Crop Science 41:806-809 (2001)
© 2001 Crop Science Society of America
TURFGRASS SCIENCE
Dollar Spot Resistance among Blends of Creeping Bentgrass Cultivars
S.D. Abernathya,
R.H. White*a,
P.F. Colbaughb,
M.C. Engelkec,
G.R. Taylor, IIa and
T.C. Halea
a Texas A&M Univ. (TAMU), College Station, TX 77843-2474
b Dep. of Plant Pathology and Microbiology, TAMU-Dallas-Research and Extension Center, Dallas, TX 75252
c Soil & Crop Sciences, TAMU-Dallas-Research and Extension Center, Dallas, TX 75252
* Corresponding author (rh-white{at}tamu.edu)
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ABSTRACT
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Disease is a major problem in creeping bentgrass (Agrostis stolonifera L.) on golf course putting greens. Genetic composition and uniformity of host populations can affect disease development. This study was conducted to determine the effects of blending creeping bentgrass cultivars on dollar spot (caused by Sclerotinia homoeocarpa F. T. Bennett) severity. ‘Penn A-4’, ‘Crenshaw’, ‘L-93’, ‘Mariner’, and ‘Penncross’ were planted in monostands or as two-way or three-way blends in a completely random design with three replications on a sand-based putting green in the field at College Station, TX. Disease severity was determined by the number of infection centers and by total blighted area. Crenshaw was most susceptible, L-93 most resistant, and all other cultivars were moderately resistant to dollar spot in monostands. Cultivar susceptibility in monostands to S. homoeocarpa was representative of each cultivars contribution to dollar spot severity in blends. In blends, L-93 suppressed, whereas Crenshaw increased dollar spot. Penncross, Penn A-4, and Mariner did not affect dollar spot severity across all blend combinations. Number of infection centers and infected area pooled across all monostands were similar when compared to all two- and three-way blends indicating that dollar spot activity in blends was a compromise between resistance levels of individual cultivars. Two-way blends of Penn A-4, L-93, Mariner, or Penncross with Crenshaw, however, resulted in 46 to 67% fewer infection centers and 71 to 98% less blighted area, when compared to the Crenshaw monostand. These data indicated that blending a resistant cultivar with a susceptible cultivar reduced dollar spot severity in the blended population.
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INTRODUCTION
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CREEPING BENTGRASS is a widely utilized turfgrass species on golf course putting greens across the USA and around the world. Disease is a major problem in creeping bentgrass and one that can significantly decrease putting quality. In the past, strict adherence to a preventive fungicide program has been the primary solution to disease problems. Because of the high cost of fungicide applications and growing environmental concerns, alternative solutions need to be explored. Blending cultivars to broaden the genetic base of a creeping bentgrass sward is one possible approach to reducing disease severity that merits investigation.
Genetic composition and uniformity of host populations is recognized as a potential factor affecting disease development. Blends have been shown to reduce significantly disease severity in other plant-pathogen systems. Most of the previous research on blended populations was performed with cereal crops, such as wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Development of Septoria leaf spot [caused by Septoria nodorum (Berk.) Berk.] in spring and winter wheat was reduced in mixtures to levels near that of the more resistant pure stand (Jeger et al., 1981). Barley blends were found to significantly decrease the incidence of scald [caused by Rhynchosporium secalis (Oud) Davis] (McDonald et al., 1988). Some two- and three-component blends exhibited scald resistance equal to that of the most resistant cultivar.
Little data have been published addressing the use of a blended population for different turfgrass species. Golembiewski and Danneberger (1998) reported that a 50:50 blend by weight of Crenshaw and Penncross creeping bentgrass reduced the rate of dollar spot development compared with Crenshaw alone. However, the blend did not provide commercially acceptable dollar spot suppression throughout the study. Rhizoctonia blight (caused by Rhizoctonia solani Kühn.) progression on blended populations of tall fescue (Festuca arundinacea Schreb.) composed of resistant and susceptible cultivars decreased with increasing proportions of the resistant cultivar (Green and Burpee, 1997). Melting-out (caused by Drechslera poae Drech.) resistance of specific Kentucky bluegrass (Poa pratensis L.) blends was reported to be intermediate between that of the same cultivars in monostands (Vargas and Turgeon, 1980). They concluded that the inoculum produced by a melting-out susceptible cultivar reduced the generalized resistance of a normally resistant cultivar included in a blend with a susceptible cultivar. Vargas and Turgeon (1980) also reported a similar trend for Fusarium blight [caused by Fusarium roseum f. sp. cerealis (Cke) Synd. and Hans.].
