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© 2007 Plant Management Network.
Accepted for publication 10 January 2007. Published 9 May 2007.

Hulless Barley Response to Ethephon Application

Wade E. Thomason, Assistant Professor, Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg 24061; Steve B. Phillips, Associate Professor, Department of Crop and Soil Environmental Sciences, Virginia Tech ESAREC, Painter 23420; Carl A. Griffey, Professor, Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg 24061; and Wynse S. Brooks, Research Associate, Department of Crop and Soil Environmental Sciences, Virginia Tech, Blacksburg 24060

Corresponding author: Wade E. Thomason. wthomaso@vt.edu

Thomason, W. E., Phillips, S. B., Griffey, C. A., and Brooks, W. S. 2006. Hulless barley response to ethephon application. Online. Crop Management doi:10.1094/CM-2007-0509-01-RS.

Abstract

Ethephon [(2-chloroethyl) phosponic acid] is commonly used in mid-Atlantic barley production to reduce plant height and lodging, but is known to reduce grain yield and test weight in some barley cultivars. Management practices that produce high yield and good grain quality in traditional mid-Atlantic winter barley have yet to be evaluated for hulless barley. This research examined response of three winter hulless barley genotypes to ethephon plant growth regulator (PGR) and provides recommendations for appropriate PGR rates. Ethephon applied at 2.5 oz a.i./acre resulted in decreased plant height (8.3 inches) and lodging index (1.2 units). With higher rates, a trend toward continued decreased height and lodging was seen even when differences were not significant. Grain yield was decreased by an average of 20 bu/acre in four of 15 site year-genotype combinations. Grain test weight was increased in one instance but impacts of ethephon varied by genotype, which may warrant further study. Labeled rates of ethephon are appropriate for application to a range of hulless barley cultivars but rates above 2.5 oz a.i./acre should be avoided unless severe lodging is anticipated. Ethephon application should occur only when moisture and temperature are favorable for plant growth and not when the crop is under stress.

Hulless Barley

Winter barley is well suited to the mid-Atlantic region because of high yields and crop rotation benefits. However, demand for high-energy, low-fiber grain by the vertically integrated swine and poultry industries, and the availability of brewers' and distillers' grains for the beef and dairy industries have greatly reduced the market for traditional barley in the mid-Atlantic. Compared to traditional barley, hulless barley is more attractive to the animal and poultry feeding industries because of lower fiber concentration and higher metabolizable energy content.

Hulless barley grows and looks like traditional barley until nearly mature. Glumes begin to separate from the seed when it is almost mature and become totally separated when the grain is threshed. Hullessness is controlled by the recessive allele nud which is near the centromere on chromosome 7H (4) and is expressed in all environments. Historically, hulless barley yield has been less than hulled barley (10) and many earlier lines retained a large percentage of hulls. Breeding efforts are focused on improving these traits. Current releases and experimental lines offer higher yield, higher test weight, and better dehulling than those previously available (2).

Plant Growth Regulator Effects on Barley

Synthetic plant growth regulators (PGRs), such as ethephon [(2-chloroethyl) phosponic acid], are commonly used in barley production in the mid-Atlantic. At the recommended rate of 2.5 to 5.0 oz a.i./acre for hulled barley these chemicals have the ability to shorten or stiffen cereal culms (16,20). This can result in decreased plant height (3) and lodging, especially with tall cultivars under high fertility and rainfall conditions (5). Lodging lowers grain yield and increases sprouting in barley (7). However, in the absence of lodging or when the crop experiences moisture and/or temperature stress, ethephon use is often associated with reduced grain yield (18). These yield decreases were attributed to reductions in individual grain weight (11,16) and decreased numbers of early tiller spikes (6). Grain protein concentration in response to ethephon has been reported to increase (12,19) or to be unaffected (8,14). Bulman and Smith (3) demonstrated that the effect on grain yield varied by cultivar. When ethephon was applied at the boot stage, yield of the cultivar ‘Leger’ was increased by 24% while yield of ‘Argyle’ decreased 19%. A significant interaction between ethephon rate and cultivar for grain yield was also reported by Ma and Smith (9) and Stobbe et al. (17).

Objectives

The development of barley lines with the hulless trait for the mid-Atlantic region is a relatively new undertaking and much still remains unknown about appropriate management for high yield and response to current management recommendations. The objectives of this research were to evaluate three diverse hulless barley genotypes for differential response to labeled rates of ethephon plant growth regulator and to develop recommendations for appropriate PGR application rates to new hulless barley cultivars.

