Animal safety of a tall fescue endophyte (Epichloë sp.) in a perennial ryegrass (Lolium perenne) host.

AIMS: To assess animal health and production in sheep grazing perennial ryegrass (Lolium perenne) infected with a tall fescue endophyte (Epichloë sp.). METHODS: Three replicates of pure perennial ryegrass pastures infected with AR501 tall fescue endophyte (AR501 HE), AR1, AR37 or standard endophyte (STD) (all >85% infection) and a low endophyte control (AR501 LE) were grazed by 10 lambs for 7 weeks during late summer/early autumn, 2017. AR501 HE and AR501 LE were in the same tetraploid cultivar and the remaining treatments were in the same diploid cultivar. Lambs were weighed on Days 0, 19, 37 and 48 and assessed for ryegrass staggers on a 0-4 tremor scale nine times from Day 13. On Days 14 and 20, rectal temperatures and respiration rates were measured in lambs grazing AR501 HE, AR501 LE and STD under heat load. Pasture samples from each treatment were taken regularly (8 times) for analysis of known endophyte secondary metabolites. RESULTS: Peak mean ryegrass staggers scores for lambs grazing STD and AR37 treatments were 3.9 and 2.7, respectively, indicating environmental conditions were conducive to toxicity. Lambs grazing AR501 HE showed no ryegrass staggers at any date. The liveweight of STD lambs was up to 6.6 kg less than some or all other treatments on Days 19, 34 and 48, but there was no evidence of a difference between the liveweight of AR501 HE lambs and AR501 LE, AR37 or AR1 lambs on any date. Rectal temperatures and respiration rates of STD lambs were higher than AR501 HE lambs by 0.2°C and 26 breaths/minute, respectively. Apart from lower rectal temperature of AR501 HE lambs on Day 14, there was no evidence of differences between the AR501 HE and AR501 LE lambs. N-Formylloline was the only loline present in AR501 HE herbage (350-860 mg/kg). Peramine in AR501 HE herbage (42-77 mg/kg) was greater than that in STD and AR1 herbage on five and seven of the eight sampling dates, respectively. CONCLUSION: Lambs grazing AR501 HE showed no ryegrass staggers, exacerbated heat stress or suppressed liveweight gain compared with lambs grazing AR501 LE in a season when endophyte-induced toxicity was evident in STD and AR37 pastures. This suggests AR501 tall fescue endophyte does not produce toxic concentrations of secondary metabolites. CLINICAL RELEVANCE: This study suggests that there are no secondary metabolites produced by the tall fescue AR501 endophyte-perennial ryegrass association which affect animal health or production.

Ergovaline does not alter the severity of ryegrass staggers induced by lolitrem B.

AIM: To investigate a possible interaction between lolitrem B and ergovaline by comparing the incidence and severity of ryegrass staggers in sheep grazing ryegrass (Lolium perenne) containing lolitrem B or ryegrass containing both lolitrem B and ergovaline. METHODS: Ninety lambs, aged approximately 6 months, were grazed on plots of perennial ryegrass infected with either AR98 endophyte (containing lolitrem B), standard endophyte (containing lolitrem B and ergovaline) or no endophyte, for up to 42 days from 2 February 2010. Ten lambs were grazed on three replicate plots per cultivar. Herbage samples were collected for alkaloid analysis and lambs were scored for ryegrass staggers (scores from 0-5) weekly during the study. Any animal which was scored ≥4 was removed from the study. RESULTS: Concentrations of lolitrem B did not differ between AR98 and standard endophyte-infected pastures during the study period (p=0.26), and ergovaline was present only in standard endophyte pastures. Ryegrass staggers was observed in sheep grazing both the AR98 and standard endophyte plots, with median scores increasing in the third week of the study. Prior to the end of the 42-day grazing period, 22 and 17 animals were removed from the standard endophyte and AR98 plots, respectively, because their staggers scores were ≥4. The cumulative probability of lambs having scores ≥4 did not differ between animals grazing the two pasture types (p=0.41). CONCLUSIONS AND CLINICAL RELEVANCE: There was no evidence for ergovaline increasing the severity of ryegrass staggers induced by lolitrem B. In situations where the severity of ryegrass staggers appears to be greater than that predicted on the basis of concentrations of lolitrem B, the presence of other tremorgenic alkaloids should be investigated.

The occurrence of ryegrass staggers and heat stress in sheep grazing ryegrass-endophyte associations with diverse alkaloid profiles.

