Endophyte Combinations Research Articles

Evaluation of the Relationship between Cultivar, Endophyte and Environment on the Expression of Persistence in Perennial Ryegrass Populations Using High-Throughput Phenotyping

Perennial ryegrass (Lolium perenne L.) is a commonly grown pasture species in temperate agriculture, mainly serving as a primary energy source for dairy cows. However, its limited persistence often leads to missed production potential and early resowing, especially in countries that experience summer drought, e.g., Australia and New Zealand. Therefore, understanding the factors influencing perennial ryegrass pasture persistence is crucial for sustainable land management and climate resilience in pasture-based animal production systems. Significant gaps in knowledge exist regarding the factors influencing pasture persistence, as the number of conducted studies in this area remains limited. This study aimed to investigate the factors influencing the expression of persistence in perennial ryegrass populations using airborne and ground-based sensors. A field experiment was conducted in the southwest region of Victoria, Australia, involving ten commercial perennial ryegrass cultivar–endophyte combinations in two different populations. Persistence was evaluated using sensor-based and conventional pasture measurements over two consecutive autumns. The results revealed significant fixed effects of cultivar, endophyte, and environment and their interactions on persistence traits of perennial ryegrass. Cultivars Alto, Samson, and One50 exhibited high levels of persistence when infected with novel endophyte strains. Furthermore, prolonged environmental stresses were found to drive directional selection within pasture populations. The findings emphasise the importance of selecting appropriate cultivar–endophyte combinations and early detection of signs of poor persistence to optimise sward longevity and financial returns from pasture-based animal production systems. This study fills a knowledge gap regarding the factors influencing pasture persistence and provides valuable insights for sustainable pasture management strategies.

Nutritive characteristics of perennial ryegrass cultivars: have they changed over time?

Improvement in nutritive characteristics resulting from breeding perennial ryegrass (PRG) cultivars used in Australia from the 1970s to the present day was quantified in a grazed field experiment in south-western Victoria. The experiment was sown in May 2014 with measurements undertaken over 3 years. The experiment contained 36 PRG treatments (cultivar–endophyte combinations), which were replicated four times, with herbage nutritive characteristics measured at each grazing. The treatments differed in estimated metabolisable energy (ME), crude protein and neutral detergent fibre (NDF) concentrations at each harvest date. The decade of cultivar release had little effect on the ME or the NDF concentration of the cultivars released from 1970s onward. Early season diploids had a lower ME concentration than did later-maturing diploid cultivars (11.0 vs 11.4 MJ/kg DM), predominantly due to a lower ME concentration in late spring and early summer (10.3 vs 11.1 MJ/kg DM). The tetraploid cultivars had a higher ME concentration (11.8 vs 11.4 MJ/kg DM) and a lower NDF (480 vs 505 g/kg DM) concentration than did the mid- and late-season diploid cultivars. These differences are likely to be of economic importance at the farm level.

Changes in estimated value of perennial ryegrass cultivar/ endophyte combinations in the DairyNZ Forage Value Index when metabolisable energy contents specific to culitvar groups are included

Further development of the DairyNZ Forage Value Index (FVI) requires accounting for genetic variation in the nutritive value of ryegrass herbage in addition to the current weightings on dry matter production traits. Performance values for metabolisable energy content (PV ME) have been identified as the most appropriate variables to use for this purpose. In this study an assessment was made of the effect of including cultivar group (mid-heading date diploid, late-heading date diploid and tetraploid) PV ME in FVI ranking calculations of eligible perennial ryegrass (Lolium perenne) cultivars. Incorporation of the seasonal ME trait into the FVI has resulted in changes in rankings of those cultivars. Although correlations were strong (0.74 for Upper South Island to 0.92 for Upper North Island) between rankings of cultivars using the current FVI and the FVI with cultivar group PV ME, marked improvements have been made in the rankings of tetraploid cultivars. On-farm persistence implications (not yet included in the FVI) of selecting tetraploid cultivars will need to be included if the ME trait is included in the FVI.

