Crop Science 42:518-523 (2002)
© 2002 Crop Science Society of America
FORAGE & GRAZING LANDS
Performance of Tall Fescue Germplasms Bred for High- and Low-Ergot Alkaloids
N. S. Hill*,a,
J. H. Boutona,
F. N. Thompsonb,
L. Hawkinsb,
C. S. Hovelanda and
M. A. McCannc
a Dep. of Crop and Soil Sciences, College of Agricultural and Environmental Sciences
b College of Veterinary Medicine, Univ. of Georgia, Athens, GA 30602
c Dep. of Animal and Dairy Sciences, Univ. of Georgia, Athens, GA 30602
* Corresponding author (nhill{at}uga.edu)
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ABSTRACT
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Field studies were conducted to examine yield, alkaloid stability, stand survival, and animal toxicity in tall fescue (Festuca arundinacea Shreb.) germplasms, infected with their endemic endophyte [Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin] and bred for high- or low-alkaloid concentration. Three germplasms selected from endophyte-infected (E+) ‘Jesup’ for low-alkaloid and two germplasms selected for high-alkaloid, along with E+ and endophyte-free (E-) Jesup, E+ and E- ‘Kentucky-31’, and E- ‘AU Triumph’ tall fescue were planted at a mountain and a piedmont location in Georgia, and the forage harvested for 3 yr. Yield was calculated and alkaloid concentration was measured. In separate experiments, stand survival of one high- and one low-alkaloid germplasm was assessed in bermudagrass [Cynodon dactylon (L.) Pers.] sod by grazing with beef cattle. Toxicity was assessed on one low-alkaloid germplasm in lamb performance trials. Yields of the low- and high-alkaloid germplasms were similar to the E+ Jesup cultivar. The low- and high-alkaloid germplasms remained low and high in alkaloids, respectively. The E+ check and the germplasms bred for both high- and low-ergot alkaloid concentration were found to have superior stand survival compared with the E- check, but the low-alkaloid germplasm had lower stand survival than the E+ check. Lambs grazing the low-alkaloid germplasm showed weight gain ranking between those on E+ and E- pasture. This study indicates that persistence and alkaloid concentration were stable over environments; however, animal toxicity and the stand reduction exhibited by the low-alkaloid producing germplasm raises when grazed questions about breeding for reduced alkaloid concentration.
Abbreviations: E+, endophyte-infected • E-, endophyte-free
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INTRODUCTION
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TALL FESCUE infected with the N. coenophialum endophyte (E+) produces loline, ergot, and peramine alkaloids. All three alkaloids have been associated with insect deterrence (Siegel, 1990) but the ergot alkaloids are responsible for the livestock syndrome known as fescue toxicosis (Hill et al., 1994). Hence, one objective for improving E+ tall fescue is to reduce ergot alkaloid concentration. Two distinct strategies are being used to pursue this objective: (i) selecting endophytes that don't produce alkaloids and inserting them into endophyte-free germplasms (Bouton, 1998; Rolston, 1993; West et al., 1998) and (ii) selecting and breeding plants for reduced alkaloids when infected with their endemic endophytes (Adcock et al., 1997). Adcock et al. (1997) postulated that two potential ecological effects could limit utilization of low-alkaloid endophyte-infected tall fescue. The first is that genetic introgression may lead to increased alkaloids in low-alkaloid populations. The second is that reduction of ergot alkaloids may concomitantly reduce the fitness of the tall fescue population. Both of these parameters are regulated by plant or endophyte genes. Therefore, examining the stability of these traits over different environments is one means of assessing the likelihood that either of these ecological paradigms may occur (Cook and Stubbendieck, 1986; Kang, 1990).
The objective of this study was to examine the yield and alkaloid stability, stand survival, and animal toxicity of N. coenophialum-infected tall fescue germplasm selected for either high- or low-alkaloid concentration.