Field Studies and Analysis

Research trials were conducted at Holland and Painter, VA, in the 2004-2005 growing season and at Blacksburg, Holland, Orange, and Painter, Va., in the 2005-2006 season. All trials were arranged in a randomized complete-block design with four replications and plot size of 45 ft². Three hulless barley genotypes selected from the Virginia Tech barley breeding program with good agronomic characteristics and diverse backgrounds were treated with ethephon at the boot stage (GS 45) (21) at rates of 0, 2.5, 3.8, and 5.0 oz a.i./acre. Ethephon was applied with a CO₂ sprayer and hand boom in 15 gal of water per acre. The cultivar ‘Doyce’ was released in 2004, has high yield potential, good test weight, leaf rust resistance, is slightly above average in height (31.9 inches), and is medium to late heading. VA00H-65 is an experimental line with high yield potential, average test weight, and excellent cold tolerance. Average plant height of VA00H-65 is two inches taller than ‘Doyce.’ VA01H-68 is an experimental line which has high yield potential, excellent test weight and low hull retention. Both experimental lines have average plant heights approximately two inches taller than ‘Doyce.’ Heading date of VA00H-65 is also similar to ‘Doyce’ and several days later than VA01H-68. Plots were planted with a Hege 1000 plot drill at a rate of 50 seeds/ft² in 7-inch rows. Nitrogen fertilizer was applied in accordance with recommended split spring management practices for barley production (1). Total nitrogen rate, and planting and harvest dates for all trials are listed in Table 1.

Table 1. Planting and harvest dates and total fertilizer nutrients applied, 2005 and 2006 harvests.

 * Experiment was not harvested due to severe weather damage.

Plant height was measured from the base of the plant to the base of the spike at three places in each plot and averaged to calculate plant height at GS 92 prior to harvest. Plots were rated for lodging, considering only the plot center, each year prior to harvest using the Belgian lodging index (13). Grain was harvested using a Massey Ferguson 8XP plot combine and plot weights measured using a Graingage system (Juniper Systems, Logan, UT). Due to late-season rainfall and weathering, the plots at Holland were not harvested in 2005-2006. Grain yields are reported on a 13.5 percent moisture basis. Test weight and moisture were determined using a Dickey-John GAC2000 grain sampler (DICKEY-john, Auburn, IL) from a grain sub-sample from each plot. Statistical analysis was performed using the GLM procedure in SAS (SAS Institute Inc., Cary, NC). Due to significant interaction among years, locations, and treatments, the effect of ethephon application on individual genotypes was analyzed using least significant differences (LSD) to separate means. Single degree of freedom contrasts were also conducted to evaluate the response trend to increasing ethephon rate by cultivar.

Plant Height

Height was reduced in a quadratic manner by increasing ethephon rate at every site year for ‘Doyce’ and five of six site years for VA00H-65 (Table 2). The line VA01H-68 exhibited the same quadratic response except at Holland and Painter in 2005. The Painter site was atypical in that a height reduction was not observed. Wet, cloudy weather immediately following ethephon application may have slowed the rate of ethylene evolution similar to that observed by Simmons et al. (16). The lack of response in this line is likely due to the fact that VA01H-68 is four to five days earlier heading than the other lines. The quadratic function was also significant in most cases and represents a further numerical decrease in plant height for the 3.8 and 5.0 oz a.i./acre rates of ethephon.

Table 2. Plant height at Zadoks GS 92 as affected by hulless barley genotype and ethephon rate, 2005 and 2006 harvests.

In every case ‘Doyce’ plant height was significantly reduced, from an average of 32.7 inches when ethephon was not applied to 23.0 inches with the 2.5 oz a.i./acre ethephon rate. Further decreases in height were not observed with rates above 2.5 oz a.i./acre which agrees with the findings of Stobbe et al. (17). Similar to ‘Doyce,’ VA00H-65 height was significantly reduced when ethephon was applied, but there was no difference among rates. Results for VA01H-68 in 2006 were similar to the other lines in that a significant decrease in plant height due to ethephon was observed (32.7 and 24.4 inches for untreated and treated, respectively).

