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Poljoprivreda, 2001,7(1):10-14.
PLEIOTROPIC EFFECT OF Rht3 DWARFING GENE ON
SOME TRAITS OF WHEAT (Tr. aestivum L. em Thell)
M. Jošt, Vesna Samobor and S. Srečec
Summary
True-isogenic lines, differing only in the semi-dominant Rht3 dwarfing gene
were developed from cross 'Tom Thumb x Bankuty 1201' during 17 years of
continuous selection on heterozygous semi-dwarf plant. The effect of double
(Rht3 Rht3 = full-dwarf), single (Rht3 rht3 =semi-dwarf), or no dwarfing gene (rht3
rht3 = tall) dosage on some plant, seed, and flour quality traits were observed in
the isogenic lines during two years field experiment planted by 'honey-comb
design' at Križevci, Croatia. Significant main effect of Rht3 gene was in
shortening of plant height for 54% and 28% in double and single gene dosage
respectively. Full-dwarf genotype (Rht3 Rht3) had by 12% more heads/plant, but
the other yield components as number of grains/head, and grain weight/head
were lower for 25 and 28% respectively, resulting in significantly lower grain
yield/plant (-27%). However, this also could be a secondary side effect of
prolonged vegetation influenced by doubled Rht3 gene. There was no significant
effect on flour protein content. Double gene effect was strong and significant for
maximum dough viscosity measured by amylograph in BU (101%). In our
environment full dwarf (Rht3 Rht3) has no agronomic value, but single gene
dosage could be of commercial interest in hybrid wheat breeding.
KEY WORDS: Wheat - Triticum aestivum, dwarfism, Rht3 gene, pleiotropic effect, yield
components, grain yield, protein content, amylogram.
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Introduction
There is a general opinion that, discovery of dwarfing genes and replacement of
conventional tall wheat cultivars by semi-dwarf ones, contributed to increase in grain
yield (PUGSLEY 1983, PINTHUS and LEVY 1984, GALE and YOUSSEFIAN 1984, W ORLAND
et al. 1990. Gent and Kiyomoto, 1998.) In spite of the fact that over twenty different
dwarfing genes were identified till today (Gene catalog-gopher, 1998), only five of
them are extensively used in World wide cultivated wheat varieties. Those are: Rht1,
Rht2, (known as 'Norin 10'), Rht1(B.dw) (known as Bezostaya 1 dwarf), rht8 (known
as 'Akakomugi') and Rht1S gene (known as Saitama 27). All of them, except
Rht1(B.dw.) originated from Japanese germplasm. While Rht1 and Rht2 are common
in American, Australian and West European cultivars, rht8 and Rht1S are prevalentin
Southern European cultivars (W ORLAND and LAW 1986). There were trials of using
some other Rht dwarfing genes, but without significant success (W ORLAND et al.
1980). For now, only strong dwarfing allel Rht3 (known as 'Tom Thumb' or 'Minister
dwarf' gene) shows some breeding value, at least for hybrid wheat (Gale et al. 1989).
The major genes Rht1 and Rht2 have been located on chromosomes 4BS (GALE and
MARSHAL 1976) and 4DS (GALE et al. 1975) respectively. The dwarfing gene Rht3 has
been located on 4BS chromosome also. It is multiple allele with Rht1, Rht1S and
Rht1(B.dw.) since all of them share a common locus of the same chromosome
(MORRIS et al. 1972; GALE et al. 1975; Worland, Petrović, 1988). The Rht1 and Rht2
are dominant genes, and the third Rht3 is semi-dominant gene with strong dwarfing
effect. All of the tree have a pleiotropic effect on plant's insensitivity to exogenous
gibberellic acid. The dwarfing gene rht8, common in South-European germplasm, has
been located on chromosome 2DL, and unlikely to previously mentioned 'Norin 10'
and 'Tom Thumb' dwarfing genes, it is recesive height promoting gene (W ORLAND and
LAW 1985) and do not confer insensitivity to exogenous gibberellic acid (W ORLAND and
LAW 1986). The Rht1S is a weak source of giberelic acid insensitivity derived from cv.