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MATERIALS AND METHODS
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Forage Yield and Ergot Alkaloid Concentration
Endophyte-infected and endophyte-free Kentucky-31 (courtesy of Dr. Henry Fribourg at the University of Tennessee) and Jesup tall fescue, AU Triumph, and three endophyte-infected tall fescue germplasms selected for low-ergot alkaloids (GA-961, 963, and 964) and two for high-ergot alkaloids (GA-962 and 965) (Adcock et al., 1997) were planted at the Mountain Branch Experiment Station at Blairsville, GA, and the Central Georgia Branch Experiment Station near Eatonton, GA. The plots were planted on 25 and 26 Sept. 1996, respectively. The low- and high-alkaloid germplasms had been selected previously from Jesup tall fescue (Adcock et al., 1997). Plots were established on a Cecil sandy clay loam soil (Typic Hapludult, clayey, kaolinitic, thermic) at Eatonton, and a Congaree clay loam (fine-loamy, mixed, non-acid, thermic, Typic Udifluvent) at Blairsville. The plot areas were fertilized with 67, 39, and 67 kg ha-1 N, P, and K to bring nutrient levels to the soil test recommendations. The plot area was prepared by disking the soil and leveling it with a smoothing harrow. The seed were planted in 1.5- by 4.6-m plots with a Hege 1000 plot planter (Heston, KS) with a seeding rate of 25 kg ha-1. The planting arrangement was a randomized complete block design with six replications at each location.
The plot areas were fertilized in late February (Eatonton) or early March (Blairsville) with an additional 67 kg ha-1 N, without additional P or K. A 0.91-m swath of forage was harvested with a flail harvester (Carter Harvester, Evansville, IN). Harvests were made on 9 April, 7 June, 1 August, and 24 November at Blairsville and 11 March, 6 May, 6 June, 8 July, and 16 December at Eatonton in 1997; 9 May and 30 June at Blairsville and 3 May and 21 June at Eatonton in 1998; 5 May, and 7 July, and 16 December at Blairsville and 12 April, 10 June, and 1 December at Eatonton in 1999. Total harvested forage was weighed, a 400-g subsample was dried at 65C to determine dry matter content of the harvested herbage, and an additional 400-g subsample was freeze-dried for subsequent ergot alkaloid analysis. Plot dry matter yield was calculated by multiplying the plot wet weight by the percentage of the oven-dry matter, and dry matter yield converted to a per hectare basis. Dry matter yield from the harvests within a year were summed to obtain an annual total dry matter yield.
Pan evaporation and precipitation were recorded daily and a monthly water balance was calculated by subtracting the monthly summed pan evaporation from monthly summed precipitation.
Following the first harvest of each year, eight tillers were excised within each plot and analyzed for presence of the endophyte by a commercial immunoblot test kit (Agrinostics Ltd. Co., Watkinsville, GA). The data were combined across replications for each cultivar–germplasm treatment and an approximation of percent endophyte infection determined from the combined data. Freeze-dried herbage was ground to pass a 1-mm screen in a cyclone-type mill. Ergot alkaloids were analyzed by competitive ELISA as described by Adcock et al. (1997). Briefly, microtiter plate wells were precoated with human serum albumin to which lysergol was conjugated. One-tenth gram of freeze-dried ground tissue was extracted with a phosphate buffer (pH 7.6) for 30 min and 50 µL of extraction solution added to the precoated wells of the mircotiter plates. Standard solutions ranging from 1.02 x 10-11 to 6.35 x 10-12 M of lysergic acid (9,10-didehydro-6-methyl-ergoline-8 -carboxylic acid; Sigma Chemical, St. Louis, MO) were made in phosphate buffer for each microtiter plate. Hybridoma media containing monoclonal antibody 15F3.E5 was diluted 1:100 (v/v) in borate saline solution, and 50 µL added to each well containing samples or standards and incubated for 2 h. After washing the plates, rabbit anti-mouse antibody with alkaline phosphatase (RAM-AP) conjugate was added to each well and incubated for 2 h. The RAM-AP was washed from the plates and p-nitrophenyl phosphate chromogen added. The reaction was stopped after 15 min by adding 50 µL of 3 M NaOH and absorbance read at 405 nm with a BioTek (Winooski, VT) Model 311 microplate reader. The standard values were fit to a logit/log mathematical function and the samples predicted from the calibration curve. All standards and samples were run in duplicates on each microtiter plate. Coefficients of determination (R2) for standards were typically 0.98 or greater with coefficients of variation for standards ranging between 0.28 and 2.0%.
Year, location, and cultivar treatment effects on forage yield and alkaloid analysis were tested for significance by analysis of variance (ANOVA) using a split-plot in time treatment assignment. The cultivar (germplasm) (fixed effect) and location (random effect) treatments were assigned to a 10 x 2 factorial within years (whole-plot random effect). Means were separated by Fisher's protected LSD at the 0.05 level of probability. The proportion of ergot alkaloids in the selected germplasms were calculated by dividing the alkaloid concentration of the selected germplasms by the alkaloid concentration of endophyte-infected Jesup, the cultivar from which they were selected. Independent calculations were made for each replicate within each harvest, location, and year. Analysis of variance was conducted on the proportional alkaloid values as an estimate of their stability over all harvests, years, and locations.
