Variation Among Orchardgrass (Dactylis glomerata) Germplasm for Choke Prevalence Caused by Epichloë typhina

Orchardgrass, or cocksfoot (Dactylis glomerata L.), is a cool-season forage grass susceptible to the choke disease caused by Epichloë typhina. Choke has been reported in orchardgrass seed production fields across the temperate regions of the world, but fungicides have not been efficacious in reducing choke incidence or prevalence. To assess the potential for genetic resistance or tolerance of orchardgrass to choke, we evaluated the variation in orchardgrass cultivars and accessions for choke prevalence and characterized infected plants for endophyte secondary metabolite and mating type gene presence. Significant variation was detected across years and locations. Choke prevalence did not always increase with the age of the stand, nor did choke prevalence correlate with flowering time or swathing time of the entries. Both mating types of E. typhina were detected in approximately equal proportions, and no evidence for loline, ergot alkaloid, or indole-diterpene biosynthesis was found. Plants with multiple infected tillers often showed more than one mating type present in the plant, indicating multiple infection events rather than a single infection event that spread to multiple tillers. Both accessions and cultivars with significant choke, and no choke, were detected, which constitute sources of germplasm for further testing and breeding.

Incidence, Identification, and Mycoparasitic Activity of Clonostachys epichloë, a Hyperparasite of the Fungal Endophyte Epichloë typhina

Fungi of the genus Epichloë (Clavicipitaceae, Ascomycota) cause choke disease in many grass species. The disease manifests itself as fungal stromata that form around developing inflorescences, thereby suppressing their maturation. Economic losses in agricultural production due to choke have long been known in the U.S.A. and France, but attempts to control choke disease have not been successful. The interaction between Epichloë typhina (Pers.) Tul. & C. Tul. and its naturally occurring fungal hyperparasite, Clonostachys epichloë (Speg.) Schroers (sexual morph Bionectria epichloë) was investigated in populations of the grass Puccinellia distans (L.) Parl. Fungal hyperparasites occur widely in nature, and many are successfully used commercially as biological control agents against plant pathogenic fungi. Microscopy of Epichloë stromata infected with C. epichloë revealed a lack of asci with ascospores in perithecia and damage to mycelia at sites colonized by C. epichloë. The ability of C. epichloë to colonize E. typhina was confirmed via two in vitro experiments. The percent inhibition of growth of E. typhina strains by C. epichloë varied from 18.40 to 46.50%, and the mycoparasite colonized up to 100% of Epichloë mycelia in a precolonization experiment. We discuss the possibility of using C. epichloë to control choke disease caused by E. typhina in grass populations.

Graminicolous fungi from Poland. I. Fungi on halophyte Puccinellia distans

The host plant <i>Puccinellia distans</i> was found to be inhabited by the following fungi: <i>Acrospermum graminum, Cladosporium herbarum, Colletotrichum capsici, Dinemasporium slrigosum, Epichloë typhina, Guignardia graminicola, Ophiosphaerella herpotricha, Phaeosphaeria eustoma, Pleospora herbarum, Pyrenophora trichostoma, Puccinia brachypodii var. poae-nemoralis, Acrospermum graminum</i> and <i>Ophiosphaerella herpotricha</i> had not been earlier reported from Poland. On living stromata of <i>Epichloë typhina</i> a mycophilous <i>Alternaria</i> sp. was noted. Mycological data have been used to establish the allocation and relation of the genus <i>Puccinellia</i> with other similar grass genera.

Survival, Germination, and Growth of Epichloë typhina and Significance of Leaf Wounds and Insects in Infection of Orchardgrass

Epichloë typhina is an important stroma-producing endophytic ascomycete that is responsible for significant yield loss in orchardgrass (Dactylis glomerata) seed production fields. Infection is presumed to occur through leaves or stems, although details of the infection process and conditions that favor leaf infection are not well understood. The primary objectives of this study were to investigate the early stages of infection, including the effect of temperature or water potential on ascospore germination and subsequent growth of E. typhina, the tolerance of ascospores to desiccation, the requirement of leaf wounds for infection of orchardgrass by E. typhina, and the potential for insects to facilitate infection. Ascospores tolerated dry conditions, with at least 40% surviving 12 days under desiccation. Germination and growth of E. typhina was greatest at 25°C, with little to no growth at 5 and 35°C. Mycelial growth decreased with decreasing water potential from –0.3 to –10 MPa. Ascospore germination on leaves was predominantly hyphal at wound sites and iterative (conidiogenous) at sites without wounds. E. typhina typically entered leaves through wounds. Direct penetration was rarely observed and appeared to be associated with ascospore clusters. Germ tubes were significantly longer at sites with honeydew deposits from the bird cherry–oat aphid than at sites without honeydew. Growth of E. typhina was also observed at feeding sites of eriophyid mites, suggesting that leaf-wounding or sap-excreting insects support epiphyllous growth of E. typhina on leaves.

The fungus Epichloë typhina in populations of a halophyte Puccinellia distans: salinity as a possible inhibitor of infection

<em>Puccinellia distans</em> is a non-agricultural halophytic grass that has become another host plant for <em>Epichloe typhina</em>, hitherto not reported from Poland. In 1992 we noticed the first symptoms of choke disease in a single population of <em>P. distans</em> in central Poland. Since then we have observed choke disease in 5 populations of <em>P. distans</em> only in man-made habitats. These habitats are strongly anthropogenically salinated but they exhibit the pattern of species composition characteristic of natural salines. In this paper we test the hypothesis that the level of salinity affects the infection of <em>P. distans</em> by the fungus <em>E. typhina</em>. Seven plots were established in the field and each plot was divided into 25 subplots. Within each plot the level of infection in a spring generation of shoots was negatively correlated with salinity (common regression within the plots, beta = -0.674, df = 117, p &lt; 0.001). Negative correlation was also found in an autumn generation within the plots (beta = -0.682, df = 94, p &lt; 0.001) after excluding plot P in which the frequency of infected individuals was the lowest and equal only to 0.05. The proportion of individuals infected by the endophytic stage of the fungus in the populations was assessed using diagnostic polymerase chain reaction. The greatest percentage (98.3%) of infected individuals was found in the population growing in the habitat of the lowest salinity. The high salinity reduces the chance of <em>P. distans</em> to become infected, but may promote the stroma formation of <em>E. typhina</em> twice in the season. Disease expression in autumn clearly represents a misadaptation which could be explained by the fact that the species interactions described here appeared relatively recently as a result of human activity. This hypothesis requires further experimental verification.