Resistance of Kentucky Bluegrass Cultivars to Necrotic Ring Spot

by Tom Hsiang and Gary A Chastagner
 

Published in: International Turfgrass Society Research Journal 8:893-904. 1997.
 

Introduction

Patch diseases of turfgrass in North America are caused by a diverse group of pathogenic fungi. There are at least 19 different patch diseases (Couch, 1995) caused by both foliar and root infecting fungi. Several distinctly different soilborne ectotrophic ascomycetes infect the roots of turfgrass causing diseases that have similar symptoms. These diseases include spring dead spot of Cynodon species (Endo et al., 1985; Wadsworth and Young, 1960; Walker and Smith, 1972), take-all patch of Agrostis species (Gould et al., 1961; Walker, 1981), and summer patch and necrotic ring spot of Poa species (Chastagner et al., 1984; Jackson 1984; Smiley and Craven-Fowler, 1984; Worf et al., 1986).

Necrotic ring spot (NRS) is a relatively new disease of turfgrass. It has been reported to affect a number of different turfgrass species, but is especially destructive on Kentucky bluegrass (Poa pratensis L.) (Smiley et al., 1992; Worf et al., 1986), which is one of the most commonly used turf species in the temperate regions of North America. NRS was first suspected as being a new disease in North America when application of the fungicide triadimefon was unsuccessful in controlling a patch disease believed to be Fusarium blight (Worf, 1980). Fusarium blight, which was first reported in 1959 (Bean, 1966; Couch and Bedford, 1966), is a patch disease that occurs in mature stands of Kentucky bluegrass. Symptoms are small, pale, straw-coloured patches of turf a few cm in diameter that increase in size to form circular or ring-shaped patches of dead turf up to 100 cm in diameter (Couch and Bedford, 1966). Fusarium roseum (L.K.) amend. Snyd. & Hans. f.sp. cerealis "Culmorum" and F. tricinctum (Cda.) Snyd. & Hans. f.sp. poa were the most common foliar organisms isolated from disease samples and were, therefore, considered the causal agents of the disease (Couch and Bedford, 1966). However, Fusarium species could not always be isolated from diseased plants exhibiting patch symptoms which had generally been attributed to Fusarium blight (Worf et al., 1986).

Smiley and Craven-Fowler (1984) identified other organisms that were associated with turf exhibiting symptoms that generally had been attributed to Fusarium blight. They isolated two ectotrophic ascomycetes that were pathogenic to Kentucky bluegrass and both caused symptoms identical to Fusarium blight. There was initially some confusion as to the identification of the causal organisms, but they are now known as Magnaporthe poae Landschoot and Jackson, causal agent of summer patch (Landschoot and Jackson, 1989), and Leptosphaeria korrae Walker & Smith (=Ophiosphaerella korrae (J. Walker & A.M. Smith) Shoemaker & Babcock) (Walker & Smith 1972), the cause of NRS.

In addition to past problems with identification of the causal agent of NRS, there also has been some taxonomic controversy. Walker & Smith (1972) named this pathogen Leptosphaeria korrae. Shoemaker & Babcock (1989) subsequently transferred it to Ophiosphaerella based on descriptions of Ophiosphaerella Speg. as described by Walker in 1980. However, in that same article, Walker (1980) retained the genus Leptosphaeria for L. korrae. Recently, Tisserat et al. (1994) sequenced and analyzed the ITS1 region of both Ophiosphaerella herpotricha and L. korrae (which they called O. korrae) and found that the homology between ITS1 regions of these two was much greater than that between L. korrae and L. maculans. Thus, along with morphological evidence presented by Shoemaker & Babcock (1989), there is supportive molecular evidence to accept L. korrae as belonging to Ophiosphaerella or at least to the same genus as O. herpotricha. The question of taxonomic identity of L. korrae is still open, and requires further study.

Because of the difficulty in accurately identifying specific patch diseases based on field symptoms, much of the recent research on L. korrae has focused on improved methods of detection (Tisserat, 1988; Nameth et al., 1990; Tisserat et al., 1991; O'Gorman et al., 1994; Tisserat et al., 1994). However, there are many aspects of the ecology and epidemiology of L. korrae which are unknown. For example basic information on the source and spread of inoculum is still lacking. Although pseudothecia can be found on plants in the field and produced in culture (Hammer, 1988), the importance of ascospores in the spread of this disease is still unknown.

