This study was conducted to explore fungal endophyte communities inhabiting native switchgrass plants from the tallgrass prairie of northern Oklahoma. The primary focus was to isolate these endophytes in pure culture from surface-sterilized plant tissues and provide taxonomic identifications based on comparative analysis of ITS rDNA gene sequences. From these data, we evaluated the biodiversity of these potentially beneficial endosymbionts from this rapidly disappearing habitat of the Great Plains. While important from a strictly conservationist standpoint, this survey further allowed us to identify candidate endophytes for introduction into commercial switchgrass cultivars for biomass enhancement. A total of 210 whole plant samples were collected at early vegetative, full reproductive and senescence stages. Fungal endophytes were isolated, identified to species level when possible, and grouped into communities based on plant part, collection month and part of the prairie from which the plants were collected. Species diversity for each community was estimated by Shannon diversity index, and differences in diversity indices were compared using a t-test. The presence of fungal species representing at least 18 taxonomic orders suggests a high level of diversity in switchgrass endophyte communities. The fungal communities from shoot tissue had significantly higher species diversity than communities from the root tissue. The abundance of taxa assigned to the order Hypocreales (to which mutualistic, clavicipitaceous endophytes of coolseason grasses belong) found in shoot (64%) and root tissues (39%) throughout the growing season suggests great potential for utilizing these endophytes for enhancing biomass production and stress resistance of this important bioenergy crop.
Studying geographic variation of microbial mutualists, especially variation in traits related to benefits they provide their host, is critical for understanding how these associations impact key ecological processes. In this study, we investigate the phylogenetic population structure of Epichloë species within Bromus laevipes, a native cool-season bunchgrass found predominantly in California. Phylogenetic classification supported inference of three distinct Epichloë taxa, of which one was nonhybrid and two were interspecific hybrids. Inheritance of mating-type idiomorphs revealed that at least one of the hybrid species arose from independent hybridization events. We further investigated the geographic variation of endophyte-encoded alkaloid genes, which is often associated with key benefits of natural enemy protection for the host. Marker diversity at the ergot alkaloid, loline, indole-diterpene, and peramine loci revealed four alkaloid genotypes across the three identified Epichloë species. Predicted chemotypes were tested using endophyte-infected plant material that represented each endophyte genotype, and 11 of the 13 predicted alkaloids were confirmed. This multifaceted approach combining phylogenetic, genotypic, and chemotypic analyses allowed us to reconstruct the diverse evolutionary histories of Epichloë species present within B. laevipes and highlight the complex and dynamic processes underlying these grass-endophyte symbioses.
Species of the genus Brachiaria originate primarily from Africa, where they are constituents of natural grasslands. Due to their adaptation to acidic, low-fertility soils, millions of hectares of Brachiaria species have been sown as improved pastures in South and Central America, especially B. brizantha cv. Marandu and B. decumbens cv. Basilisk. Due to B. decumbens' susceptibility to spittlebug insect pests in the Americas, CIAT in Colombia and EMBRAPA in Brazil initiated breeding programmes in the 1980s. First cultivars released from CIAT's breeding programmecvs. Mulato and Mulato-IIhave also been investigated in African countries. They have been examined for integration in conservation agriculture systems (Madagascar), for drought and acidic soil tolerance (Rwanda) and for intercropping forages in dairy systems (Uganda, Madagascar), among others. Seed sales to African countries suggest that an area of at least 1,000 ha has been sown so far. The largest adoption of cv. Mulato-II is currently happening in eastern Africa, where it is used by over 20,000 farmers as a trap plant in the push-pull system for control of maize stem borers and parasitic Striga weed. Cv. Mulato-II's particular advantage is its relatively high crude protein content due to greater leafiness and thinner stems than those of traditional Napier grass, resulting in higher nutritive quality. Yet new pest challenges have emerged, requiring further research attention. Diverse hybrids are in the pipeline for release, among them those that are suitable for cut-and-carry systems which are prevalent in eastern Africa. This paper reviews research, development and incipient adoption of new Brachiaria hybrids in African countries.
Seed dormancy and slow seedling establishment are two major concerns in switchgrass (Panicum virgatum L.) production, often resulting in a poor stand with reduced productivity. Studies were conducted to investigate the stability of artificial associations between switchgrass and the ectomycorrhizal fungus, Sebacina vermifera, and to evaluate the potential benefits of this novel association in seed germination and biomass production. All six strains of S. vermifera tested had a high frequency of colonization on switchgrass roots of a synthetic cultivar NF/GA-993. The positive effects of the associations were reflected in plant height, root length, and biomass production. Inoculated plants produced as much as 75%, 113%, and 18% more shoot biomass than un-inoculated control plants in the first, second, and third harvest, respectively, with no consequent reduction in root biomass. Further, culture filtrates from some strains of S. vermifera increased seed germination in the switchgrass cultivar Kanlow by 52% over the control (p<0.05). This study illustrates the great potential of microbial associations to increase biomass production and productivity of switchgrass.
Experiments were conducted to examine the effects of cocultivating the important bioenergy crop switchgrass with the ectomycorrhizal fungus Sebacina vermifera under severe drought conditions. Plants cocultivated with the fungus produced significantly higher biomass and had a higher macronutrient content than uninoculated control plants under both adequately watered and drought conditions. Drought is a predominant factor limiting plant growth and yield in both dry land and irrigated agriculture (6,27). Lack of soil water has a wide range of effects on morphological and biochemical processes in plants, including nutrient uptake from the soil, negatively impacting crop productivity (2). Unfortunately, the influence of drought on agriculture is expected to worsen in the future due to climate change (8) and increasing demands for water for municipal and residential consumption (9). Thus, various strategies are being developed to maximize water use efficiency and minimize the effects of drought on agriculture (3,12,14,18,23,26,29). However, utilization of naturally occurring symbiotic microbes to enhance drought tolerance of agricultural crops has remained largely unexplored.Most plant species in natural ecosystems are in symbiotic relationships with mycorrhizal and/or endophytic fungi (21). Members of the newly defined basidiomycete order Sebacinales naturally form a wide spectrum of mycorrhizal types of relationships (31) with the roots of various mono-and dicotyledonous plants (4,11,15,28,30). Two species in particular, Sebacina vermifera [Serendipita vermifera (Oberw.) P. Roberts, comb. nov] and its close relative Piriformospora indica, have stimulated considerable attention over the past several years, because they form endophytic and mycorrhiza-like associations with most plant species studied to date (30,32). This is of great interest, because both species are axenically cultivable, possess plant growth-promoting characteristics, and contribute several other benefits to their host plants (4,11,15,28,30). Two previous studies have shown that colonization of roots by P. indica confers drought tolerance in Arabidopsis thaliana and Chinese cabbage (24, 25). However, no similar studies have been performed to evaluate the potential of S. vermifera to impart drought tolerance to host plants. Our objective here was to investigate the effect of S. vermifera in mitigating biomass losses in switchgrass due to drought, with the ultimate goal of maximizing the utility of this important bioenergy crop and the range of lands upon which it can be grown.An in vitro study was performed using 175-ml plant containers (65 mm in diameter by 65 mm in height) with lids. The containers were filled with 25 ml of modified PNM culture medium (24) and overlaid with a nylon disk (mesh pore size, 50 m). Two strains of S. vermifera, MAFF-305828 and MAFF-305830, were used in the study. One 5-mm-diameter plug of fungal hyphae from a colony actively growing on malt extract agar (MEA) was placed at the center of the nylon disk and allowed to grow...
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