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Genetic Diversity of Hydro Priming: Comparison
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Please note this is a comparison between Version 1 by Jun-Ich Sakagami and Version 2 by Rita Xu.

Seed priming refers to seed enhancement methods that stimulate seed metabolism. This study evaluated the genetic diversity of hydro priming efficacy in 27 different genotypes of rice under dry to wet soil moisture conditions. The genotypes included 21 genotypes of Oryza sativa, five genotypes of Oryza glaberrima, and one genotype of NERICA (New Rice for Africa). The treated rice seeds were sown in plastic boxes under four soil moisture conditions (5%, 10%, 15%, and 20% (w/w)). The genotypes were categorized into six groups based on growth parameters using hierarchical cluster analysis. Furthermore, emergence properties were investigated by using principal component analysis based on the mean emergence time of control and primed seeds. Seed priming enhanced growth performance under the moderate dry conditions of 10% and 15% soil moisture. Meanwhile, priming efficacy was low in water stress conditions of 5% and 20% soil moisture. There were wide-ranging genotypic differences of priming efficacy under 20% soil moisture condition. Our findings indicate that the anaerobic-tolerant genotypes tend to exhibit priming efficacy under high soil moisture conditions. Furthermore, one group included all upland genotypes of O. sativa. This group originally adapted to 10% and 15% of dry conditions, and seed priming improved their features greatly.

  • Seed priming
  • soil moisture stress
  • O. sativa
  • O. glaberrima
  • NERICA

1. Introduction

In recent years, the growth in demand for rice has been faster in sub-Saharan Africa (SSA) than anywhere else in the world [1]. Although West Africa is still the hub of rice production in SSA, there has been a significant increase in the shortfall of rice production as the rate of consumption increases well above the rate of production [2]. Rice cultivation in SSA is conducted in four ecosystems: dryland, rainfed wetland, deep water and mangrove swamps, and irrigated wetland, with the percentages of the total cultivated area being 38%, 33%, 9%, and 20%, respectively [1]. In West Africa, 75% of the total rice production from 1993 to 2003 came from upland, hydromorphic, and lowland ecosystems, with approximately 25% coming from irrigated fields [3]. Thus, in Africa, most rice is cultivated on rainfed uplands and lowlands without an irrigation system. Balasubramanian et al. (2007) [1] reported that the boundary between wetland and dryland is often gradual on the lower slope. In upland systems, the average rice yield is approximately 1 t ha−1, and, in rainfed lowlands, the rice yield depends on the degree of water control and varies from 1 to 3 t ha−1 [3]. As is well-known, direct seeding is a standard method of rice sowing in upland rice cultivation in Africa; however, stand establishment of dry-seeded rice can be poor due to erratic rainfall and frequent drought after seeding [4]. Farooq et al. (2011) [5] reported that crop establishment is the key factor in the subsequent growth, development, and yield of direct-seeded rice. Shortage of rainfall results in poor initial growth and subsequent low yield of upland rice. Therefore, a key technology is required to improve plant emergence and establishment under unstable soil moisture conditions. Seed priming is a well-known seed enhancement method. In rice, seed priming improves seed germination, plant emergence, subsequent growth, and yield [6][7][6,7]. As reported by Khan (1992) [8], the term “priming of seed” was coined in the early 1970s. Taylor et al. (1998) [9] defined seed enhancement as a post-harvest treatment that improves germination or seedling growth or facilitates the delivery of seeds and other materials required during sowing. Priming alters enzyme activities and promotes the mobilization of sugars [6][10][6,10]. Several seed priming methods have been studied, e.g., hydro priming, osmotic-priming by using CaCl2 or KCl, and polyethylene glycol and ascorbate-priming [11][12][11,12]. As reported by Soltani and Soltani (2015) [13], hydro priming was recommended because of its affordability and enhancement of seed germination, seedling emergence, and crop yield. Thus, several studies about hydro priming techniques have been carried out in Africa [14][15][16][14,15,16]. Recent findings show that the efficacy of seed priming depends on soil moisture conditions [7] and seed genotypes [17][18][17,18].

2. Germination

The MGT of the control seed was 51.8, 33.9, 38.5, 37.2, 37.0, and 31.0 in G1, G2, G3, G4, G5, and G6, respectively (Table 1Table 2). The MGT of the primed seed was 29.9, 24.5, 27.8, 25.5, 15.6, and 20.5 in G1, G2, G3, G4, G5, and G6, respectively. The MGT of the primed seed was significantly shorter than that of the control seed in all groups according to the t-test (p < 0.05). G50 showed the same tendency as MGT, and the G50 of primed seeds was significantly shorter than that of the control in all groups except G5. In G1, germination took longer for both primed and control seeds.

