother cultivar of ant1.2. D. Culm basis of ant1.2. E. Culm basis of Bonus

Fig. 39

Barley mutants with necrotic spots. Each photo shows three mutant leaves to the left and one wild-type leaf to the right. A. Necrotic leaf spot 1 (nec1.a). B. Mutation Nec6.h is a dominant mutation. C. nec7.45. D. nec3.e. E. nec.60. F. nec.39

Fig. 40

40.1 Black pigmentation of barley mutant Black lemma and pericarp 1 (Blp1.b) (left) compared to cultivar Bowman (right). A. Spikes. B. Seeds. 40.2 Barley mutant Orange lemma 1 (rob1.a). A. An orange-colored pigmentation can be seen on kernels. Two mutant seeds at the top, two Bowman seeds at the bottom. B. Rachis of rob1.a left, Bowman right. C. Culm internodes of rob1.a left, Bowman right. 40.3 Barley mutants with changes in spike color due to increased levels of anthocyanin. A and B. Purple veined lemma 1 (Pvc1.a) to the left and Bowman to the right. C. Red lemma and pericarp 2 (Pre2.b) to the left and Bowman to the right. D. Two kernels of Pre2.b. 40.4 An example of barley mutants with a changed pigmentation in spikes due to a low amount of chlorophyll. A and B. Albino lemma 1 (alm1.a) to the left compared to Bowman. C. Spike of Yellow head 1(yhd1.a, left). D. The yellow-green phenotype of Yellow head 2 (yhd2.b, left) is possible to distinguish also at heading