Arain S

Jamali KD

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 1Coleoptile length studies in semi-dwarf wheat (Triticum aestivum L.) with different dwarfing genes  Jamali KD and Arain S Nuclear Institute of Agriculture (NIA) Tando Jam Pakistan  ABSTRACT  Eleven genotypes (seven varieties and four lines) were studied for coleoptile length.  The genotypes having Rht1, Rht2, Rht1Rht2, Rht8Rht9 and rht were compared for their coleoptile length under controlled environmental conditions.  The results suggested that the traditional tall variety C-591 (rht) had longer coleoptiles compared to the remaining varieties and genotypes.  The genotypes which had the next longest coleoptile length were Chinese Spring (rht) and Rht8-01 (Rht8).  The varieties Mara (Rht8Rht9), Sarsabz (Rht1) and Soghat-90 (Rht2) were not significantly different for their coleoptile length.  The line Rht8-02, which carries Rht8 dwarfing genes, was not significantly different to the Yecora (Rht1Rht2), a double dwarf variety.  These results suggest that the dwarfing genes probably do not affect the coleoptile length.  The genetic background may affect the coleoptile length of individual varieties.  INTRODUCTION  Lack of moisture near the soil surface commonly delays sowing, reducing grain yields of the wheat (Triticum aestivum L.) crop in Pakistan. Deep sowing would allow growers to make use of soil moisture lying below the dryer topsoil, but the short coleoptiles of semi-dwarf wheats reduce emergence when sowing at depths greater than 5 cm. Selection of longer, thicker coleoptiles would help in improving emergence in hard or crusted soils, or when deep sowing, yet little is known of genetic control of coleoptile size in wheat.  Rebetzke et al. (2004) reported that coleoptile length for progenies derived from Rht8, Rht9, and Rht12 dwarfing gene donors were generally shorter (7 to 13%) but were still an average 47% longer than coleoptiles of Rht-B1b and Rht-D1b controls.  Rebetzke et al. (2001) reported that differences in coleoptile length among varieties were substantially larger than for effects associated with either grain size or seed production source. Standard height (rht) and gibberellic acid (GA)-sensitive Rht8/9 semi-dwarf wheat varieties produced coleoptiles that were between 25 to 40% longer than GA-insensitive Rht-B1b and Rht-D1b semi-dwarf varieties. Furthermore, increasing mean soil temperature from 11 to 19 °C reduced coleoptile length by 20% in rht and Rht8/9 wheats and by as much as 50% in Rht-B1b and Rht-D1b semi-dwarfs. The selection for increased coleoptile length can be made readily in a wheat-breeding program which includes GA-sensitive parents. Bai et al. (2004) reported that coleoptile length varied among accessions from 4.4 to 11.4cm. Frequency distributions for 192-bp (with Rht8) and non-192-bp (without Rht8) genotypes showed no advantage of the 192-bp allele to coleoptile elongation. None of the 192-bp genotypes from the Great Plains showed greater coleoptile length than 'TAM 107', a hard red winter cultivar without Rht8, often chosen over contemporary cultivars for its greater emergence capacity with deeper seed placement. Since coleoptile elongation may be controlled by several quantitative trait loci, identifying only the presence of 192-bp allele of Xgwm 261 may be misleading if the primary motivation for its deployment is to increase coleoptile length in a semi-dwarf plant type. Rebetzke et al. (2007) demonstrated the importance of good seedling emergence in achieving high wheat yields, and the potential use of alternative dwarfing genes such as Rht8 in development of long coleoptile, reduced height wheat suitable for deep sowing.   