| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Dep. of Crop and Soil Sciences, Washington State Univ., Dryland Research Station, P.O. Box B, Lind, WA 99341
* Corresponding author (schillw{at}wsu.edu).
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Abbreviations: C, cultivar • DAP, days after planting • PEG, polyethylene glycol • PD, planting date • PM, priming media • PNW, Pacific Northwest • RGP, radicle germination percentage • WSU, Washington State University
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
In dry years, when seed zone water is inadequate, farmers will either plant shallowly (2–3 cm deep) into dry soil, delay planting until the arrival of rain in mid-October or later, or postpone planting until spring; all these practices reduce grain yield potential compared with planting early into stored soil water (Donaldson et al., 2001). In addition to increasing grain yield potential, successful early establishment of winter wheat on summer fallow provides protection from water erosion during winter (Papendick and McCool, 1994).
The three early phases of germination are: (i) imbibition, (ii) lag phase, and (iii) protrusion of the radicle through the testa (Simon, 1984). Priming is a procedure that partially hydrates seed, followed by drying of seed, so that germination processes begin, but radicle emergence does not occur. Methods of seed priming have been described in detail by Bradford (1986) and Khan (1992) and include soaking seed in water or osmotic solution, and intermixture with porous matrix material.
There are reports that hydration of seed up to, but not exceeding, the lag phase with priming permits early DNA replication (Bray et al., 1989), increased RNA and protein synthesis (Fu et al., 1988; Ibrahim et al., 1983), greater ATP availability (Mazor et al., 1984), faster embryo growth (Dahal et al., 1990), repair of deteriorated seed parts (Karssen et al., 1989; Saha et al., 1990), and reduced leakage of metabolites (Styer and Cantliffe, 1983) compared with checks. Priming of wheat seed in osmoticum or water may improve germination and emergence (Ashraf and Abu-Shakra, 1978) and promote vigorous root growth (Carceller and Soriano, 1972) under low soil water potential compared with checks. Osmotica that have shown good potential to enhance germination, emergence, growth, and/or grain yield of wheat include solutions of potassium hydrophosphate (KH2PO4) monobasic (Das and Choudhury, 1996), polyethylene glycol (PEG) (Dell'Aquila and Taranto, 1986), and potassium chloride (KCl) (Misra and Dwibedi, 1980). Water has also been used successfully as a seed priming medium for wheat (Harris et al., 2001).
The objective of our study was to evaluate the feasibility of seed priming for improving winter wheat production in the low-precipitation summer fallow regions of the inland PNW. Specific objectives were to determine the effectiveness of several priming media on germination, emergence, and grain yield of two soft white winter wheat cultivars in the laboratory, greenhouse, and under field conditions.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Newly harvested, untreated foundation seed was used both years. In August of 2000 and 2001, 250 g of seed of both cultivars was placed in 42 individual nylon net bags and immersed in liquid priming media. The seven priming media were: (i) water; (ii) 2% KCl (w/v); (iii) 4% KCl (w/v); (iv) 0.5% KH2PO4 (w/v); (v) 1% KH2PO4 (w/v); (vi) 10% PEG 8000 (v/v); and (vii) 20% PEG 8000 (v/v). All priming media were prepared in distilled water.
Seed was fully immersed in priming media at a temperature of 24°C for durations of 12, 24, and 36 h. The 24- and 12-h treatments were immersed 12 and 24 h after the first batch, respectively, so that all seed was removed from priming media at the same time. A nontreated check for both cultivars was also included. All seed was then rinsed thoroughly with distilled water and lightly hand dried using blotting paper. While still damp, seed (including check) was treated with [difenoconazole (R)-{(2,6-dimethylphenyl)-methoxyacetylamino}] propionic acid methyl ester fungicide at a rate of 0.65 mL kg-1 seed, then allowed to dry on paper towels at room temperature (24°C) until seed water content was 120 g kg-1 as measured with a grain moisture meter. Seed was stored at 24°C.
Laboratory Experiment
Laboratory research measured the rate of germination using a two-factor factorial completely randomized design (CRD) with 44 treatment combinations replicated four times. The two treatment factors were wheat cultivar (Edwin and Madsen) and priming duration and priming media [three priming durations (12, 24, and 36 h) x seven priming media (water, KCl- 2 and 4%, KH2PO4- 0.5 and 1%, PEG- 10 and 20%) plus a check. Fifty seeds from each of the treatments were placed on 90-mm-diam. Whatman No. 2 filter paper that was moistened with 10 mL distilled water in each glass 90-mm-inner diameter Petri dish. Seed was kept at 24°C air temperature under normal light. Radicle protrusion of 5 mm was scored as germination. Germination of individual seeds was measured at 12-h intervals and continued until no further germination occurred. The experiment was repeated in Year 2 (i.e., Run 2).