The economic value to dairy systems of genetic gains in the nutritive value of perennial ryegrass in grass–clover pastures

Perennial ryegrass (Lolium perenne L.) breeding efforts have focussed on improving pasture nutritive value by altering flowering behaviour and increasing ploidy. However, the gains in farm profitability that this has delivered are not known. The flowering behaviour, botanical composition and nutritive value of pastures based on 24 perennial ryegrass cultivar–endophyte combinations released in New Zealand since 1970 were compared under grazing for 3 years in the Waikato region of New Zealand. Cultivars were grouped into the following three functional groups for data analysis: mid-season-heading diploids, late- and very late-heading diploids, and late- and very late-heading tetraploids. The first of these groups included older, ‘standard’ cultivars, while the latter two groups were dominated by cultivars released since 2002. The appearance of reproductive tillers in grazed pastures was delayed by 4–8 weeks for the late- and very late-heading cultivars, resulting in pastures that maintained a greater proportion of green leaf and had a greater metabolisable energy (ME) concentration during spring. Tetraploid pastures had a greater ME concentration than did diploid pastures, largely due to the greater ME concentration of the perennial ryegrass component of these pastures. The gains in pasture nutritive value achieved by broadening the range of perennial ryegrass functional types have the potential to deliver economic benefits in the range of NZ$54/ha.year (late-heading diploids compared with mid-heading diploids) to NZ$232/ha.year (tetraploids compared with mid-heading diploids) to New Zealand dairy farmers. Potential economic gains can be diminished by changes in pasture botanical composition both over time and between functional groups.

The Effect of Endophytic Fungi on Nematode Populations in Summer-dormant and Summer-active Tall Fescue.

Summer-active (continental) and summer-dormant (Mediterranean) tall fescue morphotypes are each adapted to different environmental conditions. Endophyte presence provides plant parasitic nematode resistance, but not with all endophyte strains and cultivar combinations. This study sought to compare effects of four nematode genera on continental and Mediterranean cultivars infected with common toxic or novel endophyte strains. A 6-mon greenhouse study was conducted with continental cultivars, Kentucky 31 (common toxic) and Texoma MaxQ II (novel endophyte) and the Mediterranean cultivar Flecha MaxQ (novel endophyte). Endophyte-free plants of each cultivar were controls. Each cultivar × endophyte combination was randomly assigned to a control, low or high inoculation rate of a mixed nematode culture containing stunt nematodes (Tylenchorhynchus spp.), ring nematodes (Criconemella spp.), spiral nematodes (Helicotylenchus spp.), and lesion nematodes (Pratylenchus spp.). Endophyte infection had no effect on nematode population densities. The cultivar × endophyte interaction was significant. Population densities of stunt nematode, spiral nematode, and ring nematodes were higher for Flecha MaxQ than other cultivar × endophyte combinations. Novel endophyte infection enhances suitability of Flecha MaxQ as a nematode host.

Antagonism of lateral saphenous vein serotonin receptors from steers grazing endophyte-free, wild-type, or novel endophyte-infected tall fescue1,2

