Suppression of Red Thread in Fine Fescues Through Endophyte-Mediated Resistance

Stacy A. Bonos, Melissa M. Wilson, William A. Meyer, and C. Reed Funk, Department of Plant Biology and Pathology, Rutgers University, New Jersey Agricultural Experiment Station, 59 Dudley Road, Foran Hall, New Brunswick, NJ 08901-8520

Corresponding author: Stacy A. Bonos. bonos@aesop.rutgers.edu

Abstract

Endophytes provide improved insect resistance to many turfgrass species, however their association with improved disease resistance has not been frequently reported. Red thread and pink patch caused by Laetisaria fuciformis (McAlp.) Burdsall and Limnomyces roseipellis Stalpers & Loerakker, respectively, are the most important diseases affecting the turf performance of fine fescue species. A study was initiated to determine the effects of different endophyte sources in strong creeping red fescue (Festuca rubra L. subsp. rubra) and Chewings fescue (Festuca rubra L. subsp. fallax (Thuill) Nyman). Five fine fescue genotypes (two strong creeping red fescue and three Chewings fescue) were inoculated with different endophytes originating from fine fescues and Poa ampla Merr. Progeny turf plots of each endophyte-host genotype combination along with corresponding non-endophyte-infected genotypes were established in a mowed turf evaluation trial in September 1997 at Adelphia, NJ. The experiment was arranged in a randomized complete block design with three replications. A natural outbreak of red thread occurred in both spring 2001 and 2002. Turf quality (which utilized a 1 to 9 scale, 9 representing best turf quality) and percent red thread were evaluated in both years. Significant differences in red thread severity were observed between endophyte-infected and endophyte-free plots within the same host genotype. For three genotypes (1090, 1117, and 1139) at least one endophyte source significantly reduced red thread severity in both 2001 and 2002. In 2002, all endophyte sources significantly reduced red thread severity in these three genotypes. Different endophyte sources had different effects on red thread depending on the genotype inoculated. The Rose City endophyte showed the most consistent reduction in red thread severity, in several host genotypes, compared to other endophyte sources. This finding suggests that utilizing Chewings and strong creeping red fescue infected with endophytes may help suppress red thread and improve turf quality in addition to the documented improved insect resistance.

Introduction

Red thread (caused by Laetisaria fuciformis (McAlp.) Burdsall) and pink patch (caused by Limnomyces roseipellis Stalpers & Loerakker) are important diseases of all cultivated turfgrasses in temperate regions throughout the world (4,11). Raikes et al. (19) reported that red thread was the most ubiquitous fungal pathogen on winter sports turfs in the UK. Red thread severity is influenced by environmental conditions, fertilizer inputs, and host susceptibility. It is typically more severe when phosphorous, potassium and especially nitrogen are limiting (21) and can sometimes be alleviated with increased rates of nitrogen and potassium fertilizer (2).

Although the pathogen causing red thread can attack all cool-season turfgrasses it is most severe on perennial ryegrass (Lolium perenne L.) and the fine fescues (Festuca spp.). Johnson-Cicalese et al. (10) found significant differences in disease susceptibility among perennial ryegrass and fine fescue cultivars and selections indicating that selection for resistance is possible. Differences in cultivar susceptibility to red thread have been observed in many areas throughout the US (8,13) and UK (25). Among the fine fescue species, hard fescue (Festuca brevipila R. Tracey) has the best resistance, Chewings fescue (Festuca rubra L. subsp. fallax (Thuill.) Nyman) has intermediate resistance, and strong creeping red fescue (Festuca rubra L. subsp. rubra) is the most susceptible to red thread disease (13). In fact, red thread is probably the most important disease affecting strong creeping red fescue quality and performance throughout cool-humid regions where this species is utilized. Low-maintenance fine fescues are particularly susceptible to red thread because conditions of limited fertility are associated with the greatest disease severity. Identification of factors affecting disease resistance will be important for the development of improved cultivars and management of red thread disease in the fine fescues.

The mutualistic relationship that exists between some turfgrass species and the endophytic clavicipitaceous fungi manifests itself as improved growth and survival of individual host plants (16). The improvements in host fitness associated with endophyte infection are at least partly attributable to protection from abiotic stresses such as drought stress (24) and from biotic stresses, such as herbivory and disease, through the production of secondary metabolites (alkaloids).

Since the first report of endophyte-mediated plant resistance to an insect pest (Argentine stem weevil [Listronotus bonariensis (Kuschel)]) in 1982 (18), over 40 species of insects spanning several different orders have been reported to be adversely affected by endophytes (1,3,17). The role of endophytes in host resistance to disease, however, has received less attention. Gwinn and Gavin (7) found positive interactions between seedling survival and endophyte infection when tall fescue (Festuca arundinacea Schreb.) seedlings were inoculated with two isolates of Rhizoctonia zeae. Koshino and co-workers (12) found that timothy (Phleum pratense L.) infected with E. typhinum had greater resistance to Cercospora leaf spot than endophyte-free timothy. Vincelli and Powell (23) reported that ‘Manhattan II’ perennial ryegrass turf had significantly less red thread when endophyte infection levels were high than when they were low. Recently, Yue et al. (26) published an extensive study of 23 endophyte/plant combinations in a range of grass species, including Agrostis, Festuca, Lolium, and Poa. Twenty-two of these showed some anti-fungal activity against Cryphonectria parasitica (Murr.) Barr, with the greatest activity shown by E. festucae and N. tembladerae.