Turfgrass blends, which include two or more cultivars of the same species, are often recommended to improve disease resistance (Beard, 1973). Presumably, blends provide greater disease resistance than monostands (Vargas and Turgeon, 1980). The objective of this study was to determine the effects of blending creeping bentgrass cultivars on dollar spot severity.
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MATERIALS AND METHODS
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Five commercial creeping bentgrass cultivars, including Penn A4, Crenshaw, L-93, Mariner, and Penncross, were evaluated. Selection was based on known resistance to Sclerotinia homoeocarpa, as well as general quality rating indices taken from National Turfgrass Evaluation Program (NTEP) reports (National Turfgrass Evaluation Program, 1996). The chosen cultivars provided a range of turf quality attributes and resistance to pathogens.
Monostands and two-way and three-way blends were seeded 13 Nov. 1996 on an experimental green built to United States Golf Association specifications at the Texas A&M University Turfgrass Field Laboratory at College Station, TX. Equal proportions of each blend component were used. Every possible cultivar blend combination was represented and replicated three times in a completely randomized design. Plots were 3.34 m2 and seeded at 48.8 kg pure-live seed ha-1. About 80 kg P and K ha-1 and 40 kg N ha-1 were incorporated in the upper 10 cm of the root zone prior to establishment. The root-zone mix of the green was 900 g kg-1 sand and 100 g kg-1 composted rice hulls with an original pH of 6.2. Sand sizes of the medium were 152 g kg-1 coarse (0.5– 1.0 mm diameter), 586 g kg-1 medium (0.5– 0.25 mm diameter), 213 g kg-1 fine (0.25– 0.10 mm diameter) with a saturated hydraulic conductivity of 36.5 cm h-1, and a 30-cm water retention capacity of 125 g kg-1. The root-zone mix had a bulk density of 1.53 g cm-3.
The green was mowed six times per week to heights ranging from 3.2 to 4.0 mm. The turf received 290 to 390 kg N ha-1 annually, 75% of which was applied during the months of October through May. A complete analysis fertilizer (18:2:9) was used to supply N, P, and K. Supplemental applications of 24 kg K ha-1 (K2SO4) were applied monthly. Irrigation was applied every 3 to 4 d to replace the amounts of water lost from a Class A Weather Pan located within 60 m of the experimental site.
Because of limited disease activity in 1997, plots were inoculated on 24 Sept. 1997. Rye (Secale cereale L.) seeds infested with S. homoeocarpa, were used as inoculum. Four seeds were spaced evenly in three locations per plot within an area of about 12 cm in diam. After misting the seeds and turf with sterile water, a 15-cm-diam. foam plate was placed over the inoculum and secured to the turf. The inoculum and turf were covered with a foam plate to prevent feeding by birds and to maintain high relative humidity. Plates were removed 24 h after inoculation. Disease activity was assessed daily. Areas showing disease symptoms were evaluated by counting the number of individual S. homoeocarpa infection centers and by measuring total area blighted with digital calipers for all infection centers. The epidemic was allowed to progress for 5 d and then the entire study area was treated with 11 kg a.i. ha-1 chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) to end the epidemic.
Dollar spot occurred on three separate occasions in 1998. On 12 January, dollar spot activity was detected and continued through 14 January at which time environmental conditions changed and eliminated disease progress. Infection centers were counted and area measurements were taken on 12 and 14 January. On 18 March, dollar spot activity again was noted on the green and dollar spot data were obtained on 23 March. Detectable disease progress ceased after 23 March. A third dollar spot outbreak occurred on 30 September, and infection centers and area measurements were taken on 1 and 4 October.