Stand Survival
Stand survival was assessed in a separate trial. The experimental design was a randomized complete block with six replicates (blocks) and grass genotypes as treatments. Plots of each entry were established with a Hege precision drill and plot size was 1.5 by 3.5 m. Plots were mowed and fertilized uniformly with 67 kg N, 15 kg P, and 28 kg K ha-1 as a complete fertilizer at establishment and in early September in each year of the respective trial. The trial was established in a Cecil sandy loam soil (clayey, kaolinitic, thermic, Typic Hapludult) at the Central Georgia Branch Station, near Eatonton, GA, by sowing seed of the following entries into common bermudagrass sod in October 1997 and grazing with beef cattle from April until November in each of the next 2 yr. The treatments consisted of Jesup E+, Jesup E-, GA-961, and GA-962 as well as 10 additional tall fescue and seven orchardgrass (Dactylis glomerata L.) experimentals which were not directly part of the current study. Stand assessments were determined as percent stand and were made in April 1998 (initial), March 1999, and December 1999 by means of a 1.5-m rod graduated into 10-cm sections. The percent stand was calculated by dividing by the total number of sections in the rod into the number of sections containing a living tall fescue tiller and multiplying by 100. Treatment means were separated by a Fisher's protected LSD at the 0.05 level of probability.
Animal Performance
A grazing study with sheep was conducted to investigate animal response to reduced ergot alkaloids in GA-961. GA-961 was tested for a 10-wk grazing period against E+ and E- Jesup during March to June, 2000 at Eatonton, GA. One replication of each paddock treatment was planted during early October of 1997, and two replications planted in early October of 1999. The paddocks were 30 by 30 m and were planted in a randomized complete block design. The stocking rate was four 22-kg Rambouillet-Suffolk cross-bred lambs per paddock to serve as "tester" animals. On the basis of forage availability, a put-and-take system was then employed to adjust stocking rate during the 10-wk grazing period by addition of "grazer" lambs during periods of rapid pasture growth and removal of grazer lambs during periods of reduced pasture growth. The tester animals remained on the paddock the entire time. Initially, and every 2 wk for the 10-wk grazing period, lamb weight gain, rectal temperature, and serum prolactin were recorded. Forage available yield and ergot alkaloid concentration were determined by sampling 10 0.09-m2 quadrat samples throughout the paddock area. Data were analyzed by means of a fixed effects (tall fescue germplasm and replications) analysis of variance model. Means were separated by a Fisher's protected LSD at the 0.05 level of probability.
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RESULTS AND DISCUSSION
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Forage Yield and Ergot Alkaloid Concentration
Eatonton is located in the Piedmont region of central Georgia while Blairsville is in the Georgia mountains near the North Carolina border. Although climatic conditions are normally very different for the two locations, monthly mean temperatures, rainfall, and water balance deviated substantially from the 30-yr averages at both locations in at least 2 of the 3 yr of the study. Negative monthly water balances normally occur from April through October in Eatonton and from May through August in Blairsville (Table 1). In 1997, the monthly water deficits at Eatonton began in March and lasted through August, and four of the six months were below normal. In 1998, the monthly water deficits began in April, but lasted until November, and in 1999 the monthly deficits began in March and lasted until October. In each of those years, the monthly deficits were at least 1 cm greater than the 30-yr average for four of the months. The Blairsville location also had drier than normal conditions during at least four summer months in each year. Although rainfall was below normal at each location, mean monthly temperatures were also below the 30-yr average at both locations for most of the summer months in 1997 and 1999, and similar to the 30-yr average in 1998 (Table 2).
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Table 1. Mean monthly water balance compared with the 30-yr mean for the Central Georgia Station, Eatonton, and Georgia Mountain Experiment Station, Blairsville, for 1997, 1998, and 1999.
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Table 2. Mean monthly temperatures compared with the 30-yr mean for the Central Georgia Station, Eatonton, and Georgia Mountain Experiment Station, Blairsville, for 1997, 1998, and 1999.
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Endophyte infection rates were low for all endophyte-free cultivars of tall fescue included in the study (Table 3). All endophyte-infected populations initially had 82% or greater infection frequencies but were above 90% when the study was terminated in December, 1999.
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Table 3. Endophyte infection levels of the tall fescue germplasms grown at the Central Georgia Station, Eatonton, and Mountain Experiment Station, Blairsville, in spring of each year and December of the final year of the study.