Table 12.

Effects of priming on mean germination time (MGT) and time to achieve 50% germination (G50) of six genotypic groups.
  MGT (h) G50 (h)
  Control Priming Ratio t-Test Control

.

Effects of priming on time to achieve 50% plant emergence (E50), mean plant emergence time (MET), and plant emergence uniformity (EU) of six genotypic groups under four soil moisture conditions.
Soil Moisture (w/w)
Priming Ratio
  5%t-Test
  10%   15%   20%  
  Control Priming Ratio t-Test
13.4
8.8
0.66
*
15.0
12.0
0.80
ns
12.2
12.0
0.99
ns
22.7
21.6
0.95
ns

4. Plant Height

4. Plant Height

In G2, G3, G4, and G6, the PH of primed seeds was significantly higher than that of the control under the 10% soil moisture condition (Table 4). In G2, G3, and G6, the PH of primed seed was significantly higher than that of the control under the 15% soil moisture condition. A positive effect of priming was not found under the 5% and the 20% soil moisture conditions. Under the 5% soil moisture condition, the PH of primed seeds appeared to be shorter than that of control seeds, and there were significant differences in G3 and G4. Under the 10% and 15% soil conditions, the PHU of primed seeds seemed to be enhanced. We found a significant difference between the PHU of priming and control in G6 under the 10% soil moisture condition and in G1, G2, and G3 under the 15% soil moisture condition (Table 4).

In G2, G3, G4, and G6, the PH of primed seeds was significantly higher than that of the control under the 10% soil moisture condition (Table 3). In G2, G3, and G6, the PH of primed seed was significantly higher than that of the control under the 15% soil moisture condition. A positive effect of priming was not found under the 5% and the 20% soil moisture conditions. Under the 5% soil moisture condition, the PH of primed seeds appeared to be shorter than that of control seeds, and there were significant differences in G3 and G4. Under the 10% and 15% soil conditions, the PHU of primed seeds seemed to be enhanced. We found a significant difference between the PHU of priming and control in G6 under the 10% soil moisture condition and in G1, G2, and G3 under the 15% soil moisture condition (Table 3).

 

Table 34.

Effects of priming on plant height (PH) and plant height uniformity (PHU) of six genotypic groups under four soil moisture conditions.
Soil Moisture (w/w)
  5%   10%   15%   20%  
  Control PrimingControl Priming Ratio t-Test Ratio t-Test Control Priming RatioControl Priming Ratio t-Test Control Priming t-Test Control PrimingRatio Ratiot t-Test Control-Test
Priming Ratio t-Test
Group 1 51.8 29.9 0.58
PH (cm)    ** 60.0 28.9 0.48 **
E50 (h)                                                         
Group 2 33.9 24.5 0.72 ** 30.6 21.6 0.71 **
Group 1 - - - - 146.0 - - - 127.5 - - - - - - -
Group 1 - - - - 2.4 2.7 1.12 ns 4.3 4.1 0.96 ns 1.9 2.1 1.12 ns Group 3 38.5 27.8 0.72 ** 37.8 25.0 0.66
Group 2**
129.1 138.0 1.07 ns 101.8 81.5 0.80 * 86.3 79.3 0.92
Group 2ns 2.9 2.4 0.84118.3 108.9 0.92 nsns 6.1 8.0 1.33 * 7.9 9.8 Group 4 37.2 25.5 0.68 *** 34.7 22.5 0.65 ***
1.25 * 5.3 4.9 0.92 ns Group 3 144.3 142.7 0.99 ns
Group 3 2.4 1.5 0.62102.4 92.2 0.90 * 85.5 80.8 0.94 ns 122.4 122.0 1.00 ns *** 5.8 7.6 1.31 *** 8.4 9.7 1.15 * 4.5 4.6 Group 5 37.0 15.6 0.42 * 34.3 12.0 0.35 ns
1.03 ns Group 4 143.3 -
Group 4 2.5- - 98.1 86.5 0.88 1.4*** 0.54 Group 6 31.0 20.5 0.66 ** 28.8 17.3 0.60 **

