Pleiotropic effects of Norin-10 dwarfing genes in wheat (Triticum aestivum L.)
Karim Dino Jamali
Nuclear Institute of Agriculture (NIA), Tando Jam, Pakistan
Corresponding author: Karim Dino Jamali
E-mail: karimdino2001@yahoo.co.in
Abstract
Isoline studies were carried out of semi-dwarf wheat genotypes with Rht1Rht2 (double dwarf), Rht1 or Rht2 (semi-dwarf) and tall (rht1rht2). The material consisted of four crosses viz: Anmol (Rht2) x 6-14 (Rht1), Anmol x Sarsabz (Rht1), Anmol x 7-03 (Rht1) and 6-06 (rht1rht2) x 5-05 (Rht1 and probably Rht2 (not completely sure)). The isolines were developed by selecting the lines either carrying both Rht1 Rht2, or alone Rht1 or Rht2, and rht1rht2 in F5 generation. The selection was made within each cross for double dwarf, semi-dwarf and tall plants from the same genetic background. There were 35 lines, out of which 20 double dwarf, 9 semi-dwarf lines, 2 tall lines and 4 parent varieties/ genotypes. The pleiotropic effect results suggest that most of the double dwarfs were low yielding under field conditions. Overall, the double-dwarf (Rht1Rht2) lines had 22% lower yield than semi-dwarf (Rht1 or Rht2) when both the dwarfing groups (double dwarf and semi-dwarf) were pooled separately. The performance of tall and double dwarf lines was at par, however, the tall lines exceeded by 2 % in yield than double dwarfs. The tall lines produced 19% less yield than the semi-dwarf lines. The results suggested that the selection of double dwarf (Rht1Rht2) and tall (rht) genotypes under hot and dry environments may be avoided due to their poor performance.
Key words: semi-dwarfism, agronomic characters, pleiotropic effects
Introduction
The adaption of Norin-10 height reducing genes, Rht-B1b (Rht1) and Rht-D1b (Rht2), has been associated with increased wheat yields in many regions of the world including Australia (Waddington et al., 1986); Perry and D’Antuono 1989; Slafer et al., 1994). Near-isogenic lines are excellent material to analyze pleiotropic effects of these genes. Kertesz et al., (1991) conducted near-isogenic studies of Norin-10 and Tom Thumb dwarfing genes, singly and in combination in two varietal backgrounds. They reported that Rht1 and Rht2 alleles were associated with a yield reduction of 6%, due to 25% decrease in grain weight particularly compensated by a 10% increase in grain number per ear and a 13% in tiller number per meter. Yields of Rht1+Rht2, Rht3 and Rht3+Rht2 genotypes were much reduced by 45%, 48% and 71% respectively. Allan (1997) reported from near-isogenic lines in Nugaines that lines with Rht1Rht2 (double dwarf), Rht1Rht1, Rht2Rht2 had comparatively higher grain yield by 22, 36 and 28% than their tall counterparts respectively. Rht1 had comparatively higher grain yield than Rht1Rht2 and Rht2 by 11 and 6% respectively. Both of the semi-dwarf lines either with Rht1 or Rht2 had comparatively higher grain yields than the double dwarf. Gale and Youssefian (1983) reported from isogenic studies in Maris Huntsman and M. Windgeon background that semi-dwarf genes Rht1 or Rht2 had produced 20% more grain yield than their counterpart talls. Fisher and Quail (1990) reported from F7 and F8 derived material of different crosses that double dwarf genotypes gave the highest yields. However, the Rht3 group yielded on average 3% lower, Rht2 9% lower, Rht1 11% lower, and the non dwarf or tall group (rht1rht2) yielded 24% lower than that of double dwarfs (Rht1Rht2). Youssefian et al., (1992) reported that primary effect of Norin-10 genes on growth is to reduce only the rate of stem elongation and vegetative dry matter accumulation. There is a reduced competition by the stem for nutrients; leading to a greater portion of dry mass being partitioned resulted in a greater number of competent florets, which also have a greater mass per carpel at anthesis. Both these features are considered to favour the increased grain set, which is characteristic of these dwarf genotypes. The aim of these studies was to analyse the pleiotropic effects of Norin-10 genes in wheat. There are no reports for pleiotrpic effects of these genes in this sub-continent and Australia.
Materials and Methods
The material was consisted of four crosses viz: Anmol (Rht2) x 6-14 (Rht1), Anmol x Sarsabz (Rht1), Anmol x 7-03 (Rht1) and 6-06 (rht1rht2) x 5-05 (Rht1 and probably Rht2 (not completely sure)). The progenies were maintained from single F1 plants. The isolines (similar lines only differing in semi-dwarf genes) were developed by selecting the lines either carrying both Rht1 Rht2, or alone Rht1 or Rht2, and rht1rht2 in F5 generation. The selection was made within each cross for double dwarf, semi-dwarf and tall plants from the same genetic background. Out of 35 lines, 20 were double dwarf, 9 semi-dwarf, 2 tall and 4 parent varieties/ genotypes. Each line from a cross was grown in three-meter row length with four rows in three replicates. At harvest central two rows were harvested.