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There was a germplasm x year x location interaction for forage yields. Forage yields were similar among the germplasms in 1997 and 1998 at Eatonton (Table 4). Yields were low in 1999 because of the prevailing drought conditions, but AU-Triumph significantly out yielded the other cultivars and germplasms. It is likely that AU-Triumph out yielded the other cultivars and germplasms because it has greater production potential during winter and early spring (Pedersen et al., 1983). Forage yields of the low- and high-alkaloid germplasms (GA-961 through 965) were similar and did not differ from E+ Jesup from which they were selected. Germplasm GA-962 had greater forage yield than E- Jesup and E- Kentucky-31, but the other selected germplasms were similar to E- Jesup and E- Kentucky-31 in 1999.
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Table 4. Yearly dry matter yield of tall fescue germplasms when grown at the Central Georgia Experiment Station, Eatonton, GA.
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AU Triumph had the lowest yield at Blairsville, while the high-alkaloid germplasm, 962, and E+ Jesup yielded the most in 1997 (Table 5). AU Triumph, E- Kentucky-31, E- Jesup, and the low-alkaloid germplasm GA-963 yielded the most at the Blairsville location in 1998. Endohyte-infected Jesup and the low-alkaloid germplasm, GA-961, had the lowest yields in 1998. Yields were similar among the germplasms in 1999. Thus, selection for the low-alkaloid trait did not affect yield of tall fescue when grown in small plots.
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Table 5. Yearly dry matter yield of tall fescue germplasms when grown at the Georgia Mountain Experiment Station, Blairsville, GA.
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There was a germplasm x year and location x year interactions for ergot alkaloid concentration. Alkaloid concentration was greater in forage harvested at Blairsville in 1997, alkaloid concentration in forage from the two locations were similar in 1998, and was greater in forage harvested at Eatonton in 1999 (Table 6). Alkaloid concentrations of E- Jesup, Kentucky-31, and AU Triumph were not zero (Table 7), which was a result of the plots for these populations not being entirely E- (Table 3). Endophyte-infected Kentucky-31 had a higher concentration of ergot alkaloids than E+ Jesup, and was similar to the high-alkaloid germplasms GA-962 and GA-965 in 1997 and 1998, but GA-965 and GA-962 were both higher in ergot alkaloids than Kentucky-31 in 1999 (Table 7). The low-alkaloid germplasms GA-961, GA-963, and GA-964 remained lower than E+ Jesup throughout the study.
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Table 6. Mean alkaloid concentration of all tall fescue germplasms over 3 yr when grown at the Central Georgia Station, Eatonton and Georgia Mountain Experiment Station, Blairs-ville.
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Table 7. Alkaloid concentration of tall fescue germplasms. Values are means of the first two cuts of herbage from both experiment stations.
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Alkaloid concentration of each germplasm was used to calculated the proportion of ergot alkaloids in each relative to that of E+ Jesup. Stability of the trait was estimated by conducting an analysis of variance on the proportional values and scrutinizing the variances for interactions between the germplasm and other treatment variables. The analysis of variance had no significant two-, three-, or four-way interactions between genotype and any of the other treatment variables. Therefore, only the means of the proportional values for the germplasms are reported (Table 7). GA-965 and GA962, the two genotypes that were selected for high alkaloid, and E+ Kentucky-31 had the greatest proportional values. The low-alkaloid germplasms GA-961, GA-963, and GA-964 had proportional values lower than the high-alkaloid germplasms; however, they were higher than the E- cultivars. Since the proportional values for the low-alkaloid germplasms were grouped together and because there were no genotypic interactions with the other treatment variables, the low alkaloid trait can be considered stable across environments (locations and years).
Stand Survival
Another stress factor for tall fescue pastures is encroachment by bermudagrass. This aggressive, warm-season grass has been observed to reduce the stands of both E+ and E- Jesup tall fescue (Bouton et al., 2000). Besides defining a real world, but worst-case screening environment, it allows E+ and E- tall fescue to be screened more efficiently for summer survival. When screened under grazing with bermudagrass competition at the Eatonton location, the Jesup E+ was found to have better stand survival after 1 yr than Jesup E- (Table 8). GA-961 and GA-962 had better stand survival than Jesup E- after 1 yr and were equal in survival to Jesup E+ (Table 8). Although stands of all entries were further depleted in the second year, Jesup E+, GA-961, and GA-962 were still superior to Jesup E-; however, only GA-962 was still found to be equivalent to Jesup E+ in stand survival. This indicates selection within Jesup E+ to lower total ergot alkaloids was detrimental to stand survival, even though it was better than Jesup E-. This allows one to speculate that ergot alkaloids may be beneficial for plant survival. It is also possible that when reducing ergot alkaloid concentration via selection, another unknown alkaloid(s) beneficial for plant survival may simultaneously have been reduced leading to poor stand survival. However, an earlier study comparing peramine and ergot alkaloid variation found no relationship between the two alkaloids in tall fescue (Roylance et al., 1994).