NRS is a very difficult disease to manage. Melvin and Vargas (1994) have recently shown that irrigation and fertilizer frequency can influence the incidence of NRS. Research on chemical management has demonstrated several fungicides that have efficacy against the pathogen. These chemicals include some benzimidazoles and demethylation-inhibiting fungicides. Effective control requires repeated annual applications (Chastagner and Hammer, 1987). Cultural practices that optimize turfgrass growing conditions and promote deep root development in the spring and fall are also commonly recommended as treatments that may minimize the damage caused by NRS (Chastagner and Byther, 1985; Couch, 1995).

Another method that potentially can be used to manage this disease is the use of NRS-resistant cultivars of Kentucky bluegrass. One of the problems facing sod growers, landscapers, homeowners and turf managers when selecting Kentucky bluegrass cultivars is the lack of a comprehensive evaluation of Kentucky bluegrass cultivars for NRS resistance. Equally important is the need to identify cultivars which are consistently found to be susceptible to NRS so their use can be minimized in areas where NRS problems are prevalent.

A recent review of patch disease management (Dernoedon, 1993) cites three studies in which Kentucky bluegrass cultivars were evaluated for NRS. Vargas (1994) lists five cultivars (Midnight, Monopoly, Able 1, Majestic, and America) that have been shown to be resistant in inoculated field trials, while Dernoeden (1994) indicates that Wabash, Vantage, I-13, and Adelphi have some resistance to NRS. In his recent book, Couch (1995) does not list any Kentucky bluegrass cultivars that are resistant to NRS.

In the past ten years, there have been many trials to evaluate the field resistance of Kentucky bluegrass to NRS. Some of these trials have depended upon natural inoculum to establish the disease, while others have been artificially inoculated in an effort to ensure a basic level of disease pressure. The objective of this paper is to review field trials in which the resistance of Kentucky bluegrass cultivars to NRS was tested. There is a need to compile and correlate results between trials to derive a single listing of NRS-resistant cultivars useful to turf managers.
 

Methods

We began by searching the literature for Kentucky bluegrass cultivar trials that included NRS disease evaluations. We also included data from turf field days and industry reports. Data were entered for every test as presented, except for those tests using nominal data (e.g. resistant vs. susceptible). These data were transformed to a numeric scale (0=resistant, 0.5=moderate, 1=susceptible). For any single cultivar to be included in our final analysis, it had to be represented in at least 3 different trials. This permitted better comparisons among trials, and likely increased the reliability of the assessments of cultivar resistance.

Correlation coefficients were calculated for all trials using PROC CORR in SAS® 6.04. These r-values were derived by correlating the ratings between any two sites of all cultivars shared by these two sites. This permitted comparisons of cultivars shared between trials, and also allowed for some analysis of the effects of artificial inoculation vs. natural inoculum in the different trials. Data within a site were ranked on a scale of 0 to 100 with 0 reflecting a lower level of susceptibility than 100. These ranks were then subjected to analysis of variance using PROC GLM in SAS® 6.04.

The reliability of using cultivars which were represented in 3 or more cultivar tests was assessed by performing the same analysis on cultivars that were represented in at least 5 tests. A coefficient of determination (r2) was calculated between the rankings of cultivars present in both analyses.
 

Results

Data from 15 cultivar trials were evaluated (Table 1). Using data for only those cultivars that were represented in 3 or more tests, a total of 115 out of the 265 different cultivars of Kentucky bluegrass were used in our analysis (Table 2). Turf in 6 of the 15 trials was inoculated with L. korrae, whereas the remaining trials relied on natural inoculum (Table 1). Significant differences (p0.05) were found in comparisons (Table 3) of uninoculated vs. uninoculated (r=0.46), uninoculated vs. inoculated (r=0.30), and inoculated vs. inoculated trials (r=0.46). Although none of the 115 cultivars of Kentucky bluegrass was totally resistant to NRS, cultivars clearly varied in their tolerance or resistance to this disease (Table 4). Overall disease rankings ranged from a high of 99.1 to a low of 33.0, with an LSD (p=0.05) of 30.6. The cultivars NE 80-88, Princeton 104 (=P-104), Washington, Alpine, Mystic, Joy, Miranda, Aldephi, Bristol, and Unique, which had the lowest mean susceptibility rankings, were significantly (p=0.05) more resistant than Barsweet, HV-97 (=Cocktail), Annika, Opal, BA 70-131, Amazon, BA 69-82 (=Fairfax), J-335, Sydsport or Trampas.

