James F. White

Taxonomy, life cycle, reproduction and detection of Acremonium endophytes

Abstract Endophytes referable to the deuteromycete genus Acremonium section Albo-lanosa have been found to be widespread in the subfamily Pooideae of the Poaceae. Methods used to survey grasses for endophytes are described and a list of hosts infected with endophytes is presented and discussed. Endophytic mycelium is present intercellularly in leaf sheaths, stems, and seeds and of grasses. Populations of Acremonium endophytes are classifiable into one of three categories (types) based on the degree to which stromata form in the grass population. It is proposed that the ability of endophytes to form stromata is determined by the capacity of endophyte strains to grow rapidly on sugars available in plants during culm elongation when stromata form on grasses. The mechanism of seed transmission of endophytes is described and evaluated. The mating system of Epichloe and involvement of the symbiotic fly Phorbia phrenione in vectoring conidia is also discussed. Several commonly encountered Acremonium species are described and discussed.

ENDOPHYTE-HOST ASSOCIATIONS IN FORAGE GRASSES. XI. A PROPOSAL CONCERNING ORIGIN AND EVOLUTION

Epichloe typhina and fungi thought to be closely related to it are widespread as endophytes in the Poaceae. Based on biological features of the fungus-host relationship, associations may be classified as one of three types. In type 1 associations, stromata form on most of the plants harboring endophytes. This type of association has been found in several subfamilies of grasses and sedges. In type 2 associations, stromata are formed on very few of the numerous infected individuals, while in type 3 associations stromata have not been observed on infected plants. The latter two associations are known to occur only in the subfamily Festucoideae. It is evident that coevolution has occurred between Epichloe spp. and festucoid grasses resulting in the evolution of mutualisms from primarily pathogenic relationships. It is suggested that this has occurred by selection of grass individuals which possessed the ability to suppress stromata formation by the endophytes. The mechanism for suppression of stromata may involve production of alkaloids which inhibit growth of these fungi.

ENDOPHYTE-HOST ASSOCIATIONS IN GRASSES. XIX. A SYSTEMATIC STUDY OF SOME SYMPATRIC SPECIES OF EPICHLOE IN ENGLAND

Systematic studies were conducted on populations of Epichloe species on host grasses Agrostis capillaris, Dactylis glomerata, and Holcus lanatus. Three species of Epichloe are described and two, E. baconii and E. clarkii, are proposed as new, being distinguishable from the type by disarticulation of ascospores to form uniquely shaped part-spores. The type species E. typhina does not form part-spores. Reproductive compatibility between fungi was examined. Intraspecies crosses were found to yield a dense layer of perithecia that differentiated asci and ascospores internally. Interspecies crosses gave one of three results, including no reaction, necrotic browning, or perithecia that did not mature. Cultural features of these fungi are compared. Isolates are seen to exhibit differences in growth rates on sugars and hydrolysis of milk protein and corn starch. Generic limits of Epichloe are discussed and several species are excluded. It is proposed that a biological species concept be adopted to aid definition of species within this genus.

Endophyte-host associations in forage grasses. XIV : Primary stromata formation and seed transmission in Epichloe typhina : developmental and regulatory aspects

Fungus/host interactions during primary stroma formation were investigated for Acremonium ty? phinum in Agrostis hiemalis and Elymus canadensis and found to be essentially the same in both grasses. In Festuca obtusa, where no primary conidial stroma or perithecial Epichloe typhina stroma are formed, A. typhinum is seed transmitted and has a similar habit to A. coenophialum in Festuca arundinacea. Experiments were conducted to determine the possible role of sugar utilization capacity in regulating stromata formation.

Endophyte-host associations in grasses. XX. Structural and reproductive studies of Epichloe amarillans sp. nov. and comparisons to E. typhina

Morphological and reproductive studies were made on five populations of Epichloe amarillans sp. nov. occurring on the host grass Agrostis hiemalis. The fungus was found to be similar to Epichloe typhina in ejection of filamentous ascospores without prior disarticulation. However, differences are evident in several features, including size and density of perithe? cia, and size of asci and ascospores. Crosses to stro? mata of E. amarillans were made using selected isolates of several species of Epichloeand stromata of E. amaril? lans from the five different populations. Perithecia developed in some of the crosses between different populations of stromata, which is evidence that mating types are present among the populations sampled. Perithecia developed in all intraspecific crosses in? volving a culture of E. amarillans isolated from a peri? thecial stroma, regardless of the mating type of the recipient stroma. This is taken as evidence that the culture is composed of a dikaryotic mycelium. A cul?