Greenhouse Experiment
The same seed lots used in the laboratory experiment were used in a greenhouse study. Two runs were conducted of a two-factor factorial experiment in a CRD with four replications. Factors were wheat cultivar (Edwin and Madsen) and priming media (water, KCl- 2%, KH2PO4- 0.5%, PEG- 10%, plus a check). Selection of greenhouse treatments was based on germination performance in Run 1 of the laboratory experiment. As germination was not affected by concentration of priming medium or duration of priming (result of Run 1 of the laboratory experiment), the low concentration of media with 12-h priming duration was selected for greenhouse and field studies.
The soil used was a Shano silt loam (coarse-silty, mixed, super active, mesic Xeric Haplocambids) with less than 10 g kg-1 organic matter in the surface 10 cm. Soil from the surface 15 cm of a summer-fallowed field was collected in early August 2000 and 2001 from the WSU Dryland Research Station at Lind, WA. Air-dried soil was placed in 19-cm-tall plastic pots with 18-cm diameter and gently tamped to create a 5-cm-deep soil layer with a bulk density of 
1.25 Mg m-3. The pots, which had small holes in the bottom, were placed in trays containing 5 mm standing water until soil was saturated. Pots were then removed from trays and kept on the greenhouse bench for 48 h until the soil water content was 0.15 kg kg-1. Soil was made friable by scratching the surface with a 2-cm-wide table fork to a depth of 1 cm, then 100 seeds were hand-planted in each pot and covered with 1 cm of moist soil. Immediately thereafter, dry soil was added to each pot and gently pressed with fingers to create a 15-cm-deep dry soil layer with 1.00 Mg m-3 bulk density above the moist soil. Thus, there was 16 cm of soil (1 cm moist + 15 cm dry) covering seed that accurately simulated depth of planting under summer fallow conditions. Emergence was measured by counting all individual seedlings at 24-h intervals beginning 7 d after planting (DAP) and continued until no further emergence occurred.
Field Experiment
The field site was the WSU Dryland Research Station at Lind. Seed lots and treatments were the same as those used in the greenhouse study during both years. Experimental design was a three-factor factorial (wheat cultivar, priming media, and planting date) using randomized complete blocks with four replications. There were two dates of planting, the first and fourth week of September. Planting rate was 100 and 200 seeds row-1 (22.5 and 45 kg ha-1) per individual 7-m-long plot in 2000 and 2001, respectively. A four-row deep-furrow split-packer drill with 38 cm row spacing was used for planting into summer fallow. A 16-cm-deep soil layer covered the seed.
Average annual precipitation at Lind is 243 mm. Crop year (1 September–31 August) precipitation during the experiment was 238, 211, and 220 mm for 2000 (fallow year for the 2001 crop), 2001, and 2002, respectively. Seed zone volumetric water content was measured in 2-cm increments to a depth of 22 cm from four locations within the experimental area on each planting date with an incremental soil sampler designed by Pikul et al. (1979). Emergence was measured by counting all individual seedlings from the two center rows at 11 and 20 DAP. Whole plots (all four rows) were harvested with a Hege 140 plot combine in July 2001 and 2002. Grain yield, adjusted to 120 g kg-1 moisture, was measured on a digital scale (0.1-g accuracy).
An analysis of variance for all data from laboratory, greenhouse, and field experiments was conducted by the PROC GLM procedure of SAS (SAS Inst., 1999). Treatments means were considered significantly different at P < 0.05. Mean separation was by Duncan Multiple Range Test.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
|
|
At 72 h, seven priming treatments had greater germination than the check for Edwin in Run 1, but none were higher than the check in Run 2. For Madsen, no priming treatment had greater RGP than the check at 72 h in either run (Table 2). This finding agrees with Salim and Todd (1968) and Harris et al. (2001) who also found that RGP was initially higher for primed wheat seed compared with the check, but differences diminished by 72 h.
Both cultivars showed no germination advantage, and sometimes a disadvantage, when seed was soaked in any of the priming media for more than 12 h. Similarly, higher concentrations of KCl, KH2PO4, and PEG generally did not benefit RGP (Table 2). Seed primed in KCl 4% solution showed low RGP irrespective of priming duration and cultivar, possibly due to a phytotoxic effect on the germinating embryo. Priming with water for 12 h was equal to or better than the other priming media tested for rapid germination.
Greenhouse Experiment
Seedling emergence through 16 cm of soil cover at 7, 9, and 11 DAP was always greater for Edwin compared with Madsen when averaged across all priming treatments (data not shown). Similar to the laboratory experiment, there was a highly significant C x PM interaction on all emergence count dates (Table 1b), providing further evidence of variability in seed lots in Run 1 vs. Run 2.