When using cultivars that were represented in 5 or more tests (73 cultivars), we found that the ranking results did not change significantly. The coefficient of determination between rankings of cultivars in the 3-cultivar analysis and the 5-cultivar analysis was 0.995.
 

Discussion

The lack of clear separation between the mean rankings of many cultivars listed in Table 4 and the high LSD value indicate that there is great variation between test results of different sites. This variation could arise from several sources. We examined all pair-wise correlations between inoculated vs. uninoculated trials and did not find that results from inoculated trials were more similar to each other (Table 3). Another source of variation might arise from potential differences in virulence of L. korrae in different geographic areas. Hammer (1988) found that there were strong differences in the virulence of three isolates of L. korrae that were tested at several different sites. However it has been found that isolates of L. korrae from across North America belong to a small number of clonal groups (Tisserat et al. 1991 & 1994), and that the different groups are very closely related to each other (Hsiang et al., unpublished data). The question of variation in results arising from artificially inoculated vs. natural inoculum in testing Kentucky bluegrass cultivar resistance to L. korrae needs further research.

One of the most effective and environmentally acceptable methods of managing a plant disease in general is through the use of genetically resistant cultivars. Turfgrass cultivars that vary in their disease susceptibility are often utilized in a mixture or a blend of turfgrass species are often used in an effort to avoid significant damages to turf from any single disease. Kentucky bluegrass is one of the most commonly utilized turfgrass species in the temperate regions of North America. Vargas (1994) states that to sustain a high level of quality, a cultivar of Kentucky bluegrass needs to be resistant to melting out (Drechslera poaeShoemaker), NRS, summer patch, and stripe smut (Ustilago striiformis) Westend. (Niessl.). However, all of these diseases do not necessarily occur in a given area. For example, NRS is relatively common on Kentucky bluegrass in certain areas of the Pacific Northwest, while summer patch has not yet been reported from this area (Jackson, 1993).

In areas where NRS is a problem, sod growers, hydroseeders, landscapers, turf managers, and homeowners commonly want to know what cultivars of Kentucky bluegrass are resistant to this disease. This is particularly important to sod growers where problems with NRS in recently sodded turf can result in a significant public relations problem that has, in some cases, engendered lawsuits or even forced sod producers out of business.

Our analysis of data from 15 field trials indicates that there are a number of cultivars of Kentucky bluegrass that have significantly higher levels of susceptibility to NRS than other cultivars. Furthermore, there was a strong correlation between rankings of cultivars represented in 3 or more tests compared to those represented in 5 or more tests, and this showed that the rankings were relatively stable across different tests. From our analysis, cultivars such as Barsweet, HV-97 (=Cocktail), Annika, Opal, BA 70-131, Amazon, BA 69-82 (=Fairfax), J-335, Sydsport, Trampas or other highly susceptible cultivars should probably not be utilized in sod or seed mixtures in areas where NRS is a likely problem. While there may be additional NRS-resistant or tolerant cultivars among the 150 cultivars that were not included in our analysis, additional testing of these cultivars would need to be conducted before they could be added to a recommended list.

It is difficult to determine the level of disease that is acceptable in developing a list of resistant cultivars. Our analysis indicates that the best cultivars had significantly lower levels of disease compared to the most highly susceptible cultivars. Among these, the top ten were: NE 80-88, Princeton 104 (=P-104), Washington, Alpine, Mystic, Joy, Miranda, Aldephi, Bristol, and Unique. It is possible that use of any of the top 10 or 20 cultivars would effectively minimize the potential for NRS. In Wisconsin, sod growers who changed their seed mixtures containing Ram I, Glade, Sydsport, and Baron, three of four of which are all in the more susceptible half of our rankings, to mixtures containing Midnight, Eclipse, and Adelphi, which are all in the least susceptible third of our rankings, greatly diminished their problems with NRS (Dernoeden, 1993).

In areas where NRS is a problem, the selection of cultivars of Kentucky bluegrass should be based on their tolerance to NRS, the local adaptability of the cultivar and its susceptibility to other locally important diseases. This assessment should aid in that selection.
 