Isolation of resveratrol from Festuca versuta and evidence for the widespread occurrence of this stilbene in the poaceae

Abstract Resveratrol has been isolated from Festuca versuta seed and confirmed to be present in F. arundinacea (seed and forage), in several Lolium and Hordeum species, in Stipa robusta , and in Poa alsodes . Most of the plant materials examined were naturally infected with fungal endophytes of the genus Acremonium ; however, some endophyte-free samples from these same species also contained resveratrol, usually in reduced concentrations. These observations represent the first reports of the stilbene resveratrol in the Poaceae.

ENDOPHYTE-HOST ASSOCIATIONS IN GRASSES. XVIII. MOISTURE RELATIONS AND INSECT HERBIVORY OF THE EMERGENT STROMAL LEAF OF EPICHLOE

In order to compare relative transpiration in the stromal leaf of Epichloi typhina to that ofnonstromal leaves produced on culms without stromata, translocation of dye in excised culms was monitored. Stromal leaf blades accumulated dye rapidly and became densely stained, while minimal staining occurred in nonstromal leaf blades. This is interpreted to indicate that transpiration is enhanced in stromal leaves. Sections of stromal leaves show that several cell types are hypertrophied. The epidermis contains cells with thin outer walls, where in many instances the cells have collapsed or appear ruptured. It is apparent that the stromal leaf has been anatomically modified so that evaporation of water from its surface is increased and unregulatable by the plant. In one experiment stromal leaf blades were excised from stromata resulting in desiccation of upper parts of stromata. The biological role of the stromal leaf may be to draw water through the stroma to replace evaporative loss from the stromal mycelium. Herbivory studies using fall armyworms also indicate that the stromal leaf is chemically altered to deter herbivory. Enhanced insect resistance and drought tolerance in grasses with nonstromaforming endophytes, that are believed to have evolved from Epichloi, are characteristics that may have been preadapted by the need for Epichloi to alter the stromal leaf and defend it from herbivory.

Invertase activity in Epichloë/Acremonium fungal endophytes and its possible role in choke disease

Subspecies of Festuca rubra often host fungal endophytes of the genus Epichloe. Endophyte-infection can confer significant advantages, such as insect resistance, to the grass hosts, but in some cases can also result in the pathological condition of choke disease. In choke disease, the developing inflorescence becomes trapped in the fungal mycelium, resulting in reduced seed yields. Here we report that the choke stroma tissue contains cell wall and soluble invertase activities which were greater than 10-fold higher than the activities in the subtending stem. Most of the invertase activity probably originated from the fungus. High fungal invertase activity in the stroma would improve the sink strength of the fungus for sucrose import from the plant phloem, thus providing the carbohydrate needed for the enhanced fungal growth which occurs in choke disease.

Endophyte-host associations in grasses. XXI. Studies on the structure and development of Balansia obtecta

Studies on the structure and development of Balansia obtecta (Ascomycotina, Clavicipitaceae) were conducted. Plants and sclerotia were collected at sev? eral sites in Florida. Sections of sclerotia were made and examined using light microscopy. Sclerotia were seen to be composed of both grass and fungal tissues. Sclerotia were germinated in moisture chambers. Two types of gametangial fructifications (spermogonia and ascogonia) were observed. Spermogonia were cupulate and produced masses of moist spermatia. Asco? gonia were pulvinate and were composed of aggregations of radiating hypha-like trichogynes. Both types of gametangia were produced on most sclerotia. Crossing studies were conducted and a mating system involving heterothallism was demonstrated. Ascomata developed only after spermatia were transferred to an ascogonium of a compatible mating type. An ascoma consisted of a stipe and a globose stromal head in which numerous perithecia developed.

ENDOPHYTE-HOST ASSOCIATIONS IN GRASSES. XVII. ECOLOGICAL AND PHYSIOLOGICAL FEATURES CHARACTERIZING EPICHLOE TYPHINA AND SOME ANAMORPHIC VARIETIES IN ENGLAND

Field research was conducted in central England on grasses infected by Epichloe typhina. Both asymptomatic and stromata-producing infections were encountered and examined. Isolations of endophytes were made and comparative laboratory studies conducted on sugar utilization capacities, starch and protein hydrolysis capacities, and cultural morphologies. The presence of distinct varieties of Acremonium typhinum is proposed to account for variation in ecology, physiology, and morphology of isolates.