Saitama 27.
The interest for using Rht3 gene in breeding work was renewed after discovery of its
ability to inhibit the release of the enzyme α-amylase in germinated grain, the trait
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important for regions threatened by preharvest sprouting and consequently deleterious
effect on bread quality (GALE and MARSHAL 1973).
A number of studies of possible pleiotropic effect of dwarfing genes were reported,
and often non compatible and conflicting conclusions were brought (B ORNER and
W ORLAND, 1994). Beside the positive effects on grain yield (ALLAN 1989, GALE et al.
1989 and many others), a neutral or even negative effects of the Rht genes due to a
large decrease in grain size were reported (ALLAN 1986, KERTESZ et al. 1991). There
could be several reasons for this disagreements in results obtained:
i)
some investigators prefer to perform 'inter-cultivar' rather than 'inter-gene'
comparisons, while
ii)
the others in wish to get the results as soon as possible, used near-isogenic
lines in gene action comparisons.
iii)
Influence of environmental conditions seems to be important also.
From that reason, in the present investigation, by using true-isogenic lines, the effects
of Rht3 semi-dominant gene in double, single and no-dosage on some plant, seed,
and flour characters, was examined.
Materials and Methods
Development of isogenic lines
In 1977, the F1 seed of cross 'Tom Thumb x Bankuty1201' was received from late Dr.
Zoltan Barabas, Cereal Research Institute, Szeged, Hungary. As Rht3 is semidominant gene, in the following generations segregates on true dwarf (Rht3 Rht3),
semi-dwarf (Rht3 rht3) and tall (rht3 rht3) plant types were obtained. According to
method described by ATKINS and MANGELSDORF (1942), a constant selection on
heterozygous (Rht3 rht3) semi-dwarf types were performed in each successive
generation. After 14 and 17 generations the seeds of true isogenic lines were used in
the experiment. The method described allowed us to test dosage effect for Rht3 gene
in the three true-isogenic lines, having constitution: Rht3 Rht3 (dwarf), Rht3 rht3 (semidwarf) and rht3 rht3 (tall).
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Experimental design
Es 1:2:1 segregation ratio was expected between progeny of heterozygous (semidwarf) plants, it was impossible to forecast the genotype of the certain plant. For this
reason the honeycomb design (Fasoulas 1979) was adopted in experiment planting.
In this way comparisons between the neighbor plants of the three expected different
plant type (different isolines) was possible. To ensure adequate number of
homozigous plants each second row was planted with homozigous seeds. (Fig.1) In
fact, to ensure normal stand, all seeds were planted in paper pots in October, and
than normally developed and vernalized three leaf seedlings were replanted in field in
March next year. The between plant spacing in honeycomb was 27 cm, it means the
space precise planting was performed. All together 133 plants of each homozygous
genotype and 247 progeny seedlings of heterozygous parent plants were replanted
each year.
Analytical methods
In spite of the honeycomb design applied, only a 40 couples of each of the three
possible genotype comparisons (Rht3Rht3 /Rht3rht3, Rht3Rht3 /rht3rht3, Rht3rht3 /rht3rht3)
were analyzed each year. In the field, the plant couples, sharing the same
neighborhood, were provided with adequate tags, and some characters (plant height,
number of nodes/main shoot, length of the top internode per main shoot, number of
tillers/plant, number of heads/plant and flag leaf area) were determined before
harvest. The flag leaf area was determined by the multiplying the flag leaf width,
length and coefficient 'b':
Leaf area (sq cm) = width (cm) x length (cm) x b
The coefficient b=0.739 was previously determined on representative samples of 25
leaves of each height class by gravimetric method (KVET and MARSHALL, 1971). After
harvest the other plant characteristics (ear length, number of spikelets/ear, number of
kernels/ear, grain weight/ear, grain weight/plant) were determined. The differences
between the two means were calculated and their significancy tested by t-test.
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Poljoprivreda, 2001,7(1):10-14.
The kernel and quality characteristics (moisture, test weight, thousand kernel weight,
grain protein, milling, flour ash, and flour amylogram) were determined on average
samples, without possibility of statistical measures the differences between the
means.