AIMS: To compare ryegrass pastures infected with endophytes producing diverse alkaloids for their ability to cause ryegrass staggers in grazing lambs; to compare respiration rates and rectal temperatures of these lambs after exposure to heat stress, and to compare liveweight gains during the study period. METHODS: Ryegrass pastures of cultivar Trojan infected with NEA endophytes, branded NEA2 (T-NEA2), endophyte-free Trojan (T-NIL), Samson infected with standard endophyte (S-STD), Samson infected with AR37 endophyte (S-AR37) and endophyte-free Samson (S-NIL), were grazed by lambs (n=30 per cultivar) for up to 48 days in February and March of 2012 and 2013. Pasture samples were analysed for alkaloid concentrations and lambs were scored for ryegrass staggers at intervals during the study period. Liveweight was recorded at the start (Day 0) and end of the study, and rectal temperatures and respiratory rates were measured in lambs exposed to heat stress on Days 23 and 26, in 2012 and 2013, respectively. RESULTS: Concentrations of alkaloids were lower in 2012 than 2013, associated with warmer and drier conditions in 2013, and the prevalence of ryegrass staggers was low in 2012. In 2013, concentrations of ergovaline were similar in T-NEA2 and S-STD, but concentrations of lolitrem B were lower in T-NEA2 than S-STD. S-AR37 produced epoxy-janthitrems but no lolitrem B or ergovaline. In 2013, by Day 20, 9/30 (30%) sheep grazing S-STD had severe staggers (score ≥4), and by Day 47 all sheep had been removed from this cultivar due to severe staggers. By Day 47, 18/30 (60%), 4/30 (13%) and 0/30 (0%) sheep grazing S-AR37, T-NEA2 and T-NIL pastures, respectively, had severe staggers. There were no differences in mean daily weight gain of lambs between cultivars in either year. In both years, mean rectal temperature and respiration rate following exposure to heat stress were highest in sheep grazing S-STD and T-NEA2, and lowest in sheep grazing T-NIL. CONCLUSIONS: In lambs grazing different ryegrass pastures infected with endophytes, ryegrass staggers was most severe on S-STD, less severe on S-AR37 and least on T-NEA2. When under heat stress, lambs grazing ergovaline-producing S-STD and T-NEA2 pastures had increased respiration rates and rectal temperatures compared with lambs grazing T-NIL. CLINICAL RELEVANCE: If ambient temperatures are suitable, NEA2-branded endophytes have the potential to express concentrations of ergovaline sufficient to induce heat stress in grazing sheep.

Rooting depth and root depth distribution of Trifolium repens × T. uniflorum interspecific hybrids.

Background and aims Traits related to root depth distribution were examined in Trifolium repens × T. uniflorum backcross 1 (BC1) hybrids to determine whether root characteristics of white clover could be improved by interspecific hybridization. Methods Two white clover cultivars, two T. uniflorum accessions and two BC1 populations were grown in 1 -m deep tubes of sand culture. Maximum rooting depth and root mass distribution were measured at four harvests over time, and root distribution data were fitted with a regression model to provide measures of root system shape. Morphological traits were measured at two depths at harvest 3. Key Results Root system shape of the hybrids was more similar to T. uniflorum than to white clover. The hybrids and T. uniflorum had a higher rate of decrease in root mass with depth than white clover, which would result in higher proportions of root mass in the upper profile. Percentage total root mass at 100-200 mm depth was higher for T. uniflorum than white clover, and for Crusader BC1 than 'Crusader'. Roots of the hybrids and T. uniflorum also penetrated deeper than those of white clover. T. uniflorum had thicker roots at 50-100 mm deep than the other entries, and more of its fine root mass at 400-500 mm. The hybrids and white clover had more of their fine root mass higher in the profile. Consequently, T. uniflorum had a higher root length density at 400-500 mm than most entries, and a smaller decrease in root length density with depth. Conclusions These results demonstrate that rooting characteristics of white clover can be altered by hybridization with T. uniflorum, potentially improving water and nutrient acquisition and drought resistance. Root traits of T. uniflorum are likely to be adaptations to soil moisture and fertility in its natural environment.

Formulations for delivering Trichoderma atroviridae spores as seed coatings, effects of temperature and relative humidity on storage stability.