Pharmacologic profiling of serotonin (5HT) receptors of bovine lateral saphenous vein has shown that cattle grazing endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) have altered responses to ergovaline, 5HT, 5HT2A, and 5HT7 agonists. To determine if 5HT receptor activity of tall fescue alkaloids is affected by grazing endophyte-free (EF), wild-type [Kentucky-31 (KY31)], novel endophyte AR542-infected (MAXQ), or novel endophyte AR584-infected (AR584) tall fescue, contractile responses of lateral saphenous veins biopsied from cattle grazing these different fescue-endophyte combinations were evaluated in presence or absence of antagonists for 5HT2A (ketanserin) or 5HT7 (SB-269970) receptors. Biopsies were conducted over 2 yr on 35 mixed-breed steers (361.5 ± 6.3 kg) grazing EF (n = 12), KY31 (n = 12), MAXQ (n = 6), or AR584 (n = 5) pasture treatments (3 ha) between 84 and 98 d (Yr 1) or 108 to 124 d (Yr 2). Segments (2 to 3 cm) of vein were surgically biopsied, sliced into 2- to 3-mm cross-sections, and suspended in a myograph chamber containing 5 mL of oxygenated Krebs-Henseleit buffer (95% O2/5% CO2; pH = 7.4; 37°C). Veins were exposed to increasing concentrations of 5HT, ergovaline, and ergovaline + 1 × 10(-5) M ketanserin or + 1 × 10(-6) M SB-269970 in Yr 1. In Yr 2, ergotamine and ergocornine were evaluated in presence or absence of 1 × 10(-5) M ketanserin. Contractile response data were normalized to a reference addition of 1 × 10(-4) M norepinephrine. In Yr 1, contractile response to 5HT and ergovaline were least (P < 0.05) in KY31 pastures and the presence of ketanserin greatly reduced (P < 0.05) the response to ergovaline in all pastures. However, presence of SB-269970 did not (P = 0.91) alter contractile response to ergovaline. In Yr 2, there was no difference in contractile response to ergotamine (P = 0.13) or ergocornine (P = 0.99) across pasture treatments, but ketanserin reduced (P < 0.05) the contractile response to both alkaloids. The 5HT2A receptor is involved in alkaloid-induced vascular contraction and alkaloid binding may be affected by exposure to different endophyte-fescue combinations.

Effects of selected endophyte and tall fescue cultivar combinations on steer grazing performance, indicators of fescue toxicosis, feedlot performance, and carcass traits1–3

Five tall fescue [Lolium arundinaceum (Schreb.)] pastures [wild-type 'Kentucky-31' with 78.0% of plants infected with ergot alkaloid-producing endophyte Neotyphodium coenophialum (KY31 E+), 'Jesup' AR542 endophyte-infected contaminated with 30.3% tall fescue containing ergot alkaloid producing-endophyte (Jesup AR542 E+); 'GA-186' AR584 endophyte-infected contaminated with 11.8% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 140); 'PDF' AR584 endophyte-infected contaminated with 5.5% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 144); and 'KYFA 9301' AR584 endophyte-infected contaminated with 10.0% tall fescue containing ergot alkaloid producing-endophyte (AGRFA 150)] were compared for steer growth performance, toxicity, feedlot performance, and carcass traits. Steers (mean initial BW=322 kg) grazed pastures for 84 d in spring and 56 d in autumn for 2 yr. Steers were shipped after grazing in Prairie, MS, to Macedonia, IA, for finishing. Mean herbage mass was not different (P=0.15) among pastures. Posttreatment (d 28+) serum prolactin concentrations were depressed (P=0.013) on KY31 E+. Steers grazing KY31 E+ had greater (P<0.01) posttreatment rectal temperatures during spring. Spring hair coat scores were greatest (P<0.01) on KY31 E+ at d 56 and 84. Steer ADG was least (P<0.01) on KY31 E+ in spring and depressed (P=0.014) on KY31 E+ and Jesup AR542 E+ in autumn. Spring grazing ADG was greater (P=0.049) on AGRFA 150 than Jesup AR542 E+ and AGRFA 140. No BW differences (P=0.09) among pastures were seen at reimplant during feedlot finishing. Pasture had no effect on ADG after reimplant (P=0.68), days on feed (P=0.56), or final BW (P=0.55). Exposure to fescue toxicosis did not affect (P≥0.19) carcass traits. Hair coat price discounts applied for spring-grazed steers on KY-31 E+ affected (P<0.01) initial steer monetary values. There were no pasture differences for finishing costs (P≥0.61) or final carcass value (P=0.59). Elite tall fescue cultivar and novel endophyte combinations improve growth performance of grazing calves over KY31 E+. Producers whose calves graze KY-31 E+ tall fescue should consider retaining ownership of these cattle through feedlot finishing to avoid market discounts and capture value from compensatory BW gains during finishing.