Lodging

Overall there was very little lodging of ‘Doyce’ at Holland in 2005 and Blacksburg and Orange in 2006 (Table 3). Plants were not especially short at any of these site years so the lack of lodging was probably related more to lack of late season rain or high winds. However, ethephon has been shown to strengthen straw in addition to shortening internode length (15). ‘Doyce’ did exhibit a linear decrease in lodging index in four of six site years. A significant linear decrease in lodging index for VA00H-65 was observed with increasing ethephon application rate at Holland and Painter in 2006 and for VA01H-68 at these sites as well as Blacksburg. Both of these hulless barley cultivars had significant lodging at Holland in 2006 when no ethephon was applied but none with ethephon application. When viewed across responsive site years, lodging index for VA01H-68 decreased from 1.95 when no ethephon was applied to 0.85 when 2.5 oz a.i./acre was applied and further to 0.45 when the rate was increased to 3.8 oz a.i./acre. Decreased plant lodging could result in higher grain quality and more rapid harvest.

Table 3. Plant lodging index at Zadoks GS 92 as affected by hulless barley genotype and ethephon rate, 2005 and 2006 harvests.

 * Belgian lodging index = Area × Intensity × 0.2. Area, 1-10, where 1 is barley is unaffected and 10 is entire plot affected. Intensity, 1-5, where 1 is barley standing upright and 5 is barley totally flat.

Grain Yield

All rates of ethephon significantly decreased grain yield of ‘Doyce’ over the check (122 and 94 bu/acre for untreated and treated plots, respectively) at Orange in 2006 (Table 4). Conditions at this site at the time of application were quite dry. Since water stress increases ethylene production in plants, it is possible that the combination of ethephon and drought may have resulted in severe plant stress similar to what was reported by Simmons et al. (16). However, there was no grain yield decrease of VA01H-68 at this site year. Since VA01H-68 is earlier maturing than the other cultivars in this test, some drought stress may have been avoided. At Blacksburg in 2006, yield of VA01H-68 was decreased when the 5.0 oz a.i./acre rate of ethephon was applied but at lesser rates yield was not significantly different from the check. The quadratic function was never significant for ‘Doyce.’ VA00H-65 grain yield was linearly affected by ethephon rate at three site years but yield was increased by 11.5 bu/acre at Holland in 2005 while there was an average decrease of 28 and 14 bu/acre in response to ethephon at Orange and Painter in 2006 respectively.

Table 4. Grain yield as affected by hulless barley genotype and ethephon rate, 2005 and 2006 harvests.

Test Weight

No response of ‘Doyce’ test weight was observed to increasing ethephon rates. At Blacksburg in 2006, a significant linear decrease in test weight with increasing ethephon rate was observed for VA00H-65 (Table 5). Application of ethephon at this site year resulted in an average decrease in test weight of 1.5 lb/bu. Ma and Smith (9) reported that ethephon application decreased grain weight in some instances. At Orange in 2006, both linear and quadratic decreases in test weight were associated with ethephon application rate. While the linear trend was not significant at Painter in 2006, there was a significant test weight decrease (1.5 lb/bu) associated with ethephon application of 2.5 oz a.i./acre. A linear trend for decreasing test weight was observed for VA01H-68 at Blacksburg in 2006, however differences among treatments were only significant when the 3.8 oz a.i./acre rate was compared to the check. This was not the case, however, at Orange where ethephon application decreased test weight in every case by an average of 0.9 lb/bu.

Table 5. Grain test weight as affected by cultivar and ethephon rate, 2005 and 2006 harvests.

Conclusions

Ethephon at the lowest rate of 2.5 oz a.i./acre decreased overall plant height and lodging score. Increased rates of growth regulator did not result in lower lodging scores or significantly shorter plants. Shorter plants are preferred because less straw is moved through the combine resulting in faster field speeds and less mechanical wear. Less straw left in the field also reduces residue and facilitates planting of double crop soybeans immediately following barley harvest and without tillage. Lodging is often responsible for increased seed diseases and sprouting since moisture is trapped by the down plants resulting in favorable conditions for disease development, thus grain quality is typically increased when lodging is reduced. Grain test weight, a common measure of grain quality, was increased with ethephon in one instance but decreased in several cases. Similar results were reported by other researchers (3,9) and indicates that care must be taken with growth regulator application. Test weight impacts of ethephon were found to vary by cultivar which may warrant further study. Grain yield was positively influenced by ethephon application at one site in 2005, but decreased yield was more common in 2006, especially for VA00H-65. Plant response to ethephon is impacted by environment, with drought conditions at the time of application often associated with visible plant damage and reduced grain yield.

Labeled rates of ethephon are appropriate for application to a range of hulless barley cultivars but, as is the case with other crops, care should be taken to avoid higher rates unless necessary. Application should be limited to cultivars with known lodging problems and when environmental conditions will result in the least damage, such as when plants have received adequate moisture.

Literature Cited

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