All data from monostands were ranked transformed and subjected to analysis of variance by the Statistical Analysis System (SAS Institute, 1996). Tukey's Studentized Range was used to detect differences among treatments. All other analyses were conducted using nontransformed data. Orthogonal contrasts were used to compare single cultivar treatments with all blended treatments, and all two-way and three-way blend treatments. Orthogonal contrasts also were used to define individual cultivar effects on dollar spot severity across blends.
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RESULTS AND DISCUSSION
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Although dollar spot occurred following inoculation with S. homoeocarpa, disease severity was similar among monostands on all observation dates in 1997 (data not presented). Likewise, no difference in disease severity was observed when monostands were compared with two-way and three-way blends (data not presented). Dollar spot occurred frequently in 1998 and therefore no other inoculations were performed.
Three different disease outbreaks were observed in 1998. Only measurements taken on the last day of each epidemic are presented because treatment effects were similar, regardless of observation date. Differences in dollar spot severity were evident among monostands. Crenshaw was most susceptible, L-93 most resistant, and all other cultivars were moderately resistant to S. homoeocarpa (Table 1). The susceptibility of cultivars to S. homoeocarpa in this study was similar to previous reports (National Turfgrass Evaluation Program, 1996).
As components in blends, L-93 reduced the level of dollar spot, whereas when Crenshaw was a component of the blend, there was an increase in dollar spot (Table 2). The moderately resistant cultivars, Penncross, Penn A-4, and Mariner did not affect dollar spot severity across all blend combinations. Thus, the susceptibility of cultivars in monostands to S. homoeocarpa was a good indication of the contribution of each cultivar to dollar spot severity in blends. Our results contrast with those of Finckh and Mundt (1992) who observed that cultivar performance in monostands was not always indicative of disease severity of a blend.
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Table 2. The effect of bentgrass cultivar components on S. homoeocarpa infection center number and infected area across creeping bentgrass blends, 1998.
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The mean number of infection centers and infected area data pooled across all monostands were similar to those pooled across two-way and three-way blends on all observation dates (data not presented). These data suggested that blending creeping bentgrass cultivars did not increase resistance to S. homoeocarpa, when compared with monostands. However, this observation warrants closer examination because blends were not compared with just the most susceptible cultivar, but were compared with the mean disease reaction across monostands of resistant, moderately resistant, and susceptible cultivars. Thus, when infection center and infected area data were averaged across monostands the mean resulted in an overall moderate level of resistance to dollar spot. Likewise, the mean number of infection centers and infected area for two- and three-way blends, in general, represented a moderate level of resistance. Our results support the conclusion of Vargas and Turgeon (1980). They reported that when two Kentucky bluegrass cultivars that differed in susceptibility to a specific disease were combined in a blend, disease severity usually represented a compromise in disease severity of the individual cultivars in the blend.
Although blending, in general, did not suppress dollar spot compared with the mean dollar spot levels observed across monostands, specific blends did result in disease suppression when compared with the most susceptible cultivar (i.e., Crenshaw). Examination of disease activity in two-way blends that included Crenshaw provided evidence that blending resistant and moderately resistant cultivars with a susceptible cultivar suppressed dollar spot when compared with the Crenshaw monostand. Dollar spot in Crenshaw, L-93, and the Crenshaw + L-93 blend treatments revealed positive impacts of blending on dollar spot severity (Fig. 1). Data for these comparisons were taken from the January dollar spot outbreak, because these data were representative of trends observed in all other outbreaks in 1998. The Crenshaw monostand had a greater infected area, when compared with either the L-93 monostand or the Crenshaw + L-93 blend. Dollar spot in the Crenshaw + L-93 blend was similar to dollar spot levels in the L-93 monostand. Comparison of dollar spot levels in the Crenshaw + Penn A4 and Crenshaw + Mariner blends revealed similar trends as the Crenshaw + L-93 blend (data not presented).