Effect of grass species and fungal endophyte on soil nitrification potential

This experiment tested the impact of grass species and fungal endophyte status and strain on soil nitrification. Three C3 grass–endophyte combinations were tested: Festuca arundinacea–Neotyphodium coenophialum; F. pratensis–N. uncinatum; Lolium perenne–N. lolii, and included different strains of endophyte and endophyte-free grasses. Three C4 species— Brachiaria decumbens, Paspalum dilatatum and Pennisetum clandestinum—of unknown Acremonium endophyte status, were also tested. Plants were grown for 6 weeks without fertiliser in pots in a field soil (Mollic Psammaquent), then rhizosphere soil was sampled and incubated at 27 °C with and without (NH4)2SO4. The –N production was measured weekly. The presence of plants significantly increased the nitrification rate compared with bare soil. There were significant differences (P=0.02) among plant species. In all cases, endophyte presence increased nitrification in soil samples (P<0.001) relative to endophyte-free within a species.

Agronomic Performance and Lamb Health among Several Tall Fescue Novel Endophyte Combinations in the South‐Central USA

Deployment of novel endophytes [Neotyphodium coenophialum (Morgan‐Jones &amp; Gams) Glenn, Bacon &amp; Hanlin] may expand the use of tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] in the south‐central United States. Our objectives were to compare agronomic performance of, and health of lambs (Ovis aries) grazing, several tall fescue–novel endophyte combinations in the south‐central United States. Two tall fescue populations (97TF1 and PDF) were inoculated with four novel endophytes (AR514, AR524, AR542, and AR584). At most locations, persistence of the eight combinations under grazing by beef cattle (Bos taurus) was similar to Jesup MaxQ. However, the combination PDF AR584 had greater persistence than Jesup MaxQ at Booneville, AR (24 vs. 14% stands, respectively) and Burneyville, OK (31 vs. 8% stands, respectively). Forage yields of the eight combinations were comparable to Jesup MaxQ, with PDF AR584 having greater yields on occasion. Lambs grazing PDF AR584, 97TF1 AR584, PDF AR542, PDF AR524, and Jesup MaxQ gained an average of &gt;139 g d−1, more than twice the 68 g d−1 gained by animals grazing endophyte‐infected Kentucky‐31. Prolactin and urinary alkaloid data indicated no detrimental health effects for animals grazing the novel endophyte combinations. Several tall fescue–novel endophyte combinations, and in particular PDF AR584, appear to be suited for the south‐central United States, based on competitive agronomic performance and health of grazing lambs.

A new tall fescue-novel endophyte combination for the south-central USA

Tall fescue use has been limited in the south central USA because of insufficient persistence of endophyte free cultivars and poor animal performance from tall fescue infected with wild-type endophyte. Here we report on the development of a tall fescue - novel endophyte combination with improved adaptation to the south central USA. A tall fescue ecotype from Oklahoma was infected with several novel endophytes. Small plot trials were conducted in Oklahoma and Texas to evaluate grazing tolerance, forage yield, and animal safety. One of the ecotypenovel endophyte combinations (AGRFA 144) had greater persistence and forage yield than Jesup MaxQ® in a number of environments. Lamb weight gains from the new tall fescuenovel endophyte combination were comparable to that of Jesup MaxQ and substantially greater than KY-31 infected with a toxic endophyte. Cultivar release of the new tall fescue-novel endophyte combination in 2008 is anticipated. Keywords: novel endophyte, tall fescue, cultivar