AIMS: We aimed to evaluate different formulations for their ability to adhere Trichoderma atroviridae spores to wheat seeds, and promote survival during storage at a range of temperatures and relative humidities (RH). METHODS AND RESULTS: We tested a range of formulations for their ability to adhere T. atroviridae spores to wheat seeds. Treated seeds were stored for 6 months at a range of temperatures and RH, and spore viability among formulation was compared over time. Spore survival within formulations interacted significantly with environmental conditions. Notably, under optimum conditions (low temperatures and RH) best spore survival was recorded with a xanthan-gum-based formulation. Conversely under suboptimum conditions (high temperatures and RH), survival of spores was best in a waxy-starch formulation, but very poor in the xanthan-gum formulation. CONCLUSIONS: These results indicate that T. atroviridae spores can be effectively delivered on to seeds and that a xanthan-gum formulation is promising when optimal storage conditions can be maintained. SIGNIFICANCE AND IMPACT OF THE STUDY: Most published formulation papers/patents only report survival of organisms over time at a single or limited number of temperatures and RH. For the first time, this study shows how different formulations are better suited to certain temperature and RH combinations.

Methyl bromide fumigation and delayed mortality: safe trade of live pests?

Live organisms intercepted from treated commodities during phytosanitary inspections usually arouse suspicions of treatment failure, sub-standard treatment application, or post-treatment infestation. The additional possibility that some treatments could kill slowly, meaning commodities might be inspected before pests have succumbed, is seldom considered for treatments other than irradiation. We used a novel biochemical viability assay to measure delays between methyl bromide fumigation and mortality of dipteran eggs, and evaluated the correspondence between egg viability and egg morphological features. Our experimental conditions simulated shipping of rock melons from Australia to New Zealand by sea and air. No eggs survived fumigation, but they took 3-20 days to die, whereas phytosanitary inspections of rock melons occur within 2-7 days. Delays were not influenced by methyl bromide concentration, but were significantly lengthened by cooler storage temperatures. Methyl bromide's preservative effects delayed degradation of egg morphology, so the biochemical assay detected mortality long before morphological signs of egg death appeared. The results show that commodities subjected to effective methyl bromide treatments are at risk of being inspected before all pests have either died, or started to exhibit morphological signs of death. This could cause commodities to be unnecessarily rejected by quarantine authorities. Better methods than inspection for live pests are needed to assist authorities to gain assurance that treated commodities have been effectively disinfested. These could be developed by exploiting biochemical responses of pests and commodities to treatments.

Argentine stem weevil ( Listronotus bonariensis, Coleoptera: Curculionidae) population dynamics in Canterbury, New Zealand dryland pasture.

The Argentine stem weevil (Listronotus bonariensis) was an economically important pest in New Zealand pastures until the release of the parasitoid Microctonus hyperodae. This contribution uses historical data to investigate the regulation of the pest populations prior to, and somewhat during, the establishment of this parasitoid in dryland Canterbury, New Zealand. Thus, a significant goal of this study is to provide an L. bonariensis population dynamics baseline for any future work that aims to analyse the full effects of M. hyperodae on the weevil, now that equilibrium with the weevil host has been reached.The population dynamics of L. bonariensis, based on a life-table approach, were investigated using data collected regularly for eight years from populations in Canterbury, New Zealand. The key factor affecting end-of-season L. bonariensis density was found to be variation in second generation fourth instar prepupal and pupal mortality. This may have been caused by arrested development and ongoing mortality resulting from the onset of cooler autumnal conditions.A compensatory response was found in recruitment to the second summer weevil generation, whereby the realised fecundity of the emergent first summer generation of weevils was found to be negatively related to the density of adult weevils per ryegrass tiller. This is the first time that this has been found via long-term population analysis of L. bonariensis, although indications of this have been found elsewhere in caging, pot and small plot experiments.In this study, the effect of the parasitoid biocontrol agent Microctonus hyperodae on L. bonariensis population dynamics was unclear, as the analysis covered a period when the parasitoid Microctonus hyperodae was introduced and still establishing. It does, however, raise important questions for future analysis in terms of the interaction between parasitism and unrealised fecundity.The results in this contribution also highlighted regional differences. Overwintering mortality of adult weevils in Canterbury was constant between years, whilst earlier studies in the North Island Waikato region indicated this mortality was density dependent. In addition, the availability of tillers in endophyte-free ryegrass pastures in Canterbury had no influence on egg and early-instar larval survival, which contrasts with the finding from endophytic Waikato pastures.