References
 

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Table 1. Kentucky bluegrass cultivar trials used as data sources for a review of resistance to NRS.
Site1 Reference Inoculated Rating Range
WI1 Worf et al., 1985 No Resistant, moderate or susceptible (0, 0.5, 1) 0 - 1
MI2 Melvin et al., 1990 Yes Percent area affected 0 - 23%
WA3 Chastagner et al. 1989 Yes Plots affected / 

plots inoculated (9)

 0 - 1
ID4 Brede & Williams, 1992 No rating 1-9, 9=no disease 8.3 - 9
NY5 Fowler and Hummel, 1988 (mean 6/3+6/27) Yes Plots affected / 

plots inoculated (3)

 0 - 0.67
KY62 Vincelli and Powell, 1995 No rating 0-5, 0=no damage, 5=50% damage 0 - 4.85
OR7 Chastagner, unpublished Yes Plots affected / 

plots inoculated (9)

 0 - 1
PA8 Landschoot et al. 1991 No Percent disease injury 0 - 40%
ID9 Anonymous, 1990 No Rating 1-9, 9=no disease 5.6 - 9
ID10 Anonymous, 1991 No Spots in a plot 0 - 3.7
ID11 Anonymous, 1994 No Rating 1-9, 9=no disease 3.3 - 9
ID123 Brede & Williams, 1994 No % area affected 0-100 0 - 15.6
PA134 Landschoot & Hoyland, 1992 No Horsfall Barratt 1=0% 10=100% 1 - 7
WA14 Chastagner, unpublished Yes Plots affected 

/ plots inoculated (9)

 0 - 0.67
ON15 Hsiang, 1996 Yes Plots affected 

/ plots inoculated (5)

 0.01 - 0.28

1 WI = Wisconsin, MI - Michigan, WA = Washington, ID = Idaho, NY = New York, PA = Pennsylvania, OR = Oregon, United States, and ON = Ontario, Canada

2 Earlier data from this trial were reported in Vincelli & Powell (1994)

3 These are 1992/1993 data from these plots. Earlier data from this trial were reported in ID4 (Brede & Williams 1992)

4 Earlier data from this trial were reported in Landschoot et al. (1991)
 
 
 

Table 2. Summary of necrotic ringspot ratings for 115 cultivars of Kentucky bluegrass evaluated at 15 test sites, with overall ranking.
Cultivar Test Site1
WI1 MI2 WA3 ID4 NY5 KY6 OR7 PA8 ID9 ID10 ID11 ID12 PA13 WA14 ON15 ranking2
No. cv in test 24 25 66 28 86 144 24 63 72 61 125 72 69 71 25
A-34 0.23 0.75 0.33 1.00 1.0 8.9 6 0.3 4 0 0.28 69.1
ABBEY (=BA72-441) 1.00 0.00 0.29 0.0 8.2 7.3 0.3 2.33 0.44 57.3
ABLE 1 0.00 1.00 0.15 0.0 8.7 7.3 3.5 5 0.22 67.0
ADELPHI 0.0 9.0 0.00 0.15 0.14 0.0 1.33 0.01 42.1
ALPINE 0.70 8.0 0.05 35.2
AMAZON 1.00 2.50 40.0 7.1 2.0 3.3 5.33 0.11 89.2
AMERICA 0.05 1.00 0.00 2.7 8.8 0.4 1.33 0 0.08 56.2
ANNIKA 1.00 6.8 4.5 0.33 92.0
AQUILA 0.12 0.50 0.0 7.9 1.4 58.8
ASPEN 1.00 0.00 0.00 0.0 8.0 6.3 2.1 3.33 0 67.9
ASSET 0.80 0.0 9.0 0.5 3.67 0 49.6
BA 69-82 (=FAIRFAX) 1.00 3.85 0.89 0.0 7.3 3.5 7.4 3.33 0.11 87.1
BA 70-131 4.00 0.71 5.0 89.2
BA 70-242 0.0 9.0 3.5 1.67 0 50.4
BA 73-540 (=ALLURE?) 1.00 0.67 0.0 8.1 3.3 0.4 3.33 0 71.1
BANFF 0.00 0.30 0.50 7.7 0.07 48.4
BAR VB 1169 4.65 0.3 6.7 84.0
BAR VB 534 0.80 0.0 8.0 5.1 2.67 0.56 70.7
BAR VB 577 0.0 9.0 3.2 3.67 0 58.3
BARBLUE 8.7 0.67 1.00 8.3 0.03 56.9
BARCELONA (=BAR VB 1184) 3.35 0.3 7.7 69.6
BARMAX (=BAR VB 7037) 0.00 3.0 5.0 73.0
BARON 0.5 0.09 1.00 0.33 0.65 0.0 8.9 0.0 7.3 0.3 3 0.22 0.13 64.7
BARSWEET 4.85 3.7 4.3 99.1
BARTITIA 3.15 0.3 7.0 76.2
BARZAN 1.00 9.0 0.0 8.3 0.3 0 45.2
BELMONT (=798) 1.50 0.0 7.3 0.06 53.7
BLACKSBURG 0.15 1.00 2.15 0.0 8.9 7.3 2.0 2 0.44 66.7
BRISTOL 0.09 0.25 0.33 0.17 0.0 8.8 0.0 1.67 0 42.2
CHALLENGER 0.08 0.83 0.00 0.00 0.0 8.7 8.3 0.1 3.33 0 47.2
CHATEAU 