The mechanism of endophyte-enhanced resistance to fungal pathogens has not been elucidated. Moy et al. (14) observed endophytic mycelium on the leaf surfaces of B. setifolius, F. ovina (Lam.) Koch., F. rubra, and Poa ampla Merrill. The authors suggest that these mycelial nets may act as competitors for space and infection pathways of plant pathogens. In addition, Moy et al. (15) identified an endophytic β-1,6 glucanase, which could potentially function in cell wall degradation of pathogenic fungi.

The objective of the study was to determine the effect of different endophyte sources in two strong creeping red fescue and three Chewings fescue genotypes in mowed turf plots.

Selected Fine Fescues and Endophytes

Three Chewings fescue (C) and two strong creeping red fescue (SCR) endophyte-free genotypes were inoculated with different fungal endophyte sources as described previously by Johnson-Cicalese et al. (9) (Table 1). Tillers of different SCR and C genotypes were inoculated with fungal endophytes by inserting a small piece of mycelium into a slit made at the junction of the root and shoot. By inoculating tillers, an endophyte-free clone of the same plant genotype was maintained. Infected tillers were immediately planted into potting soil as described by Johnson-Cicalese et al. (9). The enodophyte-free fine fescue plants used for the inoculation were selected from breeding nurseries and designated by their nursery identification numbers (27).

Table 1. Red thread severity (percentage of plot affected by red thread) and turf quality of fine fescue selections inoculated with different endophyte sources.

Clone + endophyte^w	Species^x	Red thread severity (%)			Turf quality average (1-9 scale)
Clone + endophyte^w	Species^x	2001^y	2002	2001-2002	1998-2002^z
1090 + CAM	C	8.7	6.7	7.3	5.3
1090 + RC	C	1.7	11.3	8.0	4.7
1090 + DL	C	14.3	9.2	11.3	5.2
1090 E-	C	15.7	31.7	25.9	4.9
LSD_0.05		9.3	16.4	12.6	0.5
1117 + PA	C	3.7	6.7	5.7	5.4
1117 + RC	C	11.3	9.2	9.9	5.4
1117 +CAM	C	22.7	15.0	17.6	5.3
1117 E-	C	31.7	33.3	32.8	4.7
LSD_0.05		22.3	11.7	11.3	0.3
1139 + RC	SCR	10.7	2.5	5.2	5.8
1139 + DL	SCR	33.3	8.3	16.7	5.0
1139 E-	SCR	31.7	29.2	30.0	4.0
LSD_0.05		15.4	10.8	7.0	0.6
1171 + RC	SCR	6.3	5.8	6.0	5.5
1171 + CAM	SCR	29.3	16.7	20.1	5.0
1171 E-	SCR	37.3	28.3	31.3	4.3
LSD_0.1		NS	NS	19.8	1.0
3188-1 + DL	C	13.3	5.8	8.3	5.3
3188-1 + CAM	C	40.0	14.2	22.8	5.2
3188-2 E-	C	38.3	25.0	29.4	4.9
LSD_0.05		NS	NS	NS	NS

^w CAM = Cambridge endophyte collected from Cambridge, MA; RC = Rose City endophyte collected from Rose City Cemetery Portland, OR; DL = Delaware endophyte collected from 4 Delaware Drive, East Brunswick, NJ; PA = Poa ampla endophyte; E- = endophyte free.

^x Species of fine fescue clones evaluated. C = Chewings fescue, SCR = Strong creeping red fescue.

^y Percent red thread in 2001 was taken June 1, 2001. Percent red thread disease in 2002 is an average of two dates taken May 25, 2002 and June 1, 2002. The combined data for both years are included to emphasize endophyte effects over two years.

^z Turf quality is an average of 5 ratings taken each year from 1998-2002. Each year’s rating was an average of 8 monthly quality ratings taken during the growing season of each year. Turf quality was rated on a 1 to 9 scale, 9 = best turf quality.

Three of the endophytes were E. festucae. One was isolated from strong creeping red fescue and designated as the Rose City endophyte (RC) (collected from the Rose City cemetery in Portland, OR) and two were isolated from Chewing fescue plants, one was designated as the Delaware endophyte (DL) collected from 4 Delaware Drive, East Brunswick, NJ and the other was designated as the Cambridge endophyte (CAM) collected from Cambridge, MA. The fourth endophyte was a Neotyphodium sp. isolated from Poa ampla (PA). It was found in ‘Service,’ a cultivar of P. ampla released by the Alaska Department of Natural Resources (27).