3. Plant Emergence

The E50 of the primed seeds tended to be shorter than that of the control seeds except under the 5% soil moisture condition (Table 2). There was an obvious priming effect in terms of more rapid plant emergence under the 10% soil moisture condition across the groups. Under the 10% soil moisture condition, the E50 of control seed was 146.0, 101.8, 102.4, 102.4, 98.1, 113.3, and 99.7 in G1, G2, G3, G4, G5, and G6, respectively, and the E50 of primed seeds was 81.5, 92.2, 86.5, 104.6, and 85.1 in G2, G3, G4, G5, and G6 respectively. In G1, the primed seed did not reach E50. There was a significant difference between control seeds and primed seeds in respect of E50, apart from in G1 and G5 under the 10% soil moisture condition. Under the 15% and the 20% soil moisture conditions, the ratio (priming/control) of E50 tended to be less than 1.00, but there were no significant differences, apart from in G6 under the 15% soil moisture condition. A priming effect on E50 was not found under the 5% soil moisture condition. With the exception of G1, the MET of primed seeds seemed to be more rapid than that of control seeds under 10% and 15% soil moisture conditions. In G3, G4, and G6, the MET of primed seeds was significantly shorter than was that of control seeds under the 10% soil moisture condition. Furthermore, in G2, G3, and G6, the MET of primed seeds was significantly shorter than that of control seeds under the 15% soil moisture condition. Conversely, under the 5% soil moisture condition, the MET of primed seeds appear to be larger than the control, and a significantly negative impact was found in G6. Under the 20% soil moisture condition, there was no significant difference, and the ratio (priming/control) of MET was 0.87, 0.91, 1.01, 1.03, 0.92, and 1.00 in G1, G2, G3, G4, G5, and G6, respectively. Compared with other parameters, EU did not show a clear tendency. There was a positive effect of priming under the 5% soil moisture condition, and there was a significant difference (

The E50 of the primed seeds tended to be shorter than that of the control seeds except under the 5% soil moisture condition (Table 3). There was an obvious priming effect in terms of more rapid plant emergence under the 10% soil moisture condition across the groups. Under the 10% soil moisture condition, the E50 of control seed was 146.0, 101.8, 102.4, 102.4, 98.1, 113.3, and 99.7 in G1, G2, G3, G4, G5, and G6, respectively, and the E50 of primed seeds was 81.5, 92.2, 86.5, 104.6, and 85.1 in G2, G3, G4, G5, and G6 respectively. In G1, the primed seed did not reach E50. There was a significant difference between control seeds and primed seeds in respect of E50, apart from in G1 and G5 under the 10% soil moisture condition. Under the 15% and the 20% soil moisture conditions, the ratio (priming/control) of E50 tended to be less than 1.00, but there were no significant differences, apart from in G6 under the 15% soil moisture condition. A priming effect on E50 was not found under the 5% soil moisture condition. With the exception of G1, the MET of primed seeds seemed to be more rapid than that of control seeds under 10% and 15% soil moisture conditions. In G3, G4, and G6, the MET of primed seeds was significantly shorter than was that of control seeds under the 10% soil moisture condition. Furthermore, in G2, G3, and G6, the MET of primed seeds was significantly shorter than that of control seeds under the 15% soil moisture condition. Conversely, under the 5% soil moisture condition, the MET of primed seeds appear to be larger than the control, and a significantly negative impact was found in G6. Under the 20% soil moisture condition, there was no significant difference, and the ratio (priming/control) of MET was 0.87, 0.91, 1.01, 1.03, 0.92, and 1.00 in G1, G2, G3, G4, G5, and G6, respectively. Compared with other parameters, EU did not show a clear tendency. There was a positive effect of priming under the 5% soil moisture condition, and there was a significant difference (

p < 0.05) in the EU of G4 and G6.

< 0.05) in the EU of G4 and G6.
 

Table 23

*
82.7
78.8
0.95 ns 112.5 109.9 0.98 ns
6.2 7.7 1.24 * 8.4 9.0 1.08 ns 5.6 4.6 0.82 ns Group 5 149.9 -
Group 5 1.6 0.9- - 113.3 104.6 0.92 ns 95.6 96.7 1.01 ns 119.9 104.8 0.52 ns 4.4 5.6 1.280.87 ns 6.5 7.1ns
1.09 ns 3.8 4.8 1.25 ns Group 6 147.1 152.3 1.04 * 99.7 85.1 0.85 *** 79.5 72.3 0.91 * 134.7 121.1 0.90 ns
Group 6 1.8 1.2 0.68 ns 6.1 8.7 1.43 ** 9.0 10.3 1.15 ** 4.0 4.9 1.22 ns MET (h)                                
PHU                             Group 1 - - - - 140.9 148.2 1.05 ns 131.6 132.3 1.00 ns 137.4 120.0 0.87 ns
   