(=BA 72-500)

 0.60 0.71 1.7 8.6 2.8 3 0 61.2
CHELSEA 2.30 0.3 6.0 82.0
CHERI 0.13 1.00 0.67 4.00 3.3 8.6 2.2 4.33 0 0.16 80.9
CLASSIC 0.00 9.0 0.00 1.30 0.00 0.0 8.9 6.7 1.1 1.67 0.11 0.05 49.7
COBALT 0.50 0.0 7.7 50.4
COMPACT 1.00 9.0 3.1 0.22 69.4
CONNI 1.00 0.35 8.9 7.7 0.4 0.44 58.7
COVENTRY (=BA 70-139) 1.00 3.15 0.63 1.7 7.1 5.0 4.2 3.33 0 78.7
CREST 0.15 0.0 6.7 55.3
CYNTHIA 1.00 2.50 0.0 7.1 0.0 6.3 15.6 1.33 0.11 75.7
DAWN 1.00 0.50 0.7 8.9 8.0 9.5 5 0.11 70.4
DESTINY 0.33 9.0 0.30 8.9 0.0 8.3 5.4 0.11 51.0
ECLIPSE 0.5 0.00 0.00 9.0 0.00 0.00 0.29 0.0 8.6 7.7 1.7 1.33 0.11 0.12 49.4
ESTATE 

(=BA 72-492)

 0.67 3.65 0.75 7.9 4.7 2.0 2.67 0.11 69.4
EVB 13.703 1.00 0.0 6.3 69.0
EVB 13.863 0.00 0.0 5.7 59.2
FORTUNA 0.00 0.0 7.0 49.8
FREEDOM (=F-1872) 1.00 0.70 9.0 0.3 8.0 0.8 0 0.27 58.4
FYLKING 9.0 0.00 1.65 0.08 72.2
GEORGETOWN 1.0 0.21 1.15 0.57 0.0 8.8 7.7 3.3 4 0 67.6
GLADE 1.0 0.07 0.89 9.0 0.33 0.00 0.75 0.0 9.0 8.3 2.9 4.67 0 60.8
GNOME 1.00 0.00 0.00 8.7 0.0 7.3 0.0 0.33 59.3
HAGA 1.0 1.00 0.00 0.00 0.0 8.8 1.3 7.7 2.6 4.33 0 69.0
HARMONY 0.50 0.00 0.0 8.9 3.3 1.67 0.11 55.8
HOLIDAY 0.00 0.0 3 70.2
HUNTSVILLE 1.00 1.85 8.6 0.0 0 60.0
HV-97 (=COCKTAIL) 1.00 25.0 7.1 8.4 4.67 0.56 96.4
I-13 0.5 0.00 1 45.1
IKONE 0.80 13.3 7.6 10.0 4.33 0 76.5
J-229 (=NUBLUE) 9.0 0.00 0.3 6.7 0.07 62.7
J-335 3.85 0.3 6.3 86.4
J-386 1.00 0.0 7.0 62.4
J34-99 9.0 0.50 7.3 59.9
JOY 0.0 9.0 0.1 1.67 0 38.7
JULIA 0.00 3.15 20.0 8.0 6.3 7.1 3 0.67 0.08 73.4
K1-152 0.50 0.67 0.0 9.0 1.7 4 0 58.4
K3-178 0.00 0.0 9.0 0.4 4 0 56.0
KELLY 