The Norin-10 dwarfing genes, Rht-B1b (Rht1) and Rht-D1b (Rht2) are commonly used to reduce plant height and increase grain yield in wheat breeding programs (Gale and Youssefian, 1985). These dwarfing genes lower sensitivity of vegetative tissue to endogenous gibberellin to reduce cell and subsequent stem elongation. This reduction in cell elongation capacity reportedly results in a concomitant reduction in coleoptile length and early vigor (leaf area), thereby affecting seedling establishment and growth. Rebetzke et al. (2001) reported that the negative genetic effect of the Rht-B1b dwarfing gene on early growth of wheat confirms phenotypic evidence of a pleiotropic effect of Rht-B1b on establishment and early vigor. Genetic increases in coleoptile length and early leaf area development are likely to be limited in wheat populations containing the Rht-B1b dwarfing gene. The aim of this study was to determine the effects of dwarfing genes on coleoptile length and other agronomic characteristics.  MATERIALS AND METHODS  Eleven genotypes (seven varieties and four advanced lines) were studied and evaluated to check the effects of height genes on coleoptile length.  The twenty seeds of each of the eleven genotypes were stained with 2% sodium hypochlorite for 2 minutes then washed in distilled water three times prior to grow.  These seeds  2were then sown on filter paper in petri dishes.  The experiment was conducted according to Hakizimana et al. (2000) and Bai et al. (2004) with some modifications.  The studies were conducted in a growth chamber with three replicates, each with 20 grains.  The temperature was maintained at 15 0C and humidity at 60% for six days. Water was applied intermittently as required. The germination rates of lines were good. The coleoptile length of each genotype was measured in centimeters (cm).  The plants were grown to maturity for agronomic studies under field conditions.   RESULTS AND DISCUSSION    COLEOPTILE LENGTH The traditional tall variety C-591 had the longest coleoptile length compared to the remaining varieties and genotypes (Table 1).  The remaining genotypes which had longest coleoptile lengths were Chinese Spring and Rht8-01, which did not differ significantly.  The varieties Mara (Rht8/9), Sarsabz (Rht1) and Soghat (Rht2) were not significantly different.  The line Rht8-2 (Rht8) was not significantly different to the Yecora (Rht1Rht2), a double dwarf variety.  Kiran-95 variety (Rht1) was not significantly different from the Yecora variety.  These results suggest that the dwarfing genes do not affect the coleoptile length; however, the genetic background may affect the coleoptile length of individual varieties.  Rebetzke et al. (2001 and 2004) reported that the coleoptile length of progenies derived from Rht8, Rht9, Rht12 and rht (tall) had comparatively longer coleoptile lengths than the progenies with GA-insensitive (Rht-B1b and Rht-D1b).  Rebetzke et al. (2007) reported that wheat containing the Rht-B1b or Rht-D1b dwarfing genes produced significantly shorter coleoptiles than both Rht8 and tall (rht) wheat. However, other workers reported that the genotypes with Rht8 (192bp) and without Rht8 had no significant differences (Bai  et al. 2004).     Table 1.    Coleoptile length and agronomic performance of wheat varieties with different dwarfing genes Lines/Variety Rht genes  Coleoptile  length (cm) Plant  height  (cm) Spike  length  (cm) No.of grains/ spike Spike grain yield (g) Mara Rht8 and Rht9 3.72 d 84.3 e 9.15 f 52.15 c 1.03 g Rht8-2 Rht8 3.17 f 68.6 h 11.3 c 67.55 b 2.10 c Anmol-91 Rht2 2.64 g 82.4 f 12.25 b 66.9 b 2.52 b Chinese Spring rht rht 4.77 b 106.5 b 8.45 h 35.30 f 0.81 h Rht8-1 Rht8 4.87 b 75.1 g 9.30 f 66.25 b 2.45 b 6-06 rht rht 4.28 c 106.2 b 13.47 a 70.65 a 2.66 a Kiran-95 Rht1 3.44 e 88.5 d 12.05 b 52.3 c 1.75 de C-591 rht rht 5.12 a 114.5 a 8.78 g 40.5 e 1.20 g Soghat-90 Rht2 3.62 d 91.1 c 10.90 d 52.8 c 1.57 f Sarsabz Rht1 3.64 d 87.3 d 11.03 d 54.85 c 1.85 d Yecora Rht1 Rht2 3.30 ef 59.1 i  10.35 e 49.1 d 1.66 ef  PLANT HEIGHT   The tall variety C-591 was the tallest (plant height) of all the varieties or lines (Table 1). Chinese Spring and another line 6-06, were also tall, but not significantly different.  