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Fig. 1. Dollar spot in Crenshaw and L-93 monostands and in the Crenshaw + L-93 blend in January 1998 from Day 0 through Day 4 of the disease outbreak. *,** Significant at the P = 0.05 and 0.01 levels, respectively. Bars represent standard error of the mean.
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When data were averaged across observations on 14 January, 23 March, and 4 October, the number of infection centers were reduced by 46 to 67% in two-way blends that included Crenshaw, when compared with the Crenshaw monostand (Table 3). Mean infected area for the same observation dates was reduced 71 to 98% in two-way blends that included Crenshaw, when compared with the Crenshaw monostand. Our results agree with those of Golembiewski and Danneberger (1998). They observed that a blend of Penncross and Crenshaw had commercially unacceptable levels of dollar spot. However, a blend of L-93 and Crenshaw exhibited a substantial reduction in dollar spot compared with the Crenshaw monostand in this study. The level of dollar spot suppression observed in our study by blending cultivars could reduce the need for preventive fungicide applications.
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Table 3. Number of S. homoeocarpa infection centers and infected area in creeping bentgrass monostands and in two-way blends with Crenshaw across three observation dates in 1998.
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CONCLUSIONS
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Our results and those of others indicate that disease in cultivar blends can be reduced, when compared with monostands of susceptible cultivars (Baker and Briggs, 1984; Gizlice et al., 1989; Trenbath, 1974; Vargas and Turgeon, 1980). Dollar spot levels among monostands and blends were similar when comparisons among pooled data for monostands and two-way and three-way blends were made. However, blending a S. homoeocarpa resistant or moderately resistant cultivar with a susceptible cultivar (i.e., Crenshaw) substantially reduced dollar spot, when compared with the Crenshaw monostand. If disease reaction in blends for other creeping bentgrass diseases were similar to results reported here for dollar spot, judicious cultivar blending could reduce the overall level of disease, despite the presence of a susceptible cultivar in the blend. This blending strategy should only be used to reduce disease incidence when the susceptible cultivar has desired attributes that are not possessed by other components in the blend.
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ACKNOWLEDGMENTS
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The authors thank the Texas Turfgrass Association for providing the R. C. Potts Fellowship and the United States Golf Association—Green Section for funds in support of this research.
Received for publication March 3, 2000.
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REFERENCES
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- Baker, R.J., and K.G. Briggs. 1984. Comparison of grain yield of uniblends and biblends of 10 spring barley cultivars. Crop Sci. 24:85–87.[Abstract/Free Full Text]
- Beard, J.B. 1973. Turfgrass: Science and culture. Prentice-Hall Inc., Englewood Cliffs, NJ.
- Finckh, M.R., and C.C. Mundt. 1992. Stripe rust, yield, and plant competition in wheat cultivar mixtures. Phytopathology 82:905–913.
- Gizlice, Z., T.E. Carter, J.W. Burton, and T.H. Emigh. 1989. Partitioning of blendingability using two-way blends and component lines of soybean. Crop Sci. 29:885–889.[Abstract/Free Full Text]
- Golembiewski, R.C., and T.K. Danneberger. 1998. Dollar spot severity as influenced by trinexapac-ethyl, creeping bentgrass cultivar, and nitrogen fertility. p. 466. In Agronomy abstracts, Madison, WI.
- Green, D.E., and L.L. Burpee. 1997. Modeling the effects of host resistance on the progress of Rhizoctonia blight in tall fescue (Festuca arundinacea Schreb.). Intl. Turfgrass Soc. Res. J. 8:883–892.
- Jeger, M.J., D.G. Jones, and E. Griffiths. 1981. Disease progress of non-specialized fungal pathogens in intraspecific mixed stands of cereal cultivars. Ann. Appl. Biol. 98:199–210.
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- National Turfgrass Evaluation Program. 1996. ‘National Bentgrass Test – 1993, Progress Report 1993–1996’. K. Morris ed., NTEP No. 97-6, USDA-ARS, Beltsville, MD.
- SAS Institute. 1996. SAS user's guide for Windows: Statistics. SAS Institute, Cary, NC.
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ABSTRACT
INTRODUCTION