(=BA 73-626)

 1.00 0.00 0.57 0.0 8.9 7.3 0.0 2.33 0.11 52.2
KENBLUE 0.02 0.00 0.15 0.0 8.9 0.0 5.7 2.4 2 0.22 58.3
KWS PP 13-2 0.00 0.3 6.3 64.3
LIBERTY 0.75 8.9 0.15 9.0 0.0 6.7 0.6 0.22 0.05 51.3
LIMOUSINE 8.3 3.50 7.0 0.09 80.5
LIVINGSTON 0.00 0.7 6.3 65.1
LOFTS 1757 0.67 0.0 8.9 0.0 3.67 0.11 0.07 51.9
MAJESTIC 0.0 9.0 0.67 2.7 3.33 75.0
MARQUIS 0.85 0.75 7.7 62.8
MERION 0.0 0.03 0.00 0.00 0.85 0.00 0.0 9.0 0.3 5.3 1.0 3 0 49.5
MERIT 0.5 0.18 1.00 0.00 0.00 0.50 0.0 9.0 0.0 7.7 3.3 3 0.22 61.8
MIDNIGHT 0.0 0.00 0.50 0.00 0.00 0.0 7.7 0.3 8.3 7.7 3 0.22 0.07 56.6
MIRACLE 0.50 0.0 8.3 42.4
MIRANDA 9.0 0.00 8.0 42.0
MONOPOLY 0.00 0.33 0.33 0.00 0.0 9.0 0.0 6.7 0.8 1.67 0.11 46.7
MYSTIC 0.0 0.02 0.00 0.00 0.0 8.9 0.0 1.33 0 38.0
NASSAU 1.0 1.00 0.00 0.15 0.0 8.3 7.7 3.1 2.33 0 0.02 60.1
NE 80-47 3.70 0.0 6.0 79.4
NE 80-88 0.67 9.0 0.2 0 30.6
NUGGET 9.0 0.00 0.35 0.07 62.3
NUSTAR 9.0 0.00 0.0 8.0 46.9
OPAL 

(=WWAG 495)

 1.00 3.70 5.6 2.0 4.3 12.0 4.33 0 90.0
PARADE 0.13 0.00 0.0 9.0 0.0 3 0.33 57.8
PARK 0.0 1.00 0.0 66.9
PLUSH 0.00 0.0 2 61.0
PRINCETON 104 (=P-104) 0.00 8.9 7.0 0.1 0 0.02 31.9
PST-CB1 1.00 9.0 1.1 0.22 63.5
RAM I 1.0 0.18 1.00 0.67 3.35 0.67 0.0 8.9 0.0 7.0 0.1 2.33 0.11 69.9
RUGBY 0.13 1.00 0.00 0.0 8.7 0.9 4 0.22 73.5
S.D. CERT. 0.50 0.0 7.0 2.67 46.9
SOMERSET 1.00 0.00 0.0 8.6 9.7 1.33 0 68.3
SOUTH DAKOTA 0.0 8.8 1.2 0.22 66.7
SR 2000 0.30 0.0 7.7 46.8
SUFFOLK (=A 239) 0.50 9.0 0.33 0.50 0.0 8.9 0.0 8.3 2.5 5 0.11 61.0
SYDSPORT 1.0 0.23 1.00 8.3 0.00 0.67 0.0 8.0 11.2 2.67 0.22 0.19 85.1
TENDOS 0.71 8.6 1.2 0.11 54.6
TOUCHDOWN 0.00 0.85 0.3 6.3 7 0.09 78.3
TRAMPAS 1.0 0.00 2.50 6.0 84.2
TRENTON 0.18 0.83 0.00 0.50 0.0 8.7 7.3 5.4 4.33 0 66.5
UNIQUE (=PST-C-76) 0.00 0.0 7.7 42.3
VANESSA 9.0 0.00 0.0 3 72.1
VICTA 0.11 1.00 0.00 0.57 0.0 7.1 0.6 2 0 62.6
WABASH 0.0 1.00 0.00 0.00 0.0 8.7 0.1 1.33 0 51.0
WASHINGTON 0.30 0.0 9.0 35.1
WELCOME 0.23 0.33 0.33 0.0 9.0 1.2 3 0.22 62.5
WWAG 468 0.0 7.6 5.6 1.67 0 65.1
WWAG 491 1.00 0.0 8.4 7.6 4 0 78.1
WWAG 496 0.75 0.0 8.3 5.6 4.33 0.11 72.7
LSD (p=0.05)3 1.35 8.4 1.8 1.1 1.9 ns 1.62 0.07 30.6