Each endophyte-inoculated and non-inoculated genotype was planted two feet apart in a spaced-plant nursery. The plants were arranged in a randomized complete block design with 10 replications, with two plants from each treatment per replication. Plants were open-pollinated and seed harvested from these plants were used to establish replicated progeny evaluation plots in September 1997 as discussed in Johnson-Cicalese, et al. (9).

Turf Plot Evaluation

Johnson-Cicalese et al. (9) determined the successful transmission of endophyte to seeds and progeny of these endophyte-inoculated plants, following establishment of the turf evaluation plots in 1997. These turf plots were maintained under medium-low maintenance for the following five years. Turf plots were maintained at 3.8 cm with a Toro 216 reel mower (Toro Corp., Bloomington, MN), mowed twice per week. The turf trial received approximately 7.2 g of N per m² as (12-1.8-6.6) N-P-K each year with no single application exceeding 2.4 g of N per m². Turf quality was evaluated once per month during the growing season of every year. Turf quality was rated on a 1 to 9 scale, with 9 representing the best turf quality. During the spring of 2001 and 2002 a natural, uniform outbreak of red thread occurred on these plots. Percent red thread severity was evaluated once in 2001 and twice in 2002.

Although Johnson-Cicalese et al. (9) evaluated the successful transmission of endophyte to the progeny following the establishment of the 1997 turf evaluation plots, four years passed before red thread was observed. The leaf tissue was re-examined for endophyte presence using the method developed by Saha (20) in order to determine the presence of endophyte in the turf evaluation plots. All turf evaluation plots identified as containing endophyte in 1997 still contained endophyte in 2001. Analysis of variance was conducted separately for each genotype in order to determine the effect of endophyte on red thread severity using PROC ANOVA in SAS (SAS Institute, Inc., Cary, NC).

Endophytes Improve Red Thread Resistance

Significant differences in red thread severity were observed in the mowed turf evaluation trial. For progeny plots of 1090 (C), 1117 (C), and 1139 (SCR), at least one of the endophyte sources significantly reduced the severity of red thread compared to endophyte-free plots of the same genotype in 2001 and 2002 (Table 1). For the same three genotypes, all endophyte sources significantly reduced the severity of red thread compared to endophyte-free plots in 2002 and when data from both years was combined (Table 1; Fig. 1). Although results were not significant for the other two genotypes (1171 and 3188) in either year, percent red thread tended to be lower in endophyte-infected plots. The Rose City endophyte consistently reduced red thread severity in progeny plots of all genotypes in which it was present. For clone 1171 (SCR), only the progeny plots inoculated with the Rose City endophyte had significantly less red thread than the endophyte-free progeny plots when the data was combined over years (Table 1). The Rose City endophyte may have been more effective in this strong creeping red fescue clone because the Rose City endophyte was isolated from strong creeping red fescue indicating possible species compatibility between plant and fungus.

Fig. 1. The effect of endophyte on red thread in strong creeping red fescue. These two plots represent seed of the same genetic background. One plot contains half sib progeny from endophyte-infected plants (E+). The other contains half sib progeny from endophyte-free plants of the same population (E-). Notice that the endophyte-infected plot has less red thread than the endophyte-free plot.

The DL and CAM endophytes had varying effects on red thread development depending on host genotype (Table 1). Similar compatibility associations between host genotype and fungus were observed in previous studies (5,22) including a study of aluminum tolerance, which utilized the same endophyte inoculated clones (27). Host genotype incompatability may have also been the reason for lack of significant response in genotypes 1139 and 3188 (Table 1).

Endophytes Improve Turf Quality

Endophyte-infected progeny plots also tended to have better turf quality compared to endophyte-free progeny plots of the same host genotype over the four year period (Table 1). This is not surprising considering that a turf plot with a large percentage of red thread would have a lower turf quality rating, especially during peak disease pressure. These results indicate the associated benefits of utilizing endophyte-infected fine fescue seed for use in turfgrass situations where fine fescues are utilized. This result supports others who have found improved turf quality associated with endophyte-infected turfgrasses (6).

Conclusions

In the current study, for most genotypes, fungal endophytes enhanced red thread resistance and improved turf quality compared to endophyte-free plots. Although disease response differed among host plant genotype and endophyte isolate, the Rose City endophyte had a more pronounced affect over all plant genotypes compared to the other endophyte sources. Continued collection of new endophyte sources should improve our ability to find superior endophytes with additional improved benefits to turfgrasses.

This study represents the first report of endophyte-mediated resistance to red thread in strong creeping and Chewings fescue species and is among the few reports that associate endophyte infection with improved resistance to fungal disease. This is an important finding because the symbiotic endophyte-turfgrass association in Chewings and strong creeping red fescue may be utilized as a control strategy for red thread especially since fungicide control options are not typically economically feasible in low-maintenance turf situations. This research emphasizes the benefits of using endophyte-infected seed sources of fine fescue cultivars.

Acknowledgments

Research was supported by the Rutgers Center for Turfgrass Science, New Jersey Agricultural Experiment Station, United States Golf Association, and New Jersey Turfgrass Association. Journal No. D-12180 – 21-05.

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