Priming media affected emergence of wheat cultivars differently. Edwin seed primed in water or KH2PO4 had enhanced emergence during both runs compared with KCl or PEG (Table 3). Emergence for the check, however, was equal to the best seed priming treatments. Final emergence from water- and KH2PO4-primed seed, and the check of Edwin was superior to KCl and PEG in both runs.
|
Field Experiment
Seed Zone Water
Seed zone water content at early planting on 5 Sept. 2000 was 0.125 cm3 cm-3 but the seed zone had dried to 0.111 cm3 cm-3 water content by late planting on 26 Sept. 2000 (Fig. 1a). Drying of the seed zone from early-to-late September was even more pronounced in 2001 (Fig. 1b). This hastening of late summer seed zone water loss occurs as a result of the annual shift in the direction of coupled heat and water flows. Increasingly low night temperatures that occur in late summer rapidly reduce soil surface temperatures while higher temperatures exist at lower depths. Under these conditions, the vapor concentration gradient toward the soil surface is high and considerable soil water loss may occur (Hillel, 1971). This drying phenomenon is the reason why farmers plant winter wheat in late August–early September, particularly in dry years, in the eastern Washington wheat–fallow area. There is often insufficient seed zone water for emergence if planting is delayed until mid-to-late September.
|
Emergence
A 10-mm rain occurred 5 d after the 5 Sept. 2000 planting at Lind, but soil crusting did not occur and seedlings emerged without undo difficulty (Table 4). Normally, as little as 3 mm of rain occurring after planting and before emergence will crust the surface soil so that wheat seedlings cannot emerge (Donaldson, 1996). As the wetting front from the heavy rain that occurred on 10 Sept. 2000 extended several centimeters into the soil, we hypothesize that wet soil may have provided physical support for the elongating coleoptile–first leaf and/or surface crusting did not occur until most seedlings had emerged. No other rain occurred for at least 15 d after the other plantings, thus soil crusting was not a factor.
|
For Madsen, none of the priming media enhanced emergence compared with the dry check in either year. Except for 11 DAP with the first planting date, emergence for water-primed Madsen was less than the check from both plantings in 2001 (Table 4).
Grain Yield
There were no grain yield differences between cultivars or among priming media except from the early 2001 planting where grain yields of Madsen primed with KCL and PEG were lower than any Edwin entries except KCL (Table 5). There were no within-cultivar grain yield differences (Table 5). Edwin was bred specifically for the low-precipitation environment, and its relatively higher grain yield compared with Madsen from the early 2001 planting may be partially due to better drought tolerance. The 2002 grain yield data agree with previous studies at Lind that show early planting generally increases grain yield compared with later planting dates (Donaldson et al., 2001). However, the YR x PD and YR x C interactions were highly significant (Table 1c). Grain yields for the dry checks were equal to or greater than any for the priming media.
|
|
SUMMARY AND CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
Greenhouse data combined across priming treatments showed that Edwin always emerged faster and achieved greater final stand than Madsen. The Edwin check was equal to the best priming treatments for emergence. However, KCl- and PEG-primed Madsen (both runs) or water-primed Madsen (Run 2 only) had greater final emergence than the check. A strong cultivar x priming media interaction suggests the effect of priming media on emergence may be cultivar dependant; priming enhanced emergence of the cultivar with moderate emergence capability (Madsen) but not the cultivar with strong emergence characteristics (Edwin).
In the field study, seed zone water at time of planting was moderately dry in early September to dry in late September in both years. Rapid drying of the seed zone occurred between the first and fourth week of September. Edwin seed primed with KCl had greater emergence than the dry check at 11 DAP during one year, but otherwise the check was equal to or better than any priming media for both Edwin and Madsen. Grain yield (averaged across cultivars and priming treatments) was greatest for late-planted wheat in 2001 and for early planted wheat in 2002. There was a strong YR x PD interaction. There were no within-cultivar grain yield differences in any of the four planting experiments.
In conclusion, although some priming media enhanced germination and emergence in the laboratory and greenhouse, there was little to no benefit for emergence or grain yield under field conditions. Thus, seed priming winter wheat appears to have limited practical value for promoting seedling emergence from deep planting depths in summer fallow. Breeding efforts to develop standard height and tall winter wheat cultivars with long coleoptiles continues to offer the best hope for farmers in dry summer fallow regions where emergence is a major concern.
Received for publication November 28, 2002.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSUMMARY AND CONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  K. D. Subedi and B. L. Ma Seed Priming Does Not Improve Corn Yield in a Humid Temperate Environment Agron. J., January 1, 2005; 97(1): 211 - 218. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