1 Test site rating scales: WI1 - resistant (0), moderate (0.5), and susceptible (1); MI2, PA8, and ID12 - % area affected, diseased or injured; WA3, NY5, OR14, ON15, and ON16 - plots affected/plots inoculated; ID10 - No. of spots/plot; and PA13 - Horsfall Barratt 1=0% and 10=100%.

2 To determine overall mean ranking, all data within a site were ranked from 0 to 100. All scales were synchronized so that 0 reflected a lower level of susceptibility than 100.

3 LSD values are as reported from each test.
 
 
 

Table 3: Correlation coefficients for different studies on Kentucky bluegrass resistance to necrotic ring spot1
UNINOCULATED SITES
 INOCULATED SITES
U 

N

I

N OC

U

L

A

T

E

D

 ID4 ID9 ID10 ID11 ID12 KY6 PA8 PA13 WI1 MI2 NY5 ON15 OR7 WA3 WA14
ID4 1.00 0.90 0.25 0.19 -0.87 -0.82 0.14 0.06 -0.56 -0.95 -0.03 -0.55 -0.51 -0.60 -0.63
ID9 0.90 1.00 -0.72 0.59 -0.60 -0.59 -0.48 -0.13 0.04 0.03 0.29 0.14 -0.44 -0.25 -0.12
ID10 0.25 -0.72 1.00 -0.59 0.31 0.35 0.81 0.70 0.38 -0.48 -0.36 0.37 -0.87 0.29 -0.42
ID11 0.19 0.59 -0.59 1.00 -0.18 -0.56 -0.10 0.06 0.19 0.01 0.20 -0.18 -0.24 -0.03 0.11
ID12 -0.87 -0.60 0.31 -0.18 1.00 0.36 0.23 0.17 0.25 0.17 -0.21 0.04 0.44 0.18 0.11
KY6 -0.82 -0.59 0.35 -0.56 0.36 1.00 0.37 0.08 0.41 0.48 0.58 0.18 0.51 0.08 -0.00
PA8 0.14 -0.48 0.81 -0.10 0.23 0.37 1.00 0.30 -0.30 0.03 0.45 -0.04 0.27 0.03 0.32
PA13 0.06 -0.13 0.70 0.06 0.17 0.08 0.30 1.00 0.46 0.30 0.25 0.32 0.60 0.30 -0.00
WI1 -0.56 0.04 0.38 0.19 0.25 0.41 -0.30 0.46 1.00 0.75 0.10 0.42 0.43 0.61 -0.05
I 

NO

C

 MI2 -0.95 0.03 -0.48 0.01 0.17 0.48 0.03 0.30 0.75 1.00 0.27 0.88 0.62 0.43 0.08
NY5 -0.03 0.29 -0.36 0.20 -0.21 0.58 0.45 0.25 0.10 0.27 1.00 0.28 0.38 -0.00 -0.13
ON15 -0.55 0.14 0.37 -0.18 0.04 0.18 -0.04 0.32 0.42 0.88 0.28 1.00 0.77 0.41 -0.19
OR7 -0.51 -0.44 -0.87 -0.24 0.44 0.51 0.27 0.60 0.43 0.62 0.38 0.77 1.00 0.77 -0.11
WA3 -0.60 -0.25 0.29 -0.03 0.18 0.08 0.03 0.30 0.61 0.43 -0.00 0.41 0.77 1.00 0.02
WA14 -0.63 -0.12 -0.42 0.11 0.11 -0.00 0.32 -0.00 -0.05 0.08 -0.13 -0.19 -0.11 0.02 1.00

1 The code for sites is presented in Table 1. Correlation coefficients (r) were calculated by correlating ratings of all cultivars common to any pair of sites. The negative value for some correlations represents the use of inverse scales (e.g. highest value is greatest severity in some scales and lowest severity for other scales). The upper left quadrant represents uninoculated vs. uninoculated sites; lower left/upper right, uninoculated vs. inoculated; and lower right, inoculated vs inoculated.
 