Group 1 - - - - 43.8 45.7 1.04 ns 66.3 56.0 0.84 * 53.4 49.1 0.92 ns Group 2 138.2 144.7 1.05 ns 112.1 94.6 0.84 ns 100.7 91.7 0.91 * 128.1 117.0 0.91 ns
Group 2 38.3 43.9 1.15 ns 28.1 22.8 0.81 ns 41.2 15.7 0.38 * 31.3 31.0 0.99 ns Group 3 149.7 154.8 1.03 ns 113.8 103.0 0.90 * 98.7 92.7
Group 3 45.2 53.3 1.18 * 27.3 24.50.94 * 124.8 0.90126.4 1.01 ns
ns 27.6 16.3 0.59 * 43.4 38.6 0.89 ns Group 4 143.4 159.0 1.11 ns 109.3 97.4 0.89 ** 94.5 91.5 0.97 ns 112.0 115.3 1.03 ns
Group 4 55.9 63.1 1.13 ns 26.0 20.9 0.80 ns 25.8 21.8 0.84 ns 23.5 34.5 1.47 ns Group 5 152.7 153.4 1.01 ns 119.6 115.4 0.97 ns 109.9
Group 5 49.8 56.7103.7 0.94 ns 127.2 116.4 0.92 ns
1.14 ns 47.5 38.8 0.82 ns 38.4 23.5 0.61 ns 39.0 27.6 0.71 ns Group 6 148.6 158.3 1.07 ** 108.7 97.1 0.89 ** 90.7 83.6 0.92 ** 131.4 131.3 1.00 ns
Group 6 49.9 62.7 1.26 ns 32.4 20.7 0.64 * 18.6 12.4 0.67 ns 47.7 37.6 0.79 ns EU                                
Group 1 - - - - 16.6 13.6 0.82 ns 20.9 21.0 1.01 ns 15.0 18.2 1.22 ns
Group 2 13.7 10.4 0.76 ns 12.7 7.8 0.61 * 21.7 12.0 0.55 * 20.7 14.4 0.70 ns
Group 3 11.4 9.0 0.79 ns 8.0 8.6 1.08 ns 12.9 9.8 0.76 ns 17.7 22.5 1.27 *
Group 4 18.1 5.3 0.29 * 14.7 7.0 0.47 * 15.5 13.2 0.85 ns 11.3 15.3 1.35 ns
Group 5 12.4 - - - 13.4 16.5 1.23 ns 20.2 13.3 0.66 ns 18.9 16.6 0.88 ns
Group 6

5. Correlation between Control and Priming

In respect of E50 and MET, we found a strongly significant positive correlation (p < 0.01) between control and primed seeds under the 10% and 15% soil moisture conditions (Table 4Table 5, Figure 1Figure 2). Under the 20% soil moisture condition, there was a significant positive correlation between E50 and MET, though the coefficient of correlation was small. We did not find a significant correlation between control and primed seeds in respect to EU under all soil moisture conditions. There was a strongly significant positive correlation (p < 0.01) between control and primed seeds in respect to PH, apart from under the 20% soil moisture condition (Table 4Table 5). There was a significant positive correlation of PHU under the 10% (p < 0.05) and the 15% (p < 0.01) soil moisture conditions. Regarding the correlation diagram of MET, most of the plots were above the dotted line under the 5% soil moisture condition, suggesting that emergence takes much longer for primed seeds than for control seeds (Figure 1Figure 2). Under the 10% and the 15% soil moisture conditions, most of the plots were below the dotted line, suggesting that emergence was faster for primed seeds than for control seed. Under the 20% soil moisture condition, some plots were on the dotted line and others were either above or below the line, suggesting there are genotypic differences in respect of priming efficacy.

Genes 11 00994 g002 550

Figure 12. Relationship between control and priming of mean emergence time (MET) in the four soil moisture conditions. The dotted line indicates position of the x value equal to y value. Each plot shows one condition. Black circles, black rhombuses, white circles, white rhombus, black triangles and white triangles indicate genotype group1, 2, 3, 4, 5 and 6, respectively. Genotype groups are determined by cluster analysis (illustrated in Figure 2).

Table 45. Correlation coefficients (r) of control and priming of the time to achieve 50% plant emergence (E50), mean plant emergence time (MET), plant emergence uniformity (EU), plant height (PH), and plant height uniformity (PHU) under four soil moisture conditions.

Soil Moisture (w/w)
  5% 10% 15% 20%
E50 0.290 ns 0.754 ** 0.814 ** 0.490 *
MET 0.532 ** 0.762 ** 0.903 ** 0.425 *
EU 0.327 ns 0.257 ns 0.201 ns 0.277 ns
PH 0.761 ** 0.779 ** 0.904 ** 0.297 ns
PHU 0.270 ns 0.400 * 0.706 ** 0.035 ns

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