Results and Discussion
A problem in explanation of this type of investigations is frequent disability to
distinguish the primary effect of dwarfing genes and the secondary effect of reduced
other values - source capacity, for instance. Beside this, till now reported results often
disagree in findings. One reason could be frequent use of near-isogenic lines, and
'inter-cultivar' rather than 'inter-gene' comparisons. In this experiment we tried to avoid
this misleading procedure by using true-isogenic lines and 'inter-gene' comparison.
The main effect of Rht3 gene is significant shortening of plant stature for about 54%
and 28% in double and single gene dosage respectively, as well as significant
decrease of α-amylase activity (determined by amylograph) in double gene dosage
only (Tab.1, Fig 2.). In double gene dosage decreased spike fertility (number of
kernels per spike for -25.04%, TKW for -16.06% and test weight for -4.08%) could not
be compensated by slightly increase in number of tillers per plant (9,69%) and spikes
per plant (12,18%). As results, in environmental conditions of Croatia, grain yield per
plant, in space planting, was strongly lowered for -26.56 in double and -7.02% in
single gene dosage respectively. To some extent this negative effect could be
compensated in dense planting due to better lodging resistance of dwarf and semidwarf plants. However, even in this case, too dense distribution of leaves in double
gene full dwarf, and bad light interception into canopy, seems to be unfavorable for
photosynthesis.
However, our findings disagree with the results obtained recently by BORNER and A.J.
W ORLAND (1994). According to them, a higher number of grains per ear was
accompanied by a lower grain weight, but depending on the climatic conditions in a
particular year, the increase in grain number was sufficient to compensate for the
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Poljoprivreda, 2001,7(1):10-14.
reduction in grain size and resulted in higher yields. Obviously, the environmental
conditions of Croatia is to worm in period of heading and flowering, resulting in empty,
non-fertilized flowers, and consequently lower grain number per head.
On the contrary, single gene dosage (heterozygous genotype - Rht3 rht3) seems more
acceptable when plant stature is in question (semi-dwarf of 83 cm). Lower grain yield
per plant in experiment (space planing) for about 7% could be compensated in dense
population in commercial planting. However, this type could be exploited only as F1
hybrid due to its heterozygous stage. In this way, the F 1 seed production could be
more efficient due to the difference in plant height (dwarf mother plant and tall
pollinator plant) and hybrid vigor could be expressed beneficially on grain yield of
semi-dwarf F1 plants.
References
1. ALLAN, R. E. 1986. Agronomic comparisons among wheat lines nearly isogenic for three
reduced-height genes, Crop Sci. 26:257-286.
2. ALLAN, R.E. 1989. Agronomic comparisons between Rht1 and Rht2 semidwarf genes in
winter wheat. Crop Sci. 29:1103-1108.
3. ATKINS, I. M., and P. C. MANGELSDORF. 1942. The isolation of isogenic lines as a means of
measuring the effects of awns and other characters in small grains. Jour. Amer. Soc.
Agron., 34:667-668.
4. BORNER, A., and A.J. W ORLAND. 1994. Breeding for lodging resistance in wheat and the
utilization of dwarfing genes. Abstracts of EUCARPIA Symp.on Prospectives of Cereal
Breeding in Europe, Landquart, Switzerland, p. 169-170.
5. FASOULAS, A. 1988. The honeycomb method of plant breeding. Aristotelian University of
Thesaloniki, Greece, p. 167.
6. GALE, M. D. and G. A. MARSHALL. 1973. Insensitivity to gibberellin in dwarf wheats. Ann
Bot. 37:729-735.
7. GALE, M. D., C. N. LAW and A. J. W ORLAND. 1975. The chromosomal location and a major
dwarfing gene from Norin 10 in new British semi-dwarf wheats. Heredity, 35(3):417-421.
8. GALE, M.D. and G.A. MARSHALL. 1976. The chromosomal location of Gai 1 and Rht 1,
genes for gibberellin insensitivity and semidwarfism, in a derivative of Norin 10 wheat.