 
 
 

Table 4. Overall disease ranking of the susceptibility of 115 cultivars of Kentucky bluegrass to necrotic ringspot from the most susceptible to the least susceptible. (This table is optional since the data was presented in Table 2. The value is that the isolates are placed in rank order)
Cultivar1 Rank2
BARSWEET 99.1
HV-97 (=COCKTAIL) 96.4
ANNIKA 92.0
OPAL (=WWAG 495) 90.0
BA 70-131 89.2
AMAZON 89.2
BA 69-82 (=FAIRFAX) 87.1
J-335 86.4
SYDSPORT 85.1
TRAMPAS 84.2
BAR VB 1169 84.0
CHELSEA 82.0
CHERI 80.9
LIMOUSINE 80.5
NE 80-47 79.4
COVENTRY (=BA 70-139) 78.7
TOUCHDOWN 78.3
WWAG 491 78.1
IKONE 76.5
BARTITIA 76.2
CYNTHIA 75.7
MAJESTIC 75.0
RUGBY 73.5
JULIA 73.4
BARMAX (=BAR VB 7037) 73.0
WWAG 496 72.7
FYLKING 72.2
VANESSA 72.1
BA 73-540 (=ALLURE?) 71.1
BAR VB 534 70.7
DAWN 70.4
HOLIDAY 70.2
RAM I 69.9
BARCELONA (=BAR VB 1184) 69.6
COMPACT 69.4
ESTATE 

(=BA 72-492)

 69.4
A-34 69.1
EVB 13.703 69.0
HAGA 69.0
SOMERSET 68.3
ASPEN 67.9
GEORGETOWN 67.6
ABLE 1 67.0
PARK 66.9
SOUTH DAKOTA 66.7
BLACKSBURG 66.7
TRENTON 66.5
LIVINGSTON 65.1
WWAG 468 65.1
BARON 64.7
KWS PP 13-2 64.3
PST-CB1 63.5
MARQUIS 62.8
J-229 (=NUBLUE) 62.7
VICTA 62.6
WELCOME 62.5
J-386 62.4
NUGGET 62.3
MERIT 61.8
CHATEAU (=BA 72-500) 61.2
SUFFOLK (=A 239) 61.0
PLUSH 61.0
GLADE 60.8
NASSAU 60.1
HUNTSVILLE 60.0
J34-99 59.9
GNOME 59.3
EVB 13.863 59.2
AQUILA 58.8
CONNI 58.7
K1-152 58.4
FREEDOM (=F-1872) 58.4
KENBLUE 58.3
BAR VB 577 58.3
PARADE 57.8
ABBEY (=BA72-441) 57.3
BARBLUE 56.9
MIDNIGHT 56.6
AMERICA 56.2
K3-178 56.0
HARMONY 55.8
CREST 55.3
TENDOS 54.6
BELMONT (=798) 53.7
KELLY (=BA 73-626) 52.2
LOFTS 1757 51.9
LIBERTY 51.3
DESTINY 51.0
WABASH 51.0
COBALT 50.4
BA 70-242 50.4
FORTUNA 49.8
CLASSIC 49.7
ASSET 49.6
MERION 49.5
ECLIPSE 49.4
BANFF 48.4
CHALLENGER 47.2
NUSTAR 46.9
S.D. CERT. 46.9
SR 2000 46.8
MONOPOLY 46.7
BARZAN 45.2
I-13 45.1
MIRACLE 42.4
UNIQUE (=PST-C-76) 42.3
BRISTOL 42.2
ADELPHI 42.1
MIRANDA 42.0
JOY 38.7
MYSTIC 38.0
ALPINE 35.2
WASHINGTON 35.1
PRINCETON 104 (=P-104) 31.9
NE 80-88 30.6
LSD (p = 0.05) 30.6

1 Cultivar equivalences were determined from listings in the trials examined

2 To determine the overall ranking, all data were ranked within each trial from 0 to 100. All scales were synchronized so that 0 reflected a lower level of susceptibility than 100.