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Table 8. Stand survival of two tall fescue genotypes. All cultivars planted into bermudagrass and grazed during April through November, 1998 through 1999 at Central Georgia Station, Eatonton.
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Animal Performance
The put-and-take method was used to maintain adequate forage mass for all entries so as not to confound overall results, and mean forage mass was similar among all treatments as a result (Table 9). It is generally accepted that forage mass to grazing animals is an indication of how they might graze plant components selectively that have higher quality as well as their ability to apprehend forage (Blaser et al., 1977). Inasmuch as forage mass was similar among all pasture treatments, it would be expected that lambs would have similar rates of gain if other antiquality variables were not present. However, lambs grazing GA-961 and E- Jesup gained more weight than those grazing E+ Jesup (Table 9). Lambs grazing the E+ pasture had suppressed serum prolactin values while lambs grazing the E- pasture had values greater than either the lambs grazing GA-961 or E+ tall fescue. Thus, lamb responses for the E+ and E- tall fescue were typical of other animal grazing studies as reviewed by Stuedemann and Thompson (1993). However, changes in body core temperature were not different among the pasture treatments. Lambs grazing GA-961 forage had better weight gain than the E+ check even though the serum prolactin levels were similar to the E+ control (Table 9). Although ergot alkaloid levels in the forage showed the GA-961 to have intermediate concentrations when compared with the controls, these levels were apparently high enough to place animals into a state of toxicity as evidenced by the prolactin data, but alkaloids were reduced enough so they were able to compensate with increased weight gain. Lambs grazing GA-961 gained less and had suppressed serum prolactin compared with the E- control.
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Table 9. Results of a lamb grazing trial during a 10-wk spring period (March–May) for 3 yr (1998–2000) at the Central Georgia Station, Eatonton.
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CONCLUSIONS
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The low-alkaloid germplasms used in this study were selected from an endophyte-infected Jesup cultivar without regard to endophyte genotype. Genetic analysis of the breeding populations indicated that paternal effects on the low-alkaloid trait were as great as the maternal effects in the breeding effort, indicating that plant genetics was involved with the low-alkaloid trait, and not strictly endophyte (Adcock et al., 1997). Others have followed a different approach towards reducing alkaloid content in endophyte-infected cool-season grasses by selecting individual endophytes which do not produce alkaloids (Rolston, 1993; Bouton et al., 1998; West et al., 1998). Each strategy has its merits but each may also have limitations. The plant breeding strategy used to create the low-alkaloid trait for the germplasms reported herein could result in populations that revert to higher alkaloid concentration because of genetic transmigration or invasion from high-alkaloid individuals if the low-alkaloid populations were not persistent. This study suggests that the alkaloid traits of the low- and high-alkaloid populations were stable over environments (locations and years).
Achievement of low-alkaloid production in the GA-961 germplasm resulted in less plant survival than E+ tall fescue but greater survival than the E- tall fescue. Animal performance improved in the low-alkaloid GA-961 germplasm when compared with the E+ tall fescue. Although alkaloids were significantly reduced by approximately 67%, there was still sufficient concentration to cause symptoms of fescue toxicity as shown by body temperature and serum prolactin. This indicates there may be a threshold level of ergot alkaloids which the forage must be below in order to eliminate all symptoms of fescue toxicity. This level was apparently not achieved with GA-961. However, if the loss of stand was a direct result of concurrently losing other alkaloids expressed by endophyte infection which are tied to survival, then the validity of this strategy of breeding for reducing alkaloid concentration will need to be examined more closely.
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ACKNOWLEDGMENTS
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The authors wish to thank Dr. Glenn O. Ware for his assistance in analyzing and interpreting the statistics in this manuscript. We are also grateful to the staff at the Georgia Central Branch Agricultural Experiment Station in Eatononton, GA, and the Georgia Mountain Branch Agricultural Experiment Station in Blairsville, GA, for their logistical support in carrying this research project to fruition. This research was supported by the University of Georgia College of Agricultural and Environmental Sciences.
Received for publication January 4, 2001.
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REFERENCES
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TOP
ABSTRACT
INTRODUCTION