Heredity. 37(2):283-289.
9. GALE, M. D. 1979. The effects of Norin 10 dwarfing genes on yield. Proc. 5th Int. Wheat
Genet. Simp., New Delhi, p. 978-987.
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10. GALE, M. D. and S. YOUSSEFIAN. 1984. Pleiotropic effects of the Norin 10 dwarfing genes,
Rht1 and Rht2, and interactions in response to chlormequat. Proc. 6th Int. Wheat Genet.
Symp. Kyoto, p. 271-277.
11. GALE, M.D., SALTER, A.M. and ANGUS, W.J. 1989. The effect of dwarfing genes on the
expression of heterozis for grain yield in F1 hybrid wheat. In: Maluszynski, M.(Ed.), Current
options for cereal improvement. Doubled haploids, mutants and heterozis. p. 49-61.
12. GENT, P.N.M., and R.K. KIYOMOTO.1998. Physiological and agronomic consequences of
Rht genes in wheat. J.Crop Prod. 1(1):27-46.
13. Gene catalog. 1998. Internet: gopher://greengenes.cit.cornell.edu:70/0R89079-92105/GeneCatalog
14. KERTESZ, Z., J.E. FLINTHAM and M.D.GALE. 1991. Effects of Rht dwarfing genes on wheat
grain yield and its components under Eastern European Conditions. Cereal Res. Comm.
19:297-304.
15. KVET, J., and J. K. MARSHALL. 1971. Relationships between linear measurements and leaf
area. In: Sestak et al. (Eds.), Plant photosynthetic production - Manual of methods. Dr.
W.Junk N.V. Publishers, The Hague, p. 526-532.
16. MCNEAL, F. H., M. A. BERG, V. R. STEWART and D. E. BALDRIDGE. 1972. Agronomic
response of three height classes of spring wheat, Triticum aestivum L., compared at
different yield levels. Agr. Journ., 64:362-364.
17. MORRIS, R, J. W. SCHMIDT and V. A. JOHNSON. 1972. Chromosomal location of a dwarfing
gene in Tom Thumb wheat derivatives by monosomic analysis. Crop Sci., 12:75-276.
18. PEPE, J. F. and R. E. HEINER. 1975. Influence of two different dwarfing sources on yield
and protein percentage in semidwarf wheat. Crop Sci., 15:637-639.
19. PINTHUS, M. J. and A. A. LEVY. 1984. Genotypic effects of height on grain yield of Triticum
aestivum L. spring wheat. Z. Pflanzenzuchtung, 93:49-55.
20. PUGSLEY, A. T. 1983. Identification and management of major genes monitoring yield and
adaptation. Proc. 6th Int.Wheat Genetics Symp., Kyoto, p. 971-974.
21. W ORLAND, A. J., C. N. LAW and A. SHAKOOR. 1980. The genetical analysis of an induced
height mutant in wheat. Heredity, 45:61-71.
22. W ORLAND, A. J., and C. N. LAW . 1985. Aneuploidy in semi dwarf wheat varieties.
Euphyitica, 34:317-327.
23. W ORLAND, A. J. and C. N. LAW . 1986. Genetic analysis of chromosome 2D of wheat. I. The
location of genes affecting height, day-length insensitivity, hybrid dwarfizm and yellow rust
resistance. Z. Pflanzenzuchtung, 96:311-345.
24. W ORLAND, A. J., C. N. LAW
and S. PETROVIC. 1990. Height reducing genes and their
importance to Yugoslavian winter wheat varieties. Savremena poljoprivreda, 38(3-4):245258.
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PLEIOTROPNI UČINAK Rht3 GENA ZA PATULJASTU STABLJIKU
NA NEKA SVOJSTVA PŠENICE (Tr. aestivum L. em Thell)
M. Jošt, Vesna Samobor and S. Srečec
Visoko gospodarsko učilište u Križevcima, Hrvatska
SAŽETAK
Tijekom 17 godina uzastopnog odabiranja heterozigotnih biljaka iz križanja 'Tom
Thumb x Bankuty 1201', stvorene su čiste izogene linije, koje su se međusobno
razlikovale samo u zastupljenosti poludominantnog gena za patuljastu slamu (Rht3). U
Križevcima, tijekom dvogodišnjih poljskih pokusa sijanih po metodi pčelinjeg saća, u
tih je linija promatran učinak prisustva Rht3 gena (Rht3 Rht3 = patuljak, Rht3 rht3 =
polupatuljak i rht3, rht3 = visoka biljka), na neka svojstva biljke, sjemena i pokazatelje
kakvoće brašna.