Plant influences on endophyte expression

Neotyphodium endophytes in the pooid grasses perennial ryegrass and tall fescue (Lolium spp.) are important ecologically and agriculturally by virtue of their ability to produce several alkaloids and their effects on host growth and responses to biotic and abiotic stresses. Such responses can be positive, neutral, or negative, and depend on the interaction of host genetics x endophyte genetics x environment (and management), which is complex and difficult to predict. Understanding the interactions is key to elucidating the ecological role of endophytes in natural and impacted ecosystems and to optimally select plant and endophyte combinations that support profitable livestock production with stable plant populations. High phenotypic variability among individual plants in an endophyte-infected population can promote population fitness across a wide range of stressful environments. Strong interactions between environmental conditions and host-endophyte combination reveal the importance of testing new grass-endophyte associations in the range of environments targeted for eventual use to determine stability of the desired traits. Care must also be taken when creating new symbiota that an important fitness trait is not lost by selecting endophytes that lack a particular alkaloid. Genetic variations within perennial ryegrass and tall fescue provide opportunities for plant breeders to perform further selections with novel symbiota to exploit host control over growth and physiology and thus overcome some of performance loss. This paper reviews the challenges of understanding grass-endophyte interactions, with particular attention to strategies of improving the performance of novel symbiota for agricultural purposes. Keywords: Lolium, Festuca, Neotyphodium, plant-endophyte interactions, symbiosis

Costs of fungal endophyte infection in Lolium perenne genotypes from Eurasia and North Africa under extreme resource limitation

The effects of asexual, leaf-inhabiting endophytes on the growth of Lolium perenne are notoriously inconsistent and appear to be contingent on environmental conditions and host genetics. Both positive and negative growth effects of endophytes have been documented in some forage crop cultivars. Because they utilize host photosynthates, it is hypothesized that endophytes would impart a growth cost to infected plants under extreme resource limitation. The potential costs of infection by the fungal endophyte Neotyphodium lolii to its host grass, L. perenne, were investigated in accessions from Italy, Turkey, Morocco and Tunisia, the native part of the host's range. Four to five infected (+E) genotypes of L. perenne per accession were cloned into ramets, and the endophyte exterminated from half of the ramets (−E). Six +E and six −E ramets per genotype were grown for 5 months in a nutrient-poor substrate (vermiculite) within temperature- and light-controlled growth chambers. Accession and genotype within accession affected dry mass. Endophyte infection significantly reduced root:shoot ratio and the proportion of the shoot that was alive and photosynthetic. Relative interaction intensity indexes were negative for most genotypes, indicating host–endophyte associations were mostly parasitic. However, there were significant infection by genotype interactions; thus, endophyte-mediated effects depend on particular host genotype–endophyte combinations. This research is one of the few that have documented costs to endophyte infection in a grass–endophyte symbiosis. This cost, manifested as reduced root:shoot ratio and photosynthetic shoot fraction, was evident for infected L. perenne growing under conditions of extremely poor substrate nutrient availability.

Stand Persistence and Animal Performance for Tall Fescue Endophyte Combinations in the South Central USA

Infection by an endophyte [Neotyphodium coenophialum (Morgan‐Jones &amp; Gams.) Glenn, Bacon, &amp; Hanlin comb. nov.] can improve persistence of tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire = Festuca arundinacea Schreb.). Novel endophytes may minimize toxicity problems associated with wild‐type endophytes, thus encouraging tall fescue use in the south central USA. The objectives of these studies were to compare stand persistence and grazing animal performance among tall fescue cultivars with different fungal endophyte combinations in the south central USA. Trials were planted in 1999 in Oklahoma and Louisiana. Tall fescue entries contained no endophyte (‘GA‐5’ E−, ‘Dovey’), a novel endophyte (‘Jesup’ MaxQ, ‘GA‐5’ MaxQ), or a wild‐type endophyte (‘KY‐31’ E+, ‘GA‐5’ E+). Weight gain data for beef cattle (Bos taurus) were collected during fall and/or spring. Estimates of stand persistence were collected periodically. In Oklahoma, average daily gain (ADG), at 0.71 kg d−1, did not differ between entries in fall. During spring, ADGs (kg d−1) were greater from Dovey (0.64), GA‐5 MaxQ (0.67), and GA‐5 E− (0.56) than from KY‐31E+ (0.29) and were intermediate for GA‐5E+ (0.47). In Louisiana, ADGs were greater from GA‐5 E− (1.20), GA‐5 MaxQ (1.06), and Jesup MaxQ (1.12) than from GA‐5E+ (0.76). In Oklahoma, stands were greater than 80% 4 yr after establishment. In Louisiana, stands declined in some E− paddocks 3 yr after planting. Thus, E− and novel endophyte–infected tall fescue resulted in greatest animal performance, whereas wild‐type and novel endophyte infection led to enhanced stand longevity. However, improved persistence is needed for broader adaptation of tall fescue to the south central USA.