Results and Discussion
The results of individual line/genotype performance are presented in Table 1, Table 2 and Table 3. In this comparison the single gene/semi-dwarf genotype (Table 2) has a positive effect on plant height, spike length, number of spikelets, number of grains per spike, main spike yield and plot grain yield compared to double dwarf and tall groups.
Days to heading
In this study the semi-dwarf genotypes were earlier than both the double dwarf and tall genotypes (Table 4). However, only the significant difference (P=0.05) was observed between semi-dwarf and tall genotypes. Days to heading of double dwarfs ranged from 69 to 70 that of the semi-dwarfs had 69 to 77 days (Table 1 and Table 2). Allan (1997) reported from near-isogenic studies that there were no significant differences for days to heading between the Rht1Rht1, Rht2Rht2 and tall (rht1rht2) except the double dwarf (Rht1Rht2). In his studies the double dwarfs were two days later than Rht1Rht1, Rht2Rht2 and tall (rht1rht2). Börner et al., (1993) reported that days to heading was unaffected by the dwarfing genes. However, they reported that there were some lines significantly earlier and some later than the tall lines, by a maximum difference of two days.
Plant height
There were significant differences for plant height, the double dwarf and semi-dwarf genotypes were 49% and 29% shorter (Table 4) than the tall lines respectively. The double dwarf lines were 28% shorter than the semi-dwarf lines. The plant height of double dwarfs ranged from 49.4 to 65.8 cm, while that of semi-dwarf between 71.9- 87.7 cm (Table 1 and Table 2). Nizam Uddin and Marshall (1989) reported that plant height of the tall; the intermediate (semi-dwarf) and dwarf (double dwarf) lines differed significantly from each other under both the irrigated and rainfed conditions. Under irrigated conditions, the tall lines averaged 20 cm taller than the intermediate and 50 cm taller than the double dwarfs.
Spike length and number of spikelets
Spike length and number of spikelets per spike were not significantly different between semi-dwarf and double dwarf genotypes (Table 4). However, tall lines produced significantly longer spikes than double dwarfs. Tall lines also had increased number of spikelets per spike than semi-dwarf and double dwarfs lines (Table 4). Borrell et al., (1991) reported from the near-isogenic lines of Triple Dirk that there were no significant differences for number of spikelets per spike between rht1, Rht1 and Rht2. Nizam Uddin and Marshall (1989) reported from near isogenic lines of semi-dwarf genes that these genes did not have significant effect on number of spikelets.
Number of grains per spike
The double-dwarf and semi-dwarf genotypes had 8% and 15% increased number of grains than their counterpart tall (rht1rht2) genotypes. The semi-dwarf genotypes had 6% more number of grains than double dwarfs. Allan (1989 and 1997) reported that Rht1 has only the significant effect on number of grains per spike. However, in his studies the tall lines were not significantly different than Rht1Rht1Rht2Rht2 (double dwarf) and Rht2Rht2. He also reported that there were no significant differences for number of grains per spike in double dwarf (Rht1Rht2) and semi-dwarf groups. Borrell et al. (1991) reported that Rht1 line had a significantly greater number of grains per ear (20%) than the rht lines. Kertesz et al., (1991) reported from near isogenic lines that the double dwarfs had comparatively reduced number of grains per spike than tall (rht), Rht1 and Rht2 lines. Youssefian et al., (1992) reported that the primary effect of the Rht allele is to reduce stem growth rate during plant development, thus increasing the proportion of assimilate available to developing ear, which results an increase in number of grains per ear. Nizam Uddin and Marshall (1989) reported that tall lines had 1.8 kernels per spikelet compared with 2.1 and 2.3 for the intermediate and dwarf lines respectively. Villareal et al. (1992) reported that Rht1 cultivars produced 4.6 and 11.7% more number of grains per spike than Rht2 and Rht1Rht2 (double dwarf) lines.
The comparative results indicate that semi-dwarf genotypes had the highest main spike grain yield than double dwarf and tall lines (Table 4 ). However, the semi-dwarf’s main spike yield was not significantly different than the tall lines. Main spike grain yield ranged from 1.37 to 2.11 g in double dwarfs, 1.5 to 2.51 g in semi-dwarf and 2.03 to 2.09 g in tall group (Table 1, Table 2 and Table 3). These results suggest that probably semi-dwarf character is more suitable under this environment.
Grain Yield
The double-dwarf genotypes had 2% lower yield than counterpart tall genotypes. The semi-dwarf genotypes had 22% and 19% more yield than double-dwarf and tall genotypes (Table 4). Plot grain yield ranged from 181 to 377 g in double dwarf, 246 to 447 g in semi-dwarf and 266 to 329 g in tall group (Table 1, Table 2 and Table 3). Allan (1997) conducted isogenic studies in different genetic backgrounds and reported that semi-dwarf wheat genotypes had 2-16% greater yield than non-semi-dwarf (rht) group. The semi-dwarf wheat genotypes had significantly higher grain yield of main spike than double dwarf and tall group (Table 4). It is therefore, concluded that under high temperature conditions the performance of double dwarf genotypes may be very poor.
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