Značajan glavni učinak Rht3 gena je smanjenje visine stabljike za 54% u homozigotnih
Rht3 Rht3 genotipova, odnosno za 28% u heterozigotnih Rht3 rht3 genotipova.
Patuljaste biljke (Rht3 Rht3) imale su 12% više klasova po biljci, ali su druge
komponente uroda – broj zrna/klas i masa zrna/klas bile slabije za 25 i 28%. Kao zbirni
rezultat, patuljaste biljke ispoljile su značajno umanjen urod zrna po biljci (-27%).
Međutim, to bi mogao biti i sekundarni postrani učinak dulje vegetacije (pet dana
kasnije klasanje). Učinak dvostruke doze Rht3 gena na količinu bjelančevina u zrnu
nije bio značajan, ali je maksimalni viskozitet tijesta mjeren amilografom u BU
jedinicama značajno (101%) izmijenjen. U klimatskim uslovima Hrvatske homozigotni
patuljci (Rht3 Rht3) nemaju agronomske vrijednosti, međutim kao heterozigoti, mogli bi
imati stanovitu vrijednost u oplemenjivanju hibridne pšenice.
Ključne riječi: pšenica - Triticum aestivum, patuljasti habitus, Rht3 gen, pleiotropni učinak,
komponente uroda, urod zrna, bjelančevine zrna, amilogram.
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
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Fig.1. The honeycomb planting design applied ( = tall rht3 rht3 homozygote, o =
segregating progeny of heterozygous Rht3 rht3 semi-dwarf plants, and  =
homozygous Rht3 Rht3 full dwarfs).
Fig. 2. Wheat near-isogenic lines differing only in Rht3 dwarfing gene dosage.
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Tab.1. Pleiotropic effect of Rht3 dwarfing gene dosage on plant, seed and flour
characteristics.
Average of two years: Križevci, 1991 and 1995
Rht3 Rht3
Semidwarf
wheat
Rht3 rht3
rht3 rht3
double:
Rht3
Rht3
single:
Rht3
Plant height (cm)
53.3
83.1
115.4
46.20**
72.01**
No. tillers per plant
25.35
24.88
23.11
109.69*
107.66NS
Top internode length (cm)
25.04
35.18
50.03
50.05**
70.32**
Flag leaf area (sq cm)
53.84
56.74
58.46
92.10*
97.06NS
No. spikes per plant
23.30
23.08
20.77
112.18*
111.12*
1st spike length (cm)
12.79
11.93
12.57
101,75NS
94.91NS
No. spikelets per 1st spike
21.89
20.56
19.98
109.56*
102.90NS
No. kernels per 1st spike
52.68
60.77
70.28
74.95**
86.47**
Kernels wt. per 1st spike (g)
2.76
3.71
3.84
71.87**
96.61NS
Grain yield per plant (g)
30.22
38.26
41.15
73.44**
92.98*
T K W (g)
43.08
49.63
51.32
83.94**
96.71
Test weight (hl/kg)
77.91
79.63
81.22
95.92**
98.04
Grain moisture (%)
15.12
13.78
13.32
113.51*
103.45
Flour extraction (%)
66.25
73.83
74.10
89.41
99.64
Flour protein (%)
13.12
12.04
13.02
100.77
92.47
Ash content (%)
0.593
0.548
0.550
107.82
99.64
Amylogram max. viscosity BU
2030
960
1010
200.99
95.04
Character
**, *,
NS
Full dwarf
wheat
Tall
wheat
Gen dosage effect if
rht3 rht3 = 100%
= significant at 0,01; 0,05 level or not significant respectively.
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