Sarsabz and Kiran-95 both carry Rht1 gene and were not significantly different.  The varieties carrying Rht8 viz. Rht8-2, Rht8-1 and Mara were significantly different. Yecora (Rht1 and Rht2) had, significantly, the shortest plant height.  SPIKE LENGTH     In this comparison the tall line 6-06 had the longest spike and was significantly different to the remaining varieties and genotypes.  The other varieties/genotypes which had long spikes were Kiran-95, and Anmol-91.  Mara and Rht8-1 both carry Rht8 gene and were not significantly different.  Sarsabz and Soghat-90 varieties had no significant differences.  NUMBER OF GRAINS PER SPIKE   The tall line 6-06 had the highest number of grains per spike than other lines and varieties.  The variety Anmol-91 with Rht2 was not significantly different from Rht8-1 and Rht8-02 lines, both carrying Rht8.  Maras, an Italian variety carrying Rht8 and Rht9, was not significantly different from Sarsabz (Rht1), Kiran-95 (Rht1) and Soghat-90 (Rht2).    MAIN SPIKE GRAIN YIELD  In this comparison line 6-06 had the highest grain yield from the main spike. The line Rht8-1 (Rht8) was not  3significantly different from Anmol-91 variety (Rht2).  Kiran-95 was not significantly different from Yecora variety which carries both dwarfing genes (Rht1 and Rht2).  Soghat-90   variety was not significantly different from Yecora a double dwarf variety.    CONCLUSION  The results suggest that the dwarfing genes do not affect the coleoptile length.  The genetic background may affect the coleoptile length of individual varieties.  REFERENCES  Bai, G., M.K. Das, B.F. Carver, X. Xu, and E.G. Krenzer (2004).  Covariation for microsatellite marker alleles associated with Rht8 and coleoptile length in winter wheat.  Crop Sci. 44: 1187-1194. Gale, M.D. and S. Youssefian (1985).  Dwarfing genes in wheat. P. 1-35. In: G.E. Russel (ed). Progress in plant breeding. I. Butterworth, London Hakizimana, F., S.D. Haley, and E.B. Turnipseed (2000).  Repeatability and genotype x  environment interaction of coleoptile length measurements in winter wheat.  Crop Sci.  40: 1233-1237. Rebetzke, G.J., R.A. Richards, V.M. Fisher and B.J. Mickelson (1999).  Breeding long coleoptile, reduced height wheats.  Euphytica.  106: 159-168. Rebetzke, G.T., R. Apples, A.D. Morrison, R.A. Richards, G. Mcdonald, M.H. Ellis, W. Spielmeyer and D.G. Bonnett (2001).  Quantitative trait loci on chromosome 4B for coleoptile length and early vigour in wheat (Triticum aestivum L.).  Aust. J. Agric. Res. 52: 1221-1234. Rebetzke, J.G., R.A. Richards, R.R Sirault, and A.D. Morrison (2004). Genetic analysis of coleoptile length and diameter in wheat. Australian Journal of Agriculture Research. 55 (7): 733-747.  Rebetzke, G.J., R.A. Richards, N.A. Fettell, M. Long, A.G. Condon, R.I. Forrester and T.L. Botwright  (2007). Genotype increases in coleoptile length improves stand establishment, vigour and grain yield of deep sown wheat.  Field Crops Research 100: 10-23. 

Coleoptile length studies in semi-dwarf wheat (Triticum aestivum L.) with different  dwarfing genes

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Coleoptile length studies in semi-dwarf wheat (Triticum aestivum L.) with different dwarfing genes

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