Incidence and Diversity of Neotyphodium Fungal Endophytes in Tall Fescue from Morocco, Tunisia, and Sardinia

There is a premium on having Neotyphodium germplasm available for temperate grass improvement programs because these fungal endophytes present opportunities for developing new grass–endophyte combinations for enhanced tolerance to abiotic and biotic stresses. Unfortunately, surveys have revealed a low incidence of Neotyphodium fungi in grass germplasm collections. This research surveyed tall fescue (Festuca arundinacea Schreb.) accessions from a 1994 Australian–U.S. plant‐collection trip to Morocco, Tunisia, and Italy (Sardinia) for viable Neotyphodium fungi and determined whether infected accessions harbor different Neotyphodium genotypes. Conidial measurements of isolates cultured on agar and bioassays of the differential survival of bird cherry‐oat aphid [Rhopalosiphum padi (L.)] on infected accessions were used to characterize Neotyphodium diversity. A secondary objective determined the consistency of a polymerase chain reaction (PCR) method to detect Neotyphodium fungi in tall fescue. Neotyphodium was detected in 336 of 439 plants (76.5%) distributed among 104 accessions, of which 99 were endophyte‐infected. Mean conidial lengths of 42 isolates ranged from 3.91 to 9.91 μm. Most of the isolates (71.4%) had conidia with mean lengths smaller than the lower limit (6.5 μm) characteristic of the tall fescue endophyte N. coenophialum (Morgan‐Jones and Gams) Glenn, Bacon, and Hanlin. In aphid assays, all endophyte‐free plants were susceptible to R. padi and all but two infected plants were resistant to this aphid. Thus, a Mediterranean plant‐collection trip secured diverse Neotyphodium endophytes in tall fescue for storage in seed banks, and a PCR assay detected Neotyphodium in tall fescue plants of diverse geographical origin.

Alkaloid Production and Chinch Bug Resistance in Endophyte-Inoculated Chewings and Strong Creeping Red Fescues

Four Chewings fescue and two strong creeping red fescue selections that had been artificially inoculated and stably maintained with four different endophytes were evaluated in feeding trials with chinch bugs (Blissus leucopterus hirtus). Significant differences in survival were found between the endophyte-inoculated plants and their endophyte-free counterparts. After seven days, 54.2% of chinch bugs were alive on endophyte-free tillers versus only 7.4% of chinch bugs fed tillers from endophyte-inoculated plants. Some differences were also found among the various plant–endophyte combinations. In Petri dish preference trials, chinch bugs showed a preference for the CA endophyte (obtained from a Chewings fescue) over the RC endophyte (obtained from a strong creeping red fescue) in Chewings fescue selection C1117. Only the inoculated plants produced erogvaline, peramine, and lolitrem B; moreover, significant differences were found among the plant–endophyte combinations in the levels of these alkaloids. The Chewings selections C1117 and C1090 produced more ergovaline, and C1090 more lolitrem B, than other plants, regardless of endophyte source. In the presence of the RC endophyte, more ergovaline and lolitrem B was produced than in the presence of the CA endophyte regardless of plant genotype. Both host plant and endophyte, therefore, contributed factors that determined alkaloid production. No significant correlations between chinch bug survival and alkaloid levels were found, however, and overall, no one plant genotype or endophyte source proved to be significantly more toxic than another to chinch bugs. Nevertheless, the results clearly demonstrated that artificial inoculations of endophyte-free fescue genotypes can produce plants with increased toxicity to chinch bugs.

Incidence of ryegrass endophyte (Neotyphodium lolii) and diversity of associated alkaloid concentrations among naturalised populations of perennial ryegrass (Lolium perenne L.)

The mutualistic association between perennial ryegrass (Lolium perenne L.) and the ryegrass endophyte Neotyphodium lolii (Latch, Christensen and Samuels) Glenn, Bacon and Hanlin, previously assigned to the genus Acremonium, is known to have a major impact on pasture and animal production. The perennial ryegrass ecotypes Victorian and Kangaroo Valley are the most widely sown varieties of grass in Australian pasture. The incidence of ryegrass endophyte (N. lolii) in these ecotypes, and the production of alkaloids associated with theryegrass endophyte, are largely unexplored. Fifty-six populations of Victorian and 45 of Kangaroo Valley were sampled from old pasture within the recognised zones of naturalisation of both ecotypes. All of the 101 populations examined were infected with ryegrass endophyte. The mean ryegrass endophyte (N. lolii) frequency for plants within the populations of the Victorian and Kangaroo Valley ecotypes was 88% and 93%, respectively. Alkaloid concentrations were determined from infected plants for 39 Kangaroo Valley populations and, in a separate study, for 24 Victorian populations. Ergovaline concentration was above the critical level of 0.4 mg/kg (above which clinical symptoms are observed) for 10% of the Kangaroo Valley populations and 17% of the Victorian populations. For lolitrem B, all Victorian populations were below the critical level of 1.8 mg/kg, but 28% of the Kangaroo Valley populations had mean concentrations above the critical level, 1.8 mg/kg. Concentrations for individual plants were &lt;5 mg/kg for ergovaline, &lt;6 mg/kg for lolitrem B, and &lt;48 mg/kg for peramine. Within each ecotype examined, significant variation (P &lt; 0.05) in the mean concentrations of ergovaline, lolitrem B, and peramine was found between the populations of naturalised perennial ryegrass. Mean concentrations for some of the various naturalised populations were higher than that observed in some of the control cultivars. Low ergovaline and lolitrem B concentrations observed for individual genotypes indicate scope for selecting grass endophyte combinations characterised by optimum production of alkaloids.

Nodulation speed of Frankia sp. on Alnus glutinosa, Alnus crispa, and Myrica gale

The question of compatibility between actinorhizal host plants and Frankia sp. was addressed using nodulation speed on Alnus spp. seedlings and Myrica gale seedlings. It was found that the speed of nodulation, defined as the mean time taken for the formation of the first prenodule, was a stable phenotype of both the Frankia strains and the host plants and that a distinction between slow-, medium-, and fast-nodulating Frankia strains could be made. The speed of nodulation of a given Frankia strain did not appear to be positively correlated to the original host plant from which isolation was first performed. It was, however, positively correlated with the Frankia strain and with the host plant species used for inoculation. Some optimal host plant – endophyte combinations were thus defined. Pure spore inocula of Frankia and in vitro propagated Alnus glutinosa plantlets were used to confirm that both the host plant and the microbial partners genetically influenced the nodulation process.

Vesicular–arbuscular endomycorrhizal inoculum production. II. Experiments with maize (Zea mays) and other hosts in nutrient flow culture

Experiments are described that led to a better understanding of nutrient requirements for mycorrhizal development in nutrient flow (NFT) culture. For maize infected with Glomus mosseae, solution P concentration around 0.5 mg L−1 was optimal, giving approximately 50% infection. With more P, infection quickly decreased, and it was also low with only 0.3 mg L−1 P. Critical solution P was thus much lower than for Phaseolus vulgaris infected with Glomus fasciculatum (E3). When rock phosphate was used as P source, solution pH was very important because of its effect on P solubility. Nitrogen source ([Formula: see text] versus [Formula: see text]) was important for the same reason. Ca levels also affected mycorrhizal development, the optimum concentration for maize (above 15 mg L−1) being higher than that needed for beans. Maize also had a much higher Fe requirement. The relative merits of rock versus soluble P are discussed. Observations are also are reported on inoculation techniques for NFT and on mycorrhizal infection with other